Thursday, July 30, 2009

From Bottleneck to Expansion

Once modern humans began to assert themselves on the landscape, data suggests they took off. ScienceDaily is reporting that beginning around 40 000 years ago, the human population began expanding:
Reconstructions of the timing and magnitude of changes in human population size are important for understanding the evolution of our species. There has been a longstanding disagreement whether humans began to increase in number as a result of innovative technologies and/or behaviors formulated by hunter-gatherer groups in the Late Pleistocene, or with the advent of agriculture in the Neolithic. Hammer's research integrates empirical genetics with discoveries in paleontology and archeology to help provide answers to interdisciplinary questions about which kinds of innovations led to the evolutionary success of humankind.
The article appears in PLoS One and can be read here. The authors conclude:
The data from the three surveyed non-African populations (French Basque, Chinese Han, and Melanesians) are inconsistent with the simple growth model, presumably because they reflect more complex demographic histories. In contrast, data from all four sub-Saharan African populations fit the two-phase growth model, and a range of onset times and growth rates is inferred for each population. Interestingly, both hunter-gatherers (San and Biaka) and food-producers (Mandenka and Yorubans) best fit models with population growth beginning in the Late Pleistocene. Moreover, our hunter-gatherer populations show a tendency towards slightly older and stronger growth (~41 thousand years ago, ~13-fold) than our food-producing populations (~31 thousand years ago, ~7-fold). These dates are concurrent with the appearance of the Late Stone Age in Africa, supporting the hypothesis that population growth played a significant role in the evolution of Late Pleistocene human cultures.
The late Stone Age at this point coincides with the recession of the ice at the tail end of the Late W├╝rm glaciation and is coincident with the appearance of modern humans in Europe and several other areas of the Old World. It also accounts (at least in part) why technology takes off at such a fantastic clip beginning with the Upper Palaeolithic period. A critical mass of people drive new ideas and technology. It also helps that your tundra line doesn't begin at Vienna.

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