[Paleopsych] BBS: (D.S. Wilson and E. Sober) Re-Introducing Group Selection to the Human Behavioral Sciences

[Premise Checker]

Re-Introducing Group Selection to the Human Behavioral Sciences
http://www.bbsonline.org/documents/a/00/00/04/60/bbs00000460-00/bbs.wilson.html

[This should be read carefully and prayerfully by all, esp. those who have not 
read their book, "Unto Others," of which this is a fine précis.]

Below is the unedited preprint (not a quotable final draft) of:
Wilson, D.S. & Sober, E. (1994). Reintroducing group selection to the
human behavioral sciences. Behavioral and Brain Sciences 17 (4):
585-654.
The final published draft of the target article, commentaries and
Author's Response are currently available only in paper.

  David Sloan Wilson
  Department of Biological Sciences
  State University of New York at Binghamton
  Binghamton New York 13902-6000
  [3]DWILSON at BINGVAXA.BitNet
  Elliott Sober
  Department of Philosophy
  University of Wisconsin
  5185 Helen C. White Hall
  600 North Park Street
  Madison Wisconsin 53706
  [4]ESober at VMS.MACC.Wisc.edu

Keywords

culture; evolution; group selection; kin selection; inclusive fitness;
natural selection; reciprocity; social organization; units of
selection.

Abstract

In both biology and the human sciences, social groups are sometimes
treated as adaptive units whose organization cannot be reduced to
individual interactions. This group-level view is opposed by a more
individualistic view that treats social organization as a byproduct of
self-interest. According to biologists, group-level adaptations can
evolve only by a process of natural selection at the group level.
During the 1960's and 70's most biologists rejected group selection as
an important evolutionary force but a positive literature began to
grow during the 70's and is rapidly expanding today. We review this
recent literature and its implications for human evolutionary biology.
We show that the rejection of group selection was based on a misplaced
emphasis on genes as "replicators" which is in fact irrelevant to the
question of whether groups can be like individuals in their functional
organization. The fundamental question is whether social groups and
other higher-level entities can be "vehicles" of selection. When this
elementary fact is recognized, group selection emerges as an important
force in nature and ostensible alternatives, such as kin selection and
reciprocity, reappear as special cases of group selection. The result
is a unified theory of natural selection that operates on a nested
hierarchy of units.

The vehicle-based theory makes it clear that group selection is an
important force to consider in human evolution. Humans can
facultatively span the full range from self-interested individuals to
"organs" of group-level "organisms." Human behavior not only reflects
the balance between levels of selection but it can also alter the
balance through the construction of social structures that have the
effect of reducing fitness differences within groups, concentrating
natural selection (and functional organization) at the group level.
These social structures and the cognitive abilities that produce them
allow group selection to be important even among large groups of
unrelated individuals.
   _________________________________________________________________

The existence of egoistic forces in animal life has long been
recognized. It is not so well known that the idea of group-centered
forces in animal life also has a respectable history. (Allee 1943, p
519)

It is a crude oversimplification to conceive of social motives as
being capable of direct derivation from a hedonic algebra of
self-interest--real or fictitious--based on a few universal human
drives, whatever the choice of the drives may be. (Tajfel 1981, p36)

These quotations illustrate a perspective in which social groups have
a primacy that cannot be reduced to individual interactions. The
group-level perspective can be found in biology and all branches of
the human behavioral sciences (e.g., Anthropology, Economics,
Psychology, Sociology). It is opposed by another perspective that
treats individuals as primary and social groups as mere consequences
of individual interactions. Although the conflict between the two
perspectives is often dismissed as semantic, it refuses to go away,
suggesting that substantive issues are involved.

In biology, the conflict between the perspectives has had a remarkable
history. Prior to 1960 it was quite acceptable to think of social
groups and even whole ecosystems as highly adapted units, similar to
individuals in the harmony and coordination of their parts1. Williams
(1966) and others argued that group-level adaptations require a
process of natural selection at the group level and that this process,
though theoretically possible, was unlikely to be important in nature.
Their verdict quickly became the majority view and was celebrated as a
major scientific advance, similar to the rejection of Lamarkianism. A
generation of graduate students learned about group selection as an
example of how not to think and it became almost mandatory for the
authors of journal articles to assure their readers that group
selection was not being invoked. Nevertheless, a positive literature
began to grow in the 1970's and is rapidly expanding today (table 1).2
It is no longer heretical for biologists to think of natural selection
as a hierarchical process that often operates at the group level.

The most recent developments in biology have not yet reached the human
behavioral sciences, which still know group selection primarily as the
bogey man of the 60's and 70's. The purpose of this paper is to re-
introduce group selection to the human behavioral sciences. We think
that group selection can provide a firm foundation for a group-level
perspective in the human sciences, as it has in biology. Before
beginning, however, it is important to note a complication.
Evolutionary approaches to human behavior have become increasingly
common, as readers of Behavioral and Brain Sciences well know.
Unfortunately, some of the most prominent evolutionary biologists
interested in human behavior have themselves failed to incorporate the
recent literature and still present group selection as a bogey man
(e.g., Alexander 1979,1987, Daly and Wilson 1988, Trivers 1985; but
see Table 1 entries marked 'H' for exceptions). We therefore must
re-introduce group selection to human sociobiology as well as to the
more traditional branches of the human sciences.

A BRIEF REVIEW OF THE GROUP SELECTION CONTROVERSY

The adaptationist program. In an influential paper, Gould and Lewontin
(1979) criticize evolutionists for using adaptation as their only
explanatory principle, to the exclusion of other factors such as
genetic drift and genetic/developmental constraints. They coined the
term "adaptationist program" as a pejorative and their conclusion that
it cannot be the only tool in the evolutionist's toolkit is well
taken. At the same time, their message should not obscure the fact
that the adaptationist program, or "natural selection thinking"
(Charnov 1982), is an extremely powerful tool for predicting the
properties of organisms.

One of the virtues of the adaptationist program is that it can be
employed with minimal knowledge of the physiological,biochemical and
genetic processes that make up the organisms under examination. For
example, imagine studying the evolutionary effects of predation on
snails, seeds and beetles. Suppose you discover that for all three
groups, species exposed to heavy predation have harder and thicker
exteriors than species not so exposed. The property ohard exterior@
can be predicted from knowledge of the selection pressures operating
on the populations. Since the exteriors of snails, beetles, and seeds
are made of completely different materials, there is a sense in which
these materials are irrelevant to the prediction (Campbell 1974,
Wilson 1988). That is why Darwin was able to achieve his fundamental
insights in almost total ignorance of the mechanistic processes that
make up organisms. Adaptationist explanations have the power to unify
phenomena that are physiologically, biochemically and genetically
quite different .

The adaptationist program is valuable even if its predictions turn out
to be untrue. If we know the traits that organisms will have if
natural selection is the only influence on evolutionary trajectories,
then deviations from these traits constitute evidence that factors
other than natural selection have played a significant role. To
discover whether adaptationism is true or false, optimality models are
indispensable (Sober 1993, Orzack and Sober in press).

Although the following discussion is, in effect, a view about how the
adaptationist program should be pursued, it involves no substantive
committment to the success of that program. Regardless of the scopes
and limits of adaptationism, the question owhat would organisms be
like if they were well adapted@ is of paramount importance in
evolutionary biology.

The adaptationist program and the biological hierarchy. The question
"What would they be like if they were well adapted?" is more
complicated than it sounds. To see this, consider an imaginary
population of rabbits inhabiting an island. A mutant arises that
grazes more efficiently--so efficiently that a population of such
mutants will overexploit their resource and go extinct. The mutation
is adaptive in the limited sense of causing its bearer to have more
offspring than other rabbits, but maladaptive in the larger sense of
driving the population extinct.

This example should sound familiar to human behavioral scientists
because it resembles the social dilemmas that abound in human life. It
corresponds to the tragedy of the commons popularized by Hardin
(1968), the voting problem of economics (Margolis 1982) and the
prisoner's dilemma of game theory (Rapoport and Chammah 1965). For
humans and nonhumans alike, individual striving can lead to social
chaos.

As previously mentioned, many biologists prior to the 1960's
uncritically assumed that natural selection evolves adaptations at
upper levels of the biological hierarchy. In our imaginary example
they would assume that the population of rabbits evolves to manage its
resources. The possibility that adaptation at one level of the
hierarchy can be maladaptive at another level was either ignored or
assumed to be resolved in favor of the higher level. These sentiments,
which today are called "naive group selectionism", permeated the
textbooks and were espoused by many eminent biologists, including
Alfred Emerson (1960), who believed that all of nature was as
functionally integrated as a termite colony. As a young post-doctoral
associate at the University of Chicago, G.C. Williams attended a
lecture by Emerson and left muttering "Something must be done...". The
result was a modern classic, Adaptation and Natural Selection
(Williams 1966)3.

Williams' argument against higher-level adaptations came in three
parts. First, he claimed that adaptation at any level of the
biological hierarchy requires a process of natural selection operating
at that level. Returning to our population of rabbits, it is easy to
see that efficient grazers will evolve because they have more
offspring than inefficient grazers. The negative consequences at the
population level are irrelevant. However, if we imagine an archipelago
of islands, only some of which contain the mutant strain, then
populations driven extinct by the mutant can be replaced by other
populations without the mutant. The population- level adaptation can
now persist, but only because we have added a process of natural
selection at that level; fit populations replace unfit populations in
the same sense that fit rabbits replace unfit rabbits within
populations. This is what evolutionary biologists term group
selection.

Second, Williams argued that group selection is unimportant in nature
despite the fact that it is theoretically possible:

It is universally conceded by those who have seriously concerned
themselves with this problem that such group-related adaptations must
be attributed to the natural selection of alternative groups of
individuals and that the natural selection of alternative alleles
within populations will be opposed to this development. I am in entire
agreement with the reasoning behind this conclusion. Only by a theory
of between-group selection could we achieve a scientific explanation
of group-related adaptations. However, I would question one of the
premises on which the reasoning is based. Chapters 5 to 8 will be
primarily a defence of the thesis that group-related adaptations do
not, in fact exist. (Williams 1966 p 92 ) Part of Williams' skepticism
can be illustrated with our rabbit example. If migration occurs
between islands, what is to prevent the mutant from "infecting" the
other islands before the original population goes extinct? Or perhaps
the mutant population doesn't go extinct but merely hobbles along in a
malnourished state, in which case the occasional migrant from other
islands would be unable to survive. At least for this example, it
seems that the parameters of the model must be very finely tuned for
group-level selection to prevail against individual-level selection.

Third, Williams developed a concept of the gene as the "fundamental
unit of selection" that has become a major theme in evolutionary
biology, especially as amplified and extended by Dawkins (1976,1982).
Williams claimed that groups and even individuals cannot be units of
selection because they are ephemeral and do not replicate with
sufficient fidelity. Every sexually reproducing organism is a unique
combination of thousands of genes that will never exist again, no
matter how successful reproductively. At the individual level, only
clonal organisms replicate with sufficient fidelity to qualify as
units of selection. For sexually reproducing organisms, the gene is
the unit that is transmitted through time with high fidelity and is
therefore the fundamental unit of selection (the replicator, in
Dawkins' terminology). This is frequently used as an argument against
group selection. For example, Alexander (1979 p36) states:

In 1966 Williams published a book criticizing what he called "some
current evolutionary thought" and chastised biologists for invoking
selection uncritically at whatever level seemed convenient. WilliamsY
book was the first truly general argument that selection is hardly
ever effective on anything but the heritable genetic units of "genetic
replicators" (Dawkins 1977) contained in the genotypes of individuals.

Individuals and groups appear in Williams' scheme, not as units of
selection, but as environments of the genes. As the simplest example,
consider two alleles (A,a) at a single diploid locus in a randomly
mating population, yielding the familiar three genotypes (AA,Aa,aa) in
Hardy- Weinberg proportions. Suppose the fitnesses of the three
genotypes are WAA=1, WAa=0.75 and Waa=0.5. From the gene's-eye view,
the A-allele can be said to inhabit two "genotypic environments", AA
and Aa, and its average fitness can be easily calculated:

WA= pWAA + (1-p)WAa (1)

The term p, in addition to being the frequency of the A-allele in the
population, is also the proportion of A-alleles that exist in the AA
"environment" in a randomly mating population. The fitness of the
a-allele can similarly be averaged across its two genotypic
environments (Aa,aa) to yield

Wa= pWAa + (1-p)Waa (2)

The A-allele will evolve whenever WA>Wa, which is always the case when
WAA>WAa>Waa. Note that A and a have the same fitness within the one
genotypic environment that they inhabit together (the heterozygote).
It is only by averaging across genotypic environments that differences
in the fitness of A and a occur. Biologically informed readers will
recognize WA and Wa as the "average effects" of the two alleles used
to calculate breeding values and narrow-sense heritability at the
individual level (e.g., Falconer 1982, Wilson and Sober 1989).

More complicated examples can be constructed in which the population
is divided into social groups that differ in allele frequencies and
genotypic fitnesses. In these cases the genes inhabit a more
complicated array of "environments" but in principle it is always
possible to calculate gene-level fitness by averaging across genotypic
and social contexts. In addition, it will always be the case that A
replaces a when WA>Wa. This is why Williams (1986,1992) refers to
genes as "bookkeeping" devices that automatically record the net
effect of multiple selection pressures.

Williams' case against group selection was strengthened by two other
theories in evolutionary biology that were developed during the 60's
and 70's. The first was inclusive fitness theory (also called kin
selection; Hamilton 1964, Maynard Smith 1964), which explained how
altruism could evolve among genetic relatives. The second was
evolutionary game theory (Axelrod and Hamilton 1981, Maynard Smith
1982, Trivers 1971, Williams 1966), which explained how cooperation
could evolve among non-relatives. These theories seemed to account for
many of the phenomena that group selection had been invoked to
explain. With the problems raised by Williams and two robust
alternatives, the theory of group selection, never well articulated to
begin with, collapsed.

