[Paleopsych] Economist: The proper study of mankind

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The proper study of mankind
http://www.economist.com/surveys/PrinterFriendly.cfm?story_id=5299220
5.12.20
[All articles in this series on human evolution below.]

New theories and techniques have revolutionised our understanding of
humanity's past and present, says Geoffrey Carr (interviewed here)

SEVEN hundred and forty centuries ago, give or take a few, the skies
darkened and the Earth caught a cold. Toba, a volcano in Sumatra, had
exploded with the sort of eruptive force that convulses the planet
only once every few million years. The skies stayed dark for six
years, so much dust did the eruption throw into the atmosphere. It was
a dismal time to be alive and, if Stanley Ambrose of the University of
Illinois is right, the chances were you would be dead soon. In
particular, the population of one species, known to modern science as
Homo sapiens, plummeted to perhaps 2,000 individuals.

The proverbial Martian, looking at that darkened Earth, would probably
have given long odds against these peculiar apes making much impact on
the future. True, they had mastered the art of tool-making, but so had
several of their contemporaries. True, too, their curious grunts
allowed them to collaborate in surprisingly sophisticated ways. But
those advantages came at a huge price, for their brains were voracious
consumers of energy--a mere 2% of the body's tissue absorbing 20% of
its food intake. An interesting evolutionary experiment, then, but
surely a blind alley.

This survey will attempt to explain why that mythical Martian would
have been wrong. It will ask how these apes not only survived but
prospered, until the time came when one of them could weave together
strands of evidence from fields as disparate as geology and genetics,
and conclude that his ancestors had gone through a genetic bottleneck
caused by a geological catastrophe.

Not all of his contemporaries agree with Dr Ambrose about Toba's
effect on humanity. The eruption certainly happened, but there is less
consensus about his suggestion that it helped form the basis for what
are now known as humanity's racial divisions, by breaking Homo sapiens
into small groups whose random physical quirks were preserved in
different places. The idea is not, however, absurd. It is based on a
piece of evolutionary theory called the founder effect, which shows
how the isolation of small populations from larger ones can accelerate
evolutionary change, because a small population's average
characteristics are likely to differ from those of the larger group
from which it is drawn. Like much evolutionary theory, this is just
applied common sense. But only recently has such common sense been
applied systematically to areas of anthropology that have
traditionally ignored it and sometimes resisted it. The result, when
combined with new techniques of genetic analysis, has been a
revolution in the understanding of humanity's past.

And anthropology is not the only human science to have been infused
with evolutionary theory. Psychology, too, is undergoing a makeover
and the result is a second revolution, this time in the understanding
of humanity's present. Such understanding has been of two types, which
often get confused. One is the realisation that many human activities,
not all of them savoury, happen for exactly the same reasons as in
other species. For example, altruistic behaviour towards relatives,
infidelity, rape and murder are all widespread in the animal kingdom.
All have their own evolutionary logic. No one argues that they are
anything other than evolutionarily driven in species other than man.
Yet it would be extraordinary if they were not so driven in man,
because it would mean that natural selection had somehow contrived to
wipe out their genetic underpinnings, only for them to re-emerge as
culturally determined phenomena.

Understanding this shared evolutionary history with other species is
important; much foolishness has flowed from its denial. But what is
far more intriguing is the progress made in understanding what makes
humanity different from other species: friendship with non-relatives;
the ability to conceive of what others are thinking, and act
accordingly; the creation of an almost unimaginably diverse range of
artefacts, some useful, some merely decorative; and perhaps most
importantly, the use of language, which allows collaboration on a
scale denied to other creatures.

There are, of course, gaps in both sets of explanations. And this
field of research being a self-examination, there are also many
controversies, not all driven by strictly scientific motives. But the
outlines of a science of human evolution that can explain humanity's
success, and also its continuing failings, are now in place. It is
just a question of filling in the canvas--or the cave wall.


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The long march of everyman

It all started in Africa

OUT of Africa, always something new", wrote Caius Plinius Secundus, a
Roman polymath who helped to invent the field of natural history.
Pliny wrote more truly than he could possibly have realised. For one
fine day, somewhere between 85,000 and 60,000 years before he penned
those words, something did put its foot over the line that modern
geographers draw to separate Africa from Asia. And that something--or,
rather, somebody--did indeed start something new, namely the peopling
of the world.

Writing the story of the spread of humanity is one of the triumphs of
modern science, not least because the ink used to do it was so
unexpected. Like students of other past life forms, researchers into
humanity's prehistoric past started by looking in the rocks. The first
fossilised human to be recognised as such was unearthed in 1856 in the
Neander Valley near Dusseldorf in Germany. Neanderthal man, as this
skeleton and its kin became known, is now seen as a cousin of modern
humans rather than an ancestor, and subsequent digging has revealed a
branching tree of humanity whose root can be traced back more than 4m
years (see article).

Searching for human fossils, though, is a frustrating exercise. For
most of their existence, people were marginal creatures. Bones from
periods prior to the invention of agriculture are therefore excedingly
rare. The resulting data vacuum was filled by speculation scarcely
worthy of the name of theory, which seemed to change with every new
discovery. Then, in the 1980s, a geneticist called Allan Wilson
decided to redefine the meaning of the word "fossil". He did so in a
way that instantly revealed another 6 billion specimens, for Wilson's
method made a fossil out of every human alive.

Living fossils

In retrospect, Wilson's insight, like many of the best, is blindingly
obvious. He knew, as any biologist would, that an organism's DNA
carries a record of its evolutionary past. In principle, looking at
similarities and differences in the DNA sequences of living organisms
should allow a researcher to reconstruct the family tree linking those
organisms. In practice, the sexual mixing that happens with each
generation makes this tedious even with today's DNA-analysis
techniques. With those available in the 1980s it would have been
impossible. Wilson, however, realised he could cut through the problem
by concentrating on an unusual type of DNA called mitochondrial DNA.

