All these work to boost health and longevity through mechanisms mentioned in this chapter. But there is more. Just as we’ve evolved the stress response to deal with imminent threats, we’ve also evolved to be social creatures, relying on one another for help. That’s why a cocktail of so-called social hormones, such as oxytocin, serotonin, and vasopressin, also play a vital role in both our mental and physical well-being, connecting the mind and the body. It can explain, for instance, why holding hands and looking others in the eye can be good for your health.
A FEW SUGGESTIONS TO BOOST YOUR LONGEVITY
Take good care of your HPA axis so it doesn’t become chronically activated—traffic squabbles are not lions trying to eat you. Have your doctor check out your heart rate variability (HRV) or buy a devise to measure it at home. It’ll give you an idea of how your vagus nerve and relaxation response are working. If you are depressed and standard pills don’t seem to do the trick, ask your doctor for anti-inflammatory drugs—our immune systems and brains are intricately connected. Tend to the microbes in your gut: don’t overdo antibiotics or antibacterial cleaning products; eat lots of fermented foods such as miso or kefir; spend time getting dirty in nature. Keep diverse friendships. Give lot of hugs to your cheerful, easygoing friends and, through microbial exchange, their attitude may rub off on you, too. Profit from the placebo effect—it may work even if you know the treatment is a sham.
3
A SNIFF OF LOVE
How Social Hormones Influence Our Relationships and Longevity
IN MY HAND, the blue-white bottle of OxyLuv felt just like any other nasal spray—a decongestant, perhaps, something I might use to relieve the symptoms of a bad cold. Yet this day I wasn’t treating a stuffy nose. Instead, I was targeting potential deficiencies in my social skills.
I removed the cap from the bottle, tilted my head forward, and slid the cold, white nozzle into my left nostril. I sprayed, inhaled, and then repeated the process on the other side. Then it was showtime. Within a few minutes I was either going to feel overwhelming love toward the entire human population of earth, or, alternatively, get a nosebleed.
According to the producer’s website, OxyLuv is supposed to “create feelings of trust between others” and reduce my “social fears, anxiety, stress.” Each spray delivered to my brain ten international units of oxytocin, dubbed by the media as the “love” or “cuddle” hormone, and which, as a hefty pile of scientific studies shows, makes people more social and friendly, improving relationships.
Fifteen minutes after my first OxyLuv shot, I began to feel more serene, as if someone had wrapped me in a blanket of calm. I looked at my husband, who was sitting across the table, and smiled. All was fine in the world. With the extra dose of oxytocin reaching my amygdala and the anterior cingulate cortex, I should be more empathic today. Maybe I would be kinder to my husband, boosting marital love. Maybe I would make new friends, or bond better with the old ones. As a result, I should prolong my life.
Oxytocin is a protein-like molecule that neurons use to communicate with each other. Outside of the brain, it can also act as a hormone, regulating many different processes in the body. Oxytocin evolved about 700 million years ago, long before the first animals set their paws on land. Over the millennia, oxytocin and its close relatives became widespread in the animal kingdom, helping with reproduction and sociality. They induce milk letdown in lactating mammals, be it squirrels or humans. They cause contractions of the gut in worms and contractions of the uterus during human childbirth. They help leeches twist. They incite male cichlid fish to be better fathers. And when you see a dog looking faithfully into his master’s eyes, oxytocin is at work, too.
These are not just some spurious connections. There are very good biological reasons why oxytocin, together with other hormones such as vasopressin, endorphins, dopamine, and serotonin, play a vital role both in our social lives and in our health, tying them together. These so-called social neuropeptides are the reason why being neighbourly or having a happy marriage may add years to your lifespan. Neurochemical links between sociality and physiology are crucial for our species. Some researchers even argue that social hormones have actually made us human. According to one theory called “the neurochemical hypothesis for the origin of hominids” (yes, it’s a mouthful), selection for high amounts of dopamine and serotonin in our brains tilted our personalities toward less aggression and higher levels of cooperation. And while over our evolutionary history we’ve become kinder, calmer, and friendlier, at the same time the scleras of our eyes turned white, our lips became pinker, and our brains shrank.
