quality, such as one including animal protein, and they would have 

 done this by scavenging and active hunting. 



It has been customary to think of humans as being unique in so 

 many ways, but this is not always true. When we look at brain 

 weight relative to that of the body, our percentage is half that of 

 squirrel monkeys of the genus Saimiri from South America; and 

 turning to energy consumption of the brain relative to that of the 

 whole body, we find that some mormyrid fishes show a figure three 

 times higher than our own (Nilsson, 2000). 



Clearly, a greatly increased brain size is not a luxury to be ac- 

 quired lightly. It is something that would only have evolved under 

 strong selective pressure, but of what did this pressure consist? For 

 many years it has been suggested that brain expansion, and the ben- 

 efits that this brings to humans, has been linked to the problems of 

 making a living in the changed and more open habitats that char- 

 acterized Africa during the last two million years. Frequently cited 

 is the need to cope with more complex foraging strategies than had 

 been the case when ancestral hominids lived in evergreen forests. I 

 have no doubt that this need would have been one of the factors. 

 The proposal that I will be putting forward in this lecture also relates 

 to survival in alien habitats, but focuses on the need to outlive the 

 ever-present threat of predation by carnivores in those habitats. It 

 seems to me that predation could constitute a large part of the se- 

 lective pressure required to promote the evolution of human brain 

 expansion. The predation in this case was uniquely an attribute of 

 the African habitats in which representatives of the genus Homo 

 evolved. But before turning to those habitats themselves and the 

 predators that they harbored, let us consider briefly how such new 

 habitats came into being. 



Cenozoic Cooling and its Effects on African Habitats 



It has become clear that a critical factor in the appearance of more 

 open habitats in tropical and sub-tropical Africa was a global cooling 

 trend. During 1979, 1 was invited by the Geological Society of South 

 Africa to give one of the Alex. L. Du Toit Memorial Lectures and 

 decided to explore the topic The evolution of man in Africa — was it 



