[Paleopsych] BBS: Archaeology and cognitive evolution
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Archaeology and cognitive evolution
[I'll be sending out several of the BBS target articles over the next few days.
I found a treasure trove of them.]
Published in Behavioral and Brain Sciences
Volume 25, Number 3: 389-402 (June 2002)
Below is the unedited, uncorrected, unquotable final draft preprint of
a BBS target article that was accepted for publication. Please visit
the Cambridge Journals Online BBS Home Page to order the full
Long abstract - 197
Short abstract - 118
Text - 12,348
References - 1,732
Entire text - 14,434
Department of Anthropology
University of Colorado
twynn at uccs.edu
Archaeology can provide two bodies of information relevant to the
understanding of the evolution of human cognition - the timing of
developments, and the evolutionary context of these developments. The
challenge is methodological. Archaeology must document attributes that
have direct implications for underlying cognitive mechanisms. One
example of such a cognitive archaeology is that for spatial cognition.
The archaeological record documents an evolutionary sequence that
begins with ape-equivalent spatial abilities 2.5 million years ago and
ends with the appearance of modern abilities in the still remote past
of 400,000 years ago. The timing of these developments reveals two
major episodes in the evolution in spatial ability, one 1.5 million
years ago and the other one million years later. The two episodes of
development in spatial cognition had very different evolutionary
contexts. The first was associated with the shift to an open country
adaptive niche that occurred early in the time range of Homo erectus.
The second was associated with no clear adaptive shift, though it does
appear to have coincided with the invasion of more hostile
environments and the appearance of systematic hunting of large
mammals. Neither, however, occurred in a context of modern hunting and
Archaeology can provide two bodies of information relevant to the
understanding of the evolution of human cognition - the timing of
developments, and the evolutionary context of these developments. To
do this, archaeology must document attributes that have direct
implications for underlying cognitive mechanisms. One example of such
a cognitive archaeology is that for spatial cognition. The
archaeological record documents an evolutionary sequence that begins
with ape-equivalent spatial abilities 2.5 million years ago and ends
with the appearance of modern abilities in the still remote past of
400,000 years ago. The timing of these developments reveals two major
episodes in the evolution in spatial ability, one 1.5 million years
ago and the other one million years later.
Archaeology and Cognitive Evolution
Department of Anthropology
University of Colorado in Colorado Springs
twynn at uccs.edu
Keywords: Archaeology, symmetry, spatial cognition, evolution, Homo
I have two goals in this article. The first is to make a case for the
relevance of archaeological contributions to studies of the evolution
of cognition. The second is to provide an example of one such
contribution, a reconstruction of aspects of early hominid spatial
cognition based on an analysis of artifactual symmetries.
Assuming that human evolution is relevant to understanding the human
condition, an intellectual position that is at the core of biological
approaches to behavior, if not yet psychology, then archaeology can
supply two important bodies of evidence: 1) actual timing of
developments, and 2) the evolutionary context of these developments.
The challenge is not epistemological; archaeology can and does supply
these things to the study of human evolution in general. The challenge
is methodological. How can archaeology inform us about the evolution
Archaeology is a set of methods for reconstructing past action from
traces that exist in the present. These traces include objects made or
modified by people in the past - tools, houses, ornaments, and so on -
but also less tidy patterns like garbage and refuse of all kinds and
evidence of past landscapes (through analysis of soils, pollen, faunal
remains, and so forth). Because some traces survive the ravages of
time better than others the archaeological record is a biased and
non-random sample of past action. Stone tools, for example, survive
well but wooden tools do not. Also, some environments preserve traces
better than others. Tropical environments are poor preservers, but
cold, dry, arctic environments are good preservers. Archaeology is an
observational discipline. Unlike laboratory scientists, archaeologists
cannot duplicate events and unlike ethologists archaeologists cannot
depend on obtaining corroborating observations, though we certainly
hope for them. There is a real element of serendipity in archaeology.
Pompeii, the "Ice man", and the recent discovery of 400,000 year old
spears at Schoeningen (Thieme 1997), are unique and wonderfully
informative but they are atypical. The archaeological record boasts
relatively few such treasures. Instead it consists largely of more
incomplete and mundane traces that allow archaeologists to reconstruct
some of what occurred in the past. The primary methodological task of
the archaeologist is this reconstruction -- translating traces into
actions -- and archaeology has developed a large body of concepts and
techniques for doing this. We are very good at reconstructing diet
from garbage, and social/political systems from the size, character,
and location of settlements. Can there be an archaeology of cognition?
This is in reality a two-part question. First, can traces of action
inform us reliably about any aspect of cognition, and second, if so,
can archaeologists overcome some rather serious methodological
roadblocks inherent to the archaeological record of such traces?
One way that psychologists learn about the mind is by observing the
actions of individuals in controlled laboratory settings or in natural
situations. Sometimes these actions leave tangible traces that become
the focus of the analysis. Children's drawing is one example; block
shuffling tests are another. The methodological task of the
psychologist is to translate the tangible results into meaningful
characterizations of the mind that produced them. Of course,
psychologists can also talk to their subjects, but in principle
psychology can and does analyze the traces of action. An archaeologist
trying to do the same faces some additional hurdles. To make a
convincing argument in cognitive archaeology, one must be able to
identify specific features of the archaeological record that can
inform about cognition in a valid and reliable way. This is the crux
of the matter. Unfortunately, the disciplines of archaeology and
psychology have never shared much in the way of theory and
methodology. For an archaeologist to make a compelling case, he or she
must not simply refer to a few selected psychological results. There
must also be some understanding of the theoretical and methodological
context of the research. With this in hand, the archaeologist can
define a set of attributes that can be applied to the archaeological
record. This definitional step is indispensable. It is very unlikely
that variables taken directly from the psychological literature could
be applied to archaeological remains. On the other hand, the
traditional categories of archaeology are inappropriate, a point that
bears emphasis. Over the last century and a half archaeology has
developed a large set of categories for the description of
archaeological remains. Some of these categories are based on presumed
function (e.g., ground stone axe, or temple complex), some on presumed
usefulness in temporal ordering (e.g., Iron Age), some on social
complexity (e.g., "Classic" Mesoamerica), and so on. None, to my
knowledge, has ever been defined with cognition in mind, and it would
be misleading to use them as such (e.g., to argue that Iron Age people
were cognitively different from Stone Age people). The cognitive
archaeologist must avoid using these traditional categories and
approach the archaeological record from the perspective of
psychological theories and methods.
Even after careful definition, archaeology faces a number of
roadblocks peculiar to its data. The first is preservation. Not only
does preservation produce a biased record, it also presents a sliding
scale of resolution. The farther back in time we look, the worse the
record. There is less preserved, and there are fewer examples of what
is preserved. This alone gives the archaeological record a
misleadingly progressive appearance; 10,000 year-old remains appear
more complex than 500,000 year-old remains partly (but not entirely)
because we have so many more of them. The second caveat is logical.
How can we be sure that archaeological remains are a reliable
reflection of the cognitive abilities of past people? Might not these
people have invested their cleverest thinking in domains that are
archaeologically invisible? There is no infallible way around this
problem. Archaeologists can only assess the minimum competence
necessary to produce a particular pattern. Our only comfort comes from
increasing the number and, especially, the variety of corroborating
Finally, cognitive archaeology works best on an evolutionary scale of
resolution. The ultimate achievement of cognitive archaeology would be
to provide descriptions of the cognitive life-world of human
antecedents at many points in evolution. Such descriptions would
provide an evolutionary foundation for understanding the modern mind.
I have long harbored the desire to provide a comprehensive account of
the mind of Homo erectus, a very successful ancestor who was the
immediate precursor of Homo sapiens. Surely, an understanding of Homo
erectus' cognition would illuminate aspects of the modern mind; there
must be much of Homo erectus with us still. Unfortunately, I do not
think such a comprehensive description is possible; the archaeological
record is too incomplete.
