The Survival of the More Versatile

Dr. Rick Potts, from “The Adaptable Human,” NOVA, October 26, 2009:

Dr. Rick Potts holds one of 500 handaxes made by Homo erectusthat he and his team uncovered at his research site at Olorgesailie, Kenya. Photo credit: © Jason F. NicholsClimate change had always been on people's minds when it came to human evolution. The idea that was around for a long time is that the establishment of a savanna environment, the grassy environment with a few trees, was critical to human evolution early on, and that and the Ice Age later on presented the challenging environment in which humans evolved.

But when I began the work here at Olorgesailie, we kept seeing layer after layer of environmental change, from soils to volcanic ashes to a lake to a drought when the lake completely evaporated. We saw this through 700,000 years, and I began to think, well, maybe it's not the particular environment of a savanna that was important, but the tendency of the environment to change, to vary in very dramatic ways. And we saw that the large grazing animals of the savanna—elephants, baboons, pigs, zebras, all of whom ate grass—disappeared in the time period when worldwide climate began to vary the most.

So it dawned on me: Rick, you're an anthropologist. Maybe this has something to do with human evolution, and it's not the survival of the fittest in any one environment but the survival of the more versatile, the more general and flexible creatures that would really persist over time. This gave me a new insight into human evolution. The origin of stone tools, the expansion of the brain, and the complexity of social life that we see with the emergence of our own species may actually be a response not to just the dry savanna or the cold Ice Age but to the wide and dramatic variability of climate over time.