Why do Sichuan golden snub-nosed monkeys look so polite, while Tibetan macaques like to "rob"?

Produced by: Science Popularization China

Author: Zhao Xumao (Young Researcher, Lanzhou University)

Producer: China Science Expo

Recently, a video went viral online: A Sichuan golden snub-nosed monkey in Shaanxi sat on the side of the road watching people coming and going. When a tourist offered it an apple, it politely took it. It would rather eat leaves than take the tourists' food. Netizens couldn't help but sigh: This monkey is really polite, it really deserves to be the aristocrat among monkeys.

When people praise the polite behavior of Sichuan golden snub-nosed monkeys, they also make fun of the Tibetan macaques on a certain mountain. The Tibetan macaques are ferocious and rude. Once they enter the scenic area, they will rob food at the least and attack humans at the worst. Compared with the Sichuan golden snub-nosed monkeys, people can't help but sigh: They are both monkeys, but why is there such a big difference?

Sichuan golden monkey

Image source: Photographed by Zhao Xumao

This is no ordinary monkey.

What we need to understand is that whether it is the polite Sichuan golden snub-nosed monkey or the arrogant Tibetan macaque in the video, their behavior is no longer the nature of monkeys, but a group of monkeys habituated to humans.

The so-called habituation means getting animals used to the presence of humans. Both Sichuan golden snub-nosed monkeys and Tibetan macaques are very afraid of humans in the wild, and they regard humans as their natural enemies.

For example, once the Yunnan snub-nosed monkeys in the wild discover humans, they will immediately send out an alarm call of "Jia-jia-jia", and then the group will immediately move, just like how they would behave when encountering a natural enemy.

This also brings a problem: in the wild, it is very difficult for humans to get close to wild monkeys. In order to track and study monkeys for a long time, scientists must first find a way to get the monkeys accustomed to the presence of humans, which requires sending one or two people to track the monkeys for a long time.

At the beginning, the monkeys still avoided humans. After a long time, the monkeys found that humans did not harm them, so they gradually got used to the existence of humans. This is the process of habituation of the monkeys. After habituation, the monkeys are no longer afraid of humans. The monkeys in the scenic area belong to this type.

Sichuan golden monkey

Image source: Photographed by Zhao Xumao

They are both monkeys, why are there such big differences?

So why do Sichuan golden snub-nosed monkeys and Tibetan macaques, both of which are habituated monkeys, behave differently?

This first starts with the eating habits of the two.

In the video, a netizen said: "The Sichuan golden snub-nosed monkey would rather eat leaves than take the initiative to reach out to grab tourists' food." This sentence vividly summarizes the habits of the Sichuan golden snub-nosed monkey. The Sichuan golden snub-nosed monkey belongs to the genus Snub-nosed monkey of the subfamily Colobinae of the family Monkeyidae. Monkeys in this subfamily are usually herbivorous.

In order to digest plant fiber, Sichuan golden snub-nosed monkeys independently developed a complex stomach similar to that of ruminants, and their intestinal microorganisms may be involved in the fermentation and digestion of cellulose. In the long-term adaptive evolution of herbivory, Sichuan golden snub-nosed monkeys can eliminate the toxicity of plant secondary metabolites, and their olfactory genes are good at sensing the smell of fruits and plants.

On the other hand, the Tibetan macaque belongs to the genus Macaca, subfamily Cephalopodidae, and is the largest of the genus Macaca. Most of the individuals of the genus Macaca are omnivorous animals. Among them, the Tibetan macaque has a complex diet, usually mainly branches, leaves, fruits, roots, etc., and also eats some insects.

Tibetan macaque

Image source: Photographed by Lu Qianle

In addition, the social structure of Sichuan golden snub-nosed monkeys is also different from that of Tibetan macaques. Compared with the polygamous social structure of Tibetan macaques, Sichuan golden snub-nosed monkeys belong to a multi-layered society, which is a relatively advanced social structure among primates.

Specifically, multiple one-male-multiple-female units and one all-male unit form a team, and multiple teams form a monkey group. This social structure is relatively stable, and in the non-breeding group, the competition pressure on individuals is relatively small.

Why do Tibetan macaques always like to steal people’s things?

After habituation, they should be friendly to humans. Why are there so many news reports of Tibetan macaques robbing humans? In fact, monkeys rob humans out of helplessness. Monkeys generally meet two conditions when they rob humans:

First, they are close to humans. This is easy to understand. Monkeys living in the deep mountains and forests never see humans, so how can they rob humans?

Second, the proportion of young monkeys in the monkey group is relatively high. Monkey groups are divided into levels, and this level is generally manifested in two ways: one is the right to mate; the other is the right to possess food. The former is basically irrelevant to humans, so we will focus on the latter.

Young monkeys have a relatively low status in the monkey group, which is reflected in their food rights - they are not qualified to forage for food in places with the most abundant food because those places are occupied by higher-level individuals.

There is an old Chinese saying that goes, "When you are poor, you will think of change." When these young monkeys do not have the opportunity to enjoy abundant food, they often have a "pioneering spirit" and find new sources of food. At this time, coupled with the first condition, some monkeys will set their sights on human food, and then monkeys will rob humans.

Of course, robbery is not that easy. We have seen such scenes in many places: Tibetan macaques dare to rob tourists, but immediately run away when they see the forest rangers in uniform. This is probably a learned behavior of the monkeys.

There is a compensation hypothesis for learning behavior, that is, when learning a new behavior can bring more benefits than the original behavior, then people are willing to learn it. For example, when monkeys rob tourists' food, tourists generally dare not resist. The reward for this behavior is much higher than finding food in the wild, so this behavior will continue.

On the contrary, when monkeys rob forest rangers, they not only fail to get food but also get beaten. The benefits they get are far lower than foraging in the wild, so they will not rob forest rangers.

Tibetan macaque saluting

Image source: Photographed by Zhao Xumao

Of course, not all Tibetan macaques are so barbaric. There is a Tibetan macaque in Sichuan that can salute. When it salutes tourists, it can get food, which becomes an incentive. Over time, it salutes tourists.

To put it bluntly, whether it's saluting or robbing, everyone is just trying to survive! Life is not easy, so cherish every moment of it!

Editor: Wang Tingting

References:

Zhou X et al. 2016. Whole-genome sequencing of the snub-nosed monkey provides insights into folivory and evolutionary history. Nat Genet. 2014 Dec;46(12):1303-10.