LECTURE 12

THE ORIGIN OF MODERN HUMANS

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1. AN OUTLINE OF HUMAN PHYLOGENY

Human behaviour needs to be understood in the context of its evolution. As psychologists, we do not want to go into great detail about the course of human evolution, and the following brief summary is sufficient to introduce the names of 'key players' in the emerging story, names that will crop up in subsequent readings. However, there is a lot of good material available if you want to get a better command of this topic, and links to this can be found below.

1. Overview

In 1871 Charles Darwin was able to propose that we were most probably of African origin and most closely related to the Great Apes of Africa. Biochemical evidence now reinforces this conclusion and indicates that the divergence of our lineage, the Hominidae, from the African apes took place between 5 and 8 million years ago (m.y.a.).

There are no fossils now believed to lie within our hominid lineage before c.6.0 m.y.a. The earliest group of well-known undoubted hominid fossils comes from Laetoli in Tanzania, and dates from c.3.7 m.y.a. These belong to the genus Australopithecus, which is considered to range in time from c.5 m.y.a. to 1 m.y.a., and appears to have been confined to the continent of Africa. Australopithecus was a bipedal, small-brained hominid, which later diversified into 2-3 more robustly built species, as well as probably giving rise to members of our own genus, Homo.

The earliest fossil remains that are classified as Homo, and thought to be our direct ancestors, come from south-west Ethiopia and adjacent Kenya. They are dated to c.2 m.y.a. This species, named Homo habilis, possessed a somewhat larger brain than Australopithecus, and appears at approximately the same time as the earliest stone tools. The successor to Homo habilis was the much more modern-looking Homo erectus. The earlier specimens are from Kenya, and date to c.1.5-1.8 m.y.a. Only after c.1.0 m.y.a. do we find that this species of Homo has spread into Eurasia. Archaic forms of Homo sapiens are variously recognized from Afro-Eurasian specimens dated to c.300 000 years ago. Recent biochemical data suggest that modern humans, Homo sapiens sapiens, arose in Africa c.200 000 years ago. This fits in well with the available fossil evidence from Africa and the Near East, where human skeletal material with completely modern features is known from an earlier date than elsewhere.

[This overview is taken from Campbell, 1996]

Over the years, as more remains are uncovered, and old remains are re-studied and re-interpreted, the provisional story as to the likely path of human evolution changes. If you want to check a more recent version, see this site. The best source for keeping up with new discoveries and where they are inferred to fit into the larger picture is the 'Talk Origins' site.

The following material between the horizontal lines is not essential course material, but I've included it here should you want to follow up this topic of our origins.


2. Details of Hominid Species

3. Hominid Fossil Specimens

If you have always wondered how people reconstruct fossil finds to retrieve what is thought to be the original anatomical arrangement, then it's worth looking at a site put up byIBM about the way in which a particular human skull, possibly late Homo erectus or early archaic Homo sapiens from Salť in Morocco has been worked on. A point to remember if you take a look is that very little of the evidence we now recover from nature is exactly as it was when it was first formed. The evidential bases of our knowledge have themselves to be reassembled on the basis of the knowledge we already have. Often, our 'theories' can blind us in the way we reconstruct our facts. The classic case of this in the field of human evolutionary remains is the Piltdown hoax.

4. Illustrations of Specimens

5. Skulls and Crania

i. Comparison of all skulls

Click on any picture for a larger version




  • Chimpanzee, Gorilla
  • Sts 5, Stw53, OH 24, ER 1813
  • Java Man, Peking Man, ER 1470
  • ER 3733, WT 15000, Petralona, Rhodesian Man

