“How about breasts?” The question came from a jock-y guy in one of my graduate school classes on human evolution.

Far from offensive, the query was appropriate and astute. My classmates and I nodded approval, and the professor added it to a growing list on the board.

We were brainstorming features that distinguish our species, Homo sapiens, from other primates. That list includes human peculiarities like big brains, upright walking, language, furless bodies … and permanently enlarged