July 11, 1999

Sundays are liberty for the crew, giving people the opportunity to go into town, write letters to loved ones back home or to simply sleep in a bit later than normal. For me, it was a day of preparing notes for two talks to be given at a meeting of the International Union of Quaternary Research (INQUA), in South Africa during the first week of August.

The talks center around the research that has been going on at Olorgesailie since 1985, dealing with early humans and the interaction of early humans with the environment. One talk in particular centers on a new model for early human evolution called "Variability Selection" (VS). During the course of human evolution, the environment became increasingly variable, that is, it changed more and more dramatically. The VS hypothesis states that during this time, early humans became more adaptable and less tied to any one particular environment.

Normally, evolution is viewed as a process in which organisms adapt to a specific type of environment, and so they become more specialized and well matched to the environment they inhabit. Under the VS model, some organisms become specialized at being adaptable. There is an apparent contradiction here that can be confusing. What the model states is early humans evolved along such a trajectory as to allow them to inhabit many diverse environments, or more accurately, to allow them to continue living in an area even as the environment changed. This is not to say that humans lack specialized adaptations. To the contrary, evolutionary adaptations such as bipedalism and large brains are changes that are highly specialized, but they allowed our early human ancestors to meet the challenges of a changing physical world by making them more versatile.

As we begin to understand more clearly the dramatic changes that the Earth's environments have gone through during the past several million years, and we begin to investigate how organisms evolved during these times, we must consider that there may be two modes of evolution acting. In the first, an organism becomes specialized to fully exploit an environment, and is extremely successful. However, when climatic variability removes this environment, extinction occurs. The second is the VS model, whereby an organism evolves specialized structures that confer upon it the advantage of versatility. As climatic changes occur, the organism is able to adapt to the changing environment.