ABSTRACT
Expansion ................................................................................... 289 33.8 Which Theory Is Best? ............................................................... 291 33.9 Summary .................................................................................... 291
33.1 SCOPE
One of the most interesting problems in human evolution is the question of why human brains grew so big and what evolutionary factors were responsible for making it happen. The Australopithecines underwent a remarkable process of becoming skillful bipedal walkers. Yet, over the two or three million years of their existence, their brain size changed very little. When the Homo lineage developed some two million years ago, their brain size underwent an incredible expansion where it tripled in size. Humans then had the greatest brain-to-body size ratio of any creature on Earth. How did it happen and why did it happen? We will explore these questions in this chapter.