Not all evolutionary biologists are familiar with the details of
Williams' arguments against group selection, but the bottom-line
conclusion has been adopted with such conviction that we will call it
Williams' first commandment: "Thou shalt not apply the adaptationist
program above the level of the individual." All adaptations must be
explained in terms of the relative fitness of individuals within
populations. Individual-level adaptations may have positive or
negative effects at the group level, but in both cases the group-level
effects are irrelevant to evolutionary change. Williams' first
commandment was repeated like a mantra throughout the 60's and 70's,
as every evolutionary biologist knows. Unfortunately, the mantra still
echoes through the numerous accounts of evolutionary theory that are
written for the human sciences and popular audiences today (e.g.,
Alexander 1987, Archer 1991, Cronin 1991, Daly and Wilson 1988, Frank
1988, Krebs 1987, MacDonald 1988, Noonan 1987, Sagan and Druyan 1992).

Examining the edifice. Although Williams' and Dawkins' gene-centered
view has enjoyed enormous popularity, it has one flaw that should be
obvious, at least in retrospect. Naive group selectionists thought
that upper levels of the biological hierarchy were like individual
organisms in the coordination and harmony of their parts. According to
Williams and Dawkins, however, even sexually reproducing organisms do
not qualify as units of selection because they, like groups, are too
ephemeral. If a creature such as a bird or a butterfly is not a unit
of selection, then what endows it with the internal harmony implied by
the word "organism"?

To answer this question, an entirely different concept needed to be
invoked which Dawkins (1976) called "vehicles of selection"
("interactors" in Hull's 1980 terminology). Employing one of DawkinsY
own metaphors, we can say that genes in an individual are like members
of a rowing crew competing with other crews in a race. The only way to
win the race is to cooperate fully with the other crew members.
Similarly, genes are "trapped" in the same individual with other genes
and usually can replicate only by causing the entire collective to
survive and reproduce. It is this property of shared fate that causes
"selfish genes" to coalesce into individual organisms.

So far, so good, but if individuals can be vehicles of selection, what
about groups? After all, we are interested in comparing groups with
individuals, not with genes. Yet gene-centered theorists have scarcely
addressed this question.4 The situation is so extraordinary that
historians of science should study it in detail: A giant edifice is
built on the foundation of genes as replicators, and therefore the
"fundamental" unit of selection, which seems to obliterate the concept
of groups as organisms. In truth, however, the replicator concept
cannot even account for the organismic properties of individuals.
Almost as an afterthought, the vehicle concept is tacked onto the
edifice to reflect the harmonious organization of individuals but it
is not extended to the level of groups. The entire edifice therefore
fails to address the question that it originally seemed to answer so
conclusively and that made it seem so important.

This is such a crucial and unappreciated point that we want to
reinforce it by quoting from The Ant and the Peacock (Cronin 1991),
one of the most recent book-length treatments of evolution for a
popular audience.5 Cronin is a philosopher who has a part-time
appointment at Oxford University's Zoology Department. Her book was
chosen as one of the year's best by the New York Times and has been
cited with approval by authorities such as G.C. Williams (1993) and
John Maynard Smith (1992) and Daniel Dennett (1992) 6. There is every
reason for the reader to think that it represents state-of-the-art
evolutionary biology.

Cronin agrees with us that naive group selectionists compared groups
to individuals:

Many an ecologist, equipped with no more than a flimsy analogy,
marched cheerfully from the familiar Darwinian territory of individual
organisms into a world of populations and groups. Populations were
treated as individuals that just happened to be a notch or two up in
the hierarchy of life...(p278).

Her treatment of Williams is also close to our own: "Williams
retaliated with two types of argument. He spelled out why genes are
suitable candidates for units of selection whereas organisms, groups
and so on are not...(p286)." Here Cronin commits (along with Williams)
the fallacy that we outlined above. If individuals and groups are not
replicators, then the replicator concept cannot be used to argue that
they are different from each other! Faced with this dilemma, Cronin
dutifully invokes vehicles to explain the organismal properties of
individuals, with a nod to groups:

If organisms are not replicators, what are they? The answer is that
they are vehicles of replicators...Groups, too, are vehicles, but far
less distinct, less unified...In this weak sense, then, 'group
selection' could occur...But even if they [group-level adaptations]
did arise--which as we've seen is unlikely--they would in no way
undermine the status of genes as the only units of replicator
selection. This does not mean that higher level entities are
unimportant in evolution. They are important, but in a different way:
as vehicles (p289).

But this is all that naive group selectionists ever claimed--that
groups are like individuals by virtue of the adaptive coordination of
their parts! Finally, Cronin concludes that group selection is
unimportant even in the so-called weak sense:

But group selectionism (weak group selectionism) makes claims about
adaptations, about characteristics that satisfy the fragmented
purposes of all the genes in the group and, what's more, confer an
advantage on that group over other groups. Group-level adaptations,
then, are a very special case of emergent properties--so special that
it would be rash to expect them to have played any significant role in
evolution. Of course, the question of what role they have actually
played is an empirical, not a conceptual issue. It is a factual matter
about which adaptations happen to have arisen at levels higher than
organisms, about the extent to which groups and other higher-level
vehicles happen to have been roadworthy. [p290]

Cronin is in the unhappy position of a circus artist who stands on the
backs of two horses, replicators and vehicles, as they gallop around
the ring. The only way that she can perform this dazzling feat is by
making the horses gallop in parallel. Thus, groups must fail not only
as replicators but as vehicles. What Cronin cannot bring herself to
say is that the replicator concept that forms the inspiration for her
book is totally irrelevant to the question that is and always was at
the heart of the group selection controversy--can groups be like
individuals in the harmony and coordination of their parts? To answer
this question we must restructure the entire edifice around the
concept of vehicles, not replicators. That is exactly what the
positive literature on group selection does7.

Taking vehicles seriously. The essence of the vehicle concept is
shared fate, exemplified by the adage (and by Dawkins' rowing crew
metaphor) "we're all in the same boat." Our restructured edifice must
first be able to identify the vehicle(s) of selection in any
particular biological or human situation.

In figure 1, the biological hierarchy is shown as a nested series of
units, each of which is a population of lower level units. An
individual can be regarded as a population of genes and a group is
obviously a population of individuals. A metapopulation is a
population of groups. For example, a single field might contain
hundreds of ant colonies. Each colony certainly deserves to be called
a group and yet we must also recognize the collection of groups as an
important entity. The hierarchy has been left open on both ends
because genes are composed of subunits and metapopulations can exist
in higher-order metapopulations, a fact that will become important
later.

Vehicles of selection can be identified on a trait-by-trait basis by
the following simple procedure: Starting at the lowest level of the
hierarchy8, ask the question "Do genes within a single individual
differ in fitness?" If the answer is "no", then they share the same
fate and are part of the same vehicle. Proceeding up the hierarchy,
ask the question: "Do individuals within a single group differ in
fitness?" If the answer is "no" then once again they share the same
fate and we must proceed up the hierarchy until we find the level(s)
at which units differ in fitness. This is the level (or levels) at
which natural selection actually operates, producing the functional
organization implicit in the word "organism at .9 Everything below this
level will acquire the status of organs and everything above this
level will be vulnerable to social dilemmas.10

Already we can make three fundamental points: First, focusing on
vehicles makes it obvious that the concept of "organism" is not
invariably linked to the "individual" level of the biological
hierarchy. To the extent that genes can differ in fitness within
single individuals, the genes will become the organisms and the
individual will become a dysfunctional collection of genes. To the
extent that individuals in the same group are in the same "boat" with
respect to fitness, they will evolve into harmonious organs of
group-level organization. In short, the organ-organism- population
trichotomy can be frame-shifted both up and down the biological
hierarchy. Frame-shifts in both directions have been documented and
examples will be provided below.

Second, the status of organ vs. organism vs. population must be
assigned on a trait-by-trait basis. It is possible for a single
creature such as a wasp to be an organ with respect to some traits, an
organism with respect to other traits, and a population of organisms
with respect to still other traits. This may sound strange but it
follows directly from the fact that fitness is a property of traits,
not organisms (Sober 1984). For example, in the parasitic wasp Nasonia
vitripennis, some males harbor what has been called the oultimate@
selfish gene, because it destroys all the other genes in the male to
facilitate its own transmission (Werren 1991,1992). In this case the
gene is the vehicle of selection but most other genes in the same
species evolve by standard Darwinian selection, in which case the
individual is the vehicle of selection.

Third, fitness differences are not always concentrated at one level of
the biological hierarchy. Individuals with trait A can be less fit
than individuals with trait B within single groups, while groups of
individuals with trait A are more fit than groups of individuals with
trait B. In these cases we cannot assign the status of organ, organism
or population and must settle for some hybrid designation. As one
example, Williams (1966) showed that, given certain assumptions,
natural selection within single groups favors an even sex ratio while
natural selection between groups favors an extreme female-biased sex
ratio. He thought that the absence of female-biased sex ratios in
nature provided conclusive evidence against group selection. Since
then, moderately female-biased sex ratios have been discovered in
literally hundreds of species, which reflect an equilibrium between
opposing forces of within- and between-group selection (Charnov 1982,
Colwell 1981, Frank 1986, Wilson and Colwell 1981).11 As we will show,
altruism is another example of a hybrid trait that is selected against
at the individual level but favored at the group level.

Now we will document our claim that the organ-organism-population
trichotomy can be frame-shifted both up and down the biological
hierarchy.

Individuals as dysfunctional populations of genetic elements.
Individuals are traditionally viewed as stable entities that (barring
mutation) pass the same genes in the same proportions to their
offspring that they received from their parents. However, this is not
always the case. For example, a diploid individual can be regarded as
a population of N=2 alleles at each locus. The rules of meiosis
usually dictate that each allele is equally represented in the
gametes. Occasionally a mutation arises that "breaks" the rules of
meiosis by appearing in greater than 50% of the gametes, a phenomenon
known as "meiotic drive" (Crow 1979). These same alleles often
decrease the survival of individuals that possess them and can even be
lethal in homozygous form. Let us apply our simple procedure to this
example to identify the vehicle(s) of selection. Can genes within a
single individual differ in fitness? The answer is "yes" because the
driving allele exists at a frequency of p=0.5 in heterozygotes and
occurs in the gametes of those heterozygotes with a frequency of
p>0.5. Natural selection therefore operates at the gene level,
favoring the driving allele. Now proceed up the hierarchy. Do
individuals within a single population differ in fitness? The answer
is again "yes" because individuals with the driving allele suffer
higher mortality than individuals without the driving allele. Natural
selection therefore operates against the driving allele at the
individual level. Both the gene and the individual are vehicles of
selection. If gene-level selection is sufficiently strong, the driving
allele can evolve despite its negative effects on individuals.

Many other examples of natural selection within individuals could be
cited involving chromosomal genes (Dover 1986), cytoplasmic genes
(Cosmides and Tooby 1981), and competing cell lineages (Buss 1987).
These examples have been received with great fanfare by gene-centered
theorists as some sort of confirmation of their theory. But these
examples do not confirm the thesis that genes are replicators--all
genes are replicators by definition and no documentation is needed.
These examples are remarkable because they show that genes can
sometimes be vehicles. They seem bizarre and disorienting because they
violate our deeply rooted notion that individuals are organisms. They
force us to realize that individuals are at least occasionally nothing
more than groups of genes, subject to the same social dilemmas as our
imaginary population of rabbits.

Why aren't examples of within-individual selection more common?
Several authors have speculated that the rules of meiosis and other
mechanisms that suppress evolution within individuals are themselves
the product of natural selection acting at the individual level. Genes
that profit at the expense of other genes within the same individual
are metaphorically referred to as "outlaws" (Alexander and Borgia
1978) and the regulatory machinery that evolves to suppress them is
referred to as a "parliament" of genes (Leigh 1977). Ironically, most
of the authors who employ these metaphors are reluctant to think of
real parliaments as regulatory machines that reduce fitness
differences within groups, thereby concentrating adaptation at the
group level. Gene-centered theorists frame-shift downward with
enthusiasm but they are much more reluctant to frame-shift upward.

Groups as organisms. Social insect colonies have been regarded as
"superorganisms" for centuries. Sterile castes with division of labor,
colony-level thermoregulation and patterns of information processing
that transcend single brains all suggest intuitively that colonies are
functionally organized units, built out of individual insects. This
interpretation was rejected by gene-centered theorists, however, who
claimed to explain the social insects without invoking group
selection. Their scorn for the earlier view is illustrated by
West-Eberhard (1981 p 12; parenthetical comments are hers): "Despite
the logical force of arguments against group (or colony) selection,
and the invention of tidy explanations for collaboration in individual
terms, the supraorganism (colony-level selection) still haunts
evolutionary discussions of insect sociality."

Let us apply our simple procedure to locate the vehicle(s) of
selection in the social insects. Can genes differ in fitness within
individuals? Yes-- the social insects resemble other species in this
regard--but the products of selection at this level are unlikely to
enhance colony function. Can individuals differ in fitness within
single colonies? Yes; as one example, honey bee queens usually mate
with more than one male, leading to multiple patrilines among the
workers. Many insects can detect genetic similarity using odor cues
and it is plausible to expect workers tending future queens to favor
members of their own patriline. As with evolution within individuals,
however, this kind of palace intrigue is more likely to disrupt colony
function than to enhance it (Ratnieks 1988, Ratnieks and Visscher
1989). We therefore must proceed up the hierarchy and ask "Can groups
(=colonies) differ in fitness within a metapopulation?"