Note that this caption to the figures identifies each specimen, not each species. So what is 'OH 24' or 'ER 1813' and so on? There is no one convention adopted universally for identifying individual specimens. 'OH 24' results from the field notes of the fossil finder, who listed it as 'Olduvai (place found) Hominid (itís a hominid, not just a primate), specimen number 24: 'ER 1813' is a shorthand for 'KNM-ER 1813', Kenya National Museuem (where the original is kept) East Rudolf (where it was found) 1833 (catalogue number of the specimen in the museum's collection). Try and get a feel here for the differences between these different specimens, so that you can decide on looking at the pictures which species or genus you think it has been assigned to. That's a better skill to gain than just learning a list. See if you can then list for yourself the criteria you are using to make your decisions.

ii. Crania

If you are really enthusiastic about skulls, then you might, in addition, want to see Phillip Walker and Edward Hagen's site on Human Evolution for rotating 3-D views of some specimens.

iii. Brain Size

6. Acknowledgements and Other Sources of Information

Materials locally available for these lecture notes have been sourced with his permission from Jim Foley's collection of materials on hominid evolution. These materials form part of the much larger talkorigins site, which is a goldmine of information on evolutionary versus creationist accounts of the history of life on this planet. This larger site has emerged from an earlier newsgroup, and compiles material that relates to, and now comprehensively deals with, 'frequently asked questions' (FAQs) about evolution. It contains a large amount of information and an extensive listing of links, enabling you to pursue most questions on the topic that you might want information on.


It is very easy to get hung up in this fossil material. [And imagine what the situation would be if the remains of past animals didn't fossilise!] But for psychologists, the most interesting topics are about behaviour: what did people do, and where have their abilities come from?

2. BRAINS, TOOLS AND WALKING

1. Overview

There is a major problem involved in saying anything with certainty about the evolution of human behaviour: a lack of direct evidence.

Behaviour does not fossilize. Neither do brains, along with any of the other soft tissues that make up the human body. What do survive are artefacts and bones. Consider some of the problems associated with the picture at the top of this page. How would we know if this represents something that happened? We could look at the anatomy of the individual as given by the fossil evidence of 'his' bones. The inverted commas indicate here that it is rare to find a large number of bones that unequivocally come from a single specimen: most reconstructions are a combination of a number of individuals and a dollop of informed anatomical guesswork. So we might be skeptical here, especially as the soft tissue has to be imagined over the top of the skeletal remains, but we do not need to be too skeptical. Anatomy can be reconstructed pretty well. With respect to this particular individual we would need to check foot and hip structure to ensure he (or she) could walk on two legs and balance in the posture shown, and also that the hands were able to grip an object in the manner shown.

What is this object? It's a 'stone tool'. It is being used to hit a bone. Can we get evidence that bones were worked on by stone tools? Yes, electron microscopic analyses of various old stone tools reveals different markings on their edges, depending on what they were used for, and bones often retain marks whose origins can be distinguished Ė for example, the toothmarks of large carnivores are different from cut marks inflicted by a stone tool.

We can reasonably assume that these tools were manufactured, since stones don't normally come in these forms in nature. Quite often there are good grounds for thinking that the individual species associated with tools were their makers, but clearly we can't know whether the individual above made the tool he is holding, or whether he found it, borrowed it from someone else, bartered goods in exchange for it, and so on. We also have a problem with fire. There are a vast number of dates put forward as to when humans could make or even use fire. Yet the police often have enough difficulty figuring out today how a house fire started, so what hope have we got for millions of years ago? Just because bones are associated with the remains of fires doesn't mean that the owner of the bones lit the fire.

Beyond this, what else can we draw on to substantiate or authenticate this illustration? This is worth thinking about, as otherwise we fall into a lot of traps because of the 'ideologies' we bring with us to the task of interpretation. All these problems are concretely exemplified in the case of the Piltdown hoax early in the 20th Century. Two fossil bones were found in a gravel pit at Piltdown in southern England. It has now been established that these bones come from different species. But at the time, the proximity of two bones, a jaw and a cranium, was taken to indicate that they were from the same specimen, and this was easily accepted because the view of the day was that human brains evolved before other human features, so finding a large cranium along with a much more primitive jaw fitted with people's expectations. The pre-existing story coloured the 'facts'. This is a major problem with no easy solution, because the status of all 'facts' is closely interwoven with the 'theories' that constitute them as 'facts': in a sense, facts are theories.