Mitochondria are the parts of a cell that convert energy stored in
sugar into a form that the rest of the cell can use. Most of a cell's
genes are in its nucleus, but mitochondria, which are the descendants
of bacteria that linked up with one of humanity's unicellular
ancestors some 2 billion years ago, retain a few genes of their own.
Mitochondrial genomes are easy to study for three reasons. First, they
are small, which makes them simple to analyse. Second, mitochondria
reproduce asexually, so any changes between the generations are caused
by mutation rather than sexual mixing. Third, in humans at least,
mitochondria are inherited only from the mother.

In 1987, Rebecca Cann, one of Wilson's students, applied his insight
to a series of specimens taken from people whose ancestors came from
different parts of the world. By analysing the mutational differences
that had accumulated since their mitochondria shared a common
ancestor, she was able to construct a matriline (or, perhaps more
accurately, a matritree) connecting them.

The result was a revelation. Whichever way you drew the tree
(statistics not being an exact science, there was more than one
solution), its root was in Africa. Homo sapiens was thus unveiled as
an African species. But Dr Cann went further. Using estimates of how
often mutations appear in mitochondrial DNA (the so-called molecular
clock), she and Wilson did some matridendrochronology. The result
suggests that all the lines converge on the ovaries of a single woman
who lived some 150,000 years ago.

There was much excited reporting at the time about the discovery and
dating of this African "Eve". She was not, to be clear, the first
female Homo sapiens. Fossil evidence suggests the species is at least
200,000 years old, and may be older than that. And you can now do a
similar trick for the patriline using part of the male (Y) chromosome
in the cell nucleus, because this passes only from father to son.
Unfortunately for romantics, the most recent common ancestor of the
Y-chromosome is a lot more recent than its mitochondrial equivalent.
African Adam was born 60,000-90,000 years ago, and so could not have
met African Eve. Nevertheless, these two pieces of DNA as they have
weaved their ways down the generations have filled in, in surprising
detail, the highways and byways of human migration across the face of
the planet.

Sons of Adam, daughters of Eve

Detail, however is not the same as consensus, and there are two
schools of thought about how people left Africa in the first place.
Appropriately, some of their main protagonists are at the rival
English universities of Oxford and Cambridge. The Oxford school,
championed by Stephen Oppenheimer, believes that the descendants of a
single emigration some 85,000 years ago, across the strait of Bab el
Mandeb at the southern end of the Red Sea, are responsible for
populating the rest of the world. The Cambridge school, championed by
Robert Foley and Marta Mirazón Lahr, agrees that there was, indeed, a
migration across this strait, though probably nearer to 60,000 years
ago. However, it argues that many non-Africans are the descendants of
at least one subsequent exodus.

Both schools agree that the Bab el Mandebites spread rapidly along the
coast of southern Arabia and thence along the south coast of Asia to
Australia, though Dr Oppenheimer has them turning inland, too, once
they crossed the strait of Hormuz. But it is in describing what
happened next that the two versions really part company, for it is
here that the descendants of the Oxford migration run into the
eruption of Toba.

That Toba devastated South and South-East Asia is not in doubt. Thick
layers of ash from the eruption have been found as far afield as
northern Pakistan. The question is whether there were people in Asia
at the time. One of the most important pieces of evidence for Dr
Oppenheimer's version of events is some stone tools in the ash layer
in Malaysia, which he thinks were made by Homo sapiens. Molecular
clocks have a regrettable margin of error, but radioactive dating is a
lot more accurate. If he is right, modern humans must have left Africa
before the eruption. The tools might, however, have been crafted by an
earlier species of human that lived there before Homo sapiens.

For Dr Oppenheimer, the eruption was a crucial event, dividing the
nascent human population of Asia into two disconnected parts, which
then recolonised the intermediate ground. In the Cambridge version,
Homo sapiens was still confined to Africa 74,000 years ago, and would
merely have suffered the equivalent of a nuclear winter, not an
ash-fall of up to five metres--though Dr Ambrose and his colleagues
think even that would have done the population no good.

The Cambridge version is far more gentle. The descendants of its
subsequent exodus expanded north-eastwards into central Asia, and
thence scattered north, south, east and west--though in a spirit of
open-mindedness, Sacha Jones, a research student in Dr Foley's
department, is looking in the ash layer in India to see what she can
find there.

Which version is correct should eventually be determined by the
Genographic Project, a huge DNA-sampling study organised by Spencer
Wells, a geneticist, at the behest of America's National Geographic
Society and IBM. But both already have a lot in common. Both, for
example, agree that the Americas seem to have been colonised by at
least two groups. The Cambridge school, though, argues that one of
these is derived ultimately from the first Bab el Mandeb crossing
while the other is descended from the later migrants.

Both also agree that Europe received two waves of migration. The
ancestors of the bulk of modern Europeans came via central Asia about
35,000 years ago, though some people in the Balkans and other parts of
southern Europe trace their lines back to an earlier migration from
the Middle East. But the spread of agriculture from its Middle Eastern
cradle into the farthest reaches of Europe does not, as some
researchers once thought, seem to have been accompanied by a mass
movement of Middle Eastern farmers.

The coming together of two groups of humans can be seen in modern
India, too. In the south of the subcontinent, people have
Y-chromosomes derived almost exclusively from what the Cambridge
school would interpret as being northern folk (and the Oxford school
as the western survivors of Toba). However, more than 20% of their
mitochondria arrived in Asia with the first migration from Africa (or,
according to taste, clung on along the south-eastern fringes of the
ash plume).

