Why humans have so little hair compared to other apes

Why do humans have so little hair, at least compared to all other primates? At Smithsonian, Jason Daley shares the latest genetic research on the biological factors that result in humans' minimal body hair and its unusual distribution. Daley also surveys the fascinating current theories about why we evolved into the only naked apes. From Smithsonian:

One popular idea that has gone in and out of favor since it was proposed is called the aquatic ape theory. The hypothesis suggests that human ancestors lived on the savannahs of Africa, gathering and hunting prey. But during the dry season, they would move to oases and lakesides and wade into shallow waters to collect aquatic tubers, shellfish or other food sources. The hypothesis suggests that, since hair is not a very good insulator in water, our species traded in most of our fur for a layer of fat. The hypothesis even suggests we might have developed bipedalism to become more effective waders. But this idea, which has been around for decades, hasnt received much support from the fossil record and isnt taken seriously by most researchers.

A more widely accepted theory is that, when human ancestors moved from the cool shady forests into the savannah, they needed better thermoregulation. Losing all that fur made it possible for hominins to hunt during the day in the hot grasslands without overheating. An increase in sweat glands, many more than other primates, also kept early humans on the cool side. The development of fire and clothing meant that humans could keep cool during the day and cozy up at night.