Staying in Love Monkey-Style

Why are pair-bonding tamarins and humans different from chimps?

tamarin monkey pairThe Lazy Way to Stay in Love pointed out that humans are pair bonders, with the unique ability to strengthen their romantic bonds at will. We do so by employing a special range of subconscious signals, or "bonding behaviors"

These behaviors (technically, attachment cues) include skin-to-skin contact, sensual kissing, gentle stroking, wordless sounds of contentment and pleasure, hugging or silent spooning, smiling with eye contact, caressing of breasts, penis holding, playful intimacy, relaxed intercourse, and so forth. Used daily, they effortlessly increase relationship satisfaction because they bypass the yakety-yak of our cerebral cortex and make a beeline for our limbic brain. In contrast, talk is cheap. Not only that, it gets filtered through the brain's analytical centers where we tend to add all sorts of spin to what we hear. Said one woman who experimented with daily bonding behaviors:

Those delicious warm melting tingly feelings (that make you go mmmm, ahhh, and ohhhh) that used to take a while to turn on (through kissing, caressing, sex), are now just there waiting, and don't need any time at all to awaken again. My breasts, ears and inner wrists are now like 'off pause' buttons.

Like all animals, humans are primed to perceive the signals that indicate whether or not another is safe enough to relax with. If these safety signals are not forthcoming, a subtle defensiveness creates emotional distance. This can happen even if there was lots of lovin' in the past. Bonding behaviors deliver the safe-to-bond message by relaxing the defensive mechanism of the brain (primarily the amygdala), but they need to occur frequently.

One reason that these affectionate acts increase the urge to merge with a mate is that they induce the flow of oxytocin (the "cuddle hormone"). Oxytocin lowers anxiety, increases trust, and counteracts depression. In short, we feel good interacting with this person; it's rewarding at a neurochemical, or subconscious, level. Not surprisingly, earlier this year scientists reported that those in committed relationships produce less stress-related cortisol. Mated humans also live longer, and have lower rates of psychological distress. There's even growing evidence that oxytocin (or oxytocin-producing behaviors) may prove to be effective protection against addiction in pair bonders. (Alas, pair bonders may be more prone to addiction than other mammals, due to the very brain sensitivity that makes pair bonding possible.) For us, teaming up is good medicine.

Recent research on tamarin monkeys confirms the power of simple behaviors of this type to release soothing oxytocin and keep monkey-love alive. Tamarins, like humans, are socially monogamous pair bonders that raise their young together.

In contrast, chimps and bonobos do not form pair bonds. They haven't evolved the neural machinery for it. Keep in mind that, although chimps may be our closest living genetic relatives, our paths forked about six million years ago. Our true closest genetic relatives were located on our branch even if they're no longer around. Somewhere along our branch we evolved into pair bonders, as have tamarins, gibbons and titi monkeys. Sex is rewarding for all mammals, but for pair bonders, contact with a particular mate can also register as very rewarding. (For more on the neural mechanics of pair bonding, see the remarks of Larry Young at the end of this article.)

The point is that we're part of a small club of primate species wired for the ability to fall in love and settle in with one significant other, whether or not we choose to avail ourselves of this option. We're not programmed to be "sexually monogamous." No species is. But we are "socially monogamous," that is, able to pair up. The fact that we sometimes experience lust in the absence of attachment doesn't make us bonobos, or mean we'd be happier with a more casual approach to mating.

Monkey-love detective

Researcher Chuck SnowdenAware of the link between attachment behaviors and oxytocin, University of Wisconsin researcher Chuck Snowden decided to measure both in tamarin monkey pairs that had been together for at least a year. His results revealed a wide range of oxytocin levels among the pairs. However, within each pair, mates had similar levels. Whatever they were doing clearly benefited both.

Here's the key finding: The pairs with highest oxytocin levels engaged in the most affiliative and sexual behaviors. These behaviors are tamarin versions of bonding behaviors: snuggling up with tails intertwined, grooming, tongue flicking and scent marking/investigation, erections, solicitations (flirting by either sex), investigations of genitals, and all mounts in which the female was receptive, whether or not the mount led to actual copulation—or ejaculation. No performance worries for tamarins!

Tamarins mount almost daily, regardless of where the female is in her cycle, so getting it on is not just about fertilization. In private correspondence about the role of nonconceptive sex in primate pair bonding, Snowden opined, "The physical contact of making love [is] important [and] orgasm is simply a nice and fun add-on when it happens." (For a recent book that affirms the benefits of this relaxed concept in human intimacy see Tantric Sex for Men.)

The researchers concluded that oxytocin levels probably reflect the quality of a pair bond, and are likely maintained through the behaviors they observed. Said Snowdon, "Here we have a nonhuman primate model that has to solve the same problems that we do: to stay together and maintain a monogamous relationship, to rear children, and oxytocin may be a mechanism they use to maintain the relationship."