Unlike our archipelago of rabbits, in which the metapopulation seemed
somewhat contrived, the social insects obviously exist as a population
of colonies. Consider a mutation that is expressed in honeybee workers
and increases the efficiency of the hive, ultimately causing the queen
to produce more reproductive offspring. It is obvious that this
mutation will spread, not by increasing in frequency within the hive,
but by causing hives possessing the mutation to out-produce other
hives. Thus, for the majority of traits that improve colony function,
the colony is the vehicle of selection and can legitimately be called
an organism. Focusing on vehicles, not replicators, as the central
concept makes West-Eberhard's statement sound absurd. Notice also that
Williams' first argument, that group-level adaptations require a
process of natural selection at the group level, is correct. But his
empirical claim that group selection is weak and group-level
adaptations don't exist is just plain wrong in the case of the
eusocial insects--both the process and the product are manifest. The
focus on genes as the "fundamental" unit of replication merely
distracts from the more relevant framework based on vehicles.
Fortunately, most social insect biologists now realize this and once
again regard social insect colonies as "group-level vehicles of gene
survival" (Seeley 1989), at least to the degree that they evolve by
between-colony selection.

Before leaving the social insects it is worth asking a question that
we will pose later for humans: What does it mean for a creature such
as an ant or a honeybee, itself an organism in some respects, to also
be part of a group-level organism? A partial answer is provided by
Seeley (1989), whose elegant experiments reveal the mechanisms of
colony-level adaptation. A honeybee hive monitors its floral resources
over several square miles and maximizes its energy intake with
impressive accuracy. If the quality of a food patch is experimentally
lowered, the hive responds within minutes by shifting workers away
from that patch and toward ones that are more profitable. Yet
individual bees visit only one patch and have no frame of comparison.
Instead, individuals contribute one link to a chain of events that
allows the comparison to be made at the hive level. Bees returning
from the low quality patch dance less and themselves are less likely
to revisit. With fewer bees returning from the poor resource, bees
from better patches are able to unload their nectar faster, which they
use as a cue to dance more. Newly recruited bees are therefore
directed to the best patches. Adaptive foraging is accomplished by a
decentralized process in which individuals are more like neurons than
decision-making agents in their own right (Camazine and Sneyd 1991;
see Camazine 1991, Deneubourg and Goss 1989, Franks 1989 and Wilson
and Holldobler 1988 for other examples of group-level cognition in
social insects). The image of a group-level mind composed of
relatively mindless individuals is aptly described in D. HofstadterYs
(1979) essay ant fugue. We suggest that some aspects of human
mentality can also be understood as a form of group- level cognition
(see below).

Finding the vehicles in inclusive fitness theory. How was it possible
for West-Eberhard and others to think that the social insects could be
explained without invoking group selection? Her "tidy" alternative
explanation was inclusive fitness theory, which she and almost
everyone else regarded as a robust alternative to group selection.
However, inclusive fitness theory is a gene-centered framework that
does not identify the vehicle(s) of selection. When we rebuild
inclusive fitness theory on the foundation of vehicles we discover
that it is not an alternative to the idea of group selection at all
(Michod 1982, Queller 1991,1992, Uyenoyama and Feldman 1980, Wade
1985, Wilson 1977, 1980). It would be hard to imagine a more important
discovery, yet human behavioral scientists are almost totally unaware
of it, in part because their evolutionary informants so assiduously
ignore it. Even the most recent accounts of evolution for the human
sciences treat inclusive fitness and group selection as separate
mechanisms (e.g., Alexander 1987, 1989,1992, Archer 1991, Daly and
Wilson 1988, Frank 1988, Krebs 1987, MacDonald 1988, Noonan 1987). We
will consider one of these treatments in detail because it allows us
to make a number of important points throughout the rest of our paper.
Here is Frank's (1988 p37-39) depiction of group selection.

Group-selection models are the favored turf of biologists and others
who feel that people are genuinely altruistic. Many biologists are
skeptical of these models, which reject the central Darwinian
assumption that selection occurs at the individual level. In his
recent text, for example, Trivers includes a chapter entitled "The
group selection fallacy". With thinly veiled contempt, he defines
group selection as "the differential reproduction of groups, often
imagined to favor traits that are individually disadvantageous but
evolve because they benefit the larger group". Group selectionists
have attempted to show that genuine altruism, as conventionally
defined, is just such a trait... Could altruism have evolved via group
selection? For this to have happened, altruistic groups would have had
to prosper at the expense of less altruistic groups in the competition
for scarce resources. This requirement, by itself, is not problematic.
After all, altruism is efficient at the group level (recall that pairs
of cooperators in the prisoner's dilemma do better than pairs of
defectors), and we can imagine ways that altruistic groups might avoid
being taken advantage of by less altruistic groups...

But even if we suppose that the superior performance of the altruistic
group enables it to triumph over all other groups, the group selection
story still faces a formidable hurdle. The conventional definition
again, is that nonaltruistic behavior is advantageous to the
individual . Even in an altruistic group, not every individual will be
equally altruistic. When individuals differ, there will be selection
pressure in favor of the least altruistic members. And as long as
these individuals get higher payoffs, they will comprise an
ever-larger share of the altruistic group. So even in the event that a
purely altruistic group triumphs over all other groups, the logic of
selection at the individual level appears to spell ultimate doom for
genuinely altruistic behavior. It can triumph only when the extinction
rate of groups is comparable to the mortality rate for individuals
within them. As [E.O.] Wilson stresses, this condition is rarely if
ever met in practice.

Frank's account of group selection is accurate and similar to our own
rabbit example. He also accurately depicts the climate of the group
selection debate during the 60's and 70's. Now here is Frank's
description of inclusive fitness theory (p25-27):

Biologists have made numerous attempts to explain behavior that, on
its face, appears self-sacrificing. Many of these make use of William
Hamilton's notion of kin selection. According to Hamilton, an
individual will often be able to promote its own genetic future by
making sacrifices on behalf of others who carry copies of its genes...
The kin-selection model fits comfortably within the Darwinian
framework, and has clearly established predictive power... Sacrifices
made on behalf of kin are an example of what E.O. Wilson calls "'hard
core' altruism, a set of responses relatively unaffected by social
reward or punishment beyond childhood." Viewed from one perspective,
the behavior accounted for by the kin- selection model is not really
self-sacrificing behavior at all. When an individual helps a relative,
it is merely helping that part of itself that is embodied in the
relative's genes...

FrankYs exposition certainly suggests that group selection and kin
selection are alternative theories that invoke separate mechanisms.
Frank himself regards them as so different that he calls one
non-Darwinian and the other Darwinian!12 Now consider the model in
figure 2, which rebuilds inclusive fitness theory on the foundation of
vehicles (see Michod 1982, Queller 1991,1992, Sober 1993, Uyenoyama
and Feldman 1980, Wade 1985, Wilson 1977, 1980 for more formal
treatments). A dominant allele (A) codes for a behavior that is
expressed only among full siblings. The behavior decreases the fitness
of the actor by an amount c and increases the fitness of a single
recipient by an amount b. In figure 2, adults of the three genotypes
(AA,Aa,aa) combine randomly to form six types of mating pairs (AAxAA,
AAxAa, AAxaa, AaxAa, Aaxaa, aaxaa). Each mating pair produces sibling
groups with a characteristic proportion of altruists and
non-altruists. Thus, the sibling groups derived from AAxAA matings are
entirely altruistic, the groups derived from aaxaa matings are
entirely non-altruistic and so on. Since the behavior is expressed
only among siblings, the progeny of each mated pair is an isolated
group as far as the expression of the behavior is concerned. Thus, any
model of sibling interactions invokes a metapopulation of sibgroups.

Now let us employ our simple procedure to locate the vehicles of
selection. Beginning at the lowest level of the hierarchy, there is no
meiotic drive or other forms of selection within individuals in this
example. Moving up the hierarchy, do individuals within single
sibgroups differ in fitness? Yes, and natural selection at this level
operates against the altruists. In all sibgroups that contain both
selfish (aa) and altruistic (Aa,AA) phenotypes, the former are
fitter--they benefit from the latter's help without sharing the costs.
Sibling groups are similar to other groups in this respect. Continuing
up the hierarchy, can sibgroups differ in fitness within the
metapopulation? Yes, and it is here that we find the evolutionary
force that favors altruism. Since every altruist contributes a net
fitness increment of b-c to the sibgroup, the fitness of the
collective is directly proportional to the number of altruists in the
group. Sibgroups with more altruists outproduce sibgroups with fewer
altruists.

The degree of altruism that evolves depends on the balance of opposing
forces at the group and individual levels. Figure 3 shows why kin
groups are more favorable for the evolution of altruism than groups of
unrelated individuals. In the latter case, groups of size N are drawn
directly from the global population, forming a binomial distribution
of local gene frequencies. In the former case, groups of size two (the
parents) are drawn from the global population and groups of size N
(the siblings) are drawn from their gametes. This two-step sampling
procedure increases genetic variation among groups, intensifying
natural selection at the group level. Put another way, altruists are
segregated from non-altruists more in kin groups than in randomly
composed groups. In both cases there are mixed groups, however, and
evolution within mixed groups is the same regardless of whether they
are composed of siblings or nonrelatives. Notice that this explanation
does not invoke the concept of identity by descent, which seems to be
the cornerstone of inclusive fitness theory. There is no physical
difference between two altruistic genes that are identical by descent
and two altruistic genes that are not. The coefficient of relationship
is nothing more than an index of above-random genetic variation among
groups (e.g, Falconer 1982 ch 3- 5, Queller 1991,1992).

We invite the reader to go back to Frank's account of group selection
to confirm that it exactly describes the process of kin selection that
is portrayed in figure 2. Dr. Jekyl and Mr. Hyde are the same person.
The only discrepancy between Frank's account and figure 2 involves the
concept of extinction. Sibling groups don't last for multiple
generations and don't necessarily go extinct, but rather dissolve into
the larger population when the individuals become adults and have
their own offspring. Thus, sibling groups (and social insect colonies)
differ somewhat from our population of rabbits and the groups that
Frank and Trivers had in mind. But this does not disqualify sibling
groups as vehicles of selection. After all, individuals are transient
collections of genes that "dissolve" into the gene pool as gametes.
The ephemeral nature of groups in figure 2 makes them more similar to
individuals, not less.

Frank's account of kin selection appears so different, not because it
invokes a different mechanism for the evolution of altruism, but
because it utilizes a different accounting procedure for calculating
gene frequency change that does not compare the fitnesses of
individuals within single groups. The method correctly predicts the
degree of altruism that evolves but obscures the internal dynamics of
the process. In fact, when the vehicle-centered approach was first
published, many biologists who thought they were familiar with
inclusive fitness theory found it hard to believe that altruism is
actually selected against within kin-groups and evolves only by a
process of between-group selection.

The unification of group selection and kin selection has implications
for the distinction between ogenuine@ vs. oapparent@ altruism. This in
an important distinction in the human behavioral sciences and
evolutionary accounts such as FrankYs seem to provide a tidy answer:
The altruism that evolves by group selection is "genuine" because it
entails real self- sacrifice, while the altruism that evolves by kin
selection is only "apparent" because it is just genes promoting copies
of themselves in other individuals. The unified theory reveals that
this distinction is an artifact of the way that fitness is calculated.
Any trait that is selected at the group level can be made to appear
ogenuinely@ altruistic by comparing relative fitness within groups, or
only oapparently o altruistic by averaging fitness across groups
(Wilson 1992, Wilson and Dugatkin 1992). Thus, evolutionary biologists
have so far contributed little but confusion to the distinction
between genuine and apparent altruism.13 Finding the vehicles in
evolutionary game theory. Evolutionary game theory (also called ESS
theory for "evolutionarily stable strategy") is similar to economic
game theory except that the strategies compete in Darwinian fashion,
as opposed to being adopted by rational choice. It was developed to
explore the evolution of cooperation and was universally considered to
be an individual-level alternative to group selection. For example,
Dawkins (1980 p360) states

There is a common misconception that cooperation within a group at a
given level of organization must come about through selection between
groups...ESS theory provides a more parsimonious alternative.

We will explore the relationship between game theory and group
selection with a fanciful example that is based on Dawkins' rowing
crew metaphor. A species of cricket has evolved the peculiar habit of
scooting about the water on dead leaves in search of its resource
(water lily flowers). A leaf can be propelled much better by two
crickets than by one so they scoot about in pairs. Initially they were
quite awkward but natural selection eventually endowed them with
breathtaking morphological and behavioral adaptations for their task.
Especially impressive is the coordination of the pair. They take their
stations on each side of the leaf and stroke the water with their
modified legs in absolute unison, almost as if they are part of a
single organism. Coordination is facilitated by one member of the
pair, who synchronizes the strokes by chirping at regular intervals.
On closer examination it was discovered that the chirps not only
coordinate movements but also steer the little craft. A low-pitched
chirp causes the chirper to row harder and a high-pitched chirp causes
the non- chirper to row harder. The captain (as the chirper came to be
called) adjusts its pitch to correct for asymmetries in the shape of
the leaf and also to change direction as lily pads hove into view.
Either member of the pair can act as captain; the important thing is
that there be only one.

The evolution of any particular trait in this example can be examined
with a 2-person game theory model. For example, consider two types (A1
and A2) that differ in their ability to synchronize with their
partner's movement. If p is the frequency of A1 in the population and
if pairing is at random then three types of pairs exist (A1A1, A1A2,
A2A2) at frequencies of p2, 2p(1-p) and (1-p)2. Coordination, and
therefore fitness, is directly proportional to the number of A1
individuals in the pair, as shown by the payoff matrix in figure 3a.
The fitness of the two types, averaged across pairs, is WA1=5p+4(1-p)
and WA2=4p+3(1-p).

