It’s not that I’m judging by the face, but this monkey looks really weird!

Recently, a monkey has become an Internet celebrity.

This is a black-capped macaque (Sapajus apella) at the Huju Zoo in Shengzhou, Zhejiang. It has a square face and looks just like Grandpa Niu in the movie "Big Ear Tutu".

It’s not that this monkey looks particularly different, black-capped macaques generally look quite unique…

Black-capped monkey | Basile Morin / Wikimedia Commons

Moreover, it seems that many primates have mysteriously funny faces.

Proboscis monkey Nasalis larvatus | Pixabay

Why do monkeys' faces often make us laugh? The answer is simple: primates are animals that look at faces. This "looking at faces" does not refer to beauty or ugliness, but to the fact that primates are very good at "observing words and expressions" and "expressing emotions through their eyes" - conveying information through looking at faces.

The history of face reading

Humpback whales listen to calls, rhinos smell feces, squids change color, spiders fiddle with their webs... Animals have many different ways of communicating, but primates choose to look at faces.

Primates have a long history of facial recognition, and the "Grandpa Cow" monkeys live in the Americas and are quite distantly related to us, but like humans, they can get a lot of important information from looking at faces. Black-capped monkeys can recognize whether the other person's expression is friendly or angry just by looking at an image of the monkey's face.

"Observing people's expressions and colors" requires good color vision. Most mammals are red-color blind. Apes (including us) and some monkeys are trichromatic and can see red, green and blue. Trichromatic vision not only allows us to find red fruits and tender leaves, but also allows us to observe the blood flow on the faces of our peers, and to obtain some important information by looking at whether the other person's face is red or white. It is worth noting that trichromatic vision and facial hairlessness may have evolved at the same time, and a hairless face certainly makes it easier to see the complexion.

Female Japanese macaques (Macaca fuscata) turn red during ovulation, signaling they are fertile | Pixabay

The natural selection pressure of "looking at faces" not only promoted the evolution of brain and vision, but also promoted the generation of more expressive "facial expressions". The richness and diversity of primate faces is second to none among mammals.

Saguinus imperator | Kevin Barret / Flickr

Sulawesi crested macaque Macaca nigra | _paVan_ / Flickr

Vietnamese golden monkey Rhinopithecus avunculus | Quyet Le / Flickr

Owl-faced vervet monkey Cercopithecus hamlyni | Mulhouseville / wikimedia

C. neglectus | Hans Hillewaert / wikimedia

So, what does the monkey’s face “say”?

First, identify similar ones.

A comparative study of more than 100 species of American monkeys shows that if a monkey lives in an environment with other "relatives" of the same genus, and it is relatively "lonely", tends to live alone, or has few companions, then the patterns on its face tend to be more vivid and complex. Lonely monkeys are not easy to meet, so finding a mate becomes a problem; if there are other species of monkeys around, this increases the risk of mismatching. The eye-catching large painted face can help them find their own kind and successfully match.

The strange faces of American monkeys | Santana et al. / Biological Sciences (2012)

Secondly, it is to display the information of a “person”.

The male mandrill (Mandrillus sphinx) has the most peculiar face among primates, with a red nose and blue skin in sharp contrast. The higher the status of the male mandrill, the brighter the color of his face. This is because the highest-ranking mandrills have the highest levels of male hormones. Male hormones can cause peripheral vasodilation, making the mandrill's nose more red. The blue color on both sides of the nose comes from the collagen in the special structure of the mandrill's skin. The more male hormones, the thicker the collagen layer.

The most colorful and bizarre faces among primates | Pixabay

Lipstick and contact lenses

The face not only represents a relatively stable identity, but also conveys rapidly changing information.

The most striking feature of the Yunnan snub-nosed monkeys is their pink lips - they are the only primates with red lips, except for humans. Usually, the lips of male monkeys with spouses and bachelors are similar in color, but during the breeding season, the lips of married men become brighter and the red area increases.

There are two hypotheses to explain this phenomenon: first, the "married man" uses bright red lips to show his status and warn the "bachelor" not to offend his spouse; second, the "married man" attempts to attract female monkeys from other families and gain additional mating opportunities. In the world of Yunnan snub-nosed monkeys, if the husband suddenly starts wearing lipstick, the wife had better be careful.

Normally, there is no difference between the lips of the "husband" and the "bachelor". During the breeding season, the lips of the "husband" suddenly become eye-catching | Grueter et al. / Royal Society open science (2015)

The facial muscles of primates are more complex than those of other mammals, and they can make more expressions. Compared with monkeys, the expressions of apes (including humans) are particularly delicate. This is because there are more slow-twitch muscle fibers in the facial muscles of great apes and humans, which can make slow but more delicate muscle movements.

In addition to the facial muscles, eyebrows, eyes and eyelashes also play a role in "expressing emotions with our eyes". We are accustomed to the fact that the sclera (white of the eye) of humans is white, but the sclera of most mammals is not only not white, but also rarely exposed. White sclera makes the movement of the eyes more eye-catching, allowing us to convey emotions and attention with our eyes.

A chimpanzee's face is expressive, but you can barely see its sclera | Pixabay

Those eyes... were like two balls of black mercury contained in white mercury. When she looked around, even the person sitting in the corner far away felt that Wang Xiaoyu saw me.

——Liu E, The Travels of Lao Can

Humans are so instinctive in recognizing facial expressions and eyes that we not only have a special liking for the faces of our relatives, but we also wishfully believe that some animals that cannot "express emotions with their eyes", and even inanimate objects, have eyes as bright and charming as Wang Xiaoyu. As long as this human instinct remains unchanged, after the "Niu Yeye" monkey, there will be countless more "expressive" Internet celebrities.

Could the next meme be Diodon holocanthus? | Sebas1000 / Wikimedia

Or is it the Aethia cristatella? | PIXNIO

Or a rock on Mars? The "face" in the circle is a hill called Cydonia on Mars. The first photo taken looked like a face, but later photos showed that the "face" was actually the lower left corner. | NASA

References

[1] Santana, Sharlene E., Jessica Lynch Alfaro, and Michael E. Alfaro. "Adaptive evolution of facial color patterns in Neotropical primates." Proceedings of the Royal Society B: Biological Sciences 279.1736 (2012): 2204-2211.

[2] Renoult, Julien P., et al. "The evolution of the multicoloured face of mandrills: insights from the perceptual space of color vision." PLoS One 6.12 (2011): e29117.

[3] Waller, Bridget M., et al. "The face is central to primate multicomponent signals." International Journal of Primatology (2022): 1-17.

[4] Grueter, Cyril C., et al. "Sexually selected lip color indicates male group-holding status in the mating season in a multi-level primate society." Royal Society open science 2.12 (2015): 150490.

Author: Little Wombat

Editor: pee pee shrimp

This article comes from the Species Calendar, welcome to forward

If you need to reprint, please contact [email protected]