I enjoyed reading this article on Monday, April 23, 2012, from the New York Times.
One of the comments in this article is about the emotional cement that grooming provides chimpanzees in their tribes. I had just seen the documentary film Chimpanzee the day before where there is ample demonstration of the bonding power of grooming between the animals. I hope you enjoy the article.
This week: A wildlife expedition close to home; girlfriends of many species; and puncturing a myth about obesity.
As in urban jungles, so too in jungle jungles. Researchers have lately gathered abundant evidence that female friendship is one of nature’s preferred narrative tools.
In animals as diverse as African elephants and barnyard mice, blue monkeys of Kenya and feral horses of New Zealand, affiliative, longlasting and mutually beneficial relationships between females turn out to be the basic unit of social life, the force that not only binds existing groups together but explains why the animals’ ancestors bothered going herd in the first place.
Scientists are moving beyond the observational stage — watching as a couple of female monkeys groom each other into a state of hedonic near-liquefaction — to quantifying the benefits of that well-groomed friendship to both picking partners. Researchers have discovered that female chacma baboons with strong sororal bonds have lower levels of stress hormones, live significantly longer and rear a greater number of offspring to independence than do their less socialized peers.
Similarly, wild mares with female friends are harassed less often by stallions and have more surviving foals than do mares that lack social ties. Female mice allowed to choose a friend as a nesting partner will bear more pups than females forced to share straw space with a mouse they dislike.
And female elephants keep in touch with their chums through frequent exchanges of low-pitched vocalizations called rumbles. “We liken it to an elephant cellphone,” said Joseph Soltis, a research scientist who works with elephants at Disney’s Animal Kingdom in Florida. “They’re texting each other, I’m over here. Where are you?”
Hannah may even be onto something primal, or at least primate, in setting the size of her inner circle of friends. Researchers have determined that a female baboon with a small but devoted core of grooming companions will be less prone to jagged spikes of the stress hormone cortisol than a female who casts her social net wide but not deep.
The ideal buddy count? “To have a top three seems to be what’s important here,” said Joan B. Silk, a primatologist at the University of California, Los Angeles. With a trio to lean on, she added, “you see the kind of strong, stable relationships that help females cope better with stress.”
Some signs of female camaraderie are easy to spot. Lionesses suckle each other’s cubs. Female spotted hyenas greet each other through elaborate ceremonies of mutual trust, lifting a leg and exposing their famously penislike genitals to their snuffling sisters and their bone-crushing jaws.
Elephants touch trunks, share food, play lifeguard for the day. Dr. Soltis cited the time a female elephant rescue the wayward baby of her closest friend after it stumbled headlong into the elephant submersion pool, by hauling the panicked calf out with her trunk. Hey Hortense where RU? Got Dumbo. Bring towel.
Sometimes displays of female friendship become heated, hyperbolic, a monkey chant for the home team. Marina Cords of Columbia University has spent more than 30 years studying the blue monkeys of Kenya, 10-pound primates that, their name notwithstanding, are really charcoal gray.
She has seen many violent territorial disputes between neighboring monkey groups, in which the adult females line up to fight in the treetops, the adult males mostly hang back to watch, and the young monkeys scamper obliviously below. The females scream, lunge, bite, rip the flesh of an enemy’s calf down to a bloody frill round the ankle. And when the battle ends, the salon sessions begin.
“There’s a frenzy of grooming among the females in the same group,” Dr. Cords said. “You see them huddling together in clusters, with individuals scooting from one huddle to another, as though everybody is trying to groom as many individuals as possible.” They comb and pluck with their fingers, soothe scabs and wounds with their lips.
Through grooming, the monkeys decompress, and remind one another that their fates are still linked. After all, should a group of blue monkeys grow too large it will split into factions, and the sisterly comrades of today may be flaying you a new pair of anklets tomorrow. Shall we groom?
In other cases, affiliative behaviors are subtle and difficult to track. For years female chimpanzees were viewed as asocial, content to forage alone or with dependent offspring while largely ignoring other females of their group. The males may be legendary kin-based allies, born and reared together and wedded to their natal turf. But as the so-called dispersing sex, female chimpanzees must leave their birthplace at puberty and seek asylum in another group, which means being surrounded by unrelated females all competing for the same goods. What’s to like about that?
In a 10-year study of West African chimpanzees, however, Julia Lehmann of Roehampton University in London discovered that at least for her population, the stereotype of the standoffish female was wrong. Her adult females were cultivating friendships and expressing their affections in myriad ways — staying within eye contact as they foraged by day, resting back to back while relaxing at home.
“Most of the females in my study have at least one close associate with whom they always hang out,” Dr. Lehmann said. Coalitions between the males may be showier, she said, but female friendships appear more resilient, lasting until one member of the bonded pair dies.
Dr. Lehmann does not yet know why female chimpanzees seek female friends. But it’s not as a deterrent to male aggression. “Male chimpanzees are so dominant that even two females can’t do much against them,” Dr. Lehmann said.
Instead, Dr. Lehmann and others suspect that the story for chimpanzees will turn out to be similar to what’s been shown in female baboons. For baboons, friendship is not about extra weaponry. It’s about biochemistry and predictability.
According to Robert M. Seyfarth of the University of Pennsylvania, who with his colleague Dorothy L. Cheney, recently reported in the Annual Review of Psychology on the evolutionary origins of friendship, baboon life is extremely stressful, especially for females.
Male baboons are comparatively huge and nasty. The ones you know boss you around and bite off the tip of your ear. The ones you don’t are infanticidal. Leopards are always leaping. Food is scarce.
“You have to have somebody to hang onto,” Dr. Seyfarth said. “A friend gives you an element of predictability and certainty, and you can use that to buffer you against all the things you don’t have control over. There’s a biochemical component to this.”
A familiar friend calms and equilibrates, mops up the cortisol spills that can weaken the immune system, and in so doing may help lengthen life — in baboons, humans and other group-minded kinds. “Yes, having coffee with friends is good for you,” Dr. Silk said, “and we should all do it often.”
You look gorgeous. Have a cookie. Now tell me what’s on your mind.