2. Bipedalism

'I was a victim of a series of accidents as are we all.'
Malachi Constant, in Kurt Vonnegut's novel 'The Sirens of Titan'

LucyWhat about this reconstruction of the Australopithecus afarensis specimen known as 'Lucy'? Is it fanciful to portray her in this position, or was she really bi-pedal? Her hands and feet retain some ape-like features, and her arms are comparatively longer than ours. She was anatomically able to balance her trunk on her hind limbs in a bipedal posture, but probably would not have managed the striding gait of modern humans. The length of her forelimbs has been taken by some commentators as indicating the retention of some features adapted for an arboreal life, and it may be that this animal was one that walked bipedally on the ground, but stuck close to trees to climb up so as to escape danger.

But why go bipedal? Well, we have to speculate here, but the fact is that aside from modern humans, the contemporary great apes are pretty inefficient as compared to most quadrupeds when it comes to moving on the ground, and this inefficiency is likely to have been there from way back, maybe 15 million years into the Miocene period when we find fossil 'proto-ape' specimens that are interpreted as ancestral to all the extant great apes, including us. These early specimens were probably adapted to quadrupedal climbing, rather than the brachiation (e.g., gibbons and orang-utans), knuckle-walking (e.g., chimpanzees and gorillas) or bipedalism (current humans) adopted by modern species.

The evidence for this view, that apes are inefficient in their terrestrial locomotion, comes from measurements made by Taylor & Rowntree of the energetic efficiency of hominoid locomotion. Chimpanzees are 50% less efficient than other quadrupeds at terrestrial locomotion when either knuckle-walking or walking on two legs. Basically, the ape's anatomy is just not designed for the ground, and still retains the traits that were a feature adapted to locomotion in trees. Humans have made a remarkable shift from this ancestral pattern, as is confirmed by Taylor & Rowntree's finding that when walking at normal speeds the human energetic cost is about average for the mammals, but the chimpanzee still uses about 50% more energy in proportion to its body weight. Something pushed the human line in this direction, and at least as early as the time represented by 'Lucy', c. 3.5 - 3.8 million years ago. We know this from her anatomy: but there is also an additional piece of evidence, a most remarkable set of footprints at Laetoli in present-day Tanzania that were covered by volcanic ash just after they were made.

Previously, going back as far as Darwin, the origins of bipedalism have been attributed to the advantages it gives by freeing the hands for use in foraging and feeding, for tool use, or the carrying of food and other objects. The energy issue has tended to be overlooked, expect by Henry McHenry at the University of California at Davis. When we take it into account, then we see how bipedalism may not necessarily be attributed to those advantages, but those advantages as being consequentially possible as a result. Deciding which of these is the case is almost impossible, but I tend to like the consequential scenario. Early hominids became bipedal to efficiently exploit the newly-emerging savannah environments of their world, and this, by accident, set them on the path to new behaviours that ended up transforming their descendants into the self-conscious hooligans we see today.

3. Brains

Brain sizeIn the last 3-4 million years brain volume within the hominid lineage has increased from less than 400 ml to roughly 1400 ml. The first clear increase in hominid brain size is seen in early Homo at c.2 m.y.a. in East Africa (most reliably in cranial specimen KNM-ER 1470). This is an evolutionarily significant change that cannot be simply accounted for in terms of increased body size alone. From the appearance of H. erectus at c.1.7 m.y.a. to the present, the brain increases nearly twofold: from c.800 ml to 1500 ml in Late Pleistocene H. sapiens, without any apparent change in body size.

With regard to brain reorganisation, left-right cerebral hemispheric asymmetries exist in extant pongids and the australopithecines, but neither the pattern nor direction is as strongly developed as in modern or fossil Homo. KNM-ER 1470 shows a strong pattern that may be related to handedness and tool-use/manufacture. The degree of asymmetry appears to increase in later hominids.