What Makes a Good Pet
On one YouTube video, Boris and Sophie, two cute pets, show off their tricks: they sit and lie down when prompted, then shake paws and spin in exchange for treats. If it weren’t for their magnificent, bushy tails and unusually high-pitched yelps, the animals could be mistaken for dogs. In reality, Boris and Sophie are foxes—domesticated silver foxes from Siberia, to be precise.
In 1959 a Russian geneticist named Dmitry Belyaev set up an experiment to test a new research idea: he started breeding wild silver foxes, selecting the animals for their lack of aggression or fear toward humans. After a few years—or about eight to ten fox generations—a weird thing happened: some of the foxes started to resemble dogs in both their behaviour and looks. Today, the project continues even after Belyaev’s death, and most of the domesticated silver foxes at the Siberian lab are tame creatures that are not only super-friendly, but also look considerably different from their wild ancestors.
They have floppy ears, short muzzles, and, often, white spots on the foreheads. But here is the thing: their looks are an unexpected side effect. Belyaev did not select the foxes for the floppiness of their ears or their forehead spots, no matter how cute. He selected them solely for their temperament. Yet what occurred was a whole set of appearance changes—something that scientists came to call the domestication syndrome. If you look at other species of domesticated animals, such as dogs, horses, donkeys, and rabbits, you may notice that they tend to have floppy ears, short snouts, small jaws, star-shaped marks on their foreheads, and smaller brains than their wild ancestors. Which brings us back to humans.
Richard Wrangham, a primatologist at Harvard University, believes that our ancestors self-domesticated themselves in recent evolutionary history, which resulted in milder tempers and more pro-social behaviours on one hand, and in smaller brains, smaller jaws, pink lips, white eye scleras, and flatter faces on the other (no floppy ears in our case––although I do wonder how that might have looked). And yes, you read that correctly: smaller brains. It is true that for the large part of our evolution our brains grew, but since late Pleistocene times, approximately thirty thousand years ago, they’ve actually slightly shrunk by about 10 percent. It might have been a side effect of selection for less reactive aggression, or in lay terms, better tempers.
Scientists believe that what may be responsible for such side effects, be it smaller brains or white forehead patches, is the neural crest. The neural crest is a group of stem cells found in the embryos of vertebrate animals—mammals, birds, fish, and so on—which, as the embryos develop, migrate throughout the body to give rise to different types of cells and tissues, including bones, cartilage, and melanocytes—a type of pigment-producing cell. At the same time, the neural crest cells also affect the levels of neuropeptides. In our evolutionary past, selection for better tempers meant selection for higher levels of oxytocin and serotonin, which in turn affected the neural crest cells and how far they could travel within the body. For example, when the neural crest cells don’t make it to the top of the head of an animal, melanocytes won’t develop there, resulting in depigmentation—hence the white forehead patches and white tail tips of domesticated animals. And that’s also why humans have pink lips, and so do bonobo apes.
At first glance, bonobos may look very much like chimpanzees. That’s hardly sur
prising, considering how closely the two species are related—they both belong to the genus Pan, which also makes them our nearest cousins. Yet, as zookeepers may tell you, there are some vital differences between these apes. While you might wander into a cage full of bonobos and leave unscathed, venturing into chimp territory is far more dangerous. Bonobos are nice and friendly, while the tempers of chimpanzees should not be taken lightly. Chimps kill one another, commit infanticide, and even attack their own mothers. Bonobos don’t do that. No one has ever seen a bonobo murder another bonobo.
