According to an award-winning research paper, the reason (most of) us evolved to as the only hairless apes is because, in the opinion of our ancestral mothers, hairy bodies are ugly. Judith Rich-Harris, author of The Nurture Assumption and No Two Alike: Human Nature and Human Individuality, posits that during the Stone Age, mothers decided whether to care for their babies based in part on their appearance. From Medical News Today:
If Stone Age people believed that hairless babies were more attractive than hairy ones, this could explain why humans are the only apes lacking a coat of fur. Harris suggests that Neanderthals must have been furry in order to survive the Ice Age. Our species would have seen them as "animals" and potential prey. Harris' hypothesis continues that Neanderthals went extinct because human ancestors ate them.
UPDATE: Here is the paper, titled "Parental Selection: A Third Selection Process in the Evolution of Human Hairlessness and Skin Color" Link