Archaeology can take another approach to the question of evolution, an
approach not focused on descriptions of individual antecedents, but
one focused on long term patterns of change. Even though poor in
detail, the archaeological record is very long, providing a
quasi-continuous record of products of action that spans over two
million years. Archaeologists can use this record to identify patterns
of cognitive evolution that provide insights into questions of modern
cognitive science. What follows is an example of this approach. The
focus is on spatial cognition (generally considered, including shape
recognition and image manipulation). The evidence will consist of
2. The Archaeological Record of Artifactual Symmetry
I have chosen to survey the evolution of artifactual symmetry three
reasons. First, symmetry is a pattern and a concept that is recognized
by everyone, which reduces the requirement for definition (but does
not eliminate it entirely). Second, symmetry has been incorporated
into many schemes of spatial cognitive development, and also into
theories of perception, so that it provides a direct way to articulate
the archaeological record with the cognitive science literature.
Finally, it is amenable to visual presentation.
There are several different patterns to which we apply the term
symmetry. The most familiar is reflectional symmetry, also known as
bilateral or mirror symmetry. Here one half of a pattern is duplicated
and reversed on the opposite side. Implicit in the pattern is a
central line, usually vertical, that divides the pattern into
reflected versions of one another. Bilateral symmetry is "natural" in
the sense that we see this pattern in the natural world of plants and
animals. A second symmetry is radial symmetry, in which a pattern
repeats not across a line, but continuously around a point. Similar to
radial symmetry is rotational symmetry, in which a pattern is not
reflected across a line, but rotated around a point; here the pattern
is not reversed or inverted. Finally, there is translational symmetry,
in which a pattern is repeated in a sequence, without reversal or
Symmetry is ubiquitous in the natural world and the cultural world. It
is a well-known feature of crystal growth, resulting from the chemical
structures of the molecules themselves. It also acts as a principle in
biological growth and development, as in the symmetrical duplications
of supernumerary appendages in beetles (Bateson 1972), where the
source probably lies in the genes regulating growth. On a larger
scale, symmetry is a feature of the overall body plans of many
organisms, from microscopic foraminifera to large vertebrates. In
human material culture, symmetry appears in the form of artifacts,
buildings, and built environments all over the world. It is a central
component of decorative systems in almost all human culture, and also
a component of games (e.g., string games) and mathematical puzzles
(e.g., tessellations). In many of these cases the symmetry results
from the application of transformational rules; simple figures
repeated and "moved" to produce intricate patterns. Symmetry is so
fundamental in western culture, at least, that it is often a metaphor
for balance and regularity (e.g., the "symmetrical" arrangement of
keys in The Marriage of Figaro). Moreover, it is often endowed with
meaning, carrying explicit and implicit information about fundamental
values of a culture (Washburn and Crowe 1988).
Not surprisingly, perception of symmetry has been the focus of
psychological research for over a century (Wagemans 1996). It is now
generally accepted, for example, that reflectional symmetry is
perceptually more salient than translation and rotation. Indeed, some
experimental work suggests that reflectional symmetry can be detected
pre-attentively. Reflectional symmetry across a vertical axis is more
salient than reflection across a horizontal axis, with oblique
orientations falling a distant third. In addition to such empirical
generalizations, there are competing theories of symmetry perception,
and it remains a component of general theories of perception (Tyler
1996). It has even come to be a focus in evolutionary psychology,
where detection of asymmetry is seen to be a means of mate assessment
(Gangestad 1997). Given the ubiquity of reflectional symmetry in the
natural world, and its correlation with successful ontogenetic
development in many, many, organisms, it is not at all surprising that
perceptual systems should have evolved a sensitivity to symmetry. It
is quite likely, then, that the perceptual saliency of symmetry is not
a derived feature of human perception, but is one we share with many
complex organisms. The degree to which it is shared, and whether it
has evolved independently in several taxa or is instead a very old
feature, are interesting questions, but tangential to the current
discussion. The archaeological record does not document the
development of symmetry perception per se. Instead, it documents the
imposition of symmetry on material objects. Detecting symmetry is not
sufficient for this task; other cognitive mechanisms must come into
play. The importance of the archaeological record of symmetry lies not
in the symmetry itself, but in what it reveals about these other
2.1 Stone Tools
Most of the following analysis will focus on stone tools. They are far
and away the most abundant material evidence archaeologists possess
for the majority of human evolution. The record of stone tools begins
2.5 million years ago and extends to the present. From the tools
themselves archaeologists can reconstruct a variety of actions: raw
material selectivity and procurement, manufacturing sequences, use,
and discard. Archaeologists have been most interested in
reconstructing the specific uses of stone tools, and the role these
tools played in subsistence and, sometimes, social life. But these
reconstructed actions, those of manufacturing in particular, can also
document particular cognitive abilities.
Fracturing a stone produces sharp edges; this is the basic principle
underlying almost all stone tools. Archaeologists use the term
"knapping" to refer to the stone fracturing process. In the simplest
case a stone knapper uses one stone, termed a hammer, to strike
another. If the knapper has struck with enough force, and delivered
the blow to an appropriate spot at the appropriate angle, the
receiving stone, termed a core, will break. In most instances the
knapper must direct the blow toward the edge of the core because a
blow landing toward the center is unlikely to deliver enough force to
produce a fracture. This simple act of knapping produces two
potentially useful products, a smaller sharp edged piece termed a
flake, and the larger core, which now also may have sharp edges. Even
this simplest of knapping actions requires directed blows. Randomly
bashing two rocks together can produce useful flakes but even the
earliest stone tools, 2.5 million years old, resulted from directed
blows. The subsequent development of knapping technology included
increases in the number of blows delivered to a single core, greater
specificity in the location of blows, modification of flakes, longer
sequences of action between the initial blows and the final blows, a
greater variety of hammering techniques, and more regularly shaped
Recently Stout et al. (Stout, Toth et al. 2000) have conducted a pilot
PET study of basic stone knapping using an experienced knapper (Nick
Toth) as the subject. The result showed highly significant activation
in several brain regions. Much of this activation is what one would
expect from performance of a complex motor task based on hand-eye
coordination (primary motor and somatososensory areas, and cerebellar
activity [p. 218]), but Stout et al. also recognize a significant
"cognitive" component, implied by the activation of superior parietal
"The superior parietal lobe consists of what is referred to as
"multi-modal association cortex" and is involved in the internal
construction of a cohesive model of external space from diverse
visual, tactile, and proprioceptive input" (p. 1220).
In other words, simple stone knapping is a "complex sensorimotor task
with a spatial-cognitive component" (p. 1221). These results, though
preliminary, situate most of the significant cognitive activation
within the "dorsal pathway" of visual processing (Ungerleider 1995;
Kosslyn 1999). The ventral pathway associated with object
identification and shape recognition is minimally activated, implying
that shape is not a significant component of the basic flaking task.
These results are preliminary and need confirmation. There was only
one subject, a skilled knapper, and the knapping task was brief and
basic -- removing flakes from a nodule (a Mode 1 procedure; see
below). Nevertheless, it reinforces work of cognitive archaeologists
who have focused on spatial concepts borrowed from developmental
psychology ((Wynn 1979; Wynn 1981; Wynn 1985; Wynn 1989; Robson Brown
The directed action of stone knapping preserves something of the
cognition of the knapper. Even in the simplest example, the knapper
must make a decision about where to place a blow and how much force to
use. These decisions are preserved in the products themselves. It is
now common for archaeologists to "refit" cores by placing the flakes
back together in a kind of 3-D jigsaw puzzle. Such a reconstruction
permits archaeologists to describe in detail long sequences of action
including specific location of blows, reorientation of the core by the
knapper, and subsequent modification of flakes (Schlanger 1996). But
even simple tools can be informative. The pattern of "negative scars"
on cores or modified flakes preserves the sequences of blows.
Archaeologists interested in cognition can use these preserved action
sequences to investigate a variety of cognitive abilities, including
sequencing, biomechanical skill, and spatial cognition. Even the
simplest knapping required some notions of spatial relations and as
stone tools became more complex they often preserved more complex
understandings of spatial relationships.