The appearance of a more human-like third inferior frontal convolution provides another line of evidence about evolutionary reorganisation of the brain. None of the australopithecine endocasts show this region preserved satisfactorily. There is a consensus among palaeoneurologists that the endocast of the specimen KNM-ER 1470 does show, however, a somewhat more complex and modern-human-like third inferior frontal convolution compared with those of pongids. This region contains Broca's area, which in humans is related to the motor control of speech. Unfortunately, later hominid endocasts, including H. habilis and H. erectus through archaic H. sapiens to the present, seldom show the sulcal and gyral patterns faithfully. Thus nothing palaeoneurological can be said with confidence about possible changes with the emergence of anatomically modern H. sapiens.

Both an increase in size and a reorganisation of the brain towards a more-human like configuration thus appear together at around 2 million years ago. For a fuller account of these changes, you might read an article by Wilkins and Wakefield Brain Evolution and neurolinguistic preconditions. But as with most published articles, this is long and detailed, and for our purposes we can ignore a lot of the detail. One of the essential points they argue for is that this change in the organisation of Homo habilis's brain was quite profound.

If our account proves valid, by the time of H. habilis the marked sulcal division between the parietal and occipital lobes had "disappeared." In addition, there were other significant evolutionary changes affecting the hominid brain. These include the expansion of visual cortex and of the temporal lobe. The close proximity and resultant junction of the three posterior lobes culminated in a situation in which information was readily available for processing in an overlap of the three related association areas and which could result in amodal representation.

What they are claiming is that what happened when our brains got re-organised at the time of Homo habilis, away from the pattern found in other apes and into a human-like configuration, was that three functionally different areas of it got to pool their resources. Prior to that, the abilities which these areas supported were dealt with much more independently by ape brains.

One of the consequences of this is evidenced by how poor apes are at doing something called cross-modal matching. One example is if you get someone to sketch a letter of the alphabet on your back - an 'e', say - you can still recognise it as equivalent to a letter 'e', which you normally recognise through another sensory channel - vision. Hence the term 'cross-modal' - people can integrate across different sensory modalities. Humans are really good at this, and even infants can do it. Andy Metzoff at Seattle University had infants feel different shapes without being able to see them, and then showed them to them to see if they could tell those they'd touched from entirely new ones. They can. Apes find this sort of thing a lot harder.

Why?† Because the different senses are being handled by anatomically separate bits of the brain, bits that consequently don't send much information back-and-for amongst themselves. But from Homo habilis on, human brains had lots of channels between these parts, so that hearing, seeing and feeling, for example, could be better integrated.

But Wilkins and Wakefield want to go further than this. They want to propose that the brain is dealing with a new sort of information that they term 'amodal representation'. This is something else again. Let me introduce it this way. Most birds are tone deaf. You can get a pigeon to discriminate a tune, but it doesn't show much 'stimulus generalisation' subsequently. Meaning? If you change the key of the tune it has learned, it doesn't recognise it. So in the cognitive neuropsychological paradigm they are adopting, we can say that whatever it is the pigeon is remembering about the tune it has learned to recognise, that information isn't very abstract. Itís not remembering anything about the relation between the notes. If it were, then a change in key wouldn't matter. But we can do this! Eric Clapton makes a living at it! Apes are better at it than birds. But otherwise they're about as musically inclined as dogs (ever tried dancing with a dog?). So early humans were, they suggest, beginning to abstract something about a tune 'amodally'. That is, they weren't just able to encode a specific tune in memory, but they were storing something about the relation between the notes, so that if it was played back in a different key, they would still be able to recognise it, because the relation between the notes was the same, even though the notes were different.

