Abstract

Ongoing advances in paleoclimatology and paleoecology are producing an ever more detailed picture of the environments in which our species evolved. This picture is important to understanding the processes by which our large brain evolved. Our large brain and its productions—toolmaking, complex social institutions, language, art, religion—are our most striking differences from our closest living relatives. Indeed, humans are unique in the animal world for our brain size relative to body mass and in the elaboration of our cultures. We are also the world’s dominant organism (Vitousek et al. 1997). We achieved our present anatomy and behavioral repertoire very recently. Fossil material attributable to our species goes back perhaps 200,000 years and artifacts that strike us as representing fully modern behavioral capacities are only about 50,000 years old (Klein 1999; McBrearty and Brooks 2000), about which time anatomically modern humans spread from Africa to Eurasia (Lahr and Foley 1994). Our ecological dominance began with the evolution of agriculture starting about 10,000 years ago. Explaining the late coming of human brains is a major evolutionary puzzle. Most important animal adaptations are old. Eyes, internal skeletons, adaptations for terrestrial life and for flight all date back hundreds of millions of years. Given that big brains and culture were such an overwhelming success for us why didn’t they evolve long ago?