# Evolutionary purpose of itching? **URL:** \ **Category:** Factual Questions\ **Created:** [October 7, 2011, 6:22pm UTC](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920 "2011-10-07T18:22:06Z")\ **Posts on this page:** 6\ **Page:** 2
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [October 8, 2011, 11:37am UTC](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920/21 "2011-10-08T11:37:56Z")
> [@Colibri](#): > > The itch sensation undoubtedly evolved so that we would remove irritants like ectoparasites from the skin, or avoid stinging plants, etc. This is again what I’m talking about. Evolution does not plan things. Something doesn’t mutate so that it can achieve some desired goal. Mutations occur randomly. Randomly. There is no “so.” Evolution occurs because a mutation occurs and survives. It may survive because it’s useful, it may survive because it’s linked to something positive, or it may survive from blind luck. But it is never planned for or done to meet some of goal. There’s no evolutionary committee sitting around voting on what feature to develop next and they don’t throw parties when they come in on time and under budget. ---
**Author:** ![Half\_Man\_Half\_Wit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/half_man_half_wit/32/21766_2.png) [@Half\_Man\_Half\_Wit](https://boards.straightdope.com/u/Half_Man_Half_Wit)\ **Post date:** [October 8, 2011, 12:11pm UTC](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920/22 "2011-10-08T12:11:50Z")
> [@Darth\_Panda](#): > > This is again what I’m talking about. Evolution does not plan things. Something doesn’t mutate so that it can achieve some desired goal. Mutations occur randomly. Randomly. > > There is no “so.” Evolution occurs because a mutation occurs and survives. It may survive because it’s useful, it may survive because it’s linked to something positive, or it may survive from blind luck. But it is never planned for or done to meet some of goal. There’s no evolutionary committee sitting around voting on what feature to develop next and they don’t throw parties when they come in on time and under budget. The minute I saw the thread’s title, the first question that popped into my mind was how many posts it would take for someone to pop up and demonstrate their scholarship by pointing out that evolution does not work like that, mutations are random, and so on. But it’s perfectly valid to talk like **Colibri** did, without attaching any disclaimers – because there’s a reason some mutations survive while others don’t, and that reason is that those mutations are selected for, i.e. convey an advantage to selective fitness. _Evolution_ does not refer merely to the process of random mutation, but also to the subsequent selection of these mutations, and the selection occurs for a reason; and thus, so does evolution. That does not mean that evolution plans ahead, or has a goal; but still, the itch evolved, i.e. was selected for, _because_ it conferred an advantage, i.e. the random mutation giving rise to itchiness was selected for because organisms possessing it had a greater chance at successful reproduction due to being able to recognize and remove potentially harmful parasites earlier and with greater precision. ---
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [October 8, 2011, 12:18pm UTC](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920/23 "2011-10-08T12:18:49Z")
> [@Half\_Man\_Half\_Wit](#): > > The minute I saw the thread’s title, the first question that popped into my mind was how many posts it would take for someone to pop up and demonstrate their scholarship by pointing out that evolution does not work like that, mutations are random, and so on. But it’s perfectly valid to talk like **Colibri** did, without attaching any disclaimers – because there’s a reason some mutations survive while others don’t, and that reason is that those mutations are selected for, i.e. convey an advantage to selective fitness. _Evolution_ does not refer merely to the process of random mutation, but also to the subsequent selection of these mutations, and the selection occurs for a reason; and thus, so does evolution. That does not mean that evolution plans ahead, or has a goal; but still, the itch evolved, i.e. was selected for, _because_ it conferred an advantage, i.e. the random mutation giving rise to itchiness was selected for because organisms possessing it had a greater chance at successful reproduction due to being able to recognize and remove potentially harmful parasites earlier and with greater precision. As long as people understand the way that you do, it isn’t a problem. I’m just not convinced that everyone does. But I still think that phrases “so that we would” indicate a future tense and are problematic and so to with references to the purpose of evolving things. Traits aren’t selected for because they _can_ do things, they’re selected for because they’re already doing them, helping a critter to either get laid or not die. Or, again, sometimes for no particular reason at all. ---
**Author:** ![Frylock](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@Frylock](https://boards.straightdope.com/u/Frylock)\ **Post date:** [October 8, 2011, 1:11pm UTC](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920/24 "2011-10-08T13:11:38Z")
> [@Darth\_Panda](#): > > I think we’re just using the word “purpose” differently - I was referring to the word in its sense related to “plan” (see 2) while you seem to be referring to its meaning closer to the word “function” (see 5). Both are related to 1, but in this context the use of “exists” or “is done” changes in the meaning of the first definition quite a bit, with the connotations being along the lines of the differences between 2 and 5. > > [http://dictionary.reference.com/browse/purpose](http://dictionary.reference.com/browse/purpose) You’re probably right about using the term in different ways. I meant it in the first sense–the reason for which something exists. Hearts exist because hearts pump blood. To unpack that in not nearly enough detail: hearts exist because past hearts pumped blood, which led to the propagation of the associated genes, which led to the existence of present hearts. (See Ruth Millikan for one philosopher who develops a line like this.) I think that this is by far the best way to talk about evolution, because I think that biological parts having functions is such a plainly obvious fact (at least to most people, if not really to everyone) that when someone starts saying that they _don’t_ have functions the a very likely result is confusion and disbelief. So instead of denying the existence of purpose, we should become more clear about what the purpose of biological parts consists in, and explain how it can arise in the absence of intention. ---
**Author:** ![Darth\_Panda](https://avatars.discourse-cdn.com/v4/letter/d/ee7513/32.png) [@Darth\_Panda](https://boards.straightdope.com/u/Darth_Panda)\ **Post date:** [October 8, 2011, 1:23pm UTC](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920/25 "2011-10-08T13:23:23Z")
> [@Frylock](#): > > So instead of denying the existence of purpose, we should become more clear about what the purpose of biological parts consists in, and explain how it can arise in the absence of intention. That works for me. ---
**Author:** ![Ambivalid](https://avatars.discourse-cdn.com/v4/letter/a/a5b964/32.png) [@Ambivalid](https://boards.straightdope.com/u/Ambivalid)\ **Post date:** [October 8, 2011, 6:51pm UTC](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920/26 "2011-10-08T18:51:14Z")
> [@Half\_Man\_Half\_Wit](#): > > The minute I saw the thread’s title, the first question that popped into my mind was how many posts it would take for someone to pop up and demonstrate their scholarship by pointing out that evolution does not work like that, mutations are random, and so on. But it’s perfectly valid to talk like **Colibri** did, without attaching any disclaimers – because there’s a reason some mutations survive while others don’t, and that reason is that those mutations are selected for, i.e. convey an advantage to selective fitness. _Evolution_ does not refer merely to the process of random mutation, but also to the subsequent selection of these mutations, and the selection occurs for a reason; and thus, so does evolution. That does not mean that evolution plans ahead, or has a goal; but still, the itch evolved, i.e. was selected for, _because_ it conferred an advantage, i.e. the random mutation giving rise to itchiness was selected for because organisms possessing it had a greater chance at successful reproduction due to being able to recognize and remove potentially harmful parasites earlier and with greater precision. Yes, I was guilty of a semantic error in my OP. I _do_ understand this. [Previous page](https://boards.straightdope.com/t/evolutionary-purpose-of-itching/598920.md?page=1)