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Why Humans are Hairless

Humans once possessed hairy bodies such as those possessed by chimpanzees and other
primates. However, over time, their bodies have evolved into relatively hairless ones due to
climate change which around three million years ago converted many forests in East and Central
Africa, where early humans lived, into savannah grasslands due to reduced rainfall (Jablonski,
2010). With food and water scarce, early humans began walking and running more in search of
fresh water and animals for food. Such an active lifestyle resulted in more muscle activity thus
more heat production by the body which upset homeostasis (steady internal chemical and
physical conditions). Shedding off body hair was an evolutionary mechanism to help humans
release this excess heat much more efficiently through faster evaporation of sweat thus allowing
them to retain their new active lifestyle (Jablonski, 2010).
Although humans evolved from hairy to hairless bodies to suit their new, more active
lifestyles, they retained hair in some body parts. The most obvious one is the head. Humans
retained hair on the head primarily to protect them from dangerous ultraviolet rays from the sun
and heat insulation. Of all the body parts, the head is one that is directly hit by the sun’s rays.
Losing hair on the head would have denied humans the ability to protect themselves from the
sun’s excessive heat and dangerous rays.

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References

Jablonski, N. G. (2010). The naked truth. Scientific American, 302(2), 42-49.