Names are rare in nature. Until now, we only knew of four animal species that use names to call other individuals: humans, dolphins, parrots and elephants. But according to a published study in the magazine Sciencethere is another primate that must be included in the list. This is not a great ape, but the common marmoset (Callithrix Jacchus), a small monkey from Brazil that could fit in the palm of our hand.

I must admit that this discovery did not surprise me too much. In 2019 I attended a primatology conference in Oxford. I remember that, of the nine conferences devoted to communication, three were on the marmoset. They all pointed out that these animals had unusual vocalizations, different from those of other primates.

When it comes to vocal communication, humans are more like parrots, elephants or cetaceans than other primates. We are born unable to speak and we acquire this ability through learning. In contrast, primate vocalizations are generally innate and hardly change over the course of their lives. Although we tried several times, we only succeeded in getting a few chimpanzees to learn very simple words like mom. We cannot say that our primate cousins ​​are completely devoid of vocal learning, but it is very limited.

Even vervet monkeys cannot be considered an exception. These animals have gained some fame because they emit an alarm cry when they see a snake, another when they see a leopard and another when they see an eagle. They look like words, as if they symbolize the different predators, but we already know they are not. Vervets are born knowing how to make these calls. Predators simply provoke different types of aversive emotions in them that cause them to emit different alarm calls.

Naming each of the different individuals in a group requires advanced vocal learning ability, because vocalizations must be flexible, capable of being changed, and generating a different sound for each individual in the group. So it’s no surprise that we don’t know of any named non-human primates…until now.

Marmosets have been studied extensively, both in the wild and in the laboratory, because they possess a remarkably complex vocal repertoire. Wild populations use at least 13 different vocalizations. Using cries, whistles and clicks, they mark their territory and warn that they have found food or that predators are in sight. In fact, like vervets, they differentiate between terrestrial and aerial predators.

One of their most common vocalizations is eh call, which is used to locate other individuals. It turns out that marmosets live in small, cohesive groups and are extremely social. In the jungle, the undergrowth sometimes makes it difficult for the group to regroup, so they use eh calls to establish contact dialogues with other members so that they do not get lost. They are considered dialogues because these calls are short and take turns.

The most striking thing in eh the calls are that they requires some learningwhich makes them more flexible. At birth, babies begin to make an immature version of these cries, and through feedback from their parents, they learn to pronounce them correctly. The learning time required varies greatly between individuals and depends largely on the time parents devote to them.

Where learning takes place, there is often also diversity. Several studies indicate that different marmoset populations have dialects and that these variations are not due to living in different environments or genetics. On the contrary, everything indicates that individuals learn from each other. If you move a marmoset from one population to another, it will eventually speak like its new companions.

The so-called eh

Given all this evidence, it is logical to ask whether eh calls vary depending on who they are addressed to, in other words, whether they sound like human names. To find out, a research team from the University of Jerusalem analyzed eh cries of 10 captive marmosets in several experiments.

The basic procedure was as follows: two monkeys were placed in two adjacent transparent enclosures and allowed to see each other briefly before a curtain was placed between them. THE eh the cries emitted by the marmosets were then integrated an artificial intelligence system (Random forest classifiers). This made it possible to detect differences between calls and predict which person they were intended for.

In the next step, they played the recorded calls to the marmosets to see if they responded to their names, and they did. However, each marmoset used a different name to refer to the same individual, even if those in the same group looked very similar. Again, this suggests that marmosets learn from each other.

Why are humans and marmosets the only known primates with vocal learning? Since it has been 40 million years since our lineage split from that of the marmosets, it appears that we are facing a case of convergent evolution. This occurs when the same trait appears independently in two groups of organisms, such as the wings of a butterfly and the wings of a bat. What is interesting is to understand what causes these traits to appear.

Some authors suggest that vocal learning is favored in a cooperative breeding system. Among primates, marmoset society is the only one, other than humans, in which parents and unrelated individuals actively and systematically assist parents in raising their offspring. This is necessary because marmosets always have twins, a very demanding situation from an energetic point of view. Single mothers cannot care for the pair of twins, so everyone in the group helps with transportation and feeding.

In our case, humans engage in cooperative parenting because babies are altricial, i.e. they were born underdeveloped and extremely dependent. For example, the brain of a human baby is only 25% the size of an adult brain, while that of a baby macaque is already 65%. It also means that we are born without the ability to control our voices and that we develop it under the influence of our social environment.

Some studies indicate that human infants who produce vocalizations that more closely resemble human language receive more attention from their caregivers. There is therefore a selective pressure. In this scenario, where there are many potential caregivers, infants compete for more attention. The sooner a baby learns to speak, the better he or she will do.

Interestingly, although marmosets grow twelve times faster than humans, their descendants are also altricial. Due to twin pregnancy, organ formation is delayed during gestation and they are born less developed than most primates. Among other characteristics, this is reflected in the poor locomotor abilities of newborn marmosets.

We therefore find a parallel between humans and marmosets which could have favored the emergence of vocal learning: both are born altricial in a cooperative breeding system where the babies compete for attention. This is a hypothesis and more research is needed for it to be accepted, but it shows very clearly why studying animal behavior is essential to understanding human beings.

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