# Why no blue human hair? **URL:** \ **Category:** Cecil's Columns/Staff Reports\ **Created:** [December 28, 2009, 5:21pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812 "2009-12-28T17:21:17Z")\ **Posts on this page:** 11\ **Page:** 2
**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\ **Post date:** [January 4, 2010, 11:40pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/21 "2010-01-04T23:40:02Z")
What gives blueberries their color? It’s the one naturally blue food that jumps to mind. ---
**Author:** ![Silvermink](https://avatars.discourse-cdn.com/v4/letter/s/c37758/32.png) [@Silvermink](https://boards.straightdope.com/u/Silvermink)\ **Post date:** [January 5, 2010, 4:15pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/22 "2010-01-05T16:15:35Z")
> [@MEBuckner](#): > > First off, I don’t know if anyone has come up with any clever ways to test the hypothesis that sloths have evolved to “purposefully” cultivate the algae in their fur in order to aid in camouflage. But as to the question “Why aren’t other animals sporting algae camouflage?”–you could also ask why don’t sloths just sprint really fast and outrun the jaguars, or grow big spines on their backs, or grow wings and fly away. There are lots of ways to be successful in the great game of life; sloths do so by being slow, not using much energy, being hard to see, and as a last resort having pretty powerful claws. > > (You could test whether or not the algae actually _aids_ in camouflage: Get a bunch of sloths and tag them all with radio collars so you can keep track of them. Give half of them a good shampooing. See if the now algae-free sloths are more likely to be eaten by jaguars. Probably give the control group a good rub-down with something that doesn’t actually get rid of the algae, just in case the whole experience of being captured and messed around with by scary fast bipeds freaks out sloths so badly they become suicidally depressed and deliberately seek out jaguars in order to end it all. Whether nor not anyone has bothered to do this I don’t know, and even if experiment showed that algae actually aid in camouflage I guess you could still argue over whether this is just a lucky break for the sloths or something they have actually evolved to encourage.) Isn’t it the very nature of Natural Selection that lucky breaks and favorable mutations are encouraged to evolve by allowing creatures to survive and reproduce easier? As for Blue dye, it makes me wonder why companies use products that are 95% undigestable in their food. I really should read ingredient lists better. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [January 5, 2010, 7:04pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/23 "2010-01-05T19:04:43Z")
Because those products are non-toxic and non-absorbed by the body, so they are harmless, and they aid in the palatability of the product in some way (texture, taste, appearance)? And they’re cheap? **MEBuckner** said: > [@](#): > > First off, I don’t know if anyone has come up with any clever ways to test the hypothesis that sloths have evolved to “purposefully” cultivate the algae in their fur in order to aid in camouflage. As I said, if you catch sloths applying algae to their bodies (or each other), that might indicate the intentional use of camoflage. But what I suspect you will find is just that the algae accumulates there naturally. So sloths with algae may survive better, which would have provided a selection pressure on sloths that were good environments for algae over sloths that were less hospitable (ones that scratched themselves a lot?). Algae may be providing camoflage the helps the sloth survival, but that is a far cry from saying sloths _use_ algae for camoflage. **Silvermink** said: > [@](#): > > Isn’t it the very nature of Natural Selection that lucky breaks and favorable mutations are encouraged to evolve by allowing creatures to survive and reproduce easier? I wouldn’t use the word “encourage”. But I would say that Natural Selection is a process where lucky breaks and favorable mutations that allow creatures to survive and reproduce easier are thereby spread within the population. ---
**Author:** ![DSYoungEsq](https://avatars.discourse-cdn.com/v4/letter/d/c6cbf5/32.png) [@DSYoungEsq](https://boards.straightdope.com/u/DSYoungEsq)\ **Post date:** [January 5, 2010, 11:59pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/24 "2010-01-05T23:59:12Z")
> [@Irishman](#): > > As I said, if you catch sloths applying algae to their bodies (or each other), that might indicate the intentional use of camoflage. But what I suspect you will find is just that the algae accumulates there naturally. So sloths with algae may survive better, which would have provided a selection pressure on sloths that were good environments for algae over sloths that were less hospitable (ones that scratched themselves a lot?). Algae may be providing camoflage the helps the sloth survival, but that is a far cry from saying sloths _use_ algae for camoflage. I agree. It’s also a far cry from saying that the algae is there because it provides the purported benefit. It may be there simply because it grows there, and it isn’t a detriment. After all, something that isn’t detrimental (relatively speaking) to the survival of the grandchildren of the species isn’t weeded out by natural selection. ---
