Bipedalism didn’t 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. Wilkinson and Ruxton came to this
conclusion after analyzing a mathematical mod