This is not a very interesting game theory model because it doesn't
pose a dilemma. WA1>WA2 for all values of p, making it obvious that A1
will evolve. However, this should not obscure a more fundamental
point, that the pair is the vehicle of selection. If we apply our
procedure we find no fitness differences between individuals within a
pair, in which case A1 can evolve only by causing pairs to succeed
relative to other pairs. The fact that the pairs are ephemeral,
perhaps lasting only a fraction of an individual's lifetime, is
irrelevant. Persistence is a requirement for replicators, not
vehicles. Coordination evolves among the individuals for exactly the
same reason that it evolves among genes within individuals, because
they are "in the same boat" as far as fitness differences are
concerned.

More generally, evolutionary game theory deploys a metapopulation
model, in which individuals exist within groups that exist within a
population of groups. When this elementary fact is recognized,
Dawkins' statement quoted above looks just as absurd as
West-Eberhard's statement about the social insects. Cooperation
evolves by group-level selection in a game theory model as surely as
cooperation among genes evolves by individual-level selection in a
standard population genetics model.14 In fact the two models are
mathematically identical; we can go from one to the other merely by
relabelling A1 and A2 as "alleles" rather than as "individuals" and
calling the pair a zygote (Hamilton 1971, Holt 1983, Maynard Smith
1987, Wilson 1983, 1989, 1990).

Continuing our example, suppose that a mutant type (A3) arises that
rushes onto the lily pad at the moment of arrival, kicking the boat
away and setting its hapless partner adrift. If both members of the
pair are the A3 type, however, they collide and have a probability of
drowning. The pay-off matrix for this situation is shown in figure 3b
and the average fitness of the two types is WA1=p(5)+(1-p)(0) and
WA3=p(10)+(1-p)(2).

This model is more interesting because it constitutes a social
dilemma. A3 evolves despite the fact that it disrupts group-level
functional organization. Applying our procedure, we find that the
nasty behavior is favored by within-group selection; A3 is more fit
than A1 within pairs. Cooperation, as before, is favored by between
group-selection; A1A1 and A1A3 pairs are more fit than A3A3 pairs. By
renaming the individuals "alleles" and the pairs "zygotes", we have
the example of meiotic drive described on page 14.

Continuing our example, suppose that a new mutant (A4) arises that can
remember the previous behavior of its partner. It acts honorably
toward new partners and thereafter imitates its partner's previous
behavior. This is the famous Tit-for-Tat strategy (Axelrod and
Hamilton 1981) that can evolve above a threshold frequency, given a
sufficient probability of future interactions (fig 3c). Applying our
procedure, we find that natural selection still favors A3 over A4
within pairs because A4 loses during the first interaction. A4 reduces
but does not eliminate its fitness disadvantage within groups by
changing its behavior and it evolves only because groups of A4A4
outperform groups of A4A3 and A3A3.15

Finally, suppose that yet another mutant arises (A5) that grabs hold
of its partner with one of its free legs, preventing it from leaping
prematurely onto the lily pad. The pay-off matrix for A5 vs. A3 is
shown in figure 3d. Applying our procedure, we find that fitness
differences within groups have been eliminated while between-group
selection still favors A5A5 and A5A3 over A3A3. A5 is like a dominant
allele in the sense that A5A5 and A5A3 groups are phenotypically
identical. Within- group selection has been eliminated by an evolved
trait. Once again the pair has achieved a harmony and coordination
that invites comparison with an organism, but with some safe-guards
built in, similar to the rules of fair meiosis at the genetic level.

How was it possible for Dawkins and virtually all other evolutionary
biologists to regard game theory as an individualistic theory that
does not require group selection? The answer is that groups were
treated as "environments" inhabited by individuals, in exactly the
same sense that Williams regarded individuals as "environments"
inhabited by genes. Averaging the fitness of individual types across
groups combines selection at all levels into a single measure of
"individual fitness" that correctly predicts the outcome of natural
selection but loses sight of the vehicles that natural selection
actually acts upon. Selection can operate entirely at the group level
(as it does in figure 3a and d) and still be represented in terms of
individual fitnesses simply because the average A2 (or A5) is more fit
than the average A1 (or A3). This definition of what "individual
selection" favors is synonymous with "anything that evolves,
regardless of the vehicles of selection". Of course, individuals are
not replicators and we can make them disappear along with groups by
averaging the fitness of genes across all contexts, arriving at a
definition of "gene selection" as "anything that evolves, regardless
of the vehicles of selection". These bloated definitions of individual
and gene selection have misled a generation of biologists into
thinking that natural selection almost never occurs at the level of
groups.

In this review we have concentrated on showing how the seemingly
alternative theories of kin selection, evolutionary game theory and
group selection have been united into a single theory of natural
selection acting on a nested hierarchy of units. The unified theory
does more than redescribe the familiar results of kin selection and
game theory, however; it also predicts that natural selection can
operate on units that were never anticipated by kin selection and game
theory, such as multigenerational groups founded by a few individuals
(e.g., Aviles 1993, Wilson 1987), large groups of unrelated
individuals (Boyd and Richerson 1985, 1990a,b), and even multispecies
communities (Goodnight 1990a,b; Wilson 1976,1980, 1987). For example,
accounts of human evolution that are based on nepotism and reciprocity
often conclude that prosocial behavior in modern humans is maladaptive
because it is not confined to genetic relatives and is often given
without expectation of return benefits (e.g., Ruse 1986; but see
Alexander 1987). Later we will argue that these prosocial behaviors
can be adaptive because group-level vehicles exist that are larger
than the kin groups and very small groups modelled by kin selection
and evolutionary game theory.

We summarize our review of group selection in biology as follows:
Williams' (1966) argument against group selection came in three parts:
a) higher-level adaptations require higher levels of selection, b)
higher levels of selection are theoretically possible but unlikely to
occur in nature, c) the gene is the fundamental unit of selection
because it is a replicator. The third part of this argument is
irrelevant to the question of whether groups can be like individuals
in the harmony and coordination of their parts. As far as we can tell,
all gene-centered theorists now concede this point (e.g., Dawkins
1982, 1989, Grafen 1984, Williams 1992). Taking vehicles seriously
requires more than acknowledging a few cases of group selection,
however; it demands a restructuring of the entire edifice. It is a
mistake to think there is one weak group-level theory and two strong
individual-level theories to explain the evolution of
altruism/cooperation. Rather, there is one theory of natural selection
operating on a nested hierarchy of units, of which inclusive fitness
and game theory are special cases. When we focus on vehicles of
selection, the empirical claim that constitutes the second part of
Williams' argument disintegrates but the first part remains intact.
Adaptation at any level of the biological hierarchy requires a process
of natural selection at that level.

As might be expected from such a radical restructuring, some
biologists who previously regarded group selection with contempt have
found it difficult to accept this Cinderella-like reversal of
fortunes. Thus, a large group of knowledgeable biologists who are
perfectly comfortable with the hierarchical approach (see table 1)
coexists with another large group whose members adhere to the earlier
view. We think that the views of the former group are in the process
of replacing the views of the latter. The replacement process is
painfully slow, however, partly because the gene- centered view is so
thoroughly entrenched and partly because the major gene-centered
theorists have been reluctant to acknowledge the consequences of
taking vehicles seriously. As one example, Sterelny and Kitcher (1988)
manage to defend the selfish gene concept without even considering the
question of whether groups can be vehicles of selection.16 We make
these bold statements to provoke a response. If gene-centered
theorists wish to rebut our account, let them speak in the commentary
section that follows this paper. Otherwise, let the replacement
process continue at a faster pace. All of the major developments that
we have reviewed are over ten years old and it is time for them to be
acknowledged generally.

GROUP SELECTION AND HUMAN BEHAVIOR17

In his description of honey bee colonies as superorganisms, Seeley
(1989 p546) wrote that "...larger and more complex vehicles have
evidently proved superior to smaller and simpler vehicles in certain
ecological settings. By virtue of its greater size and mobility and
other traits, a multicellular organism is sometimes a better
gene-survival machine than is a single eukaryotic cell...Likewise, the
genes inside organisms sometimes fare better when they reside in an
integrated society of organisms rather than in a single organism
because of superior defensive, feeding, and homeostatic abilities of
functionally organized groups."

This statement applies almost as well to humans as to honeybees.
Nevertheless, group-level functional organization in humans is usually
portrayed as a byproduct of individual self-interest. Even the most
recent evolutionary accounts of human behavior are based on Williams'
first commandment and the triumph of "individual selection" in biology
is often used to justify the individualistic perspective in the human
behavioral sciences.

We think that the hierarchical theory of natural selection leads to a
very different conclusion. Individualism in biology and in the human
sciences both fail for the same reasons. As far as human evolution is
concerned, group-level functional organization is not a "byproduct" of
self-interest in humans any more than it is in honeybees. The
metapopulation structure of human interactions is manifest;
individuals live in social groups which themselves comprise a
population of social groups. Even a relatively small social unit such
as a village is a metapopulation of still smaller groups such as
kinship units or coalitions of unrelated individuals. Genetic
variation among human groups is not as great as among bee hives, but,
as we will attempt to show, human cognitive abilities provide other
mechanisms for concentrating natural selection at the group level,
even when the groups are composed of large numbers of unrelated
individuals (also see Alexander 1987, 1989, Boyd and Richerson
1985,1990, Knauft 1991).

Individualistic accounts of human behavior do not ignore these facts
(e.g., Alexander 1979, 1987, 1989, 1992), but they are able to remain
individualistic only by ignoring the concept of vehicles. As soon as
we make vehicles the center of our analysis, group selection emerges
as an important force in human evolution and the functional
organization of human groups can be interpreted at face value, as
adaptations that evolve because groups expressing the adaptations
outcompeted other groups. The same adaptations can be and often are
selectively neutral or even disadvantageous within groups. In the
following sections we will sketch some of the implications of the
hierarchical view for the study of human behavior.

The new group selection is not a return to naive group selection. Some
biologists have been reluctant to accept group selection in any form
because they fear it will encourage the uncritical thinking of Emerson
and others who simply assumed the existence of higher-level
adaptations (e.g., Maynard Smith 1987a,b). Behavioral scientists may
share this reluctance because every branch of the human sciences seems
to have thinkers like Emerson (1960) and Wynne-Edwards (1962, 1986)
who treat social groups as the unit of adaptation as if individuals
and their strivings scarcely exist. We therefore want to stress, in
the strongest possible terms, that these views are not supported by
modern group selection theory. Consider the example within biology of
the Gaia hypothesis (Lovelock 1979), which portrays the entire planet
as a self-regulating organism. Even a passing knowledge of group
selection theory exposes Gaia as just another pretty metaphor because
planet-level adaptation would require a process of between-planet
selection (Wilson and Sober 1989). Grandiose theories of human
societies as organisms would be correct only if natural selection
operated entirely at the society level, which no one proposes. The
hierarchical theory's attention to mechanism makes it easy to
discredit such "theories" both in biology and the human sciences.

Groups are real. Having distanced ourselves from naive group
selection, we want to stress with equal force that it is legitimate to
treat social groups as organisms, to the extent that natural selection
operates at the group level. Williams' first commandment ("Thou shalt
not apply the adaptationist program above the individual level") is
fundamentally wrong. To see this, consider a simplified situation in
which natural selection acts entirely at the individual level, in
which case genes within individuals become entirely cooperative and
individuals within the population frequently face conflicts of
interest that lead to social dilemmas. Employing the adaptationist
program at the individual level leads to the celebrated insights that
we discussed at the beginning of this paper. Employing the
adaptationist program at the population level leads to the errors of
naive group selection that Williams so effectively exposed. But now
suppose that someone misleadingly suggests that we should not employ
the adaptationist program at the individual level--that the fitness of
individuals is actually irrelevant to the evolutionary process; it is
only gene-level fitness that counts. This misleading advice would have
us apply the adaptationist program below the level at which natural
selection actually operates.

In a sense, this is just what the gene's-eye view of Williams and
Dawkins invites us to do. Even they do not take it seriously enough to
abandon the individual's-eye view, however, since they assert the
equivalence of gene fitness and individual fitness when the latter are
vehicles of selection. In practice, most biologists pay passing
tribute to the gene as the "fundamental" unit of selection and think
about adaptation at the individual level as they always have (e.g.,
Grafen 1984, quoted in note 4; Maynard Smith 1987a, p 125). We submit
that evolutionary biologists would be severely handicapped if they
could not ask the simple question "what would a well adapted
individual be like?" Yet that is the very question that is prohibited
at the group level by Williams' first commandment. If commandments are
needed, we suggest the following: "Thou shalt not apply the
adaptationist program either above or below the level(s) at which
natural selection operates". This statement avoids both the excesses
of naive group selection and the excesses of naive individual and gene
selection that we have outlined above.

According to Campbell (1993 p1), the human behavioral sciences are
dominated by something very similar to Williams' first commandment:

Methodological individualism dominates our neighboring field of
economics, much of sociology, and all of psychology's excursions into
organizational theory. This is the dogma that all human social group
processes are to be explained by laws of individual behavior--that
groups and social organizations have no ontological reality--that
where used, references to organizations, etc. are but convenient
summaries of individual behavior...We must reject methodological
individualism as an a priori assumption, make the issue an empirical
one, and take the position that groups, human social organizations,
might be ontologically real, with laws not derivable from individual
psychology...One of my favorite early papers (Campbell 1958)
explicitly sides with that strident minority of sociologists who
assert that "Groups are real!" even though it finds human
organizations "fuzzier" than stones or white rats.