That discovery speaks volumes about what happened when the two groups
met. It suggests that many modern south Indians are descended from
southern-fringe women, but few from southern-fringe men--implying a
comprehensive conquest of the southerners by the northerners, who won
extra southern wives.

This observation, in turn, helps explain why Y-chromosome Adam lived
so much more recently than mitochondrial Eve. Displacement by conquest
is one example of a more general phenomenon--that the number of
offspring sired by individual males is more variable than the number
born by individual females. This means that more males than females
end up with no offspring at all. Male gene lines therefore die out
faster than female ones, so those remaining are more likely,
statistically, to converge in the recent past.

Successful male gene lines, though, can be very successful indeed.
Students of animal behaviour refer to the top male in a group as the
"alpha". Such dominant animals keep the others under control and
father a large proportion, if not all, of the group's offspring. One
of the curiosities of modern life is that voters tend to elect alpha
males to high office, and then affect surprise when they behave like
alphas outside politics too. But in the days when alphas had to fight
rather than scheme their way to the top, they tended to enjoy the
sexual spoils more openly. And there were few males more alpha in
their behaviour than Genghis Khan, a man reported to have had about
500 wives and concubines, not to mention the sexual opportunities that
come with conquest. It is probably no coincidence, therefore, that one
man in every 12 of those who live within the frontiers of what was
once the Mongol empire (and, indeed, one in 200 of all men alive
today) have a stretch of DNA on their Y-chromosomes that dates back to
the time and birthplace of the great Khan.


http://www.economist.com/surveys/PrinterFriendly.cfm?story_id=5299196
Meet the relatives

A large and diverse family

WHEN Homo sapiens emerged as a species, he was not alone. The world he
entered was already peopled by giants and dwarfs, elves, trolls and
pixies--in other words, creatures that looked humanlike, but were not
the genuine article. Or, at least, not as genuine as Homo sapiens has
come to believe himself to be.

Like the story of Homo sapiens himself, the story of the whole human
family begins in Africa. About 4.5m years ago, probably in response to
a drying of the climate that caused forest cover in that continent to
shrink, one species of great ape found itself pushed out into the
savannah, an ecological niche not normally occupied by apes. Over the
next 300,000 years these apes evolved an upright stance. No one know
for sure why, but one plausible explanation, advanced by Peter Wheeler
of John Moores University in Liverpool, is that standing upright
reduces exposure to sunlight. To an animal adapted to the forest's
shade, the remorseless noonday sun of the savannah would have been a
threat. Dr Wheeler's calculations suggest that walking upright
decreases exposure at noon by a third compared with going on all
fours, since less of the body's surface faces the overhead sun.
Humanity, in the form of Australopithecus anamensis, had arrived.

Australopithecines of various species lasted for over 3m years. But
half-way through that period something interesting happened. One of
them begat a species known to science variously as Homo rudolfensis
and Homo habilis. All modern great apes make tools out of sticks and
leaves to help them earn their living, and there is no reason to
believe that this was not true of australopithecines. But, aided by
hands that no longer needed to double as part-time feet, Homo habilis
began to exploit a new and potent material that needs both precision
and strength to work--stone. This provided its immediate descendants
with a powerful technology, but also gave its distant descendants in
human palaeontology laboratories an additional way of tracing their
ancestry, for stone tools often survive where bones do not.

Homo habilis's successor species, Homo erectus, did not bestride the
globe in the way that his eventual descendant Homo sapiens did, but he
certainly stuck his nose out of Africa. Indeed, the first fossil
erectus discovered was in Java, in 1891, and the second one, several
decades later, turned up in China, near Beijing. It was not until 1960
that erectus bones were found in Africa.

Homo erectus is a frustrating species. His tools are found all over
the southern half of Eurasia, as well as in Africa. But China and Java
aside, his bones are scarce outside Africa. There are two skullcaps
from Georgia and half of one from India. He did, however, leave lots
of descendants.

Naming fossils is a game that beautifully illustrates Henry
Kissinger's witticism about academic disputes being so bitter because
the stakes are so low. The best definition of a species that
biologists have been able to come up with is "a group of creatures
capable of fertile interbreeding, given the chance", which clearly
makes it hard to determine what species a particular fossil belongs
to. Researchers therefore have to fall back on the physical
characteristics of the bones they find. That allows endless scope for
argument between so-called splitters, who seem to want to give a new
name to every skull discovered, and lumpers, who like to be as
inclusive as possible.

Some splitters, for example, argue that the African version of Homo
erectus should be called Homo ergaster. Whatever the niceties, it is
clear that by 500,000 years ago, if not before, Homo erectus was
breaking up into anatomically different populations. Splitters would
like to turn the Georgia fossils, an early twig of the erectus tree,
into Homo georgicus. There is also Homo rhodesiensis, found in
southern Africa, Homo heidelbergensis from Europe, and a whole
drawer's-worth of specimens known to some as Homo helmei and to others
as archaic Homo sapiens.

How little is really known, though, was thrown into sharp relief by
the announcement just over a year ago that yet another species, Homo
floresiensis, had been found. It was discovered on Java's nearish
neighbour island, Flores. Finding a new species of human is always
exciting, but what is particularly intriguing about Homo floresiensis
is how small it was--barely a metre tall when fully grown. Perhaps
inevitably, though to the disgust of its discoverers, Homo
floresiensis became known to journalists as the hobbit, after J.R.R.
Tolkien's fictional humanoid. Homo neanderthalensis, the descendant of
Homo heidelbergensis, by contrast, was if not a giant then at least a
troll. Though he stood five or ten centimetres shorter than a modern
European Homo sapiens, the thickness of his bones suggests he was a
lot heavier.

Both Homo neanderthalensis and Homo floresiensis were certainly around
when Homo sapiens left Africa--whichever version of that story turns
out to be the correct one. There may also have been some lingering
populations of other hominid species. That raises the intriguing
question of what happened when these residents met the sapiens wave.