There is a problem with intentionality. All stone tools have a shape,
and this shape preserves spatial relationships, but how intentional
were they? Here I do not mean the layers of intentionality invoked in
theory of mind literature, but the simple question of whether or not a
stone knapper intended to produce a particular shape. The basic action
of stone knapping will produce useful results without the knapper
intending the final core and flakes to have any specific appearance
whatsoever. It is even possible for the iterative application of a
specific flaking procedure to produce a final core with a regular
shape, completely unintended. The shape itself, and the location and
extent of modification producing the shape can often, but not always,
document intention. For example, the artifact in FIG 5 has extensive
trimming on one side that produces a "shoulder" mirroring a natural
configuration on the opposite side. This is unlikely to have been an
2.2 What about apes?
It is appropriate and traditional to begin discussions of human
evolution with a discussion of modern apes. Much of our anatomy and
behavior is shared with apes, including characteristics of the brain
and cognition. A necessary first step in any evolutionary analysis is
the identification of what is peculiarly human, for this allows
correct focus of the undertaking. If modern apes, especially
chimpanzees, employed all of the spatial abilities used by humans,
then our evolutionary understanding must focus on the evolution of
apes in general. It is also an axiom of paleoanthropology that human
anatomy and behavior evolved out of those of an African ape, so that a
description of this ancestor is a logical starting point for any
summary. Our best information concerning this common ancestor comes
from the living African apes (who, of course, have also evolved, but
because their anatomy and habits appear more like those of a "general
ape" than the anatomy and habits of the obviously unusual humans, they
are a better candidate than ourselves).
Whatever the cognitive requirements of stone knapping are, they are
within the abilities of apes, at least at the basic level of using a
hammer to remove a flake. Nick Toth and Sue Savage-Rumbaugh have
taught a bonobo to flake stone, and the results of their research help
identify what might have been different about the cognition of the
earliest stone knappers(Toth, Schick et al. 1993; Schick, Toth et al.
1999). Kanzi, a bonobo also known for his ability to understand spoken
English and use signs, learned how to remove flakes from cores by
observing a human knapper; he also learned to use the sharp flakes to
cut through a cord that held shut a reward box. After observing the
procedure, Kanzi perfected his technique by trial and error. His
initial solution, interestingly, was not to copy the demonstrator's
action, but to hurl the core onto a hard surface and then select the
sharp pieces from the shattered remnants. He clearly understood the
notion of breakage and its consequences. When experimenters padded the
room, he then copied the hammering technique used by the knapper. From
this experiment (and an earlier one by Wright(Wright 1972)), it is
clear that fracturing stone is within the cognitive abilities of apes.
However, Kanzi is not as adept as human knappers. " (A)s yet he does
not seem to have mastered the concept of searching for acute angles on
cores from which to detach flakes efficiently, or intentionally using
flake scars on one flake of a core as striking platforms for removing
flakes from another face"(Toth et al. 1993: 89). These abilities are
basic to modern knapping and, more telling, are evident in the tools
made two million years ago. Toth et al. suggest that this represents a
significant cognitive development, though they do not specify just
what cognitive ability may have evolved. Elsewhere (Wynn, Tierson et
al. 1996)I have suggested that it may represent an evolutionary
development in "spatial visualization," which is the ability to
discriminate patterns in complex backgrounds. If true, this would
represent a minor cognitive development, of interest primarily because
it is a cognitive ability tied to tool manufacture and use. Kanzi is
also not very accurate in delivering blows, and this is harder to
assess. It could simply be a matter of biomechanical constraint (i.e.,
he does not have the necessary motor control), or it could result from
an inability to organize action on the small spatial field of the
core. It is the organization of such action, fossilized as patterns of
flake scars, that developed significantly over the two million years
following the first appearance of stone tools.
While apes can knap stone, they do not produce symmetries (at least
not yet). The only possible example of symmetry produced by apes in
the wild is the chimpanzee sleeping nest, which has a kind of radial
symmetry that is produced when the individual reaches out from central
position and pulls branches inward. Here the symmetry is a direct
consequence of a motor habit pattern, and one need not posit some idea
of symmetry (Wynn and McGrew 1989). There are no other ethological
examples, at least to my knowledge. However, there has been a
significant amount of research with captive apes, especially
chimpanzees, including a fascinating literature about chimpanzee art
and drawing, from which one can examine the ways apes arrange elements
Work with ape art has been of two kinds. In the first, researchers
present an ape with appropriate media (finger paints, brushes and
paint, etc.) and encourage it to create. In the second, researchers
control the productions by supplying paper with pre-dawn patterns. The
former is the more "archaeological", in that researchers have not
tried to coax particular pattern productions. Perhaps not
surprisingly, these spontaneous productions are patterned primarily by
motor patterns. Fan shapes are common, as are zig-zags produced by
back and forth arm motion.
Desmond Morris(Morris 1962), the most well-known researcher in ape
art, thought that these productions may demonstrate a sense of
balance, and tried to coax it out with a series of experiments using
sheets with stimulus figures already printed on (Figure 1B), following
earlier lead of Schiller(Schiller 1951). Morris's work led to a number
of subsequent experiments by others using similar techniques. The
results have been enigmatic at best. Most chimpanzees presented with a
figure that is offset from the center of the paper will mark on the
opposite side, or on the figure itself (Fig. 2B). Morris suggested,
cautiously, that this confirmed a notion of balance. Later Smith(Smith
1973) and Boysen(Boysen, Berntson et al. 1987) confirmed these
results, but argued that the pattern resulted from the chimpanzee's
placing marks toward the center of the vacant space; balance was an
It is hard to know what to make of this evidence. First, even with the
few experimental subjects, there was a lot of individual variability.
Indeed, each chimpanzee had an idiosyncratic approach to both the
controlled and uncontrolled drawing. Second, most repetitive patterns
resulted from repetitive motor actions. Nevertheless, the individuals
did appear to place their marks non-randomly, and did attend to
features of the visual field. Other, non-graphic, experiments have
indicated that chimpanzees can be taught to select the central element
of a linear array(Rohles and Devine 1967), so chimpanzees can clearly
perceive patterns in which balance is a component. But they do not
appear able to produce symmetrical patterns.
2.3 Tools of Early Hominids
The earliest hominids left no archaeological record. Studies of blood
chemistry and DNA indicate that humans and chimpanzees shared a common
ancestor as recently as five million years ago. By four millions year
ago the evolutionary split between hominids and the other African apes
had occurred. There is fossil evidence for these early hominids, but
it is fragmentary and more tantalizing than informative in regard to
adaptive niches(Tattersall 2000). Between 4 million and 2.5 million
years ago several different hominids lived in Africa. They differed
from one another in habitat and adaptive niche, but shared the basic
suite of hominid characteristics: bipedal locomotion, and relatively
small canines and large molars. None had a particularly large brain
(though slightly larger, relatively, than that of chimpanzees), and
none left any archaeological traces. If any or all of these hominids
made and used tools, as modern chimpanzees clearly do, then they have
not been preserved. We can assume that tool use must have been in the
repertoire of at least one of these hominids, only because it seems
unlikely that stone tool manufacture could have developed without
To date, the oldest reliably dated stone tools are 2.5 million years
old (Harris 1983). These earliest stone tools exhibit no convincingly
symmetrical patterns. Archaeologists assign these tools to a category
termed "Oldowan," because of their first discovery at Olduvai Gorge in
Tanzania. A better label was proposed several decades ago by Graham
Clark(Clark 1977), who termed them a Mode 1 technology, a term based
on technological characteristics, with no time-space implications.
Mode 1 tools first appeared about 2.5 million years ago in what is
today Ethiopia, and were the only kind of stone technology in evidence
for the next one million years. After 1.5 million years ago, Mode 1
technologies continued to be produced in many areas and, indeed, were
made into historic times. As such Mode 1 represents a common,
"generic" stone tool industry. It was also the earliest
The emphasis of Mode 1 tools is on the edges(Toth 1985). Simple stone
flakes can have very sharp edges, and are useful cutting tools without
further modification. The cores from which the flakes were removed
also have useful edges. These are not as sharp as the flakes, but the
cores are usually heavier, and the result is a tool that can be used
for chopping, crushing, and heavy cutting. Mode 1 tools exhibit little
or no attention to the overall shape of the artifact. The only
possible examples of a shaped tool occur in relatively late Oldowan
assemblages, where there are a few flakes with trimmed projections
(termed awls). Here a two-dimensional pattern of sorts has been
imposed on the artifact, but it is a very "local" configuration, one
that is tied to the nature of the edge itself.
