Why don’t mammals ever have green or blue hair? I mean, the pigments are certainly found in the external coverings of other animals (cf. this as an example). Does it have something to do with the “fact”(–?) most mammals are color-blind (but of course, humans aren’t color blind)?
Thank you in advance to all who reply:)
Some sloths have blue-green fur. But I believe it some kind of bacteria growing on their fur.
It’s not hair, but the Mandrill is a very brightly colored mammal.
I think camouflage vs. sexual attraction is a big factor. Birds don’t need to avoid predation as much as mammals in general. That doesn’t explain everything though. You would expect some green or blue monkeys in the Amazon on that basis.
Another factor is the better olfactory senses of mammals that make visual distinction less important.
In summary; blue/green pigments (in the technical sense of the word) are actually quite rare in the animal kingdom, as the conjugated structures that typically create color can’t really interact with photons as low-energy as green and blue. It’s an organic chemistry thing. Yellowish and orangey things are much easier, see: gasoline, carrots, and autumn leaves.
These hues are more often created using physical, rather than chemical, structures, in which lots of tiny interwoven structures create color by either scattering the light, which results in blue via the same mechanism that creates a blue sky (blue scatters more, basically) or by bouncing it around in what are essentially diffraction gratings.
ETA: I should probably mention that while purely organic structures aren’t capable (to my knowledge) of rendering blue/green pigments, adding transition metals simplifies things significantly - copper in particular is famous for its blue color, and is responsible for cyanoglobin, which creates blue blood in creatures like octopi.
Sorry - that should be HIGH energy photons (ULTRAviolet and all that). My bad.
As IST notes, blues and greens are mainly structural colors. It may be that mammalian hair does not easily lend itself to the kind of structures that produce such colors compared to scales and feathers. And the fact that most mammals with the exception of some primates lack good color vision may also be involved.
It’s algae.
I thought I had heard algae before, but wasn’t sure, and did recall hearing about bacteria. So I’ve just checked Wikipedia (far from indisputable), and here it reports there is cyanobacteria on the fur.. It doesn’t say this is responsible for coloring, but does call it camouflage. Do you have any info to clear this up? I’m just kind of curious.
Colorblind in this context does not mean “only sees black and white.” The form of colorblindness possessed by most mammals means that they can easily distinguish most forms of green vs. blue, so that distinction is not lost.
One theory is that the more colorful primate species tend to be the ones with “full” three-cone color vision. The Mandrill is a Old World monkey, and all of these are not colorblind and tend to be colorful, or especially have faces that have less fur. Many New World monkeys have less colorful, hairy faces, and are almost all colorblind (with one species being an exception, and the females of many other species sometimes are not colorblind for complex reasons).
Cyanobacteria is often referred to as “blue-green algae.” So technically you’re both right.
Others have implied it but nobody’s said it directly: there is no blue pigment in the photo that the OP uses as an example of blue pigment. If you crushed up those feathers, you’d end up with a lot of greyish dust.
According tothis article, the color is mostly due to green algae, which are eukaryotes, although cyanobacteria/“blue-green algae” also are known to occur.
Thanks, both of you. Interesting tidbit.
And virtually the only green pigment found in bird feathers is turacoverdin, found mostly in the African turacos.
I remember reading something very similar about one or two species of African birds with blue pigment. Huh.