Some researchers believe there was interbreeding, echoing the ideas of
an older school of palaeoanthropology called multiregionalism. The
multiregionalists thought either that pre-sapiens hominids were all a
vast, interbreeding species that gradually evolved into sapiens
everywhere, or, against all Darwinian logic, that Homo sapiens arose
independently in several places by some unknown process of parallel
evolution.

As recently as 2002, Alan Templeton, then at the University of
Washington at St Louis, claimed to have found a number of genetic
trees whose roots were 400,000-800,000 years old, and yet which
included non-Africans. That, if confirmed, would support
multiregionalism. Meanwhile, John Relethford, of the State University
of New York's campus at Oneonta, has criticised the conclusions of
studies on mitochondrial DNA extracted from the bones of Neanderthals.
This does not resemble DNA from any known modern humans, which led the
authors of the work to conclude there was no interbreeding. Dr
Relethford points out that Neanderthal DNA brought into the sapiens
population by interbreeding could subsequently have been lost by
chance in the lottery of who does and who does not reproduce. Similar
losses are known to have happened in Australia, where mitochondrial
DNA from human fossils is absent from modern Australians.

Most students of the field, though, think there was no interbreeding,
full stop. Either Homo sapiens persecuted his cousins into extinction
or, with his superior technology, he outhunted, outgathered and
outbred them. The next question is where that technology--or, rather,
the brainpower to invent and make it--came from.


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If this is a man

Why it pays to be brainy

THANKS to Dr Cann and her successors, the story of how Homo sapiens
spread throughout the world is getting clearer by the day. But why did
it happen? What was it that gave the species its edge, and where did
it come from? Here, the picture blurs.

Until recently, it was common to speak of an Upper Palaeolithic
revolution in human affairs--what Jared Diamond, of the University of
California at Los Angeles, called the Great Leap Forward. Around
40,000 years ago, so the argument ran, humanity underwent a mental
step-change. The main evidence for this was the luxuriant cave art
that appeared in Europe shortly after this time. Palaeopsychologists
see this art as evidence that the artists could manipulate abstract
mental symbols--and so they surely could. But it is a false conclusion
(though it was widely drawn before Dr Cann's work) that this mental
power actually evolved in Europe. Since all humans can paint (some,
admittedly, better than others), the mental ability to do so, if not
the actual technique, must have emerged in Africa before the first
emigrants left. Indeed, evidence of early artistic leanings in that
continent has now turned up in the form of drilled beads made of
shells and coral, and--more controversially--of stones that have
abstract patterns scratched on to them and bear traces of pigment.

That certainly pushes the revolution back a few tens of millennia. The
oldest beads seem to date from 75,000 years ago, and an inspired piece
of lateral thinking suggests that clothing appeared at about the same
time. Mark Stoneking and his colleagues at the Max Planck Institute
for Evolutionary Anthropology in Leipzig, Germany, applied the
molecular-clock technique to human lice. They showed that head lice
and body lice diverged 75,000 years ago. Since body lice live in
clothing, and most other species of mammal support only one species of
louse, the inference is that body lice evolved at the same time as
clothes.

That is an interesting coincidence, and some think it doubly
interesting that it coincides with the eruption of Toba. It may be
evidence of a shift of thought patterns of the sort that the Upper
Palaeolithic revolutionaries propose. On the other hand, there are
also signs of intellectual shifts predating this period. Sally
McBrearty, of the University of Connecticut, and Alison Brooks, of
George Washington University, have identified 14 traits, from making
stone blades to painting images, which they think represent important
conceptual advances. Ten of them, including fishing, mining, engaging
in long-distance trade and making bone tools, as well as painting and
making beads, seem to be unique to modern Homo sapiens. However, four,
including grinding pigments (for what purpose remains unknown, but
probably body painting), stretch back into the debatable past of Homo
helmei.

Given the fragmentary nature of the evidence from Africa, which has
not been explored with the same sort of archaeological fine-tooth comb
as Europe, the speed of the emergence of modern behaviour is still
debatable. One thing, however, that clearly played no part in
distinguishing Homo sapiens from his hominid contemporaries was a
bigger brain.

Modern people do, indeed, have exceedingly large brains, measuring
about 1,300 cm³. Other mammals that weigh roughly the same as human
beings--sheep, for example--have brains with an average volume of
180cm³. In general, there is a well-established relationship between
body size and brain size that people very much do not fit. But as Dr
Oppenheimer shows (see chart 2), most of this brain expansion happened
early in human evolutionary history, in Homo habilis and Homo erectus.
The brains of modern people are only about 6% larger than those of
their immediate African predecessors. Perhaps more surprisingly, they
are smaller than those of Neanderthals. There is no doubt that this
early brain growth set the scene for what subsequently happened to
Homo sapiens, but it does not explain the whole story, otherwise Homo
erectus would have built cities and flown to the moon.

Flying to the moon may, in fact, be an apt analogy. Just as a space
rocket needs several stages to lift it into orbit, so the growth of
human intelligence was probably a multi-stage process, with each
booster having its own cause or causes. What those causes were, and
when they operated, remains a matter of vehement academic dispute. But
there are several plausible hypotheses.

The most obvious idea--that being clever helps people to survive by
learning about their surroundings and being able to solve practical
problems--is actually the least favoured explanation, at least as the
cause of the Great Leap Forward. But it was probably how intelligence
got going in the pre-human primate past, and thus represented the
first stage of the rocket.

