A study published in iScience reveals the existence of social traditions in vervet monkeys. Until now, most of the traditions described in animals have been of a technical nature, such as the use of tools or food. However, there are very few examples in the social domain. This study, carried out over nine consecutive years, suggests that a wide variety of basic behavioral traditions form the basis of animal cultures.
Numerous examples of traditions, mainly related to food or the use of tools, have been described in various animal species such as birds and primates, but relatively few traditions belonging to the social domain have been described. In a study published in iScienceThe scientists have demonstrated the existence of a social tradition, i.e. a habit that is transmitted under social rather than ecological or genetic influence, within three groups of vervet monkeys from the same wild population.
The iNkawu Vervet Project has been running since 2010, and every day, scientists follow groups of monkeys from morning to night, identifying each individual, observing them and noting a large number of affiliative behaviors, such as playing, sitting side by side and grooming, as well as agonistic behaviors such as conflict. Vervet monkeys, a monkey species found from the Sahel to South Africa, live in multi-male-multifemale groups ranging from a dozen to around 80 individuals. Females stay with their group all their lives, forming its social core. Males, on the other hand, leave their natal group when they reach sexual maturity and leave to join a new group. Over the course of their lives, they will migrate several times to other groups.
A process of behavioral mimicry acting as a social glue
Over 84,702 social interactions collected ad libitum (a behavior is recorded each time it is observed) were analyzed between 2012 and 2020 on 247 monkeys. Several indices were measured: a sociality index estimating the propensity of individuals to be rather affiliative or agonistic, an index measuring reciprocity in their delousing exchanges and an index called "Matri-love" quantifying the social behaviors emitted in the direction of individuals from the same maternal line. The results show that one group of monkeys was globally more affiliative, with more reciprocal delousing than the other two groups; this was true throughout the 9 years of the study and independently of certain differences between the groups such as socio-demographic variations: sex ratio, age of individuals and group size.
Furthermore, these observed differences in sociality between groups cannot be explained solely by ecological and genetic differences, as the three groups share a very similar environment with overlapping territories, and gene flow is ensured by the movement of males between groups. These results strongly suggest a social origin for these differences in sociality between groups. According to the scientists, monkeys in the first group have developed a more affiliative "social tradition" than those in other groups, under the social influence of the group or of certain "key" individuals. Individuals could thus behave like others through a process of behavioral mimicry acting like a social glue.
Basic behaviors form the foundation of these cultures
Surprisingly, the scientists showed that over the course of the study, six adult males dispersed from one group to another and adapted their sociality to that of their new group. Thus, males who left the most social group - to join the other two - became less social, and vice versa. In a previous study, it was shown that in a food-choice experiment, males abandoned their initial preference for one food to conform to the local dietary norm of their new group. This study reveals that such conformity may extend to natural observations of social behavior.
Why not enjoy unlimited reading of UP'? Subscribe from €1.90 per week.
This study contributes to a better understanding of the behavioral traditions of vervet monkeys in their natural state, compared with those of great apes, which are much better studied and documented. Primate cultures are made up of a greater variety of behavioral traditions than was thought even a few years ago. The more research progresses, the more we discover that basic behaviors form the bedrock of these cultures.
Source CNRS
Header photo : © Charlotte Canteloup / Photo d'épouillage social