Now, there is no guarantee that the information coming in through the different senses is amodally represented in the same way by each of the senses. So, even if you bring the information from the different senses together, there's no guarantee that they'll be compatible.† It could be as if they 'talked' different languages. So either the whole booming, buzzing confusion of sensory data has to be stored in the same way, or some efficient translation device has to be constructed if the senses are to integrate with each other efficiently.

Wilkins and Wakefield suggest that the solution was amodal storage, and this occurred when the separate bits of the cortex came together in Homo habilis. The brain thus got bigger so as to better process the contents of its own workings!

The claim is that we humans have brains that deal with the world 'amodally'. Itís a new way of handling things. This is the evolution of a new psychological ability. Not just brains getting bigger, or bits of them moving about in relation to other bits, but a whole new way of operating.

Now could this Homo habilis talk? Well, that's a whole bigger question.... Let's think about tools for a minute, and then come back to it.


But before that itís also worth your looking at Dean Falk's research on what it was that enabled the brain to get bigger in the first place. She has proposed the 'radiator theory'. Brains metabolise a lot of energy, and this produces heat. If you walk around under the African sun, you gain a lot of heat too. Unless you can get rid of this, your brain is going to fry. If you get a bigger brain, then it will get frazzled more quickly, unless you can get rid of the heat it generates and you absorb on top. So, until a cooling system is in place, bigger brains will provide no advantages to you. Unless you became nocturnal: but would you like to walk around wild Africa in the dark? So a cooling system it is, or wear a hat - except it took another 2 million years before we could make them.


4. Tools

Oldowan stone toolOnly tools made of stone or bone survive in the archaeological record. Any other material perishes. H. habilis is regarded as having made stone tools referred to as the Oldowan industry, consisting of simple core and flake tools of basalt, quartz and quartzite. Wynn (1996: 267) notes of these tools that:

There is considerable question as to the reality of the tool types in the Oldowan. If by type we mean a well-defined category of tool that existed in the minds of the tool-makers, then we would be unable to argue for their existence. ... It is doubtful whether there were any design criteria whatsoever, beyond perhaps big and little.


Similarly, Toth and Schick (1993: 349) note of the core 'tools' that they are 'not necessarily tools, nor do they necessarily correspond to 'mental templates' held by their early makers'. Toth and Schick (1993) and Fagan (1989) confirm the view that this is an ad hoc technology, and 'Oldowan tools did not require a particularly sophisticated intelligence.' (Wynn, 1996: 267). However, these writers consider the cognitive capabilities of the tool-makers may show some advance over that of modern apes in the area of planning the sequence of motor actions needed to produce a tool, as well as in judging the angles and overhangs of the 'blank' cores with respect to the angle and force of blow required to effectively flake the stone.

Acheulean stone toolThe technology associated with early forms of H. erectus, by contrast, appears to be much more sophisticated, and the typical Acheulean 'hand axe' or 'biface' is 'the first type tool that is clearly outside the range of an ape technology' (Wynn, 1996: 269). The later bifaces have a three-dimensional symmetry. For example, as viewed, the tool in the figure is bi-laterally symmetrical. If you reoriented it so as to see it from the side, it is also bilaterally symmetrical. And so it is as well if you turn it end on. If you compare the bottom right portion of the tool to the bottom left, you will see that a lot more work or 'retouching' has been done there to achieve the final shape. Wynn comments on such actions that 'In order to do this the maker had to have a competence in the relation of whole to parts' (1979: 377): thus, the end result appears to have been anticipated, or imagined, prior to the observable retouching.

Similarly, a lot of work has been done down the left and right edges to get a straight line. Wynn comments (albeit with respect to a different sample tool than the one illustrated here, but his point still holds):

Both faces of the original flake have been retouched to yield a remarkably straight edge. ... in order to have produced such artificial straightness the knapper had to have related each flake removal to all the others and also to a stable point of view (1979: 378).

That stable point of view had to be 'conserved in the knapper's imagination during the actual flaking process' (ibid: 380). On this basis, Wynn (1979: 371) concludes that:

these artifacts required the organizational abilities of operational intelligence and ... therefore, the hominid knappers were not significantly less intelligent than modern adults.

