Effect of Human Brain Size on Labor and Bipedalism

The real obstetrical dilemma came long after Lucy and her colleagues became extinct, when there was a sudden upsurge in brain expansion. About 1.5 million years ago, die adult hominid brain went from the Australopithecine size of 400 cubic centimeters to 750 cubic centimeters in a species called Homo habilis, the first member of our genus. In other words, the brain just about doubled in size. A mere million years later. the hominid brain doubled once again until it reached its present average...