The number of social connections and their strength are more important for survival than short contacts with immediate benefit or communication with individuals from other social groups. Scientists came to this conclusion after seven years of observing three hundred monkeys. Those individuals that formed a large number of weak interactions with other monkeys, or small but strong ones, were more likely to live longer. To all appearances, both of these strategies can turn out to be beneficial under certain conditions. The work was published in the journal Proceedings of the Royal Society B.
There is ample evidence that social bonds promote longevity and reduce the risk of certain age-related diseases, such as neurodegenerative diseases. However, how exactly these two parameters are related is still not entirely clear. Perhaps this is due to a reduced level of stress, but other mechanisms can also be imagined - for example, that a person or an animal integrated into a social structure receives more resources.
The analysis of this relationship is complicated by the fact that social ties themselves are a complex concept. One can imagine an animal that rarely contacts, but with a large number of different relatives, or often - but with the same ones. In these two cases, the benefits for him may be different.
Samuel Ellis from the University of Exeter and his colleagues tried to find out which components of social connections are most important for the longevity of animals. As a model object, the scientists chose females of rhesus monkeys living in the wild. In total, the researchers analyzed the behavior of 319 monkeys over seven years.
Scientists have identified four types of social bonds that, in their opinion, could somehow affect the lifespan of macaques. They called the first social integration - this is frequent contacts with a large number of partners in the population. Its immediate benefit is a reduction in group aggression. The second type is dyadic connections - tight interactions with a small number of partners. This type can be useful for cooperation, for example, in the extraction of resources. The third type - structural connections - means that the animal is in contact with representatives of different groups and statuses within the population and is thus built into the structure. This type of bond can help raise the social status of an individual. Finally, the last type - direct connections - refers to short interactions with quick results, such as grooming. It does not necessarily affect the position of an individual in the population, but it brings immediate benefits.
Observing animals, the authors of the work used the proximity of animals in space and grooming as indicators of their social interaction and built a map of communication of all females in the population. Then, for each female, they calculated many values: the number of social interactions, the relative strength of each of them separately, the stability of dyadic interactions, and so on. Then they assessed the severity of different types of social connections in each individual and compared these data with the survival curve of monkeys in this population.
On average, females of the rhesus macaque species had from 1 to 14 interaction partners, but this parameter did not correlate in any way with their mortality (p = 0.11), as well as the strength of these connections. However, scientists noticed that survival correlated with the number of weak ties: the more there are, the higher the female's chance of living longer. Thus, social inclusion has proven to be an important factor in longevity.
Dyadic bonds also correlated with life expectancy: the stronger the bonds with 1-3 of the closest partners, as well as with all stable partners, the higher the chance of survival (p = 0.031). But for the other two types of connection - structural and direct - scientists did not find any correlation with survival (p <0.05).
Thus, the researchers found that social connections affect survival not directly (like grooming), but indirectly. In this case, it is not the animal's integration into the social structure that is important, but its contacts with closest partners. And here two strategies are possible: a large number of weak ties or a small number of strong ones. The authors of the work note that the strategies are mutually exclusive, that is, females with strong bonds rarely had many of them, and vice versa. This means that both of them can be effective, depending, probably, on the conditions or characteristics of a particular animal.
Previously, scientists have found that among people, tall women are more likely to be centenarians, as well as optimists. And how in fact optimism and other lifestyle features can be associated with longevity, read our text "Long Happy Life".