The hierarchical theory of natural selection provides an excellent
justification for regarding groups as "real". Groups are "real" to the
extent that they become functionally organized by natural selection at
the group level. However, for traits that evolve by within-group
selection, groups really should be regarded as by-products of
individual behavior. Since group selection is seldom the only force
operating on a trait, the hierarchical theory explains both the
reality of groups that Campbell emphasizes and the genuinely
individualistic side of human nature that is also an essential part of
his thinking.18

Altruism and organism. Group selection is often studied as a mechanism
for the evolution of altruism. We have also seen that groups become
organisms to the extent that natural selection operates at the group
level. Although the concepts of altruism and organism are closely
related, there is also an important difference. Altruism involves a
conflict between levels of selection. Groups of altruists beat groups
of nonaltruists, but nonaltruists also beat altruists within groups.
As natural selection becomes concentrated at the group level,
converting the group into an organism, the self-sacrificial component
of altruism disappears. In other words, an object can be an organism
without tts parts behaving self- sacrificially.

The distinction between altruism and the interactions among parts of
an organism is illustrated by our fanciful cricket example. The four
pay- off matrices in figure 3 represent a) pure between-group
selection, b) strong conflict between levels of selection, c) weak
conflict between levels of selection, and d) a return to pure
between-group selection. Within-group selection is absent from the
first example by virtue of the situation, since coordination has an
equal effect on both occupants of the leaf. Within-group selection is
absent from the fourth example by virtue of an adaptation, since the
"outlaw" A3 type cannot operate in the presence of the "parliament" A5
type.

It might seem that group-level adaptations would be easiest to
recognize in group-level organisms. Ironically, the opposite is true,
at least from the individualistic perspective. Individualists
acknowledge group-level adaptations when they are easily exploited
within groups, but when they are protected, or when exploitation is
not possible by virtue of the situation, group-level adaptations are
seen as examples of individual self-interest, despite the fact that
they evolve purely by between-group selection and result in total
within-group coordination. Payoff matrices such as 3a and 3d are
seldom even considered by game theorists because their outcome is so
obvious. In the absence of fitness differences within groups, any
amount of genetic variation between groups is sufficient to select for
A1 and A5, including the variation that is caused by random pairing.
It is only by adding within-group selection that we can generate the
social dilemmas that are deemed interesting enough to model. But A1
and A5 should not be viewed as examples of self-interest just because
they easily evolve! As we have seen, groups are the vehicles of
selection in these examples as surely as individuals are the vehicles
in standard Darwinian selection. To call A1 and A5 examples of
self-interest is to place them in the same category as A3, which
evolves by within-group selection and disrupts group-level
organization. Putting it another way, by lumping together the products
of within- and between-group selection, the individualistic
perspective does not distinguish between the outlaw and the
parliament, turning oself-interest@ into a concept that is as empty as
it is universal.

Failure to recognize group-level adaptation in the absence of altruism
extends far beyond game theory. We present an example from Alexander
(1987) in detail, in part because he is one of the most influential
biologists writing on human evolution. Alexander envisions moral
systems as levelers of reproductive opportunities within groups:

The tendency in the development of the largest human groups, although
not always consistent, seems to be toward equality of opportunity for
every individual to reproduce via its own offspring. Because human
social groups are not enormous nuclear families, like social insect
colonies, ...competition and conflicts of interest are also diverse
and complex to an unparalleled degree. Hence, I believe, derives our
topic of moral systems. We can ask legitimately whether or not the
trend toward greater leveling of reproductive opportunities in the
largest, most stable human groups indicates that such groups (nations)
are the most difficult to hold together without the promise or reality
of equality of opportunity (p69).19

Alexander explicitly compares human moral systems to the genetic rules
of meiosis that eliminate fitness differences within individuals:

A corollary to reproductive opportunity leveling in humans may occur
through mitosis and meiosis in sexual organisms. It has generally been
overlooked that these very widely studied processes are so designed as
usually to give each gene or other genetic subunit of the genome...the
same opportunity as any other of appearing in the daughter cells...It
is not inappropriate to speculate that the leveling of reproductive
opportunity for intragenomic components--regardless of its
mechanism--is a prerequisite for the remarkable unity of
genomes...[p69]

Since the rules of meiosis concentrate natural selection at the
individual level, producing individual-level organisms, moral rules
must concentrate natural selection at the group level, producing
group-level organisms--right? Wrong. Here is Alexander's verdict on
group selection:

Finally, many easily made observations on organisms indicate that
selection is most effective below group levels. These include such
things as evidence of conflicts among individuals within social
groups, failure of semelparous organisms (one-time breeders) to forego
reproduction when resources are scarce, and strong resistance to
adopting nonrelatives by individuals evidently long evolved in social
groups. None of these observations is likely if the individual's
interests are consistently the same as those of the group or if, to
put it differently, allelic survival typically were most affected by
selection at the group level (p37-8).

All of these examples involve altruistic traits that are highly
vulnerable to exploitation within groups. The only evidence that
Alexander will accept for group selection is extreme self-sacrifice.
Somehow, Alexander manages to combine a strong emphasis on
between-group competition and opportunity leveling within groups with
a belief that group selection can be dismissed and that everything,
parliaments and outlaws alike, are products of self interest.20 To
make matters worse, Alexander speaks for the majority of biologists
interested in human behavior. For example, here is Daly and Wilson's
(1988 p254) tidy statement about human morality:

If conscience and empathy were impediments to the advancement of self-
interest, then we would have evolved to be amoral sociopaths. Rather
than representing the denial of self-interest, our moral sensibilities
must be intelligible as means to the end of fitness in the social
environment in which we evolved.

We hope the reader recognizes the familiar pattern of treating groups
as "environments" inhabited by individuals and defining self-interest
as "anything that evolves" without any consideration of vehicles.
Alexander, Daly and Wilson join the anti-group selection chorus and
then provide dozens of examples of human groups as vehicles of
selection without ever acknowledging what gene-centered theorists have
already conceded--that group selection is a "vehicle" question.

Alexander's theory of moral systems can be rebuilt on the foundation
of vehicles as follows: Human adaptations can evolve along two major
pathways; a) by increasing the fitness of individuals relative to
others within the same social group, and b) by increasing the fitness
of social groups as collectives, relative to other social groups. Both
pathways have been important in the evolution of the psychological
mechanisms that govern human behavior. Sometimes group selection is
important just by virtue of the situation. For example, the only way
to defend a village might be to build a stockade, which benefits the
collective by its nature. We are not surprised to see villagers
building stockades, even when they are genetically unrelated to each
other. We are not surprised when they coordinate their efforts in ways
that invite comparison to a single organism. Nor do we regard them as
especially morally praiseworthy as they feverishly work to save their
collective skins. But building the stockade is not selfish just
because it is reasonable. Applying our procedure, we find that the
village is the vehicle of selection. We expect the stockade to be
built for the same reason that we expect A1 and A5 to evolve in the
game theory models; because in this particular situation group-level
selection is very strong relative to within-group selection. If we
define behaviors on the basis of fitness effects (as all evolutionists
do), and if we want our terminology to reflect the vehicle(s) that
natural selection acts upon, we should call stockade-building
groupish, not selfish.

Many other situations in human life provide opportunities for
adaptation via the first pathway, by increasing the fitness of
individuals relative to others within the same social group. Even with
our stockade example we can imagine a temptation to selfishly
cultivate one's own garden or romantic possibilities as others build
the stockade. The use of the word selfish is fully appropriate here
because the individual is the vehicle of selection whose behaviors
tend to disrupt group-level functional organization.

The balance between levels of selection is not determined exclusively
by the situation, however. Adaptive human behavior not only reflects
the balance between levels,but also can alter the balance between
levels. Moral sentiments and moral social systems may function as
"rules of meiosis" that often concentrate fitness differences, and
therefore functional organization, at the group level. This is the
core of Alexander's thesis. When stated in terms of vehicles, however,
AlexanderYs theory acquires a familiar and conventional ring that is
absent from his own account. Moral systems are defined as "social
organizations designed to maximize the benefit of the group as a
collective." Immoral behaviors are defined as "behaviors that benefit
individuals at the expense of other individuals within the same
group." These are close to the concepts of moral and immoral behavior
in folk psychology.21 The shock value of Alexander's account, in which
the gentle reader is made to face the grim reality that all is
self-interest, evaporates when we realize that for Alexander,
self-interest is everything that evolves, at all levels of the
biological hierarchy.22

We will return to moral systems with an empirical example, but first
we must consider the important issue of psychological motivation.

Psychological selfishness and its alternatives. Dawkins portrays genes
as psychologically selfish entities that manipulate their environment,
including the genotypic environment in which they reside, to increase
their own fitness. This image is obviously metaphorical, allowing
Dawkins to use a familiar human reasoning process to describe the
outcome of natural selection. The metaphor is relatively innocuous
because there is no danger that it can be taken literally. No one
believes that genes are intentional systems of any sort, much less
systems motivated by self interest.

Frame-shifting upward, it is possible to portray individuals as
psychologically selfish entities that manipulate their environment,
including the social environment in which they reside, to increase
their own fitness. This image of "selfish individuals" may also be
metaphorical but it is more insidious because it can be taken
literally. In other words, it is possible to believe that individuals
really are intentional systems motivated entirely by self-interest and
this is, in fact, the individualistic perspective that pervades the
human sciences.

To distinguish mechanisms from metaphors, it is useful to think of a
psychological motive as a strategy in the game theoretic sense, which
produces a set of outcomes when it interacts with itself and with
other strategies. Thus, a psychologically selfish individual (however
defined) will be motivated to behave in certain ways with consequences
for itself and others. A psychologically altruistic individual
(however defined) will be motivated to behave in other ways with a
different set of payoffs. Within an evolutionary framework, the
empirical claim that individuals are motivated entirely by
self-interest must be supported by showing that the psychologically
selfish strategy prevails in competition with all other strategies.

Psychological motives have seldom been analyzed in this way (but see
Frank 1988, Alexander 1987) and we suggest that it will be a
productive line of inquiry in the future. We also predict that two
general conclusions will emerge: First, it is extremely unlikely that
any single strategy will prevail against all other strategies. Even
the famous Tit-for-Tat strategy, which is robust in the narrow context
of Axelrod's (1980 a,b) computer tournaments, is vulnerable to a host
of other strategies in more complex and realistic environments (e.g.,
Boyd and Lorberbaum 1987, Dugatkin and Wilson 1991, Feldman and Thomas
1987, Peck and Feldman 1986). Thus, any monolithic theory of proximate
motives is destined to fail, including the monolithic theory of
psychological selfishness. We should expect a diversity of motives in
the human repertoire that is distributed both within and among
individuals.

Second, the very opposite of psychological selfishness can be highly
successful, especially when natural selection operates at the group
level. To see this, consider an individual who identifies so
thoroughly with his group that he doesn't even consider the
possibility of profiting at the expense of his fellows. This
individual will be vulnerable to exploitation by members of his own
group who are less civic-minded. But groups of individuals who think
in this way will probably be superior in competition with other groups
whose members are less civic-minded. It follows that intense
between-group competition will favor psychological mechanisms that
blur the distinction between group and individual welfare,
concentrating functional organization at the group level. Alexander
(1988) himself provides a good example in a review of Richards (1987)
when he describes his own military experience:

In the army in which I served one was schooled so effectively to serve
the welfare of his unit (community?) that not only the contract
altruism that Richards says is inferior to his "pure" altruism, but
the intent that he requires,both disappear in a kind of automaticity
that ceases to involve any deliberateness, either in maintenance of
the contract signed when drafted or enlisted, or in explicitly serving
the rest of one's unit [p443].

Quibbles about the definition of altruism aside, nothing more is
required to convert a social group into an organism. Critics may argue
that the selfless attitude of a well-trained soldier is not adopted by
individual choice but imposed by an indoctrination process and
reinforced by sanctions against disloyalty that make it
disadvantageous to cheat. We disagree in two ways. First, individuals
are not always drafted into these groups and often rush to join them,
enthusiastically embracing the doctrine, refraining from cheating and
enforcing the sanctions against others. Their self-interest is not
taken from them but willingly abandoned. Second, even when imposed,
indoctrination and sanctions are best regarded as group-level rules of
meiosis that reduce the potential for fitness differences within
groups, concentrating functional organization at the group level. An
entity can be an organism without the parts behaving
self-sacrificially (for an evolutionary model of psychological
altruism per se, see Frank 1988).

Since humans have lived in small groups throughout their history, it
is reasonable to expect the evolution of psychological mechanisms that
cause them to easily become "team players" in competition with other
groups. We do not expect these to be the only motives that guide human
behavior, but rather a module that is facultatively employed under
appropriate conditions. In fact, there is abundant empirical evidence
that humans coalesce into cooperative teams at the merest suggestion
of a metapopulation structure in which groups can compete against
other groups (e.g., Dawes et al 1988, Hogg and Abrams 1988, Sherif et
al 1961, Tajfel 1981 ). Members of the same group often share a
feeling of high regard, friendship and trust that is based not on any
prior experience but merely by the fact that they are members of the
same group. Exploitation within groups is often avoided even when
opportunities are experimentally provided without any chance of
detection (e.g., Caporeal et al 1989). Group formation is as
spontaneous in children as in adults (e.g., Sherif et al 1961). These
are the earmarks of an evolved "Darwinian algorithm" (sensu Cosmides
and Tooby 1987) that predisposes humans for life in functionally
organized groups. The algorithm appears paradoxical only when we
consider its vulnerability to more selfish algorithms within groups.
The advantages at the group level are manifest.

It is important to stress that we have not merely converged on a view
that is already well accepted within the human sciences. Proponents of
alternatives to psychological selfishness are better described as an
embattled minority who must constantly defend themselves against a
monolithic individualistic world view (e.g., Batson 1991, Caporeal et
al 1989, Campbell 1993, Mansbridge 1990, Simon 1991). As one example,
most economists assume that individuals act in the interest of the
company that employs them only because the company pays them enough to
make it worthwhile from the standpoint of the individual's personal
utility. According to Simon (1991), real people who are satisfied with
their jobs do not distinguish between their own and their company's
utility, but rather adopt the company's interest as their own
interest. Even the lowest level employees make executive decisions
that require asking the question "what is best for the company?" and
which go far beyond the actual requirements of the job. In fact, one
of the most effective forms of protest by dissatisfied employees is
"work to rule", in which people perform their jobs to the letter and
the company comes to a grinding halt. In modern life as in ancient
times, group-level function requires individuals who to a significant
degree take the group's goals as their own. This is a radical proposal
within economics, however, and not the majority view.