Snowdon's team suggested that close contact and nonconceptive sexual behavior might also predict the quality and duration of human relationships. Sadly, we humans often overlook the importance of these comforting signals.

How many couples, after the honeymoon frenzy subsides, have occasional sex but rarely engage in affectionate, sexy (but non-goal-oriented) contact? Intermittent orgasms may simply not be enough to keep their oxytocin up or their bonds strong. Occasional sex is like turning a water faucet on...and then off. Daily bonding behaviors are like a steady flow of water that keeps your pipes from freezing. True, some couples attempt to keep their bonds strong with intense sexual stimulation in the belief that frequent orgasms are the best glue. Yet it may be that this narrow focus causes them to overshoot the more easygoing rhythm of pair-bonder romance or, paradoxically, numb their pleasure response.

In The Myth of Monogamy David Barash points out that in pair-bonding mammals sex is not "especially fervent." (At least not after the initial frenzy.) Many interactions between mates take the form of resting together, mutual grooming, and hanging out.

Regular affection protects against porn addictionThe interesting point is that human lovers have a choice. Unlike other mammals, we can consciously enhance the quality and satisfaction of our unions by increasing our mutual oxytocin levels with simple, nearly effortless signals. We simply use our expanded cerebral cortex to jumpstart our brain's limbic love machinery. Maybe the thirteen percent of couples  who maintain juicy bonds somehow stumble upon this secret early in their unions without consciously realizing it.

Has romance failed you in the past? Did you offer your fellow pair-bonding mammal enough of the bonding signals to keep your mutual perception of each other rosy, allow you to overlook errors, and deepen the intimacy between you? If not, take a lesson from your pair-bonding primate cousins.


[From Speaker Summary of talk by Larry Young, PhD entitled, "Neurobiology of Social Bonding and Monogamy..."]

Prairie voles, like humans, are highly social and form long-lasting pair bonds between mates. This is in contrast to 95 percent of all mammalian species, which do not appear capable of forming long lasting social bonds between mates. Studies examining the brain and genetic mechanisms underlying pair bonding have revealed an important role for a few key chemicals in the brain in establishing social relationships. Oxytocin and vasopressin appear to focus the brain’s attention to the social signals in the environment. During pair bond formation, these chemicals interact with the brain’s reward system (e.g. dopamine) to establish an association between the social cues of the partner and the rewarding nature of mating. So why are some species capable of forming social bonds while others are not? Research comparing the brains of monogamous and non-monogamous species reveals that it is the location of the receptors that respond to oxytocin and vasopressin that determines whether an individual will be capable of bonding. For example, monogamous male prairie voles have high concentrations of vasopressin receptors in a ventral forebrain reward center that is also involved in addiction. Non-monogamous meadow voles lack receptors there. However, if receptors are inserted into this reward center in the non-monogamous meadow vole, these males suddenly develop the capacity to form bonds. These studies also suggest that pair bonding shares many of the same brain mechanisms as addiction. Genetic studies have revealed that DNA sequence variation in the gene encoding the vasopressin receptor affect the level of receptor expression in certain brain regions and predict the probability that the male will form a social bond with a female.

Recent studies in humans have revealed remarkable similarities in the roles of oxytocin and vasopressin in regulating social cognition and behavior in vole and man. Variation in the DNA sequence of the human vasopressin receptor gene has been associated with variation in measures of romantic relationship quality. In humans, intranasal delivery of oxytocin enhances trust, increases gaze to the eyes, increases empathy and enhances socially-reinforced learning. Indeed it appears that stimulating the oxytocin system in humans increases the attention to social cues in the environment....

Bonding Behaviors Among Pair-Bonding Crows

Nurturing Nests Lift These Birds to a Higher Perch

Crows and bonding behaviors
Amid all the psychosocial caterwauling these days over the relative merits of tiger mothers and helicopter dads, allow me to make a pitch for the quietly dogged parenting style of the New Caledonian crow.

New Caledonian crows are renowned for their toolmaking skills.

In the complexity, fluidity and sophistication of their tool use, their ability to manipulate and bird-handle sticks, leaves, wires, strings and any other natural or artificial object they can find into the perfect device for fishing out food, or fishing out second-, third- or higher-order tools, the crows have no peers in the nonhuman vivarium, and that includes such textbook dexterous smarties as elephants, macaques and chimpanzees.

Videos of laboratory studies with the crows have gone viral, showing the birds doing things that look practically faked. In one famous example from Oxford University, a female named Betty methodically bends a straight piece of wire against the outside of a plastic cylinder to form the shape of a hook, which she then inserts into the plastic cylinder to extract a handled plug from the bottom as deftly as one might pull a stopper from a drain. Talking-cat videos just don’t stand a chance.