2.3.2 Cognitive implications
The work of Stout et al. discussed earlier supports an emphasis on the
spatial cognition required by basic kind stone knapping typical of
these Mode 1 artifacts. Cognitive psychology supplies some more
specific variables that are also applicable to the analysis of these
early tools. Forty years ago Piaget and Inhelder (Piaget and Inhelder
1967) introduced basic topological notions in their analysis of
children's spatial ability, and these still have descriptive power. In
particular, the relations of proximity, order and boundary are all
required for the placing of trimming on Mode 1 tools. More recently,
Linn and Petersen (Linn and Petersen 1986) have identified "spatial
perception", the ability to detect features among complex backgrounds,
as one of the four components of spatial cognition. This ability
appears to be required when a knapper selects a platform with an
appropriate angle for striking. What does not appear to be necessary
for these tools is any kind of shape recognition or imagery. Basic
flaking procedure and simple spatial relations are sufficient. The
knappers imposed no overall shapes.
In this respect, at least, these early hominids were very ape-like.
Indeed, when we expand our perspective to other features of tool
making and use, we find that it was ape-like in most respects (Wynn
and McGrew 1989). Yes, use of stone tools to butcher parts of animal
carcasses obtained through scavenging was a novel component to the
adaptation (Toth and Schick 1986; Potts 1988; Schick and Toth 1993),
but at this point in hominid evolution it appears to have been merely
a variant on the basic ape adaptive pattern, with no obvious leap in
intellectual ability required. Indeed, there is no compelling
archaeological reason to grant tool making any special place in the
selective forces directing the first three million years of human
cognitive evolution. But sometime after two million years ago the
2.4 The First Hominid Imposed Symmetry
About 1.4 million years ago hominids in East Africa, presumably Homo
erectus, began making large stone tools with an overall
two-dimensional shape. Many (but not all) of these "bifaces" were made
by first detaching a very large flake from a boulder-sized core using
a two-handed hammering technique (Jones 1981). The knapper then
modified this large flake by trimming around the margins (usually onto
both faces of the flake, hence the term biface). The uses to which
these tools were put are unknown, though experimental evidence
indicates that they can be effective butchery tools (Toth and Schick
1986). Archaeologists recognize two types of biface, the handaxe and
the cleaver. Handaxes have a point or tip, and cleavers have a
transverse "bit" that consists of an untrimmed portion of edge
oriented perpendicular to the long axis of the tool.
Both varieties of biface can have reflectional symmetry, and it is
primarily this symmetry that produces the overall shape. However, not
all bifaces of this age are nicely symmetrical, and even the nicest
examples look crude compared to the symmetry of later tools. Are we
justified in attributing some kind of symmetry concept to the knapper?
Might not the symmetry lie only with archaeologist, who "reads" what
was in no way intended by the knapper? This is a knotty problem that
has become the center of an interesting, if parochial, controversy
among cognitive archaeologists (Noble and Davidson 1996). Most
archaeologists, myself included, argue that the symmetry is real.
First, the most symmetrical examples are also the most extensively
trimmed, indicating that the knapper devoted more time to production.
Second, and more telling, on some bifaces the trimming mirrors a
natural shape on the opposite edge. Such artifacts do not have the
best symmetry, but the economy of means by which the symmetry was
achieved reveals that some concept of mirroring must have guided the
In addition to handaxes and cleavers, a third variety of biface occurs
in low numbers in some sites in this time period. These are
"discoids", so called because of their round shapes. Like the other
bifacial tools, the nicest, in this case the roundest, are also the
most extensively modified. Here again we can recognize symmetry, in
this case radial rather than reflection.
2.4.2 Cognitive implications
In most respects the cognitive requirements of these early bifaces
resemble those of the earlier (and presumably antecedent) Mode 1
artifacts. But the symmetry presents a puzzle for cognitive
interpretation. There are at least three possibilities:
1) The symmetry (and regular radii) are purely a consequence of a
technique of manufacture using large flakes as blanks. The placement
of trimming on some pieces argues against this, but the absence of
congruency means that the symmetry is always crude and, for many
archaeologists, unconvincing (Noble and Davidson 1996). Any cognitive
significance would have to lie in the techniques of blank production.
Although the two handed hammering technique (Jones 1981) clearly
qualifies as an invention, its cognitive prerequisites seem no
different from those of other direct percussion techniques used in
Mode 1 technologies.
2) The symmetry was intended, but was not "new." Rather it is a
pattern that is salient in the shape recognition repertoire of apes in
general. What was new was the imposition of this shape on modified
objects, something other apes never do.
3) Symmetry was a new acquisition in the shape recognition repertoire
of these hominids and was applied to stone tools.
Conservatism inclines me towards the second hypothesis. But even if
symmetry in pattern recognition is old, there was still a cognitively
significant development associated with these bifaces. The stone
knappers produced a symmetry by mirroring or reflecting the shapes
from one lateral edge to the other. True, the edges are not exact
mirrors. They are rarely if ever congruent in a modern geometric
sense, but they are inversions of a two-dimensional shape. It is not
even necessary that a particular overall shape have existed as an
image prior to manufacture. The knapper could simply have mirrored one
of the edges naturally provided him or her. In such a case the knapper
would need to invert a shape. More significant, the knapper had to
ignore part of the shape of the original large flake in order to
impose a symmetrical edge. This is a kind of frame independence, the
ability to see past the constraints imposed by a spatial array (Linn
and Petersen 1986). The discoids suggest that the knappers were also
able to employ a notion of spatial amount, in this case a diameter.
The knappers trimmed the tool until all of the diameters were roughly
equal. While not an abstract quantity like an inch, a diameter is
nevertheless a spatial amount, albeit local and limited. But what is
most significant is that these biface knappers incorporated a shape
component into the knapping problem. This shape component need not
have been an abstract concept. It could simply have been shape
"recognition," matching to unimodal representation (Kosslyn 1999), in
this case reflectional symmetry. Such a unimodal representation is
almost certainly in the shape recognition repertoire of apes in
general. What is significant here is its manifestation in the
otherwise spatial task of knapping.
This new development required coordination of spatial abilities with a
previously separate cognitive component (or neural network in
Kosslyn's sense(Kosslyn 1994)), that of shape recognition.
The imposition of shape is a feature of virtually all human material
culture. But the first time it ever occurred was with these early
bifaces. Prior to the appearance of bifaces, stone knappers attended
to the configuration of edges and to size. The earlier Mode 1 tools
were arguably an ad hoc technology (Wynn 1981; Isaac 1984; Toth 1985)
made for immediate use. It is unlikely that they existed as "tools" in
the minds of the knappers. But tools, in the guise of bifaces, almost
certainly did exist as a category in the mind of Homo erectus (Wynn
1993; Wynn, Tierson et al. 1996).
2.5 Late Bifaces: Congruent and Three-Dimensional Symmetries
Three developments in hominid imposed symmetry appear in the
archaeological record sometime after 500,000 years ago. These are: 1)
congruency; 2) three-dimensional symmetries; and 3) broken symmetry.
While the reflectional symmetry of early bifaces was rough and
imprecise, the symmetry of late examples clearly suggests attention to
congruency. The mirrored sides are not just qualitative reversals, but
quantitative duplicates, at least to the degree that this is possible
given the constraints of stone knapping. Many, but certainly not all,
late handaxes and cleavers present such congruent symmetries, and this
is one of the features that makes them so attractive to us. Such a
symmetry was not limited to a single shape. Late bifaces demonstrate a
considerable amount of variability in overall plan shape. Some are
long and narrow, others short and broad. Some have distinct shoulders,
while others are almost round. Although there is some evidence that
this variability was regional(Wynn and Tierson 1990), much of it is
related to raw material, and much appears to have been idiosyncratic.
But in almost every assemblage of this time period there will be a few
bifaces with fine congruent symmetry, whatever the overall shape.
The second development in symmetry was the appearance of reflectional
symmetry in three dimensions. Many of these bifaces have reflectional
symmetry in profile as well as in plan. In the finest examples this
symmetry extends to all of the cross-sections of the artifacts,
including cross-sections oblique to the major axes, as we would define
Once again, this feature is not universally true, and many, many
bifaces do not have it, but it is present on at least a few artifacts
from most assemblages.
