Compare the article below with Nina G Jablonski's in Scientific American, February 2010.
According to Nina Jablonski: The combination of naked skin and watery sweat that
sits directly atop it, rather than collecting in the fur, allow humans to
eliminate excess heat very efficiently.
In fact, our cooling system is
superior to most animals.
Around three million years ago global cooling caused a drying effect in
East Africa, where human ancestors lived. With a decline in regular rainfall,
wooded environments gave way to the Savannah.
This meant travelling ever longer distances
in search of water, edible plant foods and (later) prey animals.
The elevated activity
levels came at a price: A greatly increased risk of overheating. Early humans had to enhance
eccrine sweating ability and lose body hair to avoid overheating.
Hair on the head is retained to shield against excess heat on top of the head.
While hair in the armpit and groin serves to propagate pheromones.
With better temperature regulation the human brain could be enlarged.
Human traits such as social blushing and complex facial expressions evolved to compensate
for our lost ability to communicate through our fur.
The aquatic ape theory, below, is according to Jablonski - and most others - wrong.
E.g. Watery habitats were thick with hungry crocodiles. And the theory is overly complex
compared to the standard story.
According to the fossil record it is more straightforward
to assume that humans always lived on land....