• Question: Why do we only grow long hairs on our heads?

    Asked by meg123 to Amy, Karen, Sarah, Will on 20 Jun 2012.
    • Photo: Karen Reed

      Karen Reed answered on 20 Jun 2012:

      Hiya Meg – I like this question – but don’t know the answer. MY guess is the hair folicale cells (where the hair grows from) are different on our scalp and more adapt at growing longer hairs – but anther good question is how do those cells know how long the hair is – so why for example aren’t the leg hairs long – maybe they’ve got pressure sensors in them and stop growing when the pressure from the hair reaches a certain level. I don’t know – good question – if you find out the answer let me know

    • Photo: Amy Birch

      Amy Birch answered on 20 Jun 2012:

      Hi meg,
      This is another great question!
      The ancestors of humans would have had hair all over their body like apes and monkeys, and this would protect them from the sun & also keep them warm in the winter. So really the question is, why did we stop growing lots of hair all over our bodies?

      One theory about this is that as the climate changed, our ancestors lost their hair so that they could cool down more efficiently by sweating. Around this time, our ancestors also evolved to walk upright instead on all fours and so the most exposed part of the body to the sun was the head, so they kept hair on their head to protect against the sun’s UV radiation.

      Another theory is that we lost our hair in response to parasites! If we have less hair then parasites like fleas and lice are less able to stay on our bodies and therefore we would get less diseases. But that doesn’t fully explain why we still have hair on our head so I prefer the 1st explanation 🙂

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