His overall conclusion is that 'essentially modern intelligence was achieved 300,000 years ago' (ibid: 371). By which time, as you will recall, brain sizes were within the modern range.

There is also evidence, which we will deal with more fully in class, that the anatomy of our upper respiratory tracts had also changed from the common mammalian pattern by at least this point in time, and changed in a direction that is best explained as an adaptation to facilitate the production of speech-like sounds. This would suggest that by around 300,000 years ago, our human ancestors were communicating vocally, had achieved the characteristic level of modern human intelligence, and controlled all this with a brain that had been fundamentally human in its organisation for a long time, and which was now within the modern range for human brain size. But the archaeological record indicates that humans were not doing anything much different than they had been doing over the previous million years or so until relatively recently. How might we understand this?

References

Darwin, C. (1871) The descent of man and selection in relation to sex. London: John Murray.

Fagan, B. (1989) People of the earth: An introduction to world prehistory, (6th edn.). Glenview, Il.: Scott, Foresman and Co.

Meltzoff, A.N. and Borton, R.W. (1979) Intermodal matching by human neonates. Nature 282: 403-4.

Taylor and Rowntree

Toth, N. and Schick, K. . (1993) Early stone industries and inferences regarding language and cognition. In K. R. Gibson and T. Ingold (eds.) Tools, language, and cognition in human evolution. Cambridge: Cambridge University Press.

Wynn, T. (1979) The intelligence of later Acheulean hominids. Man 14: 379-91.

Wynn, T. (1996) The evolution of tools and symbolic behaviour. In A.J.Lock and C.R.Peters (Eds.) Handbook of human symbolic evolution. Oxford: Clarendon Press. Pp. 263-87.

2. Distribution

Western maritime cultures obtained first-hand global knowledge of the planet by the end of the 18th century. By then, very few places - for example, the Malvinas/Falkland Islands, the Galapagos Islands, Ascension Island, Bermuda, the Seychelles - had been found to be uninhabited at first contact. Some of these 'desert' islands, such as the Pacific islands of Pitcairn, Christmas and Norfolk, have since been shown to have been inhabited previously in prehistoric times. Being remote did not imply being 'empty' of humans: Hawai'i, Easter Island and New Zealand are all remote, but all were already inhabited by humans. It was a characteristic of the time of Western explorations for Western peoples to regard various indigenous people as 'savages' of one form or another. Gamble (1993: 17) has pointed out how spatial distribution became a metaphor for temporal distribution, and he cites the early view of the French political economist Turgot lecturing in 1750 as a clear example:

'A glance over the earth puts before our eyes, even today, the whole history of the human race, showing us traces of all the steps and monuments of all the stages through which it has passed from the barbarism, still in existence, of the American peoples to the civilization of the most enlightened nations of Europe'.

And as Gamble goes on to note (op. cit.:28):

'it would be a long time before the biological unity of [hu]mankind was also interpreted as an intellectual and behavioural unity with differences between cultures attributed to history and not to ability or potential'.


Here the question asked is this: How did all these people get to be everywhere? We take it that fossils of Homo erectus represent individuals who were ancestral to us. Homo erectus was widely spread across the Old World. Are people who are born in China descended from populations represented by Asian H. erectus specimens; modern Africans from archaic African erectus populations; and so on? Or: Did the ancestors of all modern humans arise in one particular place, say where modern-day China is, and then spread out and replace the descendants of other regionally-distinct populations? Or: well, there are lots of other possibilities.