Group-level cognition. Goal-oriented behaviors are typically
accomplished by a feedback process that includes the gathering and
processing of information. While the entire process can be described
as intentional (e.g., the wolf tries to catch the deer), the elements
of the process cannot (the neuron does not try to fire; it merely does
fire when stimulated at enough synapses; Dennett 1981).

We are accustomed to regarding individuals as intentional systems with
their own self-contained feedback processes. Group selection raises
another possibility in which the feedback process is distributed among
members of the group. We have already provided an example for honeybee
colonies in which individuals behave more like neurons than as
intentional agents in their own right. Similar examples have scarcely
been considered for humans and our main purpose here is to define the
question, rather than answer it.

Modern governmental and judicial systems are sometimes designed to
produce adaptive outcomes at the level of the whole system but not at
the level of the component individuals. Science is sometimes portrayed
as a similar process that generates knowledge only at the group level
(e.g., Hull 1988, Kitcher 1993). The invisible hand metaphor in
economics invokes the image of an adaptive system that organizes
itself out of neuron-like components, although the metaphor is more
often stated as an ideology than as a testable research program.23

The invisible hand notwithstanding, research on decision making in
small groups reveals a complex process that does not always yield
adaptive solutions (Hendrick 1987a,b). Groups even make decisions that
would be regarded as foolish by every member of the group (Allison and
Messick 1987). This research is important because it shows that
intelligent individuals do not automatically combine to form
intelligent groups. Adaptive decision-making at the small group level
may require a highly specified cognitive division of labor. Since
decision-making has occurred in small groups throughout human history,
it is reasonable to expect "Darwinian algorithms" that cause
individuals to relinquish their capacity to act as autonomous
intentional agents and adopt a more limited role in a group-level
cognitive structure. The architecture of group-level cognition might
simply take the form of "leaders" who act as self- contained
intentional agents and "followers" who abide by the decisions of
others. Alternatively, even so-called "leaders" may be specialists in
a feedback process that is distributed throughout the group. These
questions can only be asked by recognizing the group as a potentially
adaptive entity.

An example of a human group-level oorganism at . We conclude by providing
a possible example of extreme group-level functional organization in
humans and the background conditions that make it possible. The
Hutterites are a fundamentalist religious sect that originated in
Europe in the sixteenth century and migrated to North America in the
nineteenth century to escape conscription. The Hutterites regard
themselves as the human equivalent of a bee colony. They practice
community of goods (no private ownership) and also cultivate a
psychological attitude of extreme selflessness. The ultimate Hutterite
virtue is oGelassenheit@, a word that has no English equivalent, which
includes othe grateful acceptance of whatever God gives, even
suffering and death, the forsaking of all self- will, all selfishness,
all concern for private property@ (Ehrenpreis 1650/1978). Nepotism and
reciprocity, the two principles that most evolutionists use to explain
prosocial behavior in humans, are scorned by the Hutterites as
immoral. Giving must be without regard to relatedness and without any
expectation of return. The passion for selflessness is more than just
sermonizing and frequently manifests itself in action. For example,
Claus FelbingerYs oConfession of faith@ (1560/1978) provides an
eloquent statement that a Hutterite blacksmith gave to Bavarian
authorities after their efforts to make him recant had failed and
before they executed him for his beliefs.

The extreme selflessness of the Hutterites can be explained in at
least three ways. First, many authors, both inside and outside of
biology, think of culture as a process that frequently causes humans
to behave in ways that are biologically maladaptive. By this account,
the Hutterites are influenced by (unspecified) cultural forces and
their behavior cannot be explained by any biological theory, including
the theory of group selection.

Second, some evolutionists have tried to explain widespread altruism
in humans as a product of manipulation, in which the putative
altruists are essentially duped into behaving against their own
interests for the benefit of the manipulator (e.g., Dawkins
1982,1989). If people can be fooled into believing that a life of
sacrifice will lead to a pleasant afterlife, for example, then
perpetrating that belief in others becomes an example of individual
self-interest. By this account, we might expect some Hutterites (such
as the leaders) to profit at the expense of their duped brethren.

Third, it is possible that humans have evolved to willingly engage in
selfless behavior whenever it is protected by a social organization
that constitutes a group-level vehicle of selection. The relatively
small group- level vehicles of kinship groups and cooperating diads
are already well recognized. The hypothesis we wish to explore asserts
that the Hutterites constitute a less familiar case in which the
vehicle is a relatively large group of individuals and families that
are genetically unrelated to each other. If this interpretation is
correct, then group selection theory should be able to predict some
major features of Hutterite social organization and ideology, despite
the fact that it is stated in purely religious terms. In particular,
the prediction is that the bee-like behavior of the Hutterites is
promoted by a social organization and ideology that nearly eliminates
the potential for individuals to increase their fitness relative to
others within groups.24 Note that the other two interpretations do not
make the same prediction. If Hutterite society is governed by
independent cultural forces, it is unlikely to have the specific
design features of a group-level vehicle. And if selflessness is a
product of manipulation, we should find fitness differences between
the puppets and the puppeteers.

A number of caveats are in order before proceeding. First, we do not
claim to rigorously distinguish among the above three explanations in
the confines of this review article. The best that we can do is
provide a brief sketch, which is nevertheless important because it
makes the preceding discussion less abstract and gives an idea of what
a group-level vehicle of selection might look like in humans. Second,
we do not regard the Hutterite social organization as a direct product
of group selection. Rather, we conjecture that group selection has
operated throughout human history, endowing the human psyche with the
ability to construct and live within group-level vehicles of the sort
exhibited by the Hutterites.25 This enables us to make another
prediction, that the Hutterite social organization is not unique but
represents a fairly common type of social organization in ancestral
environments. Otherwise it could not be interpreted as an evolved
adaptation. As one of many possible social organizations in the human
repetoire, this one is presumably evoked only under appropriate
environmental conditions, yielding another set of testable
predictions. Third, evolutionary psychologists rely on fitness
maximizing arguments to explain the human psyche, but they do not
necessarily expect humans to maximize biological fitness in present
day environments. This is because, to the extent that humans are
oprogrammed@ by natural selection, it is not to maximize biological
fitness per se but only to achieve the more proximate goals that led
to high fitness in ancestral environments. Thus, we must focus more on
the design features and what they would have meant in ancestral
environments than on the present day consequences of the design
features (Symons 1992). This is a general issue in evolutionary
psychology that applies to the Hutterites as well as any other group.

With these caveats in mind, we now will elaborate the idea that
Hutterite society is a group-level vehicle of selection. Although
their ideology is stated in purely religious terms, it is clearly
designed to suppress behaviors that benefit some individuals at the
expense of others within groups:

That is what Jesus means by His parable of the great banquet and the
wedding of the king's son, when the servants were sent to call all the
people together. Why did his anger fall on those who had been invited
first? Because they let their private, domestic concerns keep them
away. Again and again we see that man with his present nature finds it
very hard to practice true community; true community feeds the poor
every day at breakfast, dinner, and the common supper table. Men hang
on to property like caterpillars to a cabbage leaf. Self-will and
selfishness constantly stand in the way! [Ehrenpreis 1650/1978 p
11-12]

Benefitting the group is exalted as highly as selfishness within
groups is reviled:

Where there is no community there is no true love. True love means
growth for the whole organism, whose members are all interdependent
and serve each other. That is the outward form of the inner working of
the Spirit, the organism of the Body governed by Christ. We see the
same thing among the bees, who all work with equal zeal gathering
honey; none of them hold anything back for selfish needs. They fly
hither and yon with the greatest zeal and live in community together.
Not one of them keeps any property for itself. If only we did not love
our property and our own will! If only we loved the life of poverty as
Jesus showed it, if only we loved obedience to God as much as we love
being rich and respected! If only everybody did not hang on to his own
will! Then the truth of Christ's death would not appear as
foolishness. Instead, it would be the power of God, which saves us.
[Ehrenpreis 1650/1978 p12-13]

Thus the Hutterites are as explicit as they can possibly be that their
members should merge themselves into a group-level organism. They are
also explicit about how group-level functional organization can be
accomplished. In the first place, the Hutterites believe that
selfishness is an innate part of human nature that can never be fully
irradicated:

The sinner lies in all of us; in fact to sin, to be selfish,is our
present inclination. Left to ourselves we shall end up in damnation,
but this does not mean that salvation cannot be attained. On the
contrary, salvation is possible on three conditions: we live according
to the life of Christ; we live in community; we strive very hard to
attain salvation and are prepared to suffer for our efforts. Christ
appeared to save us from our sinful nature. This nature is not easily
abjured but it can if we try hard enough, both in the sense of
personal determination and in the sense of collectively living
according to the Word (Shenker 1986 p73).

If we were to translate this sentiment into evolutionary language, we
would arrive at the claim that within-group selection has been a
powerful (but not the only) force in human evolution and has stamped
itself upon the human psyche. To the extent that humans are the
products of natural selection, they are inclined to benefit themselves
at the expense of others within their group whenever it is
evolutionarily advantageous to do so (at least in ancestral
environments). To create a group-level organism, the part of human
nature that has evolved by within-group selection must be constrained
by a social organization that plays the same functional role as the
genetic rules of meiosis.

The most important ingredient of this social organization is evidently
a sense of oshared fate@:

The community can "hang together" only through the members having an
identity of fate. In practice this means two things. Members must
identify with the past and (more important) with the future of the
community, such that their own future and the community's future are
one and the same. We rise and fall together. This is another way of
saying we have unconditional commitment to our community. We do not
say "if the community does or achieves such and such, then I will
stay, otherwise I won't", since this implies that there is an
individual identity ontologically and morally distinct from the
community's. No true community could operate successfully or manifest
its raison d'etre with such limiting conditions or separate
identities. Identity of fate also means that members relate to each
other in an atmosphere of mutual trust, i.e. they consider their
presence to stem from a common desire to express their humanity and
recognize that this can only be achieved through mutual effort. Should
one person claim that he has an inherent right to gain for himself at
the expense of others, the entire fabric collapses. Life in the
community presupposes that each will work for the benefit of others as
much as for himself, that no-one will be egoistic. The moment this
assumption is undermined, mutual suspicion, jealousy and mistrust
arise. Not only will people probably consider themselves silly for
being self- righteous while others are feathering their nest,but
operationally the community will have to take a different character
(primarily through the use of coercion) and the entire moral nature of
the community disappears. (Shenker 1986 p93)

We could not ask for a stronger correspondence between the sentiment
expressed in this passage and the concept of ovehicles@ in a group
selection model.

One way to establish a sense of shared fate is via egalitarian social
conventions that make it difficult to benefit oneself at the expense
of others. Hutterite society is elaborately organized along these
lines. In addition to practicing community of goods, they discourage
individuality of any sort, for example, in the context of personal
appearance and home furnishings. Leaders are elected democratically
and are subject to long probationary periods before they are given
their full authority. The HutteriteYs passion for fairness is perhaps
best illustrated by the rules that surround the fissioning process.
Like a honey bee colony, Hutterite brotherhoods split when they attain
a large size, with one half remaining at the original site and the
other half moving to a new site that has been pre-selected and
prepared. In preparation for the split, the colony is divided into two
groups that are equal with respect to number, age sex, skills and
personal compatibility. The entire colony packs its belongings and one
of the lists is drawn by lottery on the day of the split. The
similarity to the genetic rules of meiosis could hardly be more
complete.

In principle, we might imagine that a psychological egoist, who thinks
only in terms of personal gain, could decide to become a Hutterite if
he became convinced that the group-level benefits (which he shares)
are sufficiently great and the social conventions are sufficiently
strong that neither he nor anyone else in the group can act as a
freeloader. The Shenker passage quoted above suggests, however, that
an effective group- oriented society cannot be composed of individuals
who are motivated solely by a calculus of self-interest.26 The
external social conventions that make freeloading difficult are
evidently necessary but not sufficient and must be supplemented by a
psychological attitude of genuine concern for others; a direct
calculus of group interest rather than self interest is essential.
Recall that Simon (1991; discussed on p38) makes a similar point about
the behavior of individuals in business organizations. Thus, although
we are focusing on the Hutterites, our discussion is not limited to
esoteric communal societies, a point that we will return to below.

Even with these attitudes and social conventions, however, selfishness
in thought and action cannot be entirely eliminated. The Hutterites
therefore have a well specified procedure for dealing with members who
benefit themselves at the expense of others.

The bond of love is kept pure and intact by the correction of the Holy
Spirit. People who are burdened with vices that spread and corrupt can
have no part in it. This harmonious fellowship excludes any who are
not part of the unanimous spirit... If a man hardens himself in
rebellion, the extreme step of separation is unavoidable. Otherwise
the whole community would be dragged into his sin and become party to
it...The Apostle Paul therefore says, "Drive out the wicked person
from among you."

... In the case of minor transgressions, this discipline consists of
simple brotherly admonition. If anyone has acted wrongly toward
another but has not committed a gross sin, a rebuke and warning is
enough. But if a brother or a sister obstinately resists brotherly
correction and helpful advice, then even these relatively small things
have to be brought openly before the Church. If that brother is ready
to listen to the Church and allow himself to be set straight, the
right way to deal with the situation will be shown. Everything will be
cleared up. But if he persists in his stubbornness and refuses to
listen even to the Church, then there is only one answer in this
situation, and that is to cut him off and exclude him. It is better
for someone with a heart full of poison to be cut off than for the
entire Church to be brought into confusion or blemished.

