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Why do hair continuously grow on human heads, while the same doesn't happen on other parts of the human body? Where there are hair, they only usually grow to a fixed length; but they seem to have no limit (or at least a much higher limit) as long as the head is concerned (and the face, in men).

Why does this only happen on humans? When did it start happening? What kind of evolutionary advantage could there be in overly-long head hair, so that humans have them while other primates and mammals don't?


I know there are various questions around about why humans have much less body hair than other mammals; mine is related but different: why are we the only species with so much hair on our head, to the point that they might even become inconvenient if we don't cut them?

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marked as duplicate by WYSIWYG Jun 26 '15 at 18:11

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    $\begingroup$ There is a limit on hair growth - biology.stackexchange.com/questions/1267/… As for the rest of your question, we still haven't found the "missing link" in human evolution, so we can't really say "when" because we don't know the stages in-between. As for advantages and disadvantages, well, that seems like it might be more opinion based as I don't know if we can ever know for sure "why". $\endgroup$ – SolarLunix Jun 26 '15 at 17:28
  • $\begingroup$ Thanks for pointing that out; however, even if waist-long hair is the limit for most people (and I know for sure there are exceptions to this rule), the question still stands: why does this only happen on human heads? $\endgroup$ – Massimo Jun 26 '15 at 17:30
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    $\begingroup$ @SolarLunix there is no such thing as the "missing link". It's a fallacy dating back to the ancient Greeks, and used by creationists to attempt to disprove evolution. Look it up. $\endgroup$ – MattDMo Jun 26 '15 at 17:32
  • $\begingroup$ @Massimo Actually, it doesn't really only happen in humans. If you look at a lot of long hair breeds of dogs, there are some that need CONSTANT attention or their coats will become too long and get in their way. As for why it started, that's more of an opinion based thing, it could've been a mutation, or it could've started and continued due to a mating preference. $\endgroup$ – SolarLunix Jun 26 '15 at 17:34
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    $\begingroup$ The above comments were a suggested edit to the Q, but I think they fit better as comments, since the edit wasn't a rewrite of the Q but rather suggestions or an alternative perspective. $\endgroup$ – fileunderwater Mar 20 '18 at 21:10