Monday, 16 March 2009

Modern Human Behaviour

Anthropologists use the term modern human behaviour to refer to a list of behavioural traits that distinguish present day and recent anatomically-modern humans from earlier human species and possibly from earlier anatomically-modern humans. It is generally accepted that the “package” includes the use of abstract thought, symbolic behaviour (such as art and creative expression), use of syntactically-complex language and the ability to plan ahead, but there is no universally-agreed theoretical definition of what modern human behaviour actually is and there is considerable disagreement as to both when and how humans became behaviourally modern.

Trait lists:
Many researchers have adopted an empirical approach by drawing up a list of supposedly-modern traits and then seeking evidence of their emergence in the archaeological record. Henshilwood and Marean (2003) list the following traits as frequently viewed as evidence of modern human behaviour:

1. Burial of the dead as an indicator of ritual
2. Art, ornamentation, and decoration
3. Symbolic use of ochre
4. Worked bone and antler
5. Blade technology
6. Standardization of artifact types
7. Artifact diversity
8. Complex hearth construction
9. Organized use of domestic space
10. Expanded exchange networks
11. Effective large-mammal exploitation
12. Seasonally focused mobility strategies
13. Use of harsh environments
14. Fishing and fowling

The problem, as they point out, with this approach, is that even genuine evidence of absence of many of these traits does not preclude behavioural modernity as other environmental factors could also be responsible, making certain activities problematic or simply unnecessary.

A possible definition:
Henshilwood and Marean define modern human behaviour as “behaviour that is mediated by socially constructed patterns of symbolic thinking, actions, and communication that allow for material and information exchange and cultural continuity between and across generations and contemporaneous communities.” All extant humans are thus defined as modern by the ability to store or display data external to the human brain, rather than by their technology itself. The key criterion for modern human behaviour is not the capacity for symbolic thought but the use of symbolism to organize behaviour.

The distinction between capacity and actual use is important because the capacity for an action doesn’t mean it will necessarily happen immediately: behaviourally-modern humans clearly had the capacity for aeroplanes, mobile phones and the internet long before these things actually appeared.

Henshilwood and Marean believe that the term “modern human behaviour” should be replaced with “fully symbolic sapiens behaviour” and regard it as the culmination of a long line of developments toward modernity; the point at which it is to be recognized archaeologically being when artefacts or features carry a clear symbolic message that is exosomatic (i.e. recorded outside the brain) such as art, ornaments or decoration. Even the earliest behaviourally-modern societies should have been able to transmit arbitrary systems of beliefs and innovations, resulting in identifiable evidence of symbolism in the archaeological record.

Big Bang versus Gradualism:
There are two main views concerning the origins of modern human behaviour. The Big Bang or Great Leap Forward model views it as a single punctuated event, though opinions vary as to when it happened. Richard Klein sees it happening about 50,000 years ago, possibly as the result of a genetic mutation, but at all events long after the appearance of the first anatomically-modern humans around 200,000 years ago (Klein, 1999; Klein & Edgar, 2002). Other proponents include Jared Diamond and Steven Mithen (Diamond, 1991; Mithen, 1996).

However this view is disputed by others including Stephen Oppenheimer, Robert Foley, Sally McBrearty and Alison S. Brooks, who claim there was no “big bang” and knowledge, skills and culture gradually developed over hundreds of millennia (see Oppenheimer, 2003; Lewin & Foley, 2004; McBrearty & Brooks, 2000; McBrearty, 2007).

Evidence for the Big Bang:
What the Big Bang theory is in essence saying is that while humans who were living in Africa around 200,000 years ago might have resembled people living today, but cognitively they weren’t quite “with it” and to us would have appeared simple-minded. On the face of it, this would seem to be an odd state of affairs. Why would people with brains comparable in size to our own lack our mental capabilities?

Until fairly recently, the archaeological evidence did seem to suggest that this was indeed the case. Support for a “great leap forward” came from the Levant and from Europe.

The evidence from the Levant suggested the boundary between Neanderthals and modern humans fluctuated with environmental change, with Neanderthals moving east and south into the Levant with colder climates, while modern humans moved out of Africa into the Levant with warmer conditions. These fluctuations continued for tens of thousands of years until about 40,000 years ago, modern humans suddenly broke through the climate barrier and spread north and west into Europe. Within a comparatively short space of time the Neanderthals became extinct.