The whole aim of this order of discipline, however, is not exclusion
but a change of heart. It is not applied for a brother's ruin, even
when he has fallen into flagrant sin, into besmirching sins of
impurity, which make him deeply guilty before God. For the sake of
example and warning, the truth must in this case be declared openly
and brought to light before the Church. Even then such a brother
should hold on to his hope and his faith. He should not go away and
leave everything but should accept and bear what is put upon him by
the Church. He should earnestly repent, no matter how many tears it
may cost him or how much suffering it may involve. At the right time,
when he is repentant, those who are united in the Church pray for him,
and all of Heaven rejoices with them. After he hasshown genuine
repentance, he is received back with great joy in a meeting of the
whole Church. They unanimously intercede for him that his sins need
never be thought of again but are forgiven and removed forever.
[Ehrenpreis 1650/1978 p66-9]

We could not ask for a more explicit awareness of the freeloader
problem and what to do about it, including the elements of retaliation
and forgiveness that are also part of the tit-for-tat strategy in
diadic interactions. If we were to translate this passage into
evolutionary language, it would be as follows: Altruism can succeed
only by segregating itself from selfishness. Not only does the selfish
individual have the highest fitness within groups, but his mere
presence signifies a population structure that favors within-group
selection, causing others to quickly abandon their own altruistic
strategy. Fortunately, in face-to-face groups whose members are
intimately familiar with each other, it is easy to detect overt forms
of selfishness and exclude the offender. When osubversion from within@
can be prevented to this extent, extreme altruism, in both thought and
action, becomes evolutionarily advantageous.

It is remarkable, and crucial for the hypothesis under consideration,
that the willingness of the Hutterites to sacrifice for others is
accompanied by such an elaborate set of rules that protect
self-sacrifice from exploitation within groups. We suggest that there
is a causal relationship here, that humans are inclined to adopt
selfless behavior in social organizations that provide the functional
equivalent of the genetic rules of meiosis. Not only do these social
organizations promote selflessness at the behavioral level, but they
also promote forms of thinking and feeling that would be classified as
non-egoistic in a psychological sense. After all, what is the
advantage of psychological selfishness if the most successful way to
behave is by contributing to group-level functional organization?

It is also crucial for our hypothesis that group-level functional
organization is, in some sense, superior to what can be accomplished
by individuals when they are free to pursue their own self interest
(recall the Seeley passage quoted on pg 27). This certainly appears to
be the case for the Hutterites, who do not have to wait for the
hereafter to get their reward. By fostering a selfless attitude
towards others and minimizing the potential for exploitation within
groups, they are spectacularly successful at the group level. In
sixteenth century Europe they were alternately tolerated and
persecuted for their economic superiority, much like the Jews, another
society that, in its traditional form, is well- organized at the group
level (MacDonald 1994). In present-day Canada, Hutterites thrive in
marginal farming habitat without the benefit of modern technology and
almost certainly would displace the non-Hutterite population in the
absence of laws that restrict their expansion. The HutteritesY success
can also be measured in reproductive terms, since they have the
highest birth rate of any known human society (Cook 1954).27 Finally,
Hutterite society is internally stable, with the majority of young
people electing to remain when given a choice. Were it not for
persecution and legal restrictions imposed by their host nations,
Hutterite colonies would be far more common than they are now.

Part of our hypothesis is that the Hutterite social organization is
not a unique product of the sixteenth century but reflects an evolved
human potential to construct and live within such group-level
vehicles. It might seem that the Hutterites are such an esoteric
society that our prediction could not possibly be confirmed. On closer
reflection, however, it appears that the functional elements of
Hutterite society that act as group-level rules of meiosis are
repeated in a great many social groups that place a premium on
group-level performance, even though the ideologies are superficially
different and the purpose of the group can be diametrically opposed to
the goals of the Hutterites (e.g., an elite military group).
Furthermore, according to Knauft (1991), this kind of egalitarianism
characterizes hunter-gatherer groups whenever resources are too widely
dispersed to allow the development of status-based societies (i.e.,
most human groups throughout human evolutionary history). The ethic of
ogood company@ (which is extended to non-kin as well as kin; e.g.
Knauft 1985) and the de-emphasized sense of self-interest that
pervades many tribal societies does indeed resemble the HutteriteYs
ocommunity@ and their denigration of oself-will at .

Another part of our hypothesis is that the human potential to build
and live within group-level vehicles is facultative and evoked more
strongly in some situations than in others. Group-level vehicles
should be most commonly observed in situations that place a premium on
group-level functional organization, such as extreme physical
environments, extreme persecution, or extreme intergroup competition.
In more benign situations, the consequences of social dilemmas are not
so dysfunctional and the effort that goes into the maintenance of
group-level vehicles may be correspondingly relaxed.28

Obviously, we have only skimmed the surface of an enormously complex
and poorly understood subject. We hope we have demonstrated the
likelihood, however, that group selection in humans extends far beyond
nepotism and narrow reciprocity. These two principles cannot account
for the full range of prosocial behaviors in humans and evolutionists
who rely on them have been forced to invoke other factors; that
prosocial behavior evolved in ancestral groups of closely related
individuals and is maladaptively expressed in modern groups of
unrelated individuals (Ruse 1986); that prosocial behavior is a form
of manipulation whereby some individuals profit at the expense of
others (Dawkins 1982, 1988); or that prosocial behavior results from
cultural forces that promote biologically maladaptive behavior
(Campbell 1983). Group selection theory provides a robust alternative:
Even large groups of unrelated individuals can be organized in a way
that makes genuinely prosocial behavior advantageous.

We have emphasized group-level functional organization in humans as an
antidote to the rampant individualism we see in the human behavioral
sciences. But it is not our goal to replace one caricature with
another. Many human groups are clearly not the oorganisms@ that we
have described above and must be explained as the product of
conflicting individual interests within the group. Evolutionary theory
has the resources to understand both conflict and cooperation. Only by
pursuing both problems- -with the group as well as the individual as
possible units of functional integration--can the human sciences come
to terms with our evolutionary heritage.

CONCLUSIONS

Maynard Smith's most recent comment on group selection includes the
following passage:

It is ...perfectly justified to study eyes (or, for that matter,
ribosomes, or foraging behaviors) on the assumption that these organs
adapt organisms for survival and reproduction. But it would not be
justified to study the fighting behavior of spiders on the assumption
that this behavior evolved because it ensures the survival of the
species, or to study the behavior of earthworms on the assumption that
it evolved because it improves the efficacy of the ecosystem. (Maynard
Smith 1987b p147)

Maynard Smith still resists what we think is the most fundamental
implication of natural selection as a hierarchical process: Higher
units of the biological hierarchy can be organisms, in exactly the
same sense that individuals are organisms, to the extent that they are
vehicles of selection. Group organisms may be less common than
individual organisms and they may be more vulnerable than individuals
to subversion from within, but this must not prevent us from
recognizing group-level functional organization where it exists.

As the most facultative species on earth, humans have the behavioral
potential to span the full continuum from organ to organism, depending
on the situations we encounter and the social organizations that we
build for ourselves. We often see ourselves as "organs". We sometimes
identify ourselves primarily as members of a group and willingly make
sacrifices for the welfare of our group. We long to be part of
something larger than ourselves. We have a passion for building,
maintaining and abiding by fair social organizations. The
individualistic perspective seems to make all of this invisible.
Because group-level functional organization can be successful, it is
labelled selfish, therefore no different from the kinds of behaviors
that succeed by disrupting group-level functional organization. But
this is just a conjurer's trick. There are compelling intellectual and
practical reasons to distinguish between behaviors that succeed by
contributing to group-level organization and behaviors that succeed by
disrupting group-level organization. That is what the words "selfish"
and "unselfish", "moral" and "immoral" are all about in everyday
language. Human behavioral scientists need to focus on these ancient
concerns, rather than obscuring them with bloated definitions of
"self-interest". A concern for within-group versus between-group
processes characterizes the human mind and it should characterize the
study of the human mind as well.

ACKNOWLEDGEMENTS

Supported by NSF SBE-9212294. DSW thanks A.B. Clark, Lee Dugatkin,
Eric Dietrich, Greg Pollock and Binghamton's EEB group.

NOTES

1) In this article we use the word oindividual@ to refer to single
flesh- and-blood creatures such as a bird or a butterfly. We use the
term oorganism@ to refer to any biological entity whose parts have
evolved to function in a harmonious and coordinated fashion.

2) The purpose of this table is to provide a reasonably complete guide
to the modern literature on group selection. A number of controversies
exist within this literature that are beyond the scope of the present
paper. For completeness we provide references for all sides of these
controversies, including those with which we disagree. The
philosophical literature on levels of selection has recently been
reviewed by Sober and Wilson (1993).

3) Williams was only one of many biologists who reacted against group
selection during the 1960's, especially in response to Wynne-Edward's
(1962) Animal Dispersion in Relation to Social Behavior. We do not
mean to imply that Williams was the only articulate critic, but he has
become the icon for the individualistic perspective in biology.

4) Dawkins (1982, 1989) acknowledges that the group selection
controversy is a "vehicle" question but asserts that groups are almost
never vehicles of selection, with the possible exception of the
eusocial insects. Dawkins (1989 p 297-8) and Cronin (1991 p 290) cite
Grafen (1984) as the authoritative critique of group selection but
Grafen's treatment of groups as vehicles consists of a single
parenthetical statement (p76): "(The organismal approach suggested
here is not in conflict with the the 'gene selectionism' of Dawkins
(1982a,b). In his language, we are saying that the individual is
usually a well-adapted vehicle for gene replication, while groups are
usually not)". Williams (1986 p8) states that "selection at any level
above the family (group selection in a broad sense) is unimportant for
the origin and maintenance of adaptation. I reach this conclusion by
simple inspection." More recently, Williams (1992) acknowledges that
groups are vehicles in the specific cases of eusocial insects and
female-biased sex ratio but does not generalize to other cases.

5) Cronin's (1991) The Ant and the Peacock belongs to the same genre
as Dawkins' (1976) The Selfish Gene and Gould's (1989) Wonderful life,
in which the author attempts to make the subject accessible to a
popular audience without sacrificing scholarship. As Gould (1989 p16)
put it, "...we can still have a genre of scientific books suitable for
and accessible alike to professionals and interested laypeople".
Because these books are so accessible they tend to be influential even
among academic audiences, which is why Cronin (1991) merits criticism
despite its status as a "popular" book. Similar views can be found in
the more technical gene- centered literature (references in note 4)

6) Gould (1992) criticizes Cronin's gene-centered approach and
advocates a hierarchical view of evolution. However, he accepts the
gene-centered framework for the evolution of altruism and does not
invoke the concept of vehicles in the same sense that we do. More
generally, the concept of "species selection" that Gould emphasizes is
somewhat different from the concept of group selection that we review
here (for a discussion of the difference, see Sober 1984). This
constitutes one of the controversies within the group selection
literature mentioned in note 1.

7) The term "unit of selection" has become ambiguous because it refers
to both replicators and vehicles, depending on the author. Within the
group selection literature, "unit" equals "vehicle" and no word is
required for "replicator" because it is (and always was) assumed that
natural selection at all levels results in gene-frequency change. We
prefer the word "unit" but use the word "vehicle" in this paper to
distinguish it from replicators and also to force gene-centered
theorists to acknowledge the implications of their own framework.

8) We start at the lowest level and work up the hierarchy for
convenience, not because it is required for the procedure. Also,
unless there is uncertainty as to where fitness differences are
occuring, it is not necessary to invoke WilliamsY (1966) concept of
parsimony in this procedure.

9) Even though organisms are defined on the basis of functional
coordination among their parts, functional coordination per se does
not enter into our definition of vehicles, which is based purely on
shared fate. This is because shared fate is the crucial property of
the process of natural selection; functional coordination among the
parts is a product of the process.

10) The procedure for identifying vehicles requires some precautions
that can be illustrated by the following examples. First, imagine that
tall individuals are more fit than short individuals regardless of how
they are structured into groups. The procedure will (correctly)
identify the individual as the vehicle of selection. Nevertheless,
groups that contain more tall individuals than other groups will be
more productive, suggesting (incorrectly) that groups are also
vehicles of selection. To resolve this difficulty we must imagine
placing all individuals in a single group. Tall individuals are still
most fit, demonstrating that the metapopulation structure is
irrelevant . As a second example, imagine that the fitness of everyone
in a group is directly proportional to the average hight of the group.
Our procedure (correctly) identifies the group as the vehicle of
selection because there are no fitness differences between individuals
within groups. To confirm this result, imagine placing all individuals
in the same group. The fitness of tall and short individuals are
identical, demonstrating that the metapopulation structure is
necessary for tallness to evolve (Sober 1984; see also Goodnight et al
1992, Heisler and Damuth 1987, Walton 1991). Another problem arises
when a trait has already evolved to fixation. To apply the procedure
we must conduct a thought experiment (or a real experiment) in which
alternative types are present. Although other refinements in our
procedure may be needed, we believe that they don't require discussion
in the present context.

11) Although female biased sex ratios evolve by group selection, they
cannot be used to assess the importance of group selection in the
evolution of other traits. In other words, it does not follow that
group selection can be ignored for species that have an even sex
ratio. This is because the metapopulation structure must be defined
separately for each trait (hence the term otrait group@; Wilson 1975,
1977, 1980). The trait group for sex ratio must persist long enough
for f1 progeny to mate within the group before dispersing, a
constraint that does not necessarily apply to other traits.

12) For most evolutionists, the ultimate rejection is to be labelled
"non- Darwinian". In fact, Darwin's (1871) theory for the evolution of
human moral sentiments is remarkably similar to the vehicle-based
framework that we develop here (Richards 1987).

