Scratching and biting helps furred animals dispose parasite insects from their surface. Is it a productive action for humans who have less fur, have hands that can pinch off parasites and can help each other out?

If evolution were perfect, humans would never scratch, and to resort to pinching off any actual parasites - scratching and biting could break skin and expose it to germs.

  • $\begingroup$ What? Humans keep scratching not as vestigial reaction but as environmental response. $\endgroup$
    – Billeeb
    Nov 29, 2017 at 15:37
  • $\begingroup$ These two idioms imply a very long history of scratching: scratching one's head; scratching someone's back. $\endgroup$
    – user37894
    Nov 29, 2017 at 19:32
  • 1
    $\begingroup$ Scratching is a response to itching. Pinching an itch doesn't work nearly as well to relieve the itch. And at least in much of the technically-advanced world, itching is not caused by parasites. (Not limited to humans: both my dogs and horses like being scratched, despite no obvious signs of parasites.) $\endgroup$
    – jamesqf
    Nov 29, 2017 at 19:39

1 Answer 1


Humans usually scratch to stop itches. Because scratches are a more high-priority sensation than the itch, the nerves stop transmitting the itch signals to your brain for a while.


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