Why are we naked apes?

The BBC has an article about human hairiness:

Our hair is not quite like the fur of other animals: it grows in 'islands' around our bodies. How come?
It's not the only puzzling thing about our hair either: how does it seem to 'know' how long to grow? And why are some people hairier than others?
Hair, and its puzzling distribution across our bodies, is a topic that Adam and Hannah, the presenters of the BBC Radio 4 series The Curious Cases of Rutherford and Fry, explored this week.
In response to a question from Hannah Monteith in Scotland about leg hair, they set out to solve the mysteries of human fur, consulting anatomist Alice Roberts and dermatologist Susan Holmes.
You can listen to the episode below, or subscribe to the podcast on the Radio 4 site (featuring a few biological facts too rude to broadcast on daytime radio). It also involves a rather painful procedure for Adam*.

*No animals were harmed for this recording. Just Adam.

Rico says that, being hairier than most humans, he finds this of interest...