Australopithecus africanus (Dart 1925) 'Taung child'

Australopithecus afarensis (Johanson, White and Coppens 1978; 3.3-2.6 mya, females: 3.7 feet tall, males 5 feet tall, 'Lucy') tradtionally nests basal to Homo, but here nests basal to Pan and Gorilla as a convergent bipedal genus derived from Proconsul.

Australopithecus had a larger skull and a bigger brain. The feet were more like those of Homo without the diverging toe found in more primitive primates from Notharctus to Ardipithecus.

Loss of quadrupedalism meant babies could no longer go along for a ride on their mother’s back. Now they had to be carried. Bipedalism permitted this. Soon australopithecines were carrying tools, sticks, and anything they wanted to keep or hoard, even a second infant. Human reproductive rate is five times that of chimps.

Hair on the face and top of the head does not fall out but keeps growing as a sort of sun cap. Elsewhere hair thins, exposing more skin. Sweating develops for evaporative cooling.