system
A chat on subreddit /r/NoStupidQuestions
human
We don't know why humans lost their thick hair. 

I have heard a ton of theories on this, but I propose it's because we started using fire. This made hair a liability (flammable) and also made hair no longer essential (warmth).  This may be outdated information, but in my college days there was the idea that women largely tended the domestic area, and thus the fire, and that men roamed farther (thus big ol beards which I can vouch for as warm + protection from injury). 

Anthro profs thought that was as good as any other guess. Genetic science has advanced since then, so not sure. 

We retained hair in places for social purposes. Head for status signalling I guess + sun protection for some. And we keep it in areas for ... scent retaining. Probably sexual pheromones.
gpt
&gt;We don't know why humans lost their thick hair.

Actually, sofar as I know **this is actually solved**, and that the consensus was that it was **to sweat better**. 

Human thermoregulation is actually pretty unique in the animal kingdom - most mammals can only cool themselves through panting, humans have a special mechanism of sweating watery  sweat (rather than oily like most animals) which cools us by evaporating. 

The hair was lost so the water would evaporate even faster. 

This happened more or less at the same time as bipedalism, as an adaptation when our ancestors split from apes &amp; moved to the savannah. 

Early humans were persistence hunters &amp; could follow their prey for very long stretches. Other animals might be faster on short stretches but few animals can keep up with humans in terms of endurance. 

To this day, humans are remarkably good at long-distance walking  - there is little gender difference &amp; even surprisingly old people can keep up with younger ones, because at some point, survival depended on it. (afaik dudes **do** have an advantage when it comes to short distance sprints, though. - on average, fitness level is gonna matter more.)

So, before humans were the smart animal, they were the persistent animal that is super good at keeping cool xD 

Fire came **long after** all that. 

The bit about the sexual pheromones &amp; sun protection is correct, though (it's kept precisely where we have special scent-releasing sweat glands)