"If the misery of the poor be caused not by the laws of nature, but by our institutions, great is our sin."
- Charles Darwin

Sep 3, 2007

African Exodus Linked to Global Climate Change

The climate crisis helped us emerge from the Stone Age, will it return us to it?

Drought stricken regions of Africa today may have looked the same for
our early ancestors.

As I wrote earlier (see The Evolution of Metapopulations and the Future of Humanity) the earliest migration of fully modern humans out of Africa occurred approximately 70,000 years ago. I argued that the most likely explanation was that global climate change, as the last ice age was beginning, prompted this migration.

This hypothesis found support today in the early edition of Proceedings of the National Academy of Sciences by Christopher Scholz and colleagues who have evidence from deep sediment cores of Lake Malawi in Africa. These cores suggest a series of megadroughts that occurred between 135,000 and 75,000 years ago that reduced Lake Malawi by as much as 95% and caused many lakes throughout Africa to dry up completely. Approximately 70,000 years ago the climate stabilized in the region and was more favorable for human populations.

There has been much speculation as to why humans didn’t invent farming until only 10,000 years ago in the fertile crescent of the Middle East. This early climate crisis was probably the main reason. For sixty thousand years the climate fluctuated and droughts would strike our fledgling species. This undoubtedly made it difficult for hunter-gatherers who had the freedom to follow the herds but near impossible for any would-be agriculturists tied to one area of land. Couple this with few potential large game animals suitable for domestication in Africa (see Guns, Germs & Steel) and it’s easy to understand why there was such a delay.

This might also give us modern humans pause as we hear more reports every day about catastrophic climate change. We are a species beholden to the land we occupy in ways that are easy to forget with modern technology. Sixty thousand years may be the blink of an eye in geologic terms, but it’s fifteen times longer than humans have had the written word. The last global climate change may have been caused by fluctuations in the Earth’s orbit, but the current one is the result of our own societal imbalance.


Christopher A. Scholz et al. (2007). East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins. Proceedings of the National Academy of Sciences. Early Edition September 3, 2007. doi 10.1073 pnas.0703874104

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archaeozoo said...

I have read several blogs this morning on this topic, including ones at Archaeoblog and The interest this study seems to be generating amongst archaeologists seems to be high, not undeservedly perhaps given its implications. The impact of those sort of climatic conditions upon the human species would logically have been substantial.

As you say, however, that impact is not solely relevant to the past. It is also relevant to our future - and we would be wise to take note of the lessons the past can teach us.

John - Evolutionary Middleman said...

Let's say a climate changed forced just 7% of our species to uproot themselves and move somewhere else (probably mostly to the nearest, large, habitable cities). That would mean 455 MILLION people on the move and disrupting other environments. There's no reason to accept my arbitrary number, but it shows what could be a very nasty situation. Now, imagine if my arbitrary number were a conservative one.

sexy said...