Savanna hypothesis

The savanna hypothesis is the proposal that the major divergence between the hominins and other great apes was driven by hominins moving out of the forests and onto the grasslands. It is one of the oldest and most established hypotheses for what separated humans from the other apes, dating back to Charles Darwin's time.

The hypothesis has come under intense fire in recent years with alternative hypotheses such as rapidly fluctuating environments or the pseudoscientific aquatic ape hypothesis competing for attention. But the savanna hypothesis received new support by a proposal that humans adapted to run down animals in the hot African sun. This included the development of large leg tendons and buttocks which do not appear in the other great apes, but allow humans to run efficiently on two legs by recycling the energy of running motions, as well as the loss of hair over most of the body to allow efficient cooling. The animal chosen to be a victim would be able to sprint faster than the relentless human hunter until heat exhaustion caused it to collapse.