The most important finding in the science of friendship is that people (and animals) with more and better social relationships are healthier and live longer. In humans, social isolation is as much a risk factor as smoking. Until very recently, though, no one looked at precisely when the beneficial effects of friendship emerge and how long they last. The first such study, in humans, was published last year, and the second, in monkeys, came out this month. Intriguingly, both found differences in the effect of friendship depending on age, but the point at which those differences occurred was not the same. What’s going on?
The 2016 study, conducted by researchers at the University of North Carolina, re-analyzed data from four large, long-standing studies capturing different life stages. In adolescence and old age, having friends was associated with a lower risk of physiological problems, and the more friends you had, the lower the risk. In other words, there was a dose-response relationship. By contrast, adults in middle age were less affected by variation in how socially connected they were. But the of their social relationships—whether friendships provided support or added strain—mattered more.
In monkeys, the picture looks slightly different. The new study used decades of data on over 900 female rhesus macaques on the island of Cayo Santiago in Puerto Rico. Macaques are one of our primate cousins—though not as closely related to us as chimpanzees—and their social behavior and physiology have a lot of similarities to ours. Using the number of adult female relatives on hand as a proxy for sociality, the researchers found that social integration affected survival rates in the prime of life, but not in old age. A 12-year-old (middle-aged) monkey, for example, was more likely to make it to 13, and a 13-year-old to 14, if she was more social. Once monkeys reached the grand old age of 18 (akin to a human in their 70s), however, their social connectedness no longer correlated to their chances of making it to 19 or 20 or beyond. This seems to run counter to the findings in humans.
I asked lead author Lauren Brent, a behavioral ecologist at the University of Exeter, what might be happening in her monkeys—and in humans.
Were you surprised that friendship mattered less for the older adult monkeys?
Yes! I said, Oh, how come this stops mattering? That it matters when they’re younger fits with what we know. Social integration helps you survive. In a fight, [family and friends] will help. And you’re more likely to get at food. It’s interesting to ask why it doesn’t matter when they’re older.
My first thought was that older macaques were going to be less socially active across the board, have lower energy, be less involved in the social world, full stop. But that’s not it. The two things monkeys do in terms of social behavior is engage in grooming and aggression. The older females were receiving the same amount of grooming and giving the same amount of aggression, but not giving much grooming or receiving much aggression. If I were a monkey those are the things I wouldn’t want to do either.
Does that mean they are managing their relationships to their advantage?
It’s just a hypothesis, but their social lives are maybe nicer. They have been around a long time and have a lot of experience and they may be just slightly better at navigating the situation. So they don’t need the social support they needed when they were younger. Unlike humans in a retirement home, they also haven’t left their houses: That shakes up your whole social world. For the monkeys, the social challenges haven’t changed, but the way they cope with them is different.
That’s a bit like the findings for middle-aged people in the human study — that they’re coping on their own a bit more, and that quality but not quantity of relationships matters.
That result makes sense to me. In your 20s, that aspect of your social life—friendship—is everything. In middle age, you are sort of at your prime, you’re busy, you’re making money, you have kids who aren’t that young, you don’t need help from your parents.
Yet we keep hearing how important it is to keep up your friendships. Why?
You need to maintain them so that when your kids grow up and you do have time for your friends again, you have them. Or if something horrible goes wrong, your friends are still there for you.
Where will this research go next?
We need to know more about how sociality changes across the lifespan and what that tells us about what we do and don’t need in terms of social support. If it’s really important when you’re young and when you’re old, but not in middle-age, that tells you something about how you’re coping with your environment when you’re middle-aged, but also something about demographic differences in those other time periods.
L. J. N. Brent, A. Ruiz-Lambides, M. L. Platt. "Family network size and survival across the lifespan of female macaques." Proc. R. Soc. B 2017 284 20170515; DOI: 10.1098/rspb.2017.0515. Published 17 May 2017