Many primates, monkeys in particular, are fruit-eaters. Eating fruit
is mentally taxing in two ways. The first is that fruiting trees are
patchily distributed in both space and time (though in the tropics,
where almost all monkeys live, there are always trees in fruit
somewhere). An individual tree will provide a bonanza, but you have to
find it at the right moment. Animals with a good memory for which
trees are where, and when they last came into fruit, are likely to do
better than those who rely on chance. Also, fruit (which are a rare
example of something that actually wants to be eaten, so that the
seeds inside will be scattered) signal to their consumers when they
are ready to munch by changing colour. It is probably no coincidence,
therefore, that primates have better colour vision than most other
mammals. But that, too, is heavy on the brain. The size of the visual
cortex in a monkey brain helps to explain why monkeys have larger
brains than their weight seems to warrant.

The intelligence rocket's second stage was almost certainly a way of
dealing with the groups that fruit-eating brought into existence.
Because trees in the tropics come into fruit at random, an animal
needs a lot of fruit trees in its range if it is to avoid starving.
Such a large range is difficult for a lone animal to defend. On the
other hand, a tree in fruit can feed a whole troop. For both these
reasons, fruit-eating primates tend to live in groups.

But if you have to live in a group, you might as well make the most of
it. That means avoiding conflict with your rivals and collaborating
with your friends--which, in turn, means keeping track of your fellow
critters to know who is your enemy and who your ally. That, in turn,
demands a lot of brain power.

One of the leading proponents of this sort of explanation for
intelligent minds is Robin Dunbar, of Liverpool University in England.
A few years ago, he showed that the size of a primate's brain,
adjusted for the size of its body, is directly related to the size of
group it lives in. (Subsequent work has shown that the same
relationship holds true for other social mammals, such as wolves and
their kin.) Humans, with the biggest brain/body ratio of all, tend to
live in groups of about 150. That is the size of a clan of
hunter-gathers. Although the members of such a clan meet only from
time to time, since individual families forage separately, they all
agree on who they are. Indeed, as Dr Dunbar and several other
researchers have noticed, many organisations in the modern world, such
as villages and infantry companies, are about this size.

Living in collaborative groups certainly brings advantages, and those
may well offset the expense of growing and maintaining a large brain.
But even more advantage can be gained if an animal can manipulate the
behaviour of others, a phenomenon dubbed Machiavellian intelligence by
Andrew Whiten and Richard Byrne, of the University of St Andrews in
Scotland.

Size isn't everything

Monkeys and apes manage this to a certain extent. They seem to have a
limited "theory of mind"--the ability to work out what others are
thinking--which is an obvious prerequisite for the would-be simian
politician. They also engage in behaviour which, to the cynical human
zoologist, looks suspiciously like lying. But it is those two words,
"cynical" and "suspiciously", that give the game away. For it is
humans themselves, with their ability to ponder not only what others
are thinking, but also what those others are thinking about them, who
are the past masters of such manipulation.

And it is here that the question of language enters the equation.
Truly Machiavellian manipulation is impossible without it. And despite
claims for talking chimpanzees, parrots and dolphins, real
language--the sort with complex grammar and syntax--is unique to Homo
sapiens.

Dr Dunbar's hypothesis is that language arose as a substitute for the
physical grooming that other group-living primates use to maintain
bonds of friendship. Conversation--or gossip, as he refers to
it--certainly does seem to have the same bond-forming role as
grooming. And, crucially for the theory, groups rather than just pairs
can "groom" each other this way. Dr Dunbar sees the 150-strong group
size of Homo sapiens as both a consequence and a cause of verbal
grooming, with large groups stimulating the emergence of language, and
language then permitting the emergence of larger groups still.
Language, therefore, is the result of a process of positive feedback.

Once established, it can be deployed for secondary purposes.
Furthering the Machiavellian ends outlined by Dr Whiten and Dr Byrne
would be one such purpose, and this would drive other feedback loops
as people evolve more and more elaborate theories of mind in order to
manipulate and avoid manipulation. But language would also promote
collaborative activities such as trade and the construction of
sophisticated artefacts by allowing specialisation and division of
labour.

Not everyone agrees with the details of this thesis, but the idea that
the evolution of mental powers such as language has been driven by
two-way feedback loops rather than one-way responses to the
environment is a powerful one. Terrence Deacon, a researcher at the
University of California at Berkeley, for instance, thinks that
language evolved in a feedback loop with the complex culture that it
allowed humans to create. Changes in culture alter and complicate the
environment. Natural selection causes evolutionary changes that give
people the means to exploit their new, more complex circumstances.
That makes the cultural environment still more complicated. And so on.
Dr Deacon believes this process has driven the capacity for abstract
thought that accounts for much of what is referred to as intelligence.
He sees it building up gradually in early hominids, and then taking
off spectacularly in Homo sapiens.

The peacock mind

Perhaps the most intriguing hypothesis about the last stage of the
mental-evolution rocket, though, is an idea dreamed up by Geoffrey
Miller, of the University of New Mexico. He thinks that the human mind
is like a peacock's tail, a luxuriant demonstration of its owner's
genetic fitness.

At first sight this idea seems extraordinary, but closer examination
suggests it is disturbingly plausible. Lots of features displayed by
animals are there to show off to the opposite sex. Again, this
involves a feedback loop. As the feature becomes more pronounced, the
judge becomes more demanding until the cost to the displayer balances
the average reproductive benefit.

Frequently, only one sex (usually the male) does the showing off. That
makes the sexually selected feature obvious, because it is absent in
the other sex. Dr Miller, though, argues that biologists have
underplayed the extent to which females show off to males,
particularly in species such as songbirds where the male plays a big
part in raising the young, and so needs to be choosy about whom he
sets up home with. Like male birds, male humans are heavily involved
in childrearing, so if the mind is an organ for showing off, both
sexes would be expected to possess it--and be attracted by it--in more
or less equal measure.