The third development in symmetry was the appearance of broken
symmetry. Here a symmetrical pattern appears to have been
intentionally altered into a non-symmetrical but nevertheless regular
shape. Several cleavers from the Tanzanian site of Isimila appear
"bent," as if the whole plan symmetry, including the midline, had been
warped into a series of curved, parallel lines. These are invariably
extensively modified artifacts, whose cross-sections are symmetrical,
and the pattern is almost certainly the result of intention.
A better known example is the twisted profile, or "S-twist", handaxe.
The artifacts give the appearance of having been twisted around the
central pole. The result is an S-shape to the lateral edges, as seen
Again, these are extensively modified artifacts and we must conclude,
I think, that the pattern is the result of intention.
It is not possible to date these developments in symmetry precisely.
Archaeological systematics place all of the examples in the late
Acheulean (sometimes on morphological grounds alone, which leads to a
circular argument). All were probably made after 500,000 years ago,
perhaps even after 400,000 years ago. The Isimila artifacts, for
example, date to between 170,000 and 330,000 years ago(Howell,
Kleindienst et al. 1972). The twisted profile handaxes are probably no
earlier than 350,000, and most may be much later. Although 300,000
years is a long time in a historical framework, it represents only the
final 12% of technological evolution.
Several caveats complicate interpretation of these three developments.
One is the problem of individual skill; some prehistoric stone
knappers must have been more adept than others and better able to
achieve congruent, three-dimensional symmetries in the intractable
medium of stone. We have no way of knowing how common highly skilled
knappers were. A second caveat is raw material. Some stone is much
easier to work that others. I do not think it is entirely coincidence
that twisted profile handaxes are invariably made of flint or
obsidian, two of the most prized knapping materials. On the other
hand, raw material is not as tyrannical as one might think. The "bent"
cleavers from Isimila are made of granite.
2.5.2 Cognitive implications
The imposition of three dimensional, congruent symmetry probably
depended on cognitive abilities not possessed by the first biface
makers. The cognitive psychological literature suggests some
possibilities. The first requirement would appear to be the ability to
coordinate perspectives. While flaking the artifact, the knapper has
only one point of view. This is adequate to control edge shape, and
perhaps even two-dimensional symmetry, but to produce an artifact with
three-dimensional symmetry one must somehow "hold in mind" viewpoints
that are not available at that moment, and for the finest symmetries
viewpoints that are not directly available at all (oblique
cross-sections). The knappers must have understood the consequences of
their actions for the shape of the artifact as it appeared from these
other perspectives. Such manipulations are akin to "allocentric
perception" recognized by psychologists (Silverman, Choi et al. 2000),
and used in image manipulation tasks such as mental rotation. It is
likely that these hominids were able to manipulate mental images of
objects. Again, archaeological bias forces a conservative analysis;
however, no one has proposed a convincing simpler alternative to this
one. Application of a simple flaking procedure, without any image
manipulation, could not have produced the kinds of three-dimensional
symmetries evident on these artifacts. The second requirement,
congruency, is clearly spatial in the narrow sense of perceiving and
imaging spatial quantity. As we have seen, basic knapping is largely a
spatial problem, and was from the beginning. What is new here is the
application of metric spatial relations to a problem of shape. Simple
unimodal shape "recognition" would not have been enough. The
sophistication of this symmetrical pattern suggests that shape
"identification" is required. "When we recognize something, we know
only that we have perceived it before, that it is familiar [re. early
handaxes above]; when we identify something, we know it has a certain
name, belongs to specific categories, is found in certain locales, and
so forth"(Kosslyn 1999):1284). These handaxes were almost certainly
categories, and categories are abstract, multi-modal, and rely on
associative memory. As such they reside in declarative memory, which
"...requires associative links between several types of information
that are stored in different areas"(Ungerleider 1995):773).
These hominids could manipulate perspectives and spatial quantity,
produce congruent symmetries, and even distort these principles to
achieve striking visual effects. It is fair, I think, to attribute an
intuitive Euclidean concept of space to these stone knappers. A
Euclidean sense of space is one of three-dimensional positions. While
the human life-world is certainly organized this way, and we and other
primates clearly perceive dimensional space, it is quite another thing
to employ cognitive mechanisms that understand space in this way, and
which can be used to organize action. Such a mechanism, or mechanisms,
underpin our most sophisticated everyday navigational and mapping
2.6 After 400,000
The examples I have used thus far have all been knapped stone
artifacts. While symmetry clearly can be and was imposed on many
knapped stone artifacts, the medium is not ideal for the imposition of
form. It is not plastic, and shaping can only be done by subtraction.
Indeed, after the appearance of the symmetrical patterns just
discussed, no subsequent developments in symmetry can be recognized in
knapped stone. There were developments in technique, and perhaps
skill, but the symmetries imposed on even very recent stone tools are
no more elaborate than those imposed on 300,000 year old handaxes. As
a consequence we must turn to other materials.
Artifacts made of other materials -- bone, antler, skin, wood, fiber,
etc. -- were undoubtedly part of the technical repertoire of many
early hominids (though see(Mithen 1996) for a counter suggestion).
Because such materials are far more perishable than stone, the
archaeological record contains few of them until relatively late in
prehistory. There are a few examples that almost certainly pre-date
100,000 years ago, but all are controversial, either as to age, or as
to significance. One is an pebble from the Hungarian site of Tata, on
which someone engraved a line perpendicular to a natural
crack(Bednarik 1995). While one might be tempted to argue from it that
the maker had some notion of rotation, or radial symmetry, this is too
heavy an interpretive weight to be born by a single, isolated
artifact. More to the point, even if true, this would tell us little
more about symmetry than is supplied by contemporary bifaces. However,
it would be symmetry in a new context, a fact which if confirmed would
have possible implications for cognitive evolution.
It is not until very close to the present, indeed after 100,000 years
ago that the archaeological record presents extensive evidence of
artifacts made of perishable materials. Some archaeologists see this
timing as entirely a reflection of preservation; others see it as
evidence of new behaviors and abilities. The earliest such evidence is
African and dates from between 50 and 90,000 years ago(Yellen, Brooks
et al. 1995; Klein 2000)). These are worked bone points from a site in
the eastern Congo. While these artifacts are quite important to
several current arguments about prehistory, they reveal nothing new in
regard to hominid imposed symmetry. The European Upper Palaeolithic
provides the best documented examples of hominid imposed symmetries
for the time period between 40,000-10,000 years ago. Here we find
extensive evidence of symmetry in materials other than stone.
Perhaps most widely known are cave paintings of Franco-Cantabrian Art,
especially in compositions that are about 15,000 years old. Here we
can see possible symmetries as patterns of elements in a composition,
not just inherent in a single object. They appear to have resulted
from the application of a compositional rule. As such, they do not
inform us specifically about spatial or shape cognition and are
outside the scope of this discussion.
I suggested at the beginning of this article that archaeology can make
two important contributions to the study of the evolution of human
cognition: the timing of certain developments and a description of the
evolutionary context in which these developments occurred. The
sequence of development of hominid imposed symmetries just summarized
allows us to do both of these things.
The development of artifactual symmetry was not slow and continuous.
Instead, the archaeological evidence suggests that there were two
episodes of development, separated by as much as one million years.
During the first, hominids developed the ability to impose shape on
artifacts, an ability undocumented for any living apes. In doing this
early Homo erectus employed cognitive abilities in frame independence,
mirroring, making simple judgments of spatial quantity, and
coordination of shape recognition (symmetry) with the spatial
requirements of basic stone knapping. There may have been others, but
these are the ones evident in the archaeological record. This
development occurred early in the evolution of the genus Homo,
certainly by 1.4 million years ago. The second episode of development
occurred much later and consisted of the acquisition of a modern
Euclidean set of spatial understandings. Specific abilities evident
from the symmetrical handaxes include congruency, three-dimensional
shapes, and coordination of perspectives. The date of this development
appears to correlate with the evolutionary transition from Homo
erectus to Archaic Homo sapiens.
This timing of developments has implications for human cognitive
evolution. First, the initial hominid adaptation (4.5-1.5 mya)
apparently included a basic ape-like understanding of space and shape.
