From first principles, it seems surprising that a blow to the head would cause unconsciousness rather than just impaired function.

I've heard a lot of analogies to computers -- "Your brain has to reboot." But computers reboot when there is an error because they are explicitly designed to do so, in order to recover and prevent further damage.

So, did we evolve the capacity to get knocked out for similar reasons -- because it helped us recover or prevent further damage? Or is the capacity to get knocked out just an "accident" or an inevitable consequence of the way our brains are designed, without a good evolutionary explanation?

(I realize the answer might be: "we don't know". In that case, I'd wonder what the prevailing opinions are and what if anything we've ruled out).

  • $\begingroup$ peripheral nerves also do this, when touched (eg in surgery) they completely stop working for some time $\endgroup$ – Filipe Rocha May 20 '17 at 16:07
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    $\begingroup$ It is worth noting a blow to the head causes unconsciousness by doing enough damage to the brain to disrupt its function, a knockout is a concussion. This is why knocking someone out is actually very difficult and very risky. The movie knockout is a myth. We did not evolve to be knocked any more than we evolved to go into cardiac arrest. $\endgroup$ – John May 21 '17 at 17:47


We did not evolve in order to become knocked out. See the wikipedia link. The "water" in the head is designed to not make us get knocked out that easily. However each dampening system has a limit.


Some goats faint due to fear (https://en.wikipedia.org/wiki/Fainting_goat). This is possibly to "play dead," to basically concede to the source of the fear. There is some indication this might occur in humans who pass out due to fear (i.e., humans who pass out at the sight of blood). Maybe this is related to falling unconscious due to injury?

  • $\begingroup$ This seems feasible. If a group of related primitive humans were attacked by a predator, the first of them to get hit could be knocked out and occupy the attention of the predator (e.g. get eaten by a lion) while the rest of the group could run off (and stay safe to carry the gene for getting knocked out). $\endgroup$ – Jam May 22 '17 at 0:23
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    $\begingroup$ Downvoted since this is purely speculation and just-so stories. $\endgroup$ – iayork May 22 '17 at 12:17
  • $\begingroup$ So, what's the line between speculation / just-so-story and...something else? $\endgroup$ – sterid May 22 '17 at 19:09
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    $\begingroup$ "I think this is the kind of speculation that the site should encourage" It's sloppy thinking based on ignorance of evolution and a broad misunderstanding of science. It's pseudoscientific gibberish. I don't think it should be encouraged. $\endgroup$ – iayork May 23 '17 at 12:13
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    $\begingroup$ The request for elaboration is related specifically to your comment and it would be superfluous to start a new question just to ask about that. $\endgroup$ – sterid May 23 '17 at 17:45

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