Wrangham suspects that bonobos, just like humans, have self-domesticated. That is also why, on closer inspection, they do look a bit different from chimps—they have the smaller jaws, more feminine-looking skulls (rounder, with less pronounced brow ridges), white palms, and pink lips of domesticated animals. And, in their brains they have twice as much serotonin, one of the social neuropeptides—an increase that has also been observed in the brains of tame Siberian foxes.
When humans, just like bonobos, self-domesticated, there were obviously no Russian geneticists to select us for friendliness—we did it all ourselves. In the case of bonobos, the richer and more predictable surroundings in which they lived as compared to chimps allowed females to reject overly aggressive males. Yet in the case of our ancestors, Wrangham argues, it wasn’t mobilization of females but rather language that helped us self-select for tolerance and mild tempers.
And if you feel like pointing out that humans, with our genocides and wars, don’t appear particularly bunny-like or docile, Wrangham has an answer to that, too. It all boils down to a difference between proactive and reactive aggression. Reactive aggression is the type common among chimps—someone makes you angry, so you bite their head off, sometimes literally. Proactive aggression, on the other hand, the premeditated scheming that can lead to dropping nuclear bombs on other members of your own species, is governed by very different neural pathways in the brain.
Our evolutionary selection likely went like this: imagine you had an aggressive and untrustworthy bully in your tribe. Other males would gather, and talk up a plan to get rid of the guy. They would choose the time and place—“By the old baobab? At noon?”—and, well, get rid of the guy, maybe with the help of a spear or two. Among some tribes, such capital punishment is actually quite common. Papua New Guinea’s Etoro people, for instance, eliminate about 9 percent of men this way, inadvertently purging their ranks of the bullies’ genes for low oxytocin and serotonin.
Over our evolutionary history, selecting for more friendly hominins meant selecting those with higher levels of social hormones circulating in their bodies. After our line split from Neanderthals, such a push for more oxytocin, paired with neural crest–related depigmentation, likely changed the appearance of our eyes, too, making them quite unusual in the animal kingdom. Think of a typical wild mammal, say a deer or a zebra. Their eyes are all dark, like small lumps of coal. Human eyes, with white around the irises, certainly stand out. Of the dozens of primate species examined, only we have white scleras. That is also why, back in 2015, the photo of Nadia the gorilla went viral on the internet. In contrast to most members of her species, Nadia has white scleras, giving her a very human look.
The thing about white scleras is that without them, it’s really hard to read much from the gaze of animals—not too much in the way of emotions, or even what the creature is looking at. Evolution of white scleras, prompted by self-domestication, helped our sociality even further. We could now communicate with others simply by looking into their eyes.
Today, our self-domesticated bodies and social minds are all interconnected. Oxytocin, serotonin, vasopressin, and other social hormones still play a vital role in linking our health and our behaviours. Yet scientists have a problem. It’s not easy to study what’s going on in our brains as we interact with each other (can’t exactly cut them open). Luckily, however, there is one tiny animal species researchers can analyze instead, which offers us a unique window into the functions of several neuropeptides in both pro-social behaviours and health. I’m talking about prairie voles.
As rodents go, prairie voles are certainly among the cutest. Resembling a cross between a hamster and a mouse, they are round and fluffy, with black beady eyes and small, shapely ears. They may not look much like humans, but in many ways, they are actually rather similar to us. And it’s not just their unusual penchant for alcohol (unlike most animals, prairie voles will choose booze over water). It’s their monogamy, sociality, and parenting styles—all linked to the way their brains are wired for oxytocin.
Although prairie voles generally live in the grasslands of central North America, the most famous ones, at least from the perspective of neuroscience, inhabit the lab of Larry Young at Emory University in Atlanta. Here, though, the transparent plastic containers filled with wood shavings and occupied by prairie voles sit next to containers housing a species that in nature lives quite apart from prairie voles: montane voles of the North American mountains.
