Evolution of itch
March 7, 2012 at 10:10 am #16189biohazardParticipant
Every once in a while I have been wondering what makes an itch so annoying you just have to scratch it (and often it goes away after you have simply clawed it for a second or two, quite unlike what happens with pain). Now I need you guys to help me to figure out the evolutionary reasons behind itching.
To be more specific, I’m interested in "point itch", that is, a hair tickles your face or an ant runs down your arm – something local caused by an external factor. Persistent itching in some general area (like your nose during the allergy season or atopic dermatitis or dry skin etc. etc.) are not relevant, because the reason for those is quite likely just a side effect of the release of histamine and other such cellular mediators – and in any case the etiology of the problem is entirely different.
But back to the original problem. Quite obviously itching, unlike pain, is not a signal of acute tissue damage or the risk of it. It is easy to understand why pain requires immediate attention, because ignoring it may cause severe tissue injury and even death. However, a fly landing on your thigh while your are sunbathing hardly causes damage, but you are very likely to react to it by scratching or touching the site where the fly landed. And many times the itching sensation just won’t go away before you have manually dealt with it, even if the fly causing it has already gone away!
So my theory is that itching, from the evolutionary point of view, is a form of protection against arthropods and other similar, small creatures. The main reason for that is not that a handful of them are poisonous (only very few are poisonous enough to cause serious damage, and smacking a poisonous insect like a wasp is a bad idea anyway, since it usually just provokes a painful sting). What I think instead is that many arthropods are parasitic themselves, or carry other parasites or diseases with them, which are then easily to transmitted to humans if not dealt with fast enough. So I assume that things that cause itching are very similar in force and movement pattern etc. to that of an insect landing on or walking around your skin or hair. And the reflex of touching and scratching that site has evolved to drive off the potentially-nasty bug before it has time to bite or lay eggs or do other unwanted stuff.
So, all this may or may not make prefect sense and seem obvious, but my real question is: has anyone actually proved itching to protect us from arthropods or perhaps something else? Or is the reason something completely different that I have managed to miss?
And yes, I did take a look at Wikipedia, but the related article is not exactly one of Wikipedia’s finest and does not seem to have any information regarding the evolutionary reasons of the phenomenon in question.
March 9, 2012 at 12:58 am #110046DarbyParticipant
The question every evolutionary explanation dreads: how would you test your hypothesis?
March 9, 2012 at 7:18 am #110050biohazardParticipantquote Darby:
With knockout mice, obviously!! 😀
March 15, 2012 at 2:42 am #110161kukuhParticipant
good moorning , excuse me… I’m new member in this forum… and I’m not biologist, I from technic.
today I want to disscus about SPONTANEOUS EVOLUTIONARY, because my final project have relation about it. may be, can you help me to understand, what is spontaneous evolutionary and what is algorithm from it?
thank you very much for your regard.
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