A generalized ape repertoire of spatial concepts was adequate for this
earliest of hominid adaptive niches, including the first manufacture
and use of stone tools. A distinctive set of spatial/shape abilities
did not appear until relatively late in hominid evolution, after the
appearance of Homo erectus. Second, because these two later episodes
of cognitive development were discontinuous, and indeed rather far
from another in time, it is unlikely that they occurred in response to
the same selective factors. Whatever selected for the spatial/shape
abilities of early Homo erectus probably did not select for the
Euclidean abilities that emerged one million years later. But perhaps
the most important implication that the development of artifactual
symmetry has for the understanding of human shape and space cognition
in general, and not just its developmental sequence, is that even the
more recent developments occurred in the very remote past. In terms of
shape and spatial thinking we have not just Stone Age minds, we have
Lower Palaeolithic minds.
3.2 Evolutionary Context
Evolutionary context is the second body of information archaeology can
provide the study of the evolution of cognition. While it is well and
good to describe a sequence of development, it would also be good to
answer the questions of how, and perhaps why. In evolutionary science
this amounts to answering the question of selection. What selected for
these abilities? Evolutionary psychologists (Barkow, Cosmides et al.
1992; Bock and Cardew 1997) answer this question by looking at
evidence for adaptive design, on the assumption that past selection is
preserved in the modern architecture of the cognitive mechanisms.
Paleoanthropologists, and archaeologists in particular, are suspicious
of such reliance, and prefer to invoke the actual context of
development to help identify possible selective agents. While our
knowledge of the conditions of the evolutionary past is fragmentary
and lacking in detail, it is still an account of actual prevailing
conditions, not a reconstruction based on presumed selective
Hominid fossils and the archaeological record constitute the primary
evidence for the context of cognitive evolution, supported by a large
body of methods used for dating and for reconstructing the physical
environment. Hominid fossils provide some direct evidence of cognitive
evolution in the guise of brain size and shape. At least at our
present level of understanding this does not lead to persuasive
arguments about specific abilities, but it can identify times of brain
evolution in general, which can support arguments derived from other
evidence. Hominid fossils can also inform us about other evolutionary
developments in anatomy, which human paleontologists have used
successfully to document changes in diet, nutrition, locomotion, heat
and cold adaptation, levels of physical stress, and other aspects of
adaptive niche that are directly relevant to the context of cognitive
evolution. Archaeological evidence, because it is far more abundant
than fossils, informs about geographic distribution, habitat use,
specific dietary components, geographic range (via raw material
transport), and cultural solutions to problems (fire, weapons, boats,
etc.), in addition to the evidence for hominid cognitive abilities.
Together the fossil and archaeological evidence provide a reliable, if
incomplete, picture of the past, including the two time periods in
which the major developments in artifactual symmetry occurred.
3.2.1 Early biface makers
We know much less about the first episode of development than the
second. 1.4 million years ago, the time of the first biface industries
with their evidence for the imposition of symmetry and concomitant
modest developments in spatial thinking, was also the time of Homo
erectus. Indeed, the first Homo erectus (a.k.a. Homo ergaster
(Tattersall 2000)) had appeared in Africa (and perhaps elsewhere)
several hundred thousand years earlier, so we cannot make a simple
equation between Homo erectus and biface technology. Luckily, one of
the most spectacular fossil finds for all of human evolution is an
African Homo erectus from this time period. The Nariokotome Homo
erectus is an almost complete skeleton of a youth who died about 1.55
million years ago (Walker and Leakey 1993). The completeness of the
skeleton allows a more detailed discussion of life history and
physiological adaptation than is possible with fragmentary remains.
The youth was male, about 11 years old, stood about 160cm (63") at
time of death (estimates of adult stature for this individual are
185cm [73"]), had a tall, thin build, and evidence of strenuous
physical activity. His brain size was about 880cc, and the endocasts
demonstrate the same left parietal and right frontal petalia typical
of humans but not of apes. His thoracic spinal diameter was smaller
than that of modern humans of similar size, and he had a very small
pelvic opening, even for a thin male. This anatomy suggests several
important things about his physiology. He had the ideal body type for
heat dissipation. Added to the evidence for strenuous activity, this
suggests that exertion in hot conditions was common. Earlier hominids
had been largely woodland creatures who focused most of their activity
close to standing water. Nariokotome had the anatomy to exploit an
open tropical grassland adaptive niche. While the brain size of
Nariokotome was larger than earlier hominids, so was his body size;
there was only a small increase in relative brain size (compared to,
say, Homo habilis). Despite the modern overall shape of the brain, the
thoracic spinal diameter (and by extension the number of nerve bodies
enervating the diaphragm muscles) suggests that rapid articulate
speech was not in Nariokotome's repertoire.
In sum, Nariokotome suggests that the Homo erectus niche was
significantly different from that of earlier hominids, including
earlier Homo. It is not clear from the cranial capacity that a
significant increase in braininess accompanied this adaptive shift.
There is no good reason to think Homo erectus had speech, at least in
a modern sense (Wynn 1998). However, the niche shift itself was very
significant, and is corroborated by the archaeological evidence.
Archaeological sites from this time period are less informative about
hominid activity than many earlier sites. This seeming paradox results
from the typical sedimentary context of the sites. Most early biface
sites have been found in stream deposits, rather than the lake shore
deposits typical of earlier sites. These "high energy" environments
move objects differentially, including bones and tools. In effect they
destroy the natural associations on which archaeologists rely. Running
water also modifies bone, and to a lesser extent stone tools. The
unfortunate result is that archaeologists have few direct remains of
activity other than the stone tools themselves. However, there are
enough sites dating to this time period to allow archaeologists to
assess geographic distribution and environmental context, both of
which suggest that a significant change in niche had occurred.
Homo erectus left stone tools in stream beds because he had moved away
from permanent standing water. Archaeologists presume that the
channels of ephemeral streams, or the banks of permanent streams,
became one of the preferred activity locales. Given the absence of
associated materials, we cannot determine just what these activities
were; only the selection of locale is apparent. However, this fits
nicely with the "body cooling" anatomy of Nariokotome. On open
savannas, stream channels often support the only stands of trees (in
addition to water). Archaeologists have also found African biface
sites at higher altitudes than earlier tools sites (Cachel and Harris
1995), and, finally, there are early biface sites outside of tropical
Africa. The best known is Ubeidiya in Israel, which in most respects
resembles early biface sites in Africa (Bar Yosef 1987).
This archaeological evidence presents a picture of Homo erectus as an
expansionistic species who invaded new and varied environments. Cachel
and Harris (Cachel and Harris 1995) suggest it was a "weed species" -
never numerous individually but able to invade new habitats very
rapidly. Given the clear reliance on tools, Homo erectus' niche was at
least partly technological. Control of fire may also have been a
component (James 1989). Evidence from this time period at the south
African site of Swartkrans includes convincing evidence of the control
of fire(Brain and Sillen 1988). While control of fire may have little
cognitive significance (McGrew 1989), the importance to adaptive niche
may have been profound in terms both of warmth and predator
protection. We have little direct evidence for diet. >From
experimental studies we know that bifaces could be effective butchery
tools, but there are no obvious projectiles and no evidence for
greater reliance on meat. There is, in fact, no compelling evidence
It is not clear from this picture just what might have selected for
the development in cognitive abilities evident in artifactual
symmetry. At the outset we can consider the possibility that natural
selection acted directly on the hominid ability to recognize and
conceive of symmetry, which is, after all the pattern that is so
salient in the archaeological record. What might the perceptual
saliency of symmetry have been good for? There is considerable
evidence that body symmetry is, in fact, related to reproductive
success for males(Gangestad 1997). According to Gangestad, observable
phenotypic asymmetry (away from the reflectional symmetry coded
genetically) correlates with developmental stress, so that asymmetry
marks lower health. If a potential mate could detect this, he or she
could avoid a reproductively costly (in an evolutionary sense) mating.
But presumably this is true generally for vertebrates, and not just
for humans. Perhaps symmetry gained added importance as a clue to
general health when hominids lost thick body hair. Condition of coat
is also a good indicator of general health, and its absence may have
led to selection for a heightened ability to detect variations away
from symmetry. But the real question here is why would Homo erectus
have imposed symmetry on artifacts? Could artifacts have come to play
a role in mate selection? Could symmetry have become so salient a
pattern for mate assessment that it intruded into other shape
recognition domains? Here the saliency of symmetry has been
transferred out of the domain of the phenotypic to that of cultural
signaling, but the selective advantage is the same. In this scenario
both the ability to detect and produce symmetry would have had
reproductive consequences. Unfortunately, it is difficult to see how
such a hypothesis could be tested. It is provocative only because of
the known role of symmetry in mate selection.
