[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 [1]BBS Home Page to order the full
    published treatment.

    Long abstract - 197
    Short abstract - 118
    Text - 12,348
    References - 1,732
    Entire text - 14,434

    Thomas Wynn
    Department of Anthropology
    University of Colorado
    Colorado Springs
    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

    Short Abstract

    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
    Thomas Wynn
    Department of Anthropology
    University of Colorado in Colorado Springs
    twynn at uccs.edu

    Keywords: Archaeology, symmetry, spatial cognition, evolution, Homo

    1. Introduction

    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
    of mind?

    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
    artifactual symmetry.

    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
    final products.

    [FIG 1]

    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
    in space.

    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.

    [FIG. 2]

    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

    2.3.1 Description

    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

    [FIG 3].

    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
    situation changed.

    2.4 The First Hominid Imposed Symmetry

    2.4.1 Description

    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?

    [FIG 4]

    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

    [FIG 5]

    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.

    [FIG 6]

    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

    2.5.1 Description

    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

    [FIG 7]

    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.

    [Figure 8]

    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
    in profile.

    [Figure 9].

    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.

    [Fig. 10]

    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.

    3. 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.

    3.1 Timing

    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 Context

    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
    for hunting. Selection

    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 Context

    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
    European problem.

    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
    and gatherers.

    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. Selection

    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.

    4. Conclusion

    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
    studies of modern cognition. Archaeology can point to the times and
    contexts of cognitive evolution, but cannot itself illuminate the
    workings of the human mind. A comprehensive approach to cognitive
    evolution must therefore be multidisciplinary.

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