The archaeological record of Europe reveals an astonishing transformation from about 40,000 years ago, when the relatively crude tools of the Mousterian tradition are give way to the finely worked blade-based tools of the Upper Palaeolithic. Unequivocal evidence of artistic expression is seen for the first time in the form of beads, ornaments, figurines, carvings and the magnificent cave paintings at sites such as Chauvet, Cosquer and Lascaux.

It suggests to many a “human revolution”: the beginning of human culture: the arrival on the scene of modern Homo sapiens, fully-loaded and ready to roll. From Europe the revolution spread, eventually reaching all parts of the world. The Sistine Chapel, Shakespeare’s sonnets and Beethoven’s late stringed quartets all lay in the future, but it was on the steppes of Ice Age Europe that it all began.

Cognitive Fluidity:
But all of this begs the question: fully-modern humans are now thought to have appeared at least 200,000 years ago. If fully-modern behaviour didn’t appear until 50,000 years ago, as Klein believes, what was happening in the meantime – a matter of 150,000 years?

Steven Mithen, Professor of Archaeology at Reading University, believes that early humans, including early Homo sapiens, lacked what he refers to as “cognitive fluidity”.

In a theory first proposed in his 1996 book “The Prehistory of the Mind”, Mithen claims that the human brain originally had separate cognitive “domains” for different functions, such as social interaction, tool-making, food and resource gathering (“natural history”), etc. Modern human behaviour came about when the barriers between these domains broke down, allowing them to interact with each other. Art, religion and language all arose from the synergistic interactions between the various domains, but this was restricted to anatomically modern humans. Homo erectus and the Neanderthals quite literally never made the connection.

Mithen originally viewed “big bangs” occurring in different parts of the world at different times between 60,000-30,000 years ago, with the final leaps to full cognitive fluidity occurring by parallel evolution, though he has now revised his date for the emergence of cognitive fluidity to between 200,000-70,000 years ago, in Africa (Mithen, 1996 & 2007).

Mithen draws heavily on the work of Jerry Fodor, Annette Karmiloff-Smith, Michael Tomasello, Howard Gardiner, Leda Cosmides and John Tooby, but the idea of initially separate domains interacting may have been inspired in part by Julian Jaynes’ controversial theory about “bicameral minds”, proposed in 1976. (See Mithen, 1996; Fodor, 1983; Karmiloff-Smith, 1992; Tomasello, 1999; Gardiner, 1983 & 1999; Jaynes, 1976).

Mithen’s theory is well-argued and the existence of multiple intelligences in early humans is an intriguing possibility. Personally, though, I am somewhat sceptical as to whether anatomically-modern humans ever had this type of brain.

Stanford University’s Richard Klein is a long-time supporter of the Big Bang theory. Unlike many “big bangers” Klein does present a specific biological case for the emergence of modern human behaviour. His original “prime suspect” for the genetic mutation leading to modern human behaviour was a gene known as FOXP2, or forkhead box P2, which regulates a number of other genes, some of which are believed to play a role in the development of the parts of the brain associated with speech, although the exact genes involved are not known. The FOXP2 gene is not unique to humans, but exists with very few differences in other animals.

The first clue that FOXP2 might be a “speech gene” came from studies of Family KE, an extended British family living in London (their actual identity is not in the public domain). Some members of the family have problems with aspects of grammar, including the use of inflexions for marking tense. They also have difficulty in producing the fine movements of the tongue and lips required for normal speech. The problem affects three generations of the family and has been studied since the 1990s. In 2001 geneticists determined that the affected members of the family all have a defective version of the FOXP2 gene.

In 2002 a team led by Wolfgang Enard at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany compared the human version of the FOXP2 gene with that of the chimpanzee, gorilla, orang-utan, rhesus macaque and mouse. They found that the gene is highly conserved, with differences of just three amino acid positions out of around 700 between the human version and the mouse version. But curiously two of these changes had occurred since the split between humans and chimps, a far more recent occurrence than the split between humans and mice. They suggested that these two changes might be critical to speech and language. The beneficial mutation has been positively selected for by natural selection and they estimated that it had become fixed in the human population at some stage in the last 200,000 years (Enard et al, 2002).

Klein believed the actual date would be 50,000 years, and that FOXP2 was the “smoking gun” responsible for the Great Leap Forward. But even a date of 200,000 years would rule out behavioural modernity in the Neanderthals, who had diverged from Homo sapiens much earlier.

