2arrs, 2ells - A spot on your arm is sending signals to your...

23rd January 2010

Quote reblogged from Neven Mrgan's tumbl with 18 notes

A spot on your arm is sending signals to your brain. There is an upset area of your epidermis wanting attention. You reach for it without thinking, and you scratch, nails digging into skin repeatedly. Why? It feels better, sometimes; sometimes it doesn’t. It’s addictive, somehow. Why?

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Neven Mrgan’s tumbl: Scratching

Neven would make an excellent evolutionary biologist/psychologist.

His argument (scratching is a non-adaptive extension of an adaptive “touch is good” urge) raises the important points in a thoughtful way (i.e. identifying the difference between “it feels good,” a proximate explanation, and the more satisfying ultimate explanation “why does it feel good?”).

My hunch is that the scratching urge is adaptive on the whole. Neven underestimates the benefit to removing bugs/thorns/etc, possibly because these nuisances are much less in our clothed world. But to our evolutionary ancestors, ticks, leeches, and who knows what other kinds of pests and parasites would have been a much bigger problem. Chimps, our closest relatives, spend significant time grooming each other and removing these kinds of critters. Similarly, splinters, rocks, and thorns could become a significant problem (and a big infection risk) if not removed.

I agree with Neven that the human urge to remove scabs/itch bug bites is likely a nonadaptive extension of an adaptive trait… but I estimate the positive payoff for removing parasites/splinters to be much bigger than that for scratching off a scab + irritating a bug bite.

Tagged: evolution

Source: mrgan