comments, so we invited him and his wife to the Transvaal Museum. 

 Even though he was over 90 years old and almost blind, he felt the 

 shape of each piece between his fingers with obvious excitement. 

 Then he said, "Brain, I told you long ago that Australopithecus 

 made bone tools, but you didn't believe me. Now, what do you think 

 these were used for?" I replied that I was almost certain that they 

 had been used for digging in the ground. His mouth fell open in 

 astonishment and he sat back in his chair with an expression of 

 complete disbelief. "That," he said, "is the most unromantic expla- 

 nation that I have heard of in my life." He thereupon took the 

 sharpest of the bone tools on the table and stuck it into my ribs, 

 saying, "I could run you through with this." Hence my long-stand- 

 ing fascination with the process of predation. 



The Remarkable Phenomenon of Brain Expansion in the Human 

 Lineage and a Probable Reason for its Occurrence 



By any standards, the increase in the size of the brain relative to 

 that of the body in our human ancestors during the last two million 

 years was a remarkable zoological event. When the earliest known 

 members of the Homo lineage appeared on the scene, in the form 

 of H. habilis or H. rudolfensis, their average brain capacity was 

 about 654 cc; this had risen to about 850 cc in H. ergaster and H. 

 erectus, and to 1400 cc in archaic H. sapiens towards the end of 

 the Middle Pleistocene. As Leslie Aiello and Peter Wheeler (1995) 

 pointed out, this event is all the more remarkable because a brain 

 is built of "expensive tissue" — although a human brain may only 

 take up 2 to 3% of the weight of the whole body, it uses 16 to 20% 

 of the energy consumed by the resting body. To double the size of 

 the brain relative to that of the body would usually mean that the 

 basal metabolic rate (BMR) of the animal would have to be sub- 

 stantially increased. Oddly enough, this has not been observed in 

 humans, in comparison to related primates, and Aiello and Wheeler 

 concluded, therefore, that human brain expansion occurred at the 

 expense of the size of the gut, which has apparently shrunk during 

 the course of human evolution. To be able to function with a much 

 smaller gut implies that ancestral humans changed to a diet of higher 



