Overview of hominid evolution

trading guts for brains?

Big, bigger, biggest. The brain of Australopithecus (top) is half the size of Homo erectus (middle) and one-third the size of H. sapiens (bottom).
CREDIT: JEFFERY H. SCHWARTZ/NATIONAL MUSEUM OF KENYA

Science 15 June 2007:
Vol. 316. no. 5831, p. 1560
DOI: 10.1126/science.316.5831.1560

Aiello, L. C. and P. Wheeler (1995). "The expensive tissue hypothesis." Current Anthropology 36: 199-211.