Then in 2007 came a complete volte-face from the Max Planck Institute. The sequencing of the Neanderthal genome had revealed that Neanderthals possessed exactly the same version of FOXP2 as do modern humans (Krause et al, 2007). This not only pulled the rug from under Klein’s argument, it was also rather embarrassing for the group whose earlier 200,000 year estimate was now seen to be off by a factor of at least two. Dr. Svante Paabo, who was involved with both studies, admitted that the earlier estimates were “not flawed but rely on assumptions that are necessary but also universally known to be oversimplifications of the reality”.

Klein has nevertheless stuck to his guns. He said he was disappointed to have lost the genetic support from Paabo's work but had not changed his views. "The archaeological record suggests a major change in human behaviour 50,000 years ago," he said, "and I think there is overwhelming evidence for that" (quoted in the New York Times, 18 October 2007).

Has anybody thought of this?
There is for my mind a serious problem with the notion that a behaviourally-modern human brain could have achieved its present set of capabilities without any increase in size over the older model. We are in effect being asked to believe that while both early and present-day members of our own species had same brain-size, the version used by people today is far superior to that in use prior to 50,000 years ago.

Brains are very expensive things to run. In modern humans, they account for just 2% of our body weight, yet they take up 20% of the body’s energy-budget. Not only that giving birth to a large-brained infant poses considerable problems for women which are only partially-alleviated by human babies doing a considerable amount of their initial brain growth after birth, which in turn increased their postnatal dependency to a level way above that of other mammals (compare, for example, with a foal, which can literally hit the ground running).

Now consider the considerable increase in human brain size over that of apes. This occurred in two phases: firstly around 2.5 million years ago with the appearance of Homo habilis: and secondly around half a million years ago with the appearance of large-brained hominins such as Homo heidelbergensis. There is no doubt that these increases were driven by Darwinian selective pressure, meaning that the advantages of these larger brains outweighed the disadvantages as outlined above.

But the Big Bang theory implies that it is possible to increase brain-power by a few genetic tweaks, with no increase in actual size being necessary. This would surely give the best of both worlds – a small, fuel-efficient brain packing the same punch as a larger “gas guzzler”. If such a thing is possible, why didn’t it happen much earlier? Why did Homo habilis evolve a large, expensive-to-run brain rather than “tweaking” the smaller brain possessed by its australopithecine predecessors? The same argument could be applied to the second phase of brain expansion, 500,000 years ago.

But of course it didn’t happen that way: Nature took the apparently sub-optimal option of increasing physical brain size. This suggests to me that it wasn’t sub-optimal and was in fact the only available option for increasing brain-power.

If increasing brain-power without increasing brain-size was not possible for the first 2.5 million years of human evolution, how did it suddenly become possible 50,000 years ago?

Down with the Revolution:
In their seminal 2000 paper, Sally McBrearty and Alison Brooks suggest that the traditional interpretation of the archaeological record is seriously flawed:

“This view of events stems from a profound Eurocentric bias and a failure to appreciate the depth and breadth of the African archaeological record. In fact, many of the components of the ‘‘human revolution’’ claimed to appear at 40–50 ka are found in the African Middle Stone Age tens of thousands of years earlier.

These features include blade and microlithic technology, bone tools, increased geographic range, specialized hunting, the use of aquatic resources, long distance trade, systematic processing and use of pigment, and art and decoration. These items do not occur suddenly together as predicted by the ‘‘human revolution’’ model, but at sites that are widely separated in space and time. This suggests a gradual assembling of the package of modern human behaviours in Africa, and its later export to other regions of the Old World.” (McBrearty & Brooks, 2000).

McBrearty and Brooks claim that the “Big Bang” is in fact an illusion, arising from the fact that Europe has been studied archaeologically in far more depth than Africa, and that evidence of modern human behaviour can in fact be found in Africa that is far earlier than any seen for Europe. This is of course exactly what one would expect to find if Homo sapiens evolved in Africa and only later migrated to Africa.

The paper presents evidence for the gradual acquisition of the elements of so-called modern human behaviour over the course of 300,000 years:

Images: 40k
Beads: 60k
Microliths: 65k
Notational pieces (incised): 100k
Mining: 100k
Barbed points: 100k
Bone tools: 100k
Fishing: 110k
Long-distance exchange: 140k
Shellfishing: 140k
Points: 300k
Pigment processing: 300k
Grindstones: 300k
Blades: 300k

Four of the fourteen skills are present even before modern humans evolved and nearly all of the rest had appeared before the onset of the Upper Palaeolithic in Europe, where such technologies are associated with the supposed human revolution. While there is still not conclusive evidence to dismiss the "Big Bang" theory, my feeling is that it is now on its way out.


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© Christopher Seddon 2009

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