Why is this monkey's butt blue and mine isn't?

One of my daily tasks is to restore ancient animals. The most difficult part of my work is to restore the color and texture of animals. I often look through modern animal data as a reference for restoration. As a result, I found that among vertebrates, mammals have the most regular and conservative colors - all black, white, gray and earth tones , without the colorful patterns of birds and reptiles.

However, when further sorting out the data, it was found that although most mammals have a limited range of body colors, they can evolve a wide variety of fur color combinations and texture combinations . Even animals of the same species can have a large number of different fur colors. For example, cats have orange cats, cow cats, calico cats...

How do mammals use a limited palette of body colors to come up with so many different colors? This is very interesting.

Simple mammal

The fur color of mammals depends on the pigment in the cortex or medulla cells of the hair. Mammals have only two types of melanin, eumelanin and pheomelanin . Eumelanin can make the hair appear black and brown, while pheomelanin can make the hair appear red and yellow. These two types of melanin plus the influence of the albino gene give rise to the three basic fur colors of mammals: black, brown, and white .

Most mammals have fairly plain colors | Pixabay

The two melanin and albinism genes, through further combination of distribution patterns and quantity differences, present the three basic colors commonly seen in mammals: orange, gold, khaki, brown, chestnut, brown, grayish white, etc., as well as spots and stripes in different forms.

Since mammals lack chlorophyll and the crystals in their epidermal cells cannot diffract blue light, mammalian fur cannot have the bright colors of blue, green, and purple that are common in amphibians, reptiles, and birds. But this is not a big problem, because most mammals do not have a strong ability to distinguish colors - except for primates, most mammals have only two types of cone cells, and almost all of them are red-green color blind. Therefore, whether it is the evolution of their fur or the need for survival, mammals do not have other colors other than the three basic colors.

But someone will certainly object: mammals also have green and blue colors, such as sloths.

Some sloths in South America do look green, but that's because of the growth of green algae on their wet fur, not because of the fur itself. Similarly, polar bears kept in zoos may become "green bears" because of algae on their fur.

The sloth's fur has a pale green tint, which helps it camouflage itself | henryalien / Flickr

Some people may also think that many dolphins are blue, dark blue, dark blue, and gray blue. Isn’t there a whale called the blue whale ?

From certain angles, we may indeed see them appearing blue in one way or another, but in fact, their skin is black or gray, and it is just that the refraction of light from the sea water and the influence of sunlight may cause visual errors. Although the word "blue" is in the name of blue whales, they are actually lead gray or steel gray, but the influence of sea water often gives people the wrong impression of steel blue.

Blue whales are not actually blue! Your eyes are deceiving you! | NOAA

Mysterious blue

However, there are always one or two exceptions, and there are also a few brightly colored groups among mammals.

The first exception is primates , which have three types of cones and can distinguish more colors. Among primates, some species have parts of their bodies that appear bright blue , such as the testicles of green monkeys (Chlorocebus pygerythrus) and red monkeys (Erythrocebus patas). The exposed skin on the buttocks of male mandrills (Mandrillus sphinx) also appears in different shades of blue, and even the cheeks are blue.

The brightly coloured eggs of a green monkey | Bernard DUPONT / wikimedia

These blue patches of skin have neatly arranged differences in the collagen fibers underneath, which creates structural color and brings a blue color that is rare in mammals. The darker the blue, the more favored they are by females and the higher their status in society.

Mandrill blue butt | Jean / wikimedia

Calendar Girl's Tips

The bright blue shimmers on bird feathers, most reptile scales, and insect wings are all structural colors. However, the blue-footed booby's feet are blue because of the pigments in its food. If its feet are not blue, it means it is malnourished and will be disliked by other blue-footed boobies.

Blue-footed booby: You're bluer, you're amazing | SantiagoGG / Wikipedia Commons

Another exception is the bluebuck (Hippotragus leucophaeus) of southwestern Africa, which became extinct between 1799 and 1800 due to hunting and grazing by European colonists. Various early records and personal accounts indicate that the bluebuck had a lustrous coat with distinct pale blue, blue-grey, or even very bright blue.

The picture of the bluebuck appears gray-blue | wikimedia

However, the four fur specimens currently preserved in museums in Leiden, Stockholm, Paris and Vienna all show a dull grayish yellow or earthy yellow color , which is so different from the records in the literature that many people doubt whether they are really blue.

The specimen of the bluebuck is a plain earthy yellow | Shagshag / wikimedia

Currently, the more reliable explanation is that the black and yellow hair of the bluebuck refracts sunlight, causing the fur to look blue. When the animal dies, the eumelanin fades over a long period of time due to chemical instability, and the fur can no longer reflect blue, and may even fade further. The magical blue animal that has lost its life has become a dull khaki color.

Unfortunately, we can no longer see the blue antelope.

Author: Ammonite

Editor: pee pee shrimp

This article comes from the Species Calendar, welcome to forward

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