Given the change in niche associated with early Homo erectus, with the
accompanying increase in range and the pioneer aspects of the
adaptation, it is tempting to posit selection for spatial cognition
via navigational ability. Judging spatial quantity would be a useful
skill, for example. However, while matching diameters on tools and
judging distances to water are both matters of spatial quantity, it is
not clear that they use identical cognitive mechanisms. Indeed,
neurological research suggests that relationships in "near" and "far"
space are handled somewhat differently by the brain (Marshall and Fink
2001), though there does appear to be some correlation (Silverman,
Choi et al. 2000). The temporal association of territory expansion
with developments is shape and spatial cognition is provocative, but
hardly conclusive. Given the emphasis in some literature on sexual
division of labor (Eals and Silverman 1994; Silverman, Choi et al.
2000), it is also important to reiterate that paleoanthropologists
know nothing about division of labor in this time period.
Even though the contextual evidence provides no leading candidate for
selective agent, it does describe an adaptive milieu of relevance.
Early Homo erectus was not much like a modern hunter-gatherer. There
is no evidence for human-like foraging systems or social groups (the
probable absence of speech would itself obviate the latter). There is
not even any convincing evidence of hunting with projectiles, a
favorite of several authors (Calvin 1993). Nothing in the contextual
evidence warrants direct analogy to the adaptive problems of modern
human foragers. The challenge that Homo erectus presents to
paleoanthropologists, and other students of human evolution, is that
there are no living analogs. There is no more reason to invoke a human
model than a chimpanzee model, or neither.
3.2.2 Late biface makers
Paleoanthropologists' knowledge of evolutionary context is much better
for the time period associated with the appearance of
three-dimensional symmetries, congruency, and multiple perspectives.
These abilities were clearly in place by 300,000 years ago, and
probably by 500,000. Our knowledge is better partly because this time
period was much closer to the present (though still remote), but also
because Homo had expanded into Europe. It is true that some temperate
environments have good preservation, but the primary archaeological
effect of this expansion is that Homo moved into an area where a great
deal of modern archaeology has been done. Africa may be the home of
mankind, but Europe is the home of archaeology. Based largely on
European sites it is possible to draw an outline sketch of the
behavioral/cultural context of daily life.
The peopling of Europe is itself a fascinating topic. Some argue that
Europe was occupied relatively late, after 500,000 year ago
(Roebroeks, Conard et al. 1992). Earlier sites are certainly scarce
and often controversial. However, there are sites in Italy
(Isernia(Cremaschi and Peretto 1988), Ceprano(Ascenzi, Mallegni et al.
2000)) and Spain (Atapuerca(Bermudez de Castro, Arsuaga et al. 1997))
that provide strong evidence for the presence of Homo erectus (now
attributed by some to Homo antecessor) prior to 500,000. In many
respects these resemble earlier Homo erectus sites - poor geological
context and little to go on. There is little doubt that after 500,000
the record is better and includes the peopling of northern Europe.
There are informative sites in England, Germany, France, and the
Netherlands. Some archaeologists have suggested that this represents
an adaptive breakthrough, an evolutionary development that opened up
harsher environments (Roebroeks, Conard et al. 1992). These first
colonists in northern Europe did make bifaces, and their bifaces
required all of the cognitive abilities identified earlier in this
paper. The association is provocative, and suggests that some
evolutionary development in cognition may have been partially
responsible for this breakthrough. Of course, similar artifacts
appeared in Africa, so the breakthrough cannot have been specific to
Europe. But what specifically might have selected for cognitive
abilities evident in the fine three-dimensional symmetries of bifaces?
The archaeological record does provide some clues.
The move into northern Europe (and China) may seem a minor extension
of the much more dramatic expansion of Homo erectus 1,000,000 years
earlier. However, it may well have required some significant changes
in adaptation. Northern European climate during the Pleistocene was in
more or less constant flux, with cold glacial periods alternating with
warmer, forested, interglacial periods. During periods of maximum cold
northern Europe was uninhabitable, and indeed even the anatomically
modern of humans of 18,000 years ago were forced to the south. But
after 500,000 we have evidence of biface sites in northern Europe
during some of the warmer episodes embedded in glacial periods. The
environment during these periods was more open and less heavily wooded
than today, but also cooler than today. The adaptive problems posed by
such an environment are fairly well known. Compared to warmer
environments, even in southern Europe, there would have been fewer
edible plant species, and a concomitant requirement for increased
reliance on animals. Then there obvious problems of keeping warm,
including the likely necessity of controlling and probably even making
fire. In effect, these northern temperate environments "pushed the
envelope" of Homo's adaptation. But here our European bias risks
misleading. We see it clearly because we have the sites. We know,
however, that comparable technological developments occurred in
Africa, the Near East, and China, and it is unlikely that Europe was
in any way central (indeed cultural backwater is more likely), so what
we may be seeing is abilities that evolved elsewhere applied to a
The fossil remains from this time period present a confusing picture.
In some areas of the world, Asia in particular, Homo erectus was
clearly still present. In Africa the prevailing fossil type appears to
have been a larger brained form that still retained many Homo erectus
like features of the face. Europe is the biggest puzzle. There are few
clear Homo erectus fossils (the Mauer mandible is a probable example
(Rightmire 1992), as is the Ceprano calvaria(Ascenzi, Mallegni et al.
2000)) but most fossils attributed to the taxon have some at least
some sapient-like features. Rightmire (Rightmire 1998) now favors a
return to the use of Homo heidlebergensis for these forms. The key
issue for the present argument is that this was a time of evolutionary
change in anatomy, as well as technology and cognition. We cannot yet
describe the complex evolutionary patterns, but we do know the long
period of evolutionary stasis that was Homo erectus was coming to an
By this time it is almost certain that these Homo hunted large
mammals. Many sites have included the association of stone tools with
animal bone (Hoxne(Singer, Gladfelter et al. 1993), Boxgrove
(Wenban-Smith 1989; Roberts, Stringer et al. 1994; Roberts and Parfitt
1999)), and in some cases like Hoxne the range of body parts present
suggests that at least some of these animals had been hunted, not just
scavenged (Binford 1985). Until recently the only evidence of hunting
technique was an enigmatic sharpened stick from Clacton-on-Sea that
could have been a spear tip (Oakley, Andrews et al. 1977). In 1996,
the German site of Schoeningen dramatically confirmed this
interpretation. Here Thieme (Thieme 1997) and crew excavated three
complete spears carved out of spruce, each over two meters in length.
The spears were in direct association with the bones of horses. The
center of gravity of each of these spears was situated slightly toward
the tip, much as it is in modern javelins, and Thieme argues that Homo
must have designed these spears for throwing. If true, this suggests a
relationship between design and use that has technological and perhaps
even cognitive implications. But what bears more on the issue at hand
is that hunting with spears was obviously a component of the
behavioral/cultural context of these Homo, a component that calls up
modern human analogs.
The archaeological record does not provide much direct evidence for
group organization, or even size, at least not for this time period.
For more recent times the size and debris patterns of structures
provides much useful evidence of social organization, but such
patterns degrade rapidly and in only the most ideal conditions survive
for tens of thousands of years, let alone half a million. All of the
possible campsites from the time period of interest here are
controversial. Thirty years ago de Lumley (Lumley and Boone 1976)
presented a dramatic argument for huts, seasonal occupation, and reuse
at the French site of Terra Amata, an interpretation that still
survives in textbooks(Turnbaugh, Jurmain et al. 1999). The site has
never been published in detail, and the one independent analysis cast
considerable doubt on de Lumley's interpretation(Villa 1983). At best,
there is evidence for a few post holes, stone blocks, stone knapping
debris, and shallow hearths scooped from the sand. These may be the
remains of a flimsy shelter, and would certainly fit into a
reconstruction of a small hunter gatherer band. Unfortunately, this
optimistic picture is at least premature, and probably unwarranted.
