I bumped into a personal web site a few weeks ago and the owner had a unique
theory about the development of human breasts. (At least to him it was
unique.) He wrote that other primates have protruding jaws and the young
easily can suck on a flat-chested nipple. He theorized that as the face
flattened in humans, the female breast grew to allow sucking while still
allowing breathing.

Tom Barber