3. Multi-regional vs. Single Origins

I am not going to duplicate material that is already available. See the following pages by Michael Roberts at Linfield College, Oregon, for a detailed review of the evidence: The Origin of Modern Humans: Multiregional and Replacement Theories. For text and graphics on the current research, see this new report. Jeanne Sept also has some useful notes on these two competing models

4. Origins of Modern Behaviour

Early anatomically-modern human remains are associated with industries of greater antiquity and non-modern characteristics, leading Stringer (1989; 7), for example, to conclude that

if the postulated dispersal of anatomically modern humans from Africa was associated with new forms of cultural or behavioural expression, this was not reflected in any simple or direct way in the character of the associated lithic industries.

Thus, modern human behaviour is not a species characteristic. In fact, there is currently emerging a consensus in paleoanthropology that there is a marked temporal disjunction between the appearance of anatomically-modern human forms - the species Homo sapiens sapiens - and modern species-typical behaviour (for a marshalling of the evidence, see Noble and Davidson 1996). For the period from their emergence through to around 40,000 bp shows little substantive change in the archaeological record associated with modern human forms. Increasingly-modern humans continue to show remarkably un-modern activities. The complexity of technology stays fairly constant with respect to technique, raw materials, number of components combined together, and the number of stages involved in the construction of tools. And perhaps most tellingly, there is, as noted earlier (e.g., Chase and Dibble, 1987; Lindly and Clark, 1989), no evidence of any symbolic practices. As Lindley and Clark (1990: 233) conclude from their review:

neither archaic H. sapiens nor morphologically modern humans demonstrate symbolic behavior prior to the Upper Paleolithic.

5. Defining 'modern' behaviour

Contemporary human activities rely on the social and cultural maintenance of symbolic resources. The means of maintenance and transmission of these symbols are conservative; the symbols themselves are volatile. The physical instantiations of contemporary human symbolic activities show temporal volatility, differential spatial distribution, and spatial relocation. Temporal volatility is not necessarily associated with functional utility. Clothing, for example, is functional, but fashion is volatile for other reasons; hemlines on dresses go up and down for reasons unrelated to the function of wearing a dress, just as accepted male and female garb differs according to custom rather than function. Differential spatial distribution indicates that the pool of cultural products of human activities that would be found within 5 kilometres of where you are reading this paper will have a different constitution to those within 5 kilometres of another person in Tibet, New Guinea or elsewhere. If an inventory were available for your actual present location 5 years ago, then the temporal volatility of those products would again be apparent. At a more micro-level there exist some unique spatial distributions of cultural products; for example, people wear different clothes, jewellery, etc. Spatial relocation is demonstrable in the same way: the natural availability of the constituent products of cultural materials within 5 kilometres of any particular point is vastly different from the proportions in which they culturally occur and have been assembled. The resources available to us move over large distances; even the food on one's plate can be a geography lesson. Taking these properties as criteria for characterising modern human cultural practices, we can ask when, in the archaeological record, is there evidence that humans acted in characteristically modern ways? That is, when did the material artifacts associated with humans show patterns of temporal volatility, differential spatial distribution, and spatial relocation?

  • The evidence is negative before 40 000 years bp. Prior to 40 000bp there is abundant evidence of cultural activities, in the form of artifacts, being a characteristic of human life, way back to non-modern Homo species c.2 000 000 bp, but very little unequivocal evidence, if any, of symbolic mediation, as indexed by the above characteristics.

∑         The evidence is conclusively positive after 20 000bp (a point in time often referred to as the 'symbolic explosion'); the evidence of the intervening 20 000 years is less clear cut, but strongly supportive of human life being a symbolically-mediated activity, even if the spatial and temporal distribution of cultural artifacts were not fully modern in their characteristics.

Note, then, as a bottom line, that:

Bottom line: there is a temporal gap of around 60 000 years between the appearance of anatomically-modern humans, and their giving evidence of acting in characteristically modern ways (for reviews, see Conkey, 1996; Gamble, 1993; Lindly and Clark, 1990; Noble and Davidson, 1996; White, 1996; Wynn, 1996).