Dr Miller suggests that many human mental attributes evolved this
way--rather too many, according to some of his critics, who think that
he has taken an interesting idea to implausible extremes. But sexual
selection does provide a satisfying explanation for such otherwise
perplexing activities as painting, carving, singing and dancing. On
the surface, all of these things look like useless dissipations of
energy. All, however, serve to demonstrate physical and mental prowess
in ways that are easy to see and hard to fake--precisely the
properties, in fact, that are characteristic of sexually selected
features. Indeed, a little introspection may suggest to the reader
that he or she has, from time to time, done some of these things to
show off to a desirable sexual partner.

Crucially, language, too, may have been driven by sexual selection. No
doubt Machiavelli played his part: rhetoric is a powerful political
skill. But seduction relies on language as well, and encourages some
of the most florid speech of all. Nor, in Dr Miller's view of the
world, is the ability to make useful things exempt from sexual
selection. Well-made artefacts as much as artful decorations indicate
good hand-eye co-ordination and imagination.

Whether Dr Miller's mental peacock tails have an underlying unity is
unclear. It could be the ability to process symbols; or it could be
that several different abilities have evolved independently under a
single evolutionary pressure--the scrutiny of the opposite sex. Or it
could be that sexual selection is not the reason after all, or at
least not the main part of it. But it provides a plausible explanation
for modern humanity's failure to interbreed with its Neanderthal
contemporaries, whether or not such unions would have been fertile:
they just didn't fancy them.


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The concrete savannah

Evolution and the modern world

THE eruption of Toba marked the beginning rather than the end of
hostilities between Homo sapiens and the climate. Views differ about
whether the eruption was the trigger, but it is clear that an ice age
started shortly afterwards. Though the species spread throughout Asia,
Australia and Europe (the populating of the Americas is believed by
most researchers to have happened after the ice began to retreat,
although not everybody agrees), it was constrained by ecological
circumstances in much the same way as any other animal. The world's
population 10,000 years ago was probably about 5m--a long way from the
imperial 6-billion-strong species that bestrides the globe today.

The killer application that led to humanity's rise is easy to
identify. It is agriculture. When the glaciers began to melt and the
climate to improve, several groups learned how to grow crops and
domesticate animals. Once they had done that, there was no going back.
Agriculture enabled man to shape his environment in a way no species
had done before.

In truth, agriculture turned out to be a Faustian bargain. Both modern
and fossil evidence suggests that hunter-gatherers led longer,
healthier and more leisured lives than did farmers until less than a
century ago. But farmers have numbers on their side. And numbers beget
numbers, which in turn beget cities. The path from Catalhoyuk in
Anatolia, the oldest known town, to the streets of Manhattan is but a
short one, and the lives of people today, no matter how urbane and
civilised, are shaped in large measure by the necessities of their
evolutionary past.

That fact has, however, only recently begun to be widely recognised.
For many years, psychology, like anthropology, operated in a strange
intellectual vacuum. Psychologists did not deny man's evolutionary
past, but they did not truly acknowledge it, either. Many in the field
seemed to feel that humanity had somehow transcended evolution.
Indeed, those of a Marxist inclination more or less required that to
be true. How else could people be perfectible? Dissenters were usually
treated with disdain. But, at about the time that Dr Cann was
publishing the work that would expose the fallacy of multiregionalism,
a group who dubbed themselves "evolutionary psychologists" began to
stick their heads above the academic parapets.

Eve's psyche

Studying the behaviour of humans is more difficult than studying that
of other animals, for two reasons. One is that the students come from
the same species as the studied, which both reduces their objectivity
and causes them to take certain things for granted, or even fail to
notice them altogether. The other is that human culture is, indeed,
far more complex than the cultures of other species. There is nothing
wrong with studying that culture, of course. It is endlessly
fascinating. But it is wrong to assume that it is the cause of human
nature, rather than a consequence; that is akin to mistaking the
decorative finishes of a building for the underlying civil
engineering. The aim of evolutionary psychology is to try to detect
the Darwinian fabric through the cultural decoration, by asking basic
questions.

Many of those questions, naturally, address sensitive issues of sex
and violence--another reason evolutionary psychologists are not
universally popular. David Buss, of the University of Texas,
demonstrated experimentally what most people know intuitively--that
women value high status in a mate in a way that men do not. Helen
Fisher, of Rutgers University, has dissected the evolutionary factors
that cause marriages to succeed or fail. She thinks, for example, that
the tendency of females to prefer high-status mates is at odds with
the increasing economic independence of women in the modern world.
Laura Betzig, of the University of Michigan, put an explicitly
Darwinian spin on the tendency of powerful men to accumulate harems.

Randy Thornhill, of the University of New Mexico, has shown that
physical beauty is far from being in the eye of the beholder. In fact,
those features rated beautiful, most notably bodily symmetry, are good
predictors of healthy, desirable attributes such as strong immune
systems--in other words, aesthetic sensibilities have evolutionary
roots.

Karl Grammer, of the Ludwig Boltzmann Institute of Urban Ethology, in
Vienna, has shown that body odour, too, is correlated with symmetry
and linked to immunological strength. Dr Thornhill, meanwhile, has
raised quite a few hackles by arguing that a propensity to rape is an
evolved characteristic of men rather than a pathology. Even murder has
not escaped the attention of the evolutionary psychologists. Martin
Daly and Margo Wilson, of McMaster University in Hamilton, Ontario,
showed that adults are far more likely to kill their stepchildren than
their biological children--a fact that had escaped both police forces
and sociologists around the world. They then dared to propose a
Darwinian explanation for this, namely that step-parents have no
direct interest (in the evolutionary sense) in the welfare of
stepchildren.