13) We think that an evolutionary theory of genuine vs. apparant
psychological altruism is possible, but it must be based on the
proximate motivations of the actor, which evolutionary accounts ignore
by defining altruism and selfishness solely in terms of fitness
effects. In other words, we must ask questions such as: oWhen are the
behaviors motivated by a ZgenuinelyY psychologically altruistic
individual more fit than the behaviors motivated by an ZapparantlyY
altruistic individual?@ Frank is actually one of the few authors who
are asking these questions, so we are not criticizing his specific
proposals about emotions as commitment devices, which make more sense
within a vehicle-based framework than within a replicator-based
framework. For further discussion, see Wilson (1992) and Sober (in
press).

14) Frank (1988) anticipates this conclusion in the passage that we
quote above, but does not pursue it further.

15) Anatol Rapoport, who submitted the Tit-for-Tat strategy to
Axelrod's (1980a,b) computer tournaments, always appreciated its
group-level benefit and individual-level disadvantage (e.g., Rapaport
1991). In contrast, Axelrod and the majority of evolutionary game
theorists regard tit-for-tat as a strategy that succeeds "at the
individual level."

16) Sterelny and Kitcher recognize that Dawkins' position cannot
simply be the empty truism that evolution occurs when the genetic
composition of a population changes. They claim (p 340) that the
nontrivial thesis that Dawkins advances is that "evolution under
natural selection is thus a process in which, barring complications,
the average ability of the genes in the gene pool to leave copies of
themselves increases with time."

Although this is a nontrivial claim, it is not something we find in
Dawkins' writings, and in any case it isn't true as a generality. The
average fitness of the alleles at a locus increases under frequency-
independent selection. But when a truly selfish gene replaces an
altruistic allele, the effect is to reduce average fitness. Dawkins
frequently remarks that there is nothing to prevent natural selection
(meaning within-group selection) from driving a population straight to
extinction. It is also worth noting that group selection can lead the
average fitness of the selected alleles to increase. A gene's ability
to leave copies of itself can decline under selection as well as
increase. And which turns out to occur is a separate issue from
whether group selection is present or absent.

17) While group selection has been a controversial topic within
biology, the entire subject of evolution has been a controversial
topic when applied to human behavior. There are at least three ways
that evolution in general (and group selection in particular) can
influence human behavior. First, the psychological mechanisms that
govern human behavior can be the product of natural selection. In its
weak form this statement is uncontroversial, since everyone agrees
that basic drives such as hunger, sex and pain exist because they are
biologically adaptive. Some psychologists believe that the
adaptationist program can be used to explain the architecture of human
cognition in much greater detail, however, and this position is more
controversial (e.g., Barkow et al 1992). Second, cultural change can
itself be described as an evolutionary process with between- and
within-group components (e.g. Boyd and Richerson 1985, Findlay 1992).
Third, genetic evolution is an ongoing process that can partially
explain differences between individuals and populations. Our own
thinking is based primarily on the first and second influences. In
other words, we think it is imperative to explore the hypothesis that
group selection was a strong force during human evolution, resulting
in proximate psychological mechanisms that today are universally
shared and allow humans to facultatively adopt group-level adaptations
under appropriate conditions. The specific nature and precision of
these psychological mechanisms are empirical issues. We also propose,
along with Boyd and Richerson (1985) and Findlay (1992), that group
selection can be a strong force in cultural evolution. Thus, our
position is compatable with but does not require a strong form of
human sociobiology. Our point is not to prejudge the correctness of
adaptationist explanations, but to urge the importance of asking
adaptationist questions. Only by doing so can we find out whether and
to what degree organisms are well adapted to their environments
(Orzack and Sober, in press).

18) Sober (1981) discusses the relationship between methodological
individualism and the units of selection controversy in more detail.

19) Opportunity levelling is not restricted to the largest human
groups. According to Knauft (1992), the simplest human societies are
highly egalitarian and overtly status-oriented societies require a
concentrated and stable resource, such as crops or livestock. This
improves Alexander's general thesis, especially if the simplest
existing human societies represent ancestral conditions.

20) AlexanderYs views on group selection, presented in articles and
books from 1974 to 1993, are difficult to represent in a single
passage. When evaluating group selection in non-human species,
Alexander identifies strongly with the views of Williams and Dawkins,
as the passage quoted on p 7 shows. Alexander does speculate that
humans may be an exception to the rule because of extreme
between-group competition and regulation of fitness differences within
groups. The following passage illustrates his pro-group selection
side, which is consistent with our own interpretation: oIn sexually
reproducing organisms, such as humans, confluences of interest within
groups are likely to occur when different groups are in more or less
direct competition. As a result, the kind of selection alluded to here
[group selection] would be expected to produce individuals that would
cooperate intensively and complexly within groups but show strong and
even extreme aggressiveness between groups (Alexander 1989 p 463).@
However, in other passages, Alexander clearly minimizes the importance
of group selection and attributes the evolution of moral behavior in
humans to within-group processes. We provide his most recent statement
to this effect: oBecause selection is primarily effective at and below
the individual level, it is reasonable to expect concepts and
practices pertaining to morality--as with all other aspects of the
phenotypes of living forms--to be designed so as to yield reproductive
(genetic) gains to the individuals exhibiting them, at least in the
environments of history (Alexander 1993 p178).@

At a more technical level, Alexander occasionally seems to appreciate
the vehicle concept when evaluating levels of selection (e.g., the
1989 passage quoted above), but more often he implicitly defines
anything that evolves as oindividually@ advantageous, even when the
group is the vehicle of selection (e.g.,the discussion of Frank, 1988,
in Alexander, 1993). We think that a consistent application of our
procedure will reveal that Alexander is invoking groups as vehicles of
selection much more than he acknowledges in his own writing. We also
want to stress, however, that AlexanderYs views on indirect
reciprocity, opportunity-leveling within groups and competition
between groups remain important within a vehicle-based framework.

21) AlexanderYs theory is conventional in the sense of equating
morality with the notion of a common good. However, calling it
familiar and conventional does not belittle its importance.
Evolutionary theories of human behavior frequently make predictions
that correspond closely to folk psychology (e.g., that men tend to
value youth in women more than women value youth in men). Since the
intuitions of folk psychology are unlikely to be completely wrong, it
would be disturbing if an evolutionary theory of human behavior was
not familiar and conventional in some sense. Of course, the theory
must also go beyond folk psychology by making counter-intuitive
predictions, revealing aspects of folk psychology that are false,
refining familiar predictions, subjecting predictions to empirical
test and so on.

An evolutionary account of morality (including AlexanderYs) does
depart from folk psychology in some important respects. The
organ-organism- population trichotomy implies that there will always
be a level of the biological hierarchy at which social dilemmas will
prevail. In other words, moral behavior within groups will frequently
be used to generate immoral behavior between groups. This fits well
with observed behavior but contrasts with the concept of universal
morality that is common in folk psychology and some branches of the
human behavioral sciences (e.g., the higher stages of KohlbergYs
(1984) theory of moral development; MacDonald 1988). In addition, if
moral systems function as group-level rules of meiosis, it becomes
difficult to explain the concept of individual rights, which are moral
rules that protect individuals from groups. We think that an
evolutionary account of morality may ultimately shed light on these
topics but it will need to be more sophisticated than current
accounts.

22) We provide AlexanderYs most recent statement that humans are
motivated entirely by self interest: oIt is not easy for anyone to
believe, from his own thoughts about his personal motivation and that
of other humans, that humans are designed by natural selection to seek
their own interests, let alone maximize their own genetic reproduction
(Alexander 1993 p 191-2).@

23) The invisible hand metaphor is the economic equivalent of the Gaia
hypothesis. More generally, despite its emphasis on individual self-
interest, economic theory is like naive group selection in its
axiomatic belief that multi-individual firms maximize a collective
utility. A more sophisticated hierarchical approach to economics,
along the lines of Campbell 1993, Leibenstein 1976, Margolis 1982, and
Simon 1991 will be highly interesting.

24) The sense in which we expect an absence of fitness differences
within groups needs to be clarified. In honey bee colonies, there is a
set of adaptations that is favored by within-colony selection and has
the potential of disrupting colony function. This includes workers
laying unfertilized eggs to produce sons and workers favoring their
own patriline while tending future queens. These behaviors are seldom
observed because of evolved adaptations that prevent them, which
qualify as group-level rules of meiosis (Ratnieks 1988). Another set
of adaptations is favored by within-colony selection but does not
disrupt colony function. For example, a beneficial mutation that
increases viability will cause patrilines that have this mutation to
be more fit than patrilines that donYt, but there is no reason to
expect these kinds of fitness differences to be suppressed by
group-level rules of meiosis. Similarly, we expect the Hutterite
social organization to suppress fitness differences that correspond to
the first set but not those that correspond to the second.

25) Here we are following Tooby and Cosmides (1992) concept of
modularity, according to which natural selection has evolved a number
of cognitive subsystems that are evoked by appropriate environmental
conditions. We do not mean to exclude the possibility of open-ended
learning and cultural evolution, however, as envisioned by other
evolutionary psychologists (e.g., Boyd and Richerson 1985, Durham
1991, MacDonald 1991).

26) Two caveats are in order here. First, people do not necessarily
think the way an ideology exhorts them to think. We think it plausible
that Shenker (who was himself an Israeli Kibbutznik) is not simply
espousing an ideology but is accurately describing the attitudes and
beliefs that exist among members of communal societies. Second,
psychological egoism can be defined in many ways and some of the
broadest definitions would include the attitudes and beliefs expressed
in the Shenker passage. For example, if a Hutterite takes genuine
pleasure in helping his group, he might be classified by some as a
psychological egoist who is attempting to maximize his pleasure. For
the purposes of this discussion, we define a psychological egoist as a
person who has a category of oself@ that is separate from the category
of oothers@, who acts to maximize perceived self-interest without
regard to effects on others, and who does not axiomatically find
pleasure in helping others. See Batson 1991 for more detailed
discussions of psychological egoism.

27) Although the evaluation of psychological adaptations should be
based on design features and their reproductive consequences in
ancestral environments, it is still interesting to examine the
reproductive consequences in modern environments. The Hutterites have
been quite well studied demographically and it should be possible to
measure actual fitness differentials within groups.

28) In addition to the environmental situations that we have listed,
unstable equilibria leading to majority effects are likely to be
important in the evolution and maintenance of group-level adaptations.
In other words, group-level adaptations may have difficulty evolving
from a low frequency even when they are favored by environmental
conditions. Conversely, after they have become established,
group-level adaptations may persist even after the environmental
conditions that favored them are relaxed (Boyd and Richerson 1990).

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TABLE 1. A guide to the biological literature on group selection since
1970. "T"= theoretical models (including both mathematical and verbal
models), "E"= possible empirical examples (including examples that
have not been verified by experiments), "F"=field experiments,
"L"=laboratory experiments, "R"=literature reviews, "P"=philosophical
treatments, "C"=criticisms of group selection interpretations and
"H"=papers that are especially relevant from the standpoint of human
evolutionary biology.

FIGURE CAPTIONS

Figure 1) A nested hierarchy in which every unit is a population of
lower- level units. The hierarchy is left open on both ends because
genes are composed of subunits and metapopulations can exist in
higher-order metapopulations. For example, a valley can be a
metapopulation of villages, which in turn are metapopulations of
kinship groups.

Figure 2) A vehicle-centered version of kin selection theory. The
dominant A-allele codes for an altruistic behavior. The fitness of
altruists (WA) and nonaltruists (WS) in a given group is
WA=1-c+b(Np-1)/(N-1) and WS=1+bNp/(N-1), where p=the frequency of
altruists in the group, N=group size, c=the cost to the altruist, and
b=the benefit to the recipient. Both phenotypes have a baseline
fitness of 1. Each altruist can be a recipient for (Np-1) other
altruists in the group (excluding itself) who are distributing their
benefits among (N-1) members of the group (excluding themselves). Each
non-altruist can be a recipient for all Np altruists in the group. For
this example N=10, c=0.3 and b=1.0. Random mating among the three
genotypes (first line) produces six types of mated pairs (second
line), which in turn produce groups of siblings (third line). The
third line shows only the average sibling group for each type of mated
pair. Random sampling of the gametes will produce variation around the
averages. Sibling groups vary in the frequency of altruists (fourth
line). Altruism is selected against at the individual level because
non-altruists have the highest fitness within all mixed groups.
Altruism is favored at the group level, however, because group fitness
is directly proportional to the frequency of altruists in the group.

Figure 3. Variation among groups in the frequency of altruists.
Altruism is coded by a dominant A allele at a frequency of p=0.25 in
the metapopulation, yielding a frequency of 0.438 altruists (AA and
Aa) and 0.562 nonaltruists (aa). When groups of N=10 are composed of
unrelated individuals, the variation in the frequency of altruists
between groups has a binomial distribution, as shown by the black
curve. Sibling groups are created by a two-step sampling process in
which groups of size N=2 (the parents) are drawn from the global
population and groups of size N=10 (the siblings) are drawn from their
gametes. This two-step sampling procedure increases genetic variation
between groups, as shown by the stipled curve, intensifying natural
selection at the group level. Evolution within groups always favors
the non-altruist, regardless of whether the groups are composed of
siblings or unrelated individuals.

Figure 4. Four pay-off matrices that represent A) pure between-group
selection, B) a strong conflict between levels of selection, C) a weak
conflict between levels of selection (X is the average number of
interactions between members of each pair), and D) a return to pure
between-group selection. Within-group selection is absent from the
first example by virtue of the situation, since coordination has an
equal effect on both occupants of the leaf. Within-group selection is
absent from the fourth example by virtue of an adaptation, since the
"outlaw" A3 type cannot operate in the presence of the "parliament" A5
type.