Young and his colleagues have been comparing the two cousin species for over two decades, and their work has greatly boosted our understanding of the role oxytocin plays in love, parenting, and friendships, both of the vole and of the human kind. Unlike the monogamous prairie voles, montane voles lead far more wild lifestyles—as far as sex goes, that is. While prairie voles form lifelong bonds, for montane voles it’s all about casual rendezvous with as many partners as possible. And while prairie vole parents take care of their little ones together, with the fathers licking and grooming the kids just as the mothers do, montane vole dads prefer to leave childcare to the females.
Fascinated by the strikingly different approaches to family life between the two closely related species, researchers did what they tend to do in such situations: they opened up the brains of the animals to look for answers. Here’s what they found: the monogamous voles have a very different pattern of oxytocin and vasopressin receptors in their brains as compared to their promiscuous cousins (receptors are something akin to on/off buttons that a neuropeptide can activate). In other words, their wiring for those hormones is completely different.
The more human-like prairie voles have the oxytocin receptors located in the part of the brain that is involved in addiction. If you block those receptors, the little rodents will not fall in lifelong love and won’t care for their kids with the same devotion. On the other hand, manipulating genetics of montane voles so that their oxytocin receptors start to mimic those found in prairie voles makes them ditch their wanton ways and settle down in monogamy. And although playing with human genetics and then dissecting brains for research is a no-no in twenty-first-century science, certain inborn conditions also suggest that the way we are wired for oxytocin can affect our relationships with others.
Autism, Anti-Autism, and Oxytocin Genes
One of the first things Vanessa Coggshall noticed about her newborn daughter, Emmy, was her big smile. Even when the two were still at the hospital’s maternity ward in Summit, New Jersey, Emmy would grin ear to ear in a fashion that’s certainly not typical for little humans of just a few days of age. “I’ve never seen a baby with a smile like that,” Coggshall says.
Now, at six years old, Emmy is a particularly cheerful and friendly kid. “She goes up to everybody and says, ‘Hi my name is Emmy, what’s your name?’ She will often throw compliments at people. We might be in a grocery store and she would say to a woman there, ‘I like your shirt. That’s a nice colour on you,’ ” Coggshall says. As many parents of preschoolers, myself included, know well, kids that age are far more likely to hide shyly behind their parents’ legs when faced by an adult stranger than to start small talk. Vanessa admits that Emmy’s behaviour tends to throw people off. They often stare at her, surprised. But Emmy just shakes it off and moves on to the next person.
Sometimes called anti-autism, the condition that Emmy has is known as Williams syndrome. It’s caused by a deletion of about twe
nty-seven genes which results in attraction to strangers, happy-go-lucky personality, and a penchant for looking everybody in the eye. It may all seem like a good thing, but there is a dark side to the condition, too: heart problems, decreased bone mineral density, diabetes, and, on the behavioural side—simply trusting others too much.
Williams syndrome is very rare—it affects only about one person in ten thousand. Yet it gives researchers a unique look into genetic influences on our social brains. People like Emmy tend to have particularly high levels of oxytocin and vasopressin in their blood, which is connected to the so-called pro-sociality gene, GTF2I—and the likely reason why they are so extraordinarily friendly and trusting.
Autism, too, scientists believe, may be connected to oxytocin wiring in the brain. Mice that don’t have oxytocin receptor genes tend to behave in autistic ways––they have a penchant for repetitive behaviours, for instance. Also, some experiments have shown that spraying oxytocin into the noses of kids with autism may boost their social skills. But if you have someone with autism in your family, don’t rush to stock up on OxyLuv just yet. The work on such treatments is still in the early stages.
People with Williams syndrome or autism may stand out when it comes to their oxytocin systems, but it’s not as if the rest of us are equal where oxytocin genes and sociality are concerned. In fact, there exist many variations in oxytocin genes that can explain why not everyone has the same social temperament. You may be someone with the AA genotype, for example (not to be confused with type A personality). You can’t say “Oh, I’m a type AA personality”—you may simply have the AA genotype of one oxytocin receptor gene.
Growing Young Page 7