However, something similar to this list of human behaviours that have
yielded to evolutionary psychology could be found in many species.
Indeed, it was often comparisons with other species that sparked the
investigations in the first place. The males of many other species
gather harems, but females rarely do so; female swallows prefer their
mates to have symmetrical tails and they are also more faithful to
high-status males; both male lions and male baboons kill the infants
of females in groups they have just taken over; and so on. Where
evolutionary explanations of behaviour become really interesting is
when they home in on what is unique to humanity.

Playing games with the truth

One uniquely human characteristic is the playing of games with formal
rules. Evolutionary psychology has not yet sought to explain this, but
it has exploited it extensively to develop and test its ideas. In
their different ways, the games devised by Leda Cosmides and John
Tooby, of the University of California at Santa Barbara, and Robert
Axelrod, of the University of Michigan, have underpinned that part of
evolutionary psychology devoted to uniquely human behaviour. For not
all games are about competition. Many also require trust, a sense of
justice and sometimes self-denial.

Cases of animals apparently making sacrifices, occasionally of their
own lives, to help others are not rare in nature, but at first sight
they are surprising. What is in it for the sacrificer? The usual
answer, worked out in the 1960s by William Hamilton, is that the
beneficiary is a relative whose reproductive output serves to carry
genes found in the sacrificer into the next generation, albeit at one
remove. Translated into human terms, this is good old-fashioned
nepotism. In a few species, though--mankind being the most
obvious--people will make sacrifices for non-relatives, or "friends".
The assumption is that the favour will be paid back at some time in
the future. The question is, how can the sacrificer be sure that will
happen?

Dr Axelrod used a branch of maths called game theory to come up with
at least part of the answer. He showed mathematically that as long as
you can recognise and remember your fellow creatures, it makes sense
to follow the proverb "fool me once, shame on you; fool me twice,
shame on me" and trust them provided they don't cheat you. (Sometimes
in science it is necessary to prove the obvious before you go on to
the less obvious.) Dr Cosmides and Dr Tooby used a different sort of
game to show that humans are thus, as Dr Axelrod's model suggests they
should be, acutely sensitive to unfair treatment. They did this by
presenting some problems of formal logic to their experimental
subjects as a card game. When the problems were presented using cards
with letters and numbers on opposite faces, and the subjects had to
work out which cards needed to be turned over to yield the required
answers, people found them hard to do and more often than not got them
wrong. However, when the problems were presented in a form that
required the subjects to decide whether people were being treated
fairly or not, they found them really easy. The researchers'
conclusion is that humans are hard-wired not for logic but for
detecting injustice.

Trust, and the detection and punishment of injustice, lie at the heart
of human society. They are so important that people will actually harm
their own short-term interests to punish those they regard as behaving
unfairly. Another game, for example, involves two people dividing a
sum of money ($100, say). One makes the division and the other accepts
or rejects it. If it is rejected, neither player gets any money. On
the face of it, even a 99:1 division should be accepted, since the
second player will be one dollar better off. In practice, though, few
people will accept less than a 70:30 split. They will prefer to punish
the divider's greed rather than take a small benefit themselves.

This makes no sense in a one-off transaction, but makes every sense if
the two participants are likely to deal with each other repeatedly.
And that, before the agricultural population boom (and also, for the
most part, after it) was the normal state of affairs. The people an
individual dealt with routinely would have been the members of his
circle of 150. Strangers would have been admitted to this circle only
after prolonged vetting. Such bonds of trust, described by Matt
Ridley, a science writer, as "the origins of virtue" in his book of
that name, underlie the exchanges of goods and services that are the
basis of economics. They may also, though, underlie another sensitive
subject that social scientists do not like biologists treading on:
race.

Robert Kurzban, a colleague of Dr Cosmides and Dr Tooby, took the
racial bull by the horns by reversing the old saw about beauty. Dr
Thornhill's work overturned the folk wisdom that beauty is in the
beholder's eye by showing that universal standards of beauty have
evolved, and there are good reasons for them. Dr Kurzban, by contrast,
thinks he has shown that race really does exist only in the eye--or,
rather, the mind--of the beholder, not the biology of the person being
beheld, and does so for good Darwinian reasons.

First impressions count

Dr Kurzban observes that the three criteria on which people routinely,
and often prejudicially, assess each other are sex, age and race.
Judgments based on sex and age make Darwinian sense, because people
have evolved in a context where these things matter. But until
long-distance transport was invented, few people would have come
across members of other races. Dr Kurzban believes that perceptions of
racial difference are caused by the overstimulation of what might be
called an "otherness detector" in the human mind. This is there to
sort genuine strangers, who will need to work hard to prove they are
trustworthy, from those who are merely unfamiliar members of the clan.
It will latch on to anything unusual and obvious--and there is little
that is more obvious than skin colour. But other things, such as an
odd accent, will do equally well. Indeed, Dr Dunbar thinks that the
speed with which accents evolve demonstrates that they are used in
precisely this sort of way.

If Dr Kurzban is right (and experiments he has done suggest that
assessments of allegiance are easily "rebadged" away from skin colour
by recognisable tokens such as coloured T-shirts, as any sports fan
could probably have told him), it explains why race-perception is such
a powerful social force, even though geneticists have failed to find
anything in humans that would pass muster as geographical races in any
other species. In fact, one of the striking things about Homo sapiens
compared with, say, the chimpanzee is the genetic uniformity of the
species. The only "racial" difference that has a well-established
function is skin colour. This balances the need to protect the skin
from damage by ultraviolet light (which requires melanin, the pigment
that makes skin dark) and the need to make vitamin D (which results
from the action of sunlight on a chemical in the skin). This explains
dark, opaque skins in the tropics and light, transparent ones nearer
the poles. The test is that dark-skinned arctic dwellers, such as the
Inuit of North America, have diets rich in vitamin D, and so do not
need to make it internally. As to other physical differences, they may
be the result of founder effects, as described by Dr Ambrose, or
possibly of sexual selection, which can sometimes pick up and amplify
arbitrary features.

