Neoteny in Humans

...the concept of "neoteny"—the retention of juvenile features into adult life. It is a commonplace of human evolution that the transition from Australopithecus to Homo and from Homo habilis to Homo erectus and thence to Homo sapiens all involved prolonging and slowing the development of the body so that it still looked like a baby when it was already mature. The relatively large brain case and small jaw, the slender limbs, the hairless skin, the unrotated big toe, the thin bones, even the ...