Thursday, July 02, 2009

Culture Requires a Dense Population

Mark Thomas and his colleagues at University College, London, suggest that cultural sophistication depends on more than just the evolution of intelligence. It also requires a dense population. If correct, this would explain some puzzling features of the archaeological record that have hitherto been put down to the arbitrary nature of what has survived to the present and what has not.

They are trying to explain the pattern of apparent false-starts to modern human culture. The species is now believed to have emerged 150,000-200,000 years ago in Africa and to have begun spreading to the rest of the world about 60,000 years ago. But signs of modern culture, such as shell beads for necklaces, the use of pigments and delicate, sophisticated tools like bone harpoons, do not appear until 90,000 years ago. They then disappear, before popping up again (and also sometimes disappearing), until they really get going around 35,000 years ago in Europe.

The team drew on an earlier insight that it requires a certain number of people to maintain skills and knowledge in a population. Below this level, random effects can be important. The probability of useful inventions being made is low and if only a few have the skills to fabricate the new inventions, they may die without having passed on their knowledge.

In their model, Dr Thomas and his colleagues divided a simulated world into regions with different densities of human groups. Individuals in these groups had certain “skills”, each with an associated degree of complexity. Such skills could be passed on, more or less faithfully, thus yielding an average level of skills that could vary over time. The groups could also exchange skills.

The model suggested that once more than about 50 groups were in contact with one another, the complexity of skills that could be maintained did not increase as the number of groups increased. Rather, it was population density that turned out to be the key to cultural sophistication. The more people there were, the more exchange there was between groups and the richer the culture of each group became.

Dr Thomas therefore suggests that the reason there is so little sign of culture until 90,000 years ago is that there were not enough people to support it. It is at this point that a couple of places in Africa—one in the southernmost tip of the continent and one in eastern Congo—yield signs of jewellery, art and modern weapons. But then they go away again. That, Dr Thomas suggests, corresponds with a period when human numbers shrank. Climate data provides evidence this shrinkage did happen.

According to Dr Thomas, therefore, culture was not invented once, when people had become clever enough, and then gradually built up into the edifice it is today. Rather, it came and went as the population waxed and waned.
via The Economist

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