Darwinian thinking can lead in other unexpected directions, too.
Pursue Dr Buss's observation about women preferring high-status males
to its logical conclusion, and you have a plausible explanation for
the open-endedness of economic growth. Psychologists of a
non-evolutionary bent sometimes profess themselves puzzled by the fact
that once societies leave penury behind (the cited income level
varies, but $10,000 per person per year seems about the mark), they do
not seem to get happier as they get richer.

That may be because incomes above a certain level are as much about
status as about material well-being. Particularly if you are a man,
status buys the best mates, and frequently more of them. But status is
always relative. It does not matter how much you earn if the rest of
your clan earn more. People (and men, in particular) are always
looking for ways to enhance their status--and a good income is an
excellent way of doing so. Aristotle Onassis, a man who knew a thing
or two about both wealth and women, once said: "If women didn't exist,
all the money in the world would have no meaning." Perhaps the
founding father of economics is not really Adam Smith, who merely
explained how to get rich, but Charles Darwin, who helped to explain
why.


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Starchild

Evolution is still continuing

WHAT, then, of the future? Sitting in the comfort of the concrete
savannah, has humanity stopped evolving?

To help answer that question, it is instructive to look at a paper
published earlier this year by Gregory Cochran. Dr Cochran, a
scientist who, in the tradition of Darwin himself, works independently
of an academic institution, looked at the unusual neurological
illnesses commonly suffered by Ashkenazi Jews. Traditional wisdom has
it that these diseases, which are caused by faulty genes, are a
consequence of inbreeding in a small, closed population. The fact that
they persist is said to show that human evolution has stopped in our
ever more mollycoddled and medicalised world. Dr Cochran begged not
only to differ, but to draw precisely the opposite conclusion. He sees
these diseases as evidence of very recent evolution.

Until a century or two ago, the Ashkenazim--the Jews of Europe--were
often restricted by local laws to professions such as banking, which
happened to require high intelligence. This is the sort of culturally
created pressure that might drive one of Dr Deacon's feedback loops
for mental abilities (though it must be said that Dr Deacon himself is
sceptical about this example). Dr Cochran, however, suspects that this
is exactly what happened. He thinks the changes in the brain brought
about by the genes in question will be shown to enhance intelligence
when only one copy of a given disease gene is present (you generally
need two copies, one from each parent, to suffer the adverse
symptoms). Indeed, in the case of Gaucher's disease, which is not
necessarily lethal, there is evidence that sufferers are more
intelligent than average. If Ashkenazi Jews need to be more
intelligent than others, such genes will spread, even if they
sometimes cause disease.

The fact is, you can't stop evolution. Those who argue the opposite,
pointing to the survival thanks to modern medicine of people who would
previously have died, are guilty of more than just gross
insensitivity. They have tumbled into an intellectual pitfall that has
claimed many victims since Darwin first published his theory.
Evolution is not about progress. It is about adaptation. Sometimes
adaptation and progress are the same. Sometimes they are the opposite.
(Ask a tapeworm, which has "degenerated" into a mere egg-laying
machine by a very successful process of adaptation.) If a mutation
provides a better adaptation, as Dr Cochran thinks these disease genes
did in financiers, it will spread. Given the changes that humanity has
created in its own habitat, it seems unlikely that natural selection
has come to a halt. If Dr Deacon is right, it may even be accelerating
as cultural change speeds up, although the current rapid growth in the
human population will disguise that for a while, because selection
works best in a static population.

The next big thing

Evolution, then, has not stopped. Indeed, it might be about to get an
artificial helping hand in the form of genetic engineering. For the
fallacy of evolutionary progress has deep psychological roots, and
those roots lie in Dr Miller's peacock-tail version of events. The
ultimate driver of sexual selection is the need to produce offspring
who will be better than the competition, and will thus be selected by
desirable sexual partners. Parents know what traits are required. They
include high intelligence and a handful of physical characteristics,
some of which are universal and some of which vary according to race.
That is why, once the idea of eliminating disease genes has been
aired, every popular discussion on genetic engineering and cloning
seems to get bogged down in intelligence, height and (in the West)
fair hair and blue eyes.

This search for genetic perfection has an old and dishonourable
history, of course, starting with the eugenic movement of the 19th
century and ending in the Nazi concentration camps of the 20th, where
millions of the confrères of Dr Cochran's subjects were sent to their
deaths. With luck, the self-knowledge that understanding humanity's
evolution brings will help avert such perversions in the future. And
if genetic engineering can be done in a way that does not harm the
recipient, it would not make sense to ban it in a liberal society. But
the impulse behind it will not go away because, progressive or not, it
is certainly adaptive. Theodosius Dobzhansky, one of the founders of
genetics, once said that "nothing in biology makes sense except in the
light of evolution". And that is true even of humanity's desire to
take control of the process itself.


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Acknowledgment and sources

The author would like to acknowledge the help of the numerous
researchers named in the text. The following books and website may be
of interest to readers who wish to learn more about the subject.

"Out of Eden", by Stephen Oppenheimer (Constable and Robinson,
paperback)

"The Journey of Man", by Spencer Wells (Penguin, paperback)

"From Lucy to Language", by Donald Johanson and Blake Edgar
(Weidenfeld and Nicolson)

"Grooming, Gossip and the Evolution of Language", by Robin Dunbar
(Faber and Faber, paperback)

"The Symbolic Species", by Terrence Deacon (W.W. Norton)

"The Mating Mind", by Geoffrey Miller (William Heinemann)

"The Origins of Virtue", by Matt Ridley (Penguin, paperback)

http://www.nationalgeographic.com/genographic