Question: If chimps and monkeys are born with a full coat of hair (and they are the most similar animal to us) then why are we not born with a full coat of hair?

Lewis Dean answered on 21 Mar 2014:

That’s a really interesting question and there are many theories about it, however, it is something that we don’t really know the answer to yet.

Some people think that it may be to do with us standing on two legs – we have kept the hair on our head to protect us from the sun, but the rest of our bodies don’t need the same protection from the sun, because our body is upright (of course, we do still get sunburnt even though we are upright!).

Another theory is that perhaps at some point in our history maybe the less hairy people got fewer ticks and fleas (and other parasites) and so were healthier and able to survive and have more children. So there would have been more of their (less hairy) children in the next generation and eventually all the humans would have been less hairy.

The honest answer is that we don’t know exactly why this happened. It is a very interesting aspect of humans.