Villa's analysis indicates that the integrity of the site is much
lower than presented by de Lumley. It is in reality an accumulation of
cultural debris that has been moved and altered by natural processes.
Yes, this provides evidence of hominid activity, but not of a coherent
campsite with multiple activities and an artificial structure. There
are no better examples until much later. Indeed, Gamble (Gamble 1994;
Gamble 1999) argues that this absence of campsites is an accurate
reflection of the life ways of early Homo sapiens, and that coherent
long-term or multiple use campsites were not part of the adaptive
niche. If true, these early Homo sapiens were not like modern hunters
There are other ways in which they were not modern. As familiar as
some of this evidence is, there is a striking piece of modern behavior
that was entirely missing. We have no convincing evidence of art, or
personal ornamentation, or anything that clearly was an artifact of
symbolic culture. Many sites do have lumps of red ochre, some of which
had been scraped or ground. A few sites have enigmatic scratched
bones. None of this constitutes indisputable evidence that these
hunters and gatherers used any material symbols, of any kind
whatsoever. Compared to the abundant use of such items in sites
post-dating 50,000 this absence is telling.
In sum, the archaeological evidence indicates that by 400,000 years
ago Homo was a hunter gatherer who had invaded new, more hostile
environments, but who did not invest in symbolic artifacts. Despite
similarities to modern hunters and gatherers, these early Homo sapiens
were different in many respects.
What might have selected for the cognitive abilities required for
three-dimensional, congruent symmetries? Again, mate selection is a
possibility, this time by way of technological skill. An individual
who could produce a more regular (symmetrical) artifact would be cuing
his or her skill, and worth as a potential mate. Other things being
equal, the stone knapper who produced the fine three-dimensional
bifaces was smarter and more capable, with better genes, than one who
couldn't. Especially if knapping skill correlated with other
technological abilities this would be one means of identifying mates
with future potential as providers. Kohn and Mithen(Kohn and Mithen
1999) take this argument even farther, framing it terms of sexual
selection and emphasizing abilities other than technological.
"Those hominids...who were able to make fine symmetrical handaxes may
have been preferentially chosen by the opposite sex as mates. Just
as a peacock's tail may reliably indicate its `success', so might
the manufacture of a fine symmetrical handaxe have been a reliable
indicator of the hominid's ability to secure food, find shelter,
escape from predation and compete withing the social group. Such
hominids would have been attractive mates, their abilities
indicating `good genes'" (Kohn and Mithen 1999:521).
Modern people certainly do use material culture to mark their
individual success, and it is perhaps not far fetched to extend this
behavior into the past, perhaps even to the time of late Homo erectus
or early Homo sapiens.
As second possibility is that selection operated on enhanced spatial
and or shape cognition, with artifactual symmetry being just one
consequence. Given the co-occurrence of hunting and gathering and
modern spatial thinking in the paleoanthropological record, this
hypothesis suggests that they are somehow linked. What selective
advantage could congruency, three dimensional symmetries, and image
manipulation bestow on a hunter-gatherer? William Calvin (Calvin 1993)
has long argued that aimed throwing was a key to cognitive evolution.
While I find his argument that bifaces were projectiles far from
convincing (see also (Whittaker and McCall 2001)), the Schoeningen
spears may well have been, indeed probably were, projectiles. That
there is a spatial component to accurate throwing seems beyond
question. Calvin himself emphasizes the importance of timed release
and the computational problems of hitting moving targets. Would any of
this select for image manipulation, congruency, and so on? It is hard
to see how, unless ability to estimate distance to target selected for
abilities in judging all spatial quantities (e.g., congruent
symmetries). The selective agent, throwing, just does not match up
well with the documented abilities.
Navigation is again an alternative, and one favored by many
psychologists (e.g. (Gaulin and Hoffman 1988; Moffat, Hampson et al.
1998); (Dabbs, Chang et al. 1998; Silverman, Choi et al. 2000)). While
route following using sequential landmarks can work, using basic
topological notions like those known for chimpanzees and early
hominids, it is difficult to conceive of and follow novel routes
without a Euclidean conception of location. Arguably hunting,
especially varieties invoking long distance travel, herd following, or
intercept techniques would favor Euclidean conceptions of space. There
is now experimental evidence documenting a correlation between
navigational skill and the standard psychometric measures of spatial
cognition like mental rotation (Moffat, Hampson et al. 1998;
Silverman, Choi et al. 2000), though recall that "near" and "far"
space are not handled identically by the brain(Marshall and Fink
2001). This specific selective hypothesis, then, is a better fit than
the throwing hypothesis. Of course, navigation skill might have been
unrelated to hunting per se, and instead tied to mate searching
(Gaulin and Hoffman 1988) or any long distance travel. What is
provocative is the correlation between the earliest evidence for large
scale hunting and Euclidean spatial relations, as represented by fine
three dimensional symmetries. While the correlation between this
development in spatial thinking and navigation is provocative, it does
have two weaknesses. First, many animals are fine navigators without
relying on the enhanced spatial abilities in question. Of course, what
we are seeing here is the hominid solution to navigation problems, so
I am not too troubled by this objection. The second objection is more
bothersome. When modern people navigate, they rarely use the spatial
abilities in question. For example, when modern hunters and gatherers
move across the landscape they use established paths and routes, often
following water ways or animal trails (Baluchet 1992; Gamble 1999).
The geometric underpinning of such navigation is largely topological,
and does not rely on the kind of spatial abilities evident in the
stone tools. Yes, it is possible to imagine a form of navigation that
relies on such abilities, but this does not seem to be the way people
actually move about. Unless there is a compelling reason to think that
modern hunter-gatherers rely on Euclidean spatial relations to
navigate, it will remain a weak hypothesis.
Of course, these spatial and shape abilities may not have been
directly selected for at all. They may be by-products of natural
selection operating on other cognitive mechanisms. For example, if
Kosslyn's (Kosslyn 1994) (Kosslyn, Thompson et al.
1998)characterization of mental imaging is accurate, the key
development may have been in central processing rather than the more
encapsulated shape recognition system or spatial assessment system.
These are relatively discrete neural networks that reside in different
parts of the brain (one temporal lobe, one parietal). In order for
someone to conceive of congruency, and perhaps alternative
perspectives, the two outputs must be coordinated, and this
coordination appears to happen in the association areas of the frontal
lobe. Here the evolutionary development would be in the area of
association and central processing, and there is no reason for
selection to have been for shape recognition or spatial ability per
se. In other words, the archaeological evidence for the development of
three dimensional, congruent symmetries, may inform us about
developments in more general cognitive abilities, not just a narrowly
encapsulated module of spatial thinking.
The archaeological record of symmetry reveals two of the times at
which significant developments in hominid cognition occurred. The
first, a million and a half years ago, encompassed cognitive
developments necessary to the imposition of shape on artifacts, the
coordination of shape recognition (symmetry) and spatial thinking
(stone knapping) being the most salient. This evolutionary development
was associated with Homo erectus, and the appearance of the first
hominid adaptation that was clearly outside the range of an ape
adaptive grade. These Homo erectus were not, however, like modern
hunter/gatherers in any significant sense; indeed, there are no
appropriate analogs living today, and the precise agents selecting for
these cognitive abilities are not apparent.
The second episode evident from artifactual symmetries occurred a
million years later and encompassed the development of modern
Euclidean understandings and manipulations of shape and space. This
was the also time of the transition from Homo erectus to Archaic Homo
sapiens. The appearance of large mammal hunting in the contemporary
archaeological record lends some support to evolutionary psychological
arguments that hunting may have selected for features of human spatial
cognition, either by way of projectile use or navigation. However,
given the range of evidence documenting the appearance of many
features of hunting and gathering at this time -- not just spatial
thinking -- it is perhaps simpler to posit a few developments in
associative abilities than a raft of specific cognitive mechanisms. It
is also important to reiterate that despite being Homo sapiens, these
were not modern hunters and gatherers. They lacked the rich symbolic
milieu on which modern humans, including hunters and gatherers, rely.
Archaeology cannot itself resolve many of the controversies raised by
the evidence. Questions concerning the cognitive and neural bases of
the actions preserved in the archaeological record must be answered in
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More information about the paleopsych