Why People Lost Their Fur

The need for ancient humans to keep cool during the day might
explain their lack of body hair but not why they walked on two
feet. Bipedalism didnt evolve as a way for ancient humans to keep
cool during the heat of the day, according to a new model published
today (December 12) in Proceedings of the National Academy of
Sciences. But once hominins did start walking on two feet, it
ignited another change that allowed them to stay cool the loss of
body hair. The new model explains why similarly sized mammals that
walk on all fours and that may tend to overheat have not given up
their coats. If you are already walking upright for other reasons
it actually makes the advantage you get from losing hair bigger
than if you were on four legs, said David Wilkinson of John Moores
University in Liverpool, who authored the study along with Graeme
Ruxton of the University of Glasgow. You are moving more of your
body up above the ground and sweat evaporates more easily than it
can if you were on all fours, because more air will circulate
around you, Wilkinson explained.