Evolution of nakedness in Homo sapiens. 2007. M. J. Rantala. Journal of Zoology 273: 1-7.
Homo sapiens is the only existing primate species lacking in functionally effective thermally insulating fur. As all other primates have considerable hair covering, it has always been accepted that our ancestors must once have had a respectable amount of body hair. Unfortunately, fossils cannot help us when it comes to differences in skin and hair. Recent DNA analysis, however, has given us some idea of when and where the great denudation took place.
A number of hypotheses have been proposed to account for this feature, but none of these has gained general acceptance. All will be explained here.