So how do the birds get so crafty at crafting? New reports in the journals Animal Behaviour and Learning and Behavior by researchers at the University of Auckland suggest that the formula for crow success may not be terribly different from the nostrums commonly served up to people: Let your offspring have an extended childhood in a stable and loving home; lead by example; offer positive reinforcement; be patient and persistent; indulge even a near-adult offspring by occasionally popping a fresh cockroach into its mouth; and realize that at any moment a goshawk might swoop down and put an end to the entire pedagogical program.
Jennifer C. Holzhaider, the lead author on the two new reports, said that in one year of their three-year field study, the crows they were following gave birth to a total of eight chicks.

“We thought, yay, we’ll have eight juveniles we can watch,” she said. But the goshawks, the rats, the owls and the torrential rains took their toll, and only one of those eight chicks survived. “It’s a hard life in the jungle; that’s all there is to it,” said Dr. Holzhaider.
By studying the social structure and behavior of the crows and the details of their difficult daily lives, the researchers hope to gain new insights into the evolution of intelligence, the interplay between physical and social skillfulness, and the relative importance of each selective force in promoting the need for a big animal brain.

The researchers want to know why it is that, of the 700 or so species of crows, ravens, rooks, jays and magpies that make up the world’s generally clever panoply of corvids, the New Caledonian crow became such an outlier, an avian savant, a YouTube top of the line.

“It’s a big puzzle,” said Russell D. Gray, head of the Auckland lab. “Why them? Why is this species on a small island in the Pacific able to not just use but to manufacture a variety of tools, and in a flexible rather than a rote or programmatic way? Why are they able to do at least as well as chimpanzees on experiments of cognition that show an understanding of the physical properties of the world and an ability to generalize from one problem to the next?”

If the birds learn to avoid holes and barriers in the experimental setting of a plastic tubed box, for example, they will avoid holes and barriers in the very different conditions of a wooden table. “Knowing their social structure,” Dr. Gray said, “is one part of the jigsaw.”

New DNA studies suggest that corvids first arose at the end of the dinosaur era, roughly 65 million years ago, somewhere in the neighborhood of Australia, and radiated outward from there. The ancestors of the New Caledonian crow didn’t travel far before settling on the 220-mile-long land sprig from which the species derives its name.

The modern New Caledonian crow is funereal of bill and feather and, at an average of 12 inches in length and 12 ounces in weight, a middling sort of corvid: much smaller than a common raven, slightly more compact than the ubiquitous American crow, but beefier than a jay or a jackdaw. Brain size is another matter.

“All corvid brains are relatively big,” said Dr. Gray, “but preliminary evidence suggests that the New Caledonian brain is big even for corvids.” Moreover, the brain is preferentially enlarged, displaying impressive bulk in the avian equivalent of the cogitating forebrain, particularly structures involved in associative learning and fine motor skills.

Their bills are also exceptional, “more like a human opposable thumb than the standard corvid beak,” said Dr. Gray.
The bills “appear specialized to hold tools,” said Anne Clark, who studies American crows at the State University of New York at Binghamton but who also has observed New Caledonian crows in the field. “When I was watching them, they seemed to grab a stick whenever they appeared unable to figure something out,” she said, rather as a mathematician has trouble solving a problem without a pencil in hand.

The birds are indefatigable toolmakers out in the field. They find just the right twigs, crack them free of the branch, and then twist the twig ends into needle-sharp hooks. They tear strips from the saw-toothed borders of Pandanus leaves, and then shape the strips into elegant barbed spears.

With their hooks and their spears they extract slugs, insects and other invertebrates from deep crevices in the ground or in trees. The birds are followers of local custom.

Through an arduous transisland survey of patterns left behind in Pandanus leaves by the edge-stripping crows, Gavin Hunt of the University of Auckland determined that toolmaking styles varied from spot to spot, and those styles remained stable over time. In sum, New Caledonian crows have their version of culture.

Being cultured is hard work. In studying the birds’ social life, Dr. Holzhaider and her colleagues confirmed previous observations that New Caledonian crows are not group-living social butterflies, as many crows and ravens are, but instead adhere to a nuclear family arrangement. Males and females pair up and stay together year-round, reaffirming their bond with charming gestures like feeding and grooming each other, sitting close enough to touch, and not even minding when their partner plays with their tools.

Young birds stay with their parents for two years or more — a very extended dependency, by bird standards — and they forage together as a family, chattering all the while. “They have this way of talking in a quiet voice, ‘Waak, waak, waak,’ that sounds really lovely,” said Dr. Holzhaider.

The juveniles need their extended apprenticeship. “They’re incredibly persistent, wildly ripping and hacking at Pandanus leaves, trying to make it work,” said Dr. Holzhaider, “but for six months or so, juveniles are no way able to make a tool.”
The parents step into the breach, offering the trainee food they have secured with their own finely honed tools. “By seeing their parents get a slug out of a tree, they learn that there’s something down there worth searching for,” she said. “That keeps them going.”

The carrot-on-stick approach: It works every time.