Chapter 12
Friendship — Part 2
Cayo Santiago is a small, palm-fringed 38-acre island haven off the coast of Puerto Rico. It is home to a thriving macaque research station and up to 1,000 free-ranging rhesus macaques. The individuals in the colony are the direct descendants of 409 monkeys who were brought to the island in 1938. The colony is run and maintained by the Caribbean Primate Research Center and the University of Puerto Rico. It is akin to a school playground. Among the sociable macaques, cliques, best-friend pairs and social climbers are all much in evidence, giving scientists a close look at the primate origins of our drive to affiliate and befriend. After 70 years of research at the field site, the monkeys are well habituated to human experimenters. Due to absence of starvation and predation, this is a perfect system to study social relationships and friendships among our evolutionary close cousins. Just as studies on humans have shown, longevity among the macaques is linked to having strong social connections, including spending time together and time grooming each other’s fur, as was the case for Jojo and the kitten. The macaques of Cayo Santiago provide the perfect opportunity to study the impact of individual friendship and relationships on the ageing process and to understand when these effects start and how long they take to make a difference. In adult female macaques, close female relatives are a proxy for friendships. The number of close female relatives or friends changes depending on an individual’s age and this is driven by the need for protection. Females at the peak of reproductive activity (prime-aged) have the most friends and have better survival compared with prime-aged females with fewer friends. These friends provide protection. Older females, however, have experience in navigating the social landscape and so are less frequent targets of aggression, which precludes the need for as many friends. From this, we can see that social support promotes survival and strategies learned across the life course are important to animals in their old age as they consequently require less social support for ‘protection’. Social relationships are not just important in macaques but rather are associated with longer lifespan in many other affable species such as baboons, dolphins and rats, implying a common evolutionary basis across species for friendship. What about social relationship across the life course in us? Although the overwhelming majority of studies to date have focused on links between sociality and longevity in older people, the science has honed in on determining when these links start to emerge and how long they last. In humans, in contrast to macaques, social network size is important for physical health in both young and old adults. We use the ‘protection’ that friendship affords us both in early life and in later life.
Chapter 3: Friendship
Lisa Berkman, a friend and well-known social epidemiologist in Yale, published some of the earliest studies that detail why social interactions matter and what types of social networks affect our health and even impact when we die. The Yale group used household information from 2,229 men and 2,496 women aged 30 to 69 years who had completed a detailed questionnaire of lifestyle and social contacts, and for whom nine years of follow-up data, including data on the time and cause of death, was available. Overall, 10 per cent of men and 6 per cent of women who had filled in the questionnaire had died, representing 2.2 per cent of men aged 30–39 up to 28 per cent men aged 60–69 years. Four sources of social contact or social ‘ties’ were examined: marriage, contact with close friends and relatives, church membership and other clubs or group memberships. With few exceptions, people with each type of social tie had significantly lower death rates than people lacking such social ties. Since these studies, many longitudinal studies have reinforced the impact of social ties on death rates.
So why does the strength of social contacts and social engagement affect our mortality? Some explanations include more stress, higher levels of stress-related hormones, more heart disease and more inflammation if we lack strong social ties. Supporting these explanations, Harvard researchers, in a more recent large study of human social networks, found that greater friendship and familial ties independently predicted lower concentrations of fibrinogen, which is a clotting factor in blood and a cause of blood clots and heart attacks, and indicates inflammation. The strength of the association between fibrinogen and social isolation was remarkable. The effect was the same as for smoking, a well-recognised major risk factor for blood clots and heart attacks.
The answer for an association also lies with stress hormones. Biologist Lauren Brent reports that among the Cayo macaques, those with the weakest social networks have the highest levels of stress hormones. High stress hormones trigger a cascade of physiological responses which, if repetitive, lead to heart and brain diseases and early death, further explaining why friendship buffers against disease.
Chapter 3: Friendship
In another experiment, John Capitanio, a psychologist at the University of California, took biopsies of lymph node tissues from monkeys who had been separated from their social group and compared these with biopsies from monkeys within a social group. Lymph nodes are the engine for inflammatory and immune responses. The biopsies showed high activity in inflammatory genes and low activity in genes that protect against viruses. In other words, being friendless had switched on genes known to increase inflammation, the background for a number of age-related diseases. Thus, background inflammation and higher susceptibility to infections is another reason for the association between friendships, disease and mortality. These primate observations align with human observations in Roseto and other social network research. Reporting from southern Kenya, Lydia Denworth, a science journalist, described the human-like social gestures she observed among a troop of other gregarious mammals, baboons, who spend much of their day embracing, grooming each other and playing with one another’s babies. She related the tale of a Botswanan baboon named Sylvia, who scientists dubbed the ‘Queen of Mean’ because she ‘cut a swath through the group, scattering subordinates, biting or whacking animals that failed to move out of her way’. Sylvia’s best friend was her daughter who was unfortunately killed by a lion. Sylvia’s approach softened after her daughter’s death. Bereft of her closest companion, she began offering to groom the peers she’d once scorned, much as a former school bully might try to befriend classmates she’d bullied. This story illustrates how friendship is hard-wired; it is not a choice or a luxury but rather a necessity that is critical to our ability to succeed and thrive. It evolved due to a direct protective bearing on our mental and physical health. Given that Sylvia was hard-wired for friendship, she needed to develop new friends once her daughter was no longer. Studies also puncture the stereotype that female friendships thrive on endless chats and male ones on side-by-side activity. When pairs of male friends were instructed to ask each other deep questions about their dreams, values and relationships, the men reported being more satisfied with their friendships afterwards. They concluded that, contrary to popular belief, many male friendships also require depth which may not always be apparent at first sight. Friendship has profound genetic origins. Our closest friends, the people we consider ‘kindred spirits’, resemble us on a biological level. We share more DNA with friends than we do with other people. A Californian study showed that we share 0.1 per cent more DNA with friends than the average stranger. This may not sound like a lot but it is – it is equivalent to a level of genetic similarity expected among fourth cousins. Most people don’t even know who their fourth cousins are, yet somehow, among a myriad of possibilities, we manage to select as friends the people who resemble our kin and thereby we associate with people who are similar to ourselves.