6. Social life

This change is correlated with changes in the social organisation of human groups. Social life prior to this transition may be inferred to have moved away from its earlier characters towards more modern forms, but is still not fully modern. There is some evidence for the use of fire, and perhaps cooking, as early as 700,000 BP at Zhoukoudian (Stringer, 1985), but there is no substantive evidence for hearths, storage pits or architecture. There is some evidence for true hunting, if only of smaller mammals (Binford, 1985; Shipman and Rose, 1983), even if scavenging were still a major source of animal remains. Particular sites appear to have been used for particular activities (e.g., de Lumley, 1975; Freeman, 1975; Keller, 1973). The picture here is complex to interpret, and the evidence is scanty. Gamble concludes his review of this period by noting that:

It leaves an overwhelming impression of spontaneous, highly episodic behavior where stone tools were made to do the job in hand before being dropped and their makers moving on. ... What is lacking ... is any indication for such modern practices as detailed planning, widespread contracts, or elaborate social display. There is no physical evidence of storage, raw materials all come from within a radius of 50 km, and usually less than 5 km of the sites where they were used and any form of art, ornament, jewelry, or decoration is entirely absent. ... [But] the fifteen minute culture as revealed in the manufacture and use of stone tools is a poor guide to the length of time over which social information could be retained. The occupation of seasonal environments provides a clear indication that such memory was now substantial (Gamble, 1993: 138-9, 143).

After this transition, the evidence indicates changes in social organisation in two directions.

    • First, there is an increasing spatial and temporal extension that elaborates and sustains extended kinship networks, communication beyond face-to-face encounters and exchange of information beyond the here-and-now, the organisation of logistical economic strategies, and the extension of the time depth of adaptation to environmental fluctuations (Whallon, 1989: 451).
    • Second, there is an intensification in the organisation of the immediate social environment. Built shelters and semi-permanent 'villages' are found after 40,000 bp, not before (see, for example, Gamble, 1986). At first sight it might seem paradoxical, but these two changes reinforce each other with respect to the effects they can have in elaborating linguistically-mediated awareness of the world. Both increasingly break the commonalities of shared knowledge between an individual and others: on the one hand in the meeting of 'strangers'; and on the other, in the 'creating' of strangers through the implicit demarcation of the 'public' and 'private' within the permanent society (see, for example, Wilson, 1988, for a fuller discussion).

7. What might we make of all this?

The situation is really quite odd. The information we currently have is that after their biological form had been fixed, anatomically-modern humans continued to function in ways that were little different from other human anatomies that have lived on the planet during the past half million years or so. Today, they act in very different ways, but they are still the same species. This points to a quite remarkable conclusion: that somehow the possessors of these anatomies created for themselves new ways of behaving. The process began slowly, but has accelerated, until now it is running at break-neck speed. How has this been done? What is the 'this' that has been done?

Let me sum up the problem. Perhaps some 300,000 years or so ago, defining human characteristics can be assumed to have been in place. But in the subsequent period to around 100,000 years ago - a time when there is clear evidence in the fossil record that modern human anatomy had been established - the accompanying artifactual record shows little, if any change: it remains decidedly non-modern. That is: there is almost no regional differentiation of tool-kits, nor a variation in time, such that 'everyone', 'everywhere, appears to have been doing the same thing, over and over again. There is very little evidence of symbolic behaviour until around 40,000 years ago. There is very little evidence of stylistic variations in tool traditions until 40,000 years ago. There is very little evidence of the movement of raw materials over distances from their natural sources of more than 5 kilometres before 40,000 years ago. Tools remained simple: there are no ladders, fishing nets, needles, bone as opposed to rock tools, and so on: all these changes appear after 40,000 years ago.

This transformation led Pfeiffer (1982) to propose a 'creative explosion' occuring in human behaviour subsequent to this time, a transformation of human abilities without an accompanying biological change or speciation event. How could such an explosion occur? These are the questions I want to look at in the more depth. However, to do this requires taking a couple of excursions into different areas to get an understanding of some ideas that will assist in doing this.