**Author:** ![MEBuckner](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mebuckner/32/2896_2.png) [@MEBuckner](https://boards.straightdope.com/u/MEBuckner)\ **Post date:** [January 6, 2010, 1:33am UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/25 "2010-01-06T01:33:16Z")
In addition to behavioral adaptations from the sloths (rubbing algae all over themselves), it’s also possible there is some anatomical adaptation, i.e., sloth hair has evolved to be particularly well-suited to being a home for algae by being shaped in a particular way (as suggested by **qazwart** above). ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [January 6, 2010, 5:06pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/26 "2010-01-06T17:06:56Z")
Yes, that might be an idication that sloths that have algae are eaten less than sloths that don’t, so sloths that were particularly conducive to algae growth survived better (have hollow spots, hair that holds algae well, etc). Those would be evolutionary changes to support the algae-sloth symbiosis. But not indicators of sloths intentionally using algae as camoflage. **DSYoungEsq** said: > [@](#): > > It may be there simply because it grows there, and it isn’t a detriment. Yes, if there is no difference to the sloths between having algae and not having algae, the algae might still become prevalent just because it can. ---
**Author:** ![Irishman](https://avatars.discourse-cdn.com/v4/letter/i/b487fb/32.png) [@Irishman](https://boards.straightdope.com/u/Irishman)\ **Post date:** [January 6, 2010, 5:16pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/27 "2010-01-06T17:16:29Z")
**DSYoungEsq** said: > [@](#): > > You are joking, right? You do realize that reading a summary paragraph in an abstract of an article is hardly the equivalent of reading the article to understand what it actually concludes, the basis for that conclusion, and the validity of making that conclusion? Yes, but I wasn’t citing the article for the detailed explanation of the structure that causes the effect. I was citing the first paragraph, which is the statement: > [@](#): > > The pigment colors are black, brown, red, yellow, and in a few cases green, while the blues, whites, some of the greens and metallic and iridescent colors are due to structure. **These facts are accepted by biologists and have been worked out by them and by physicists.** Bolding added. That confirmed the answer to the question asked. Why that cite and not something else? Because that’s what google found that stated the answer. Could a different cite have addressed the question asked in more detail? Perhaps, but this is what I found and it answered the question adequately. So no, there was no need to actually read the full article and find out whether they actually discovered particular structures to the feathers and such that cause the coloration. The quoted material was sufficient. And the reason I didn’t quote it in the first place was because I couldn’t copy and paste, but had to type by hand. So I put the link to the page where y’all could read it for yourself, rather than type it out. I guess that didn’t work. ---
**Author:** ![lissener](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lissener/32/6139_2.png) [@lissener](https://boards.straightdope.com/u/lissener)\ **Post date:** [January 7, 2010, 12:58am UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/28 "2010-01-07T00:58:27Z")
> [@Tastes\_of\_Chocolate](#): > > What gives blueberries their color? It’s the one naturally blue food that jumps to mind. Blueberries are actually a dark purple-red. There’s a whitish bloom that causes them to look blue. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [January 7, 2010, 2:02am UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/29 "2010-01-07T02:02:36Z")
> [@Irishman](#): > > Yes, but I wasn’t citing the article for the detailed explanation of the structure that causes the effect. I was citing the first paragraph, which is the statement: > That confirmed the answer to the question asked. Why that cite and not something else? Because that’s what google found that stated the answer. Could a different cite have addressed the question asked in more detail? Perhaps, but this is what I found and it answered the question adequately. So no, there was no need to actually read the full article and find out whether they actually discovered particular structures to the feathers and such that cause the coloration. The quoted material was sufficient. > > And the reason I didn’t quote it in the first place was because I couldn’t copy and paste, but had to type by hand. So I put the link to the page where y’all could read it for yourself, rather than type it out. I guess that didn’t work. I have the full PDF if there is other info within the body of the article someone needs looking up. I cannot mail the PDF itself to anyone because my name isn’t Anne Bonny. ---
**Author:** ![Malleus\_Incus\_Stapes](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/malleus_incus_stapes/32/3293_2.png) [@Malleus\_Incus\_Stapes](https://boards.straightdope.com/u/Malleus_Incus_Stapes)\ **Post date:** [January 7, 2010, 2:14am UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/30 "2010-01-07T02:14:48Z")
> [@Irishman](#): > > Interestingly, the blue in bird feathers isn’t a blue pigment, it is also an optical trick for a darker color. I think there’s one family of birds (in Africa?) that has true blue pigment. ---
**Author:** ![Powers](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@Powers](https://boards.straightdope.com/u/Powers)\ **Post date:** [January 8, 2010, 2:22pm UTC](https://boards.straightdope.com/t/why-no-blue-human-hair/522812/31 "2010-01-08T14:22:02Z")
> [@](#): > > I think there’s one family of birds (in Africa?) that has true blue pigment. No, that’s the African swallow (unladen). You’re thinking of the Norwegian Blue (beautiful plumage!). Powers &8^] [Previous page](https://boards.straightdope.com/t/why-no-blue-human-hair/522812.md?page=1)