Fossil evidence has been found that the earliest humans cared for rather than abandoned or killed their disabled young. From the story:
The discovery of the oldest known infant born with a skull deformity hints that, contrary to popular belief, early humans might not have immediately abandoned or killed their abnormal offspring, a new study says. Many mammals are known to reject newborns with severe deformities. Scientists had therefore assumed that ancient humans behaved likewise . . .
The surprise comes because many scientists see us as just animals. But there is something—dare I say it, exceptional—about the human species, and apparently this distinction that makes such a huge difference has been part of us from the time we first began to emerge/evolve/were created (take your pick).
Yes, yes, I know: Human societies have killed or exposed disabled children. Heck, the Dutch do today in their neonatal care units—indicating to me that Dutch society has experienced a serious ethical regression from the most ancient of times. But this story vividly illustrates that being human is something different in kind from any other known life form that has ever existed in the universe.