In class last night we talked about our earliest ancestors, about Australopithecus, Homo Erectus and the whole gang, the distant relatives on our ever-so-shaggy family tree.

A key trait, of course, is bipedalism, walking on two legs. In Maps of Time, David Christian talks about the hazards of this posture, especially for women, who had to bear children with large heads that required turning as they passed through the birth canal. 

For this, they needed help. Thus did a physical trait engender cooperation, social behavior, the collective efforts of women helping women during childbirth. And later on, the collective efforts of raising young humans, who are far more helpless at birth than most mammals. 

We don’t walk on two legs because we’re human. We’re human, in part, because we walk on two legs.

(One of my favorite toddlers shows off her stride.)