The Fear Factor Read online

  This elixir is directly responsible for the emergence of all the diverse modern-day mammals that populate the earth today, humans included. We could never have survived without it. It’s little wonder that mammals were named for the very glands that produce it. Milk allows metabolically greedy mammalian babies to be born small and underdeveloped and to survive their vulnerable infancy by receiving all of their nourishment from their mother while staying warm and expending almost no effort—not even chewing. It allows mammalian babies to thrive in nearly any ecological niche, since they need neither to compete with adults for food nor to find an alternative—and likely inferior—food source. This makes milk a likely reason that so many mammals survived the aftermath of the cataclysmic asteroid strike that killed off the dinosaurs. Milk also allows mammals to sustain unusual and beneficial growth patterns, like disproportionately rapid growth of the head and brain soon after birth. And finally, milk ultimately transformed the social life of the mammals who consume and produce it as well. Consuming milk is no mere luxury for mammalian babies but a necessity, so milk is the reason that mammalian babies remain dependent on and attached to their mothers for weeks or months or years—and the reason that their mothers remain attached to their offspring as well.

  Milk is, in other words, the prime mover behind many of the psychological, behavioral, and social features that separate mammals from all the creatures who came before them, and from many who came after as well. This was an inevitable outcome, since the ability to produce milk would be a useless adaptation in isolation. It’s only worthwhile if accompanied by a suite of other changes that ensure that infants actually benefit from the milk.

  What is the first and most essential of these changes?

  Love.

  Or, if it makes you uncomfortable to think of the same animals that we eat for dinner and experiment on in laboratories experiencing love, call it caring, which is love’s behavioral expression. It doesn’t really matter what you call it—it all boils down to the same thing.

  And that thing is that producing milk to sustain altricial offspring is useful only if the mother stays in frequent and very close contact with her offspring to feed them the milk—literally pressing her body against them or cradling them or hovering directly above them for stretches of time every day for weeks or months to allow them to drink their fill. And no mother is going to do this every day, without fail, for every infant or litter of infants she produces, breeding season after breeding season, unless some powerful motivational tether keeps pulling her back to her babies again and again when she could be out doing something easier or more fun or interesting than hanging around being drained of her own liquefied flesh and bone. And that tether is love.

  That love underlies the urge to be in physical contact with the newborn offspring as much as possible. To smell their intoxicating smell, to gaze at the endless wrinkles and curves of their small, strange bodies. To find their simple presence wildly reinforcing, and to feel the fierce longing of an addict when separated from them. To want to stroke them or cradle them or lick them or nuzzle them (depending on the species and available appendages) and protect them from the amorphous terrible dangers of the world. And of particular interest, to care about their welfare: to fly into action when they are distressed or in danger, and to feel pleasure in their contentment. Human mothers share these urges with every mammalian mother alive today—all thanks to our cynodont ancestors.

  I am a mother myself, twice over, and I am all too aware of how heady and overpowering maternal love can be. That said, the births of my daughters did not represent the first or only times I have experienced fierce, heady, gripping love. You may recognize many of the features of maternal love from other loving relationships you’ve had—romantic love in particular has many of the same intoxicating qualities. There is a reason for that. It is thought that the capacity for love and caring of all kinds, from romantic to filial to sibling love, even love of friends or pets, grew out of the capacity for maternal love. Once the proto-mammalian brain was equipped with the wholly novel and evolutionarily necessary capacity to care about the welfare of other beings outside the self, there was no limit to what other kinds of love could theoretically be felt. It’s little wonder that the ethologist Irenäus Eibl-Eibesfeldt viewed the emergence of maternal nurturing as “a turning point in the evolution of vertebrate behavior—one of those celestial moments that [a poet] would call a star hour.”

  I don’t think that is an understatement. As far as we know, the vast, cold universe existed for billions of years without love existing anywhere within it. Then, following the need of a few furry protomammals to keep their young fed and warm, it did. It was an explosion into being as magnificent as the birth of any star.

  One of maternal love’s most impressive properties is its capacity for spontaneous combustion. Ideally, a burst of love goes off like gunpowder inside every new mother’s brain when she gets her first look at or whiff of her offspring and feels their first fumbling efforts to feed. The love needs to come on rapidly and powerfully in part because it needs to override or eliminate any fear she might otherwise have of the strange new creatures before her. Altricial babies need food and warmth right away—there is no time for a protracted warming-up period.

  If it strikes you as silly to be afraid of a baby, that’s only because you are the descendant of cynodonts. Objectively speaking, altricial mammalian babies look funny and smell funny and make horrible, strange noises, and to top it all off, they are by definition complete strangers. Their mother has never encountered them before in her life. Normally, a little healthy fear of anything strange and new is a good thing. But a mammalian mother can’t be put off by her babies’ funny looks or smells or newness. Her love must draw her near to these little strangers immediately and keep her there, giving them food and warmth despite everything. And, as long as she’s going to commit all these resources to her babies, it would really be ideal if her babies survived to make her investment worthwhile. So she needs to not only stay physically close but to pay close attention to the welfare of each baby too. Is it content? Or is it upset? Does it need something? More food? Warmth? Did it somehow stray from the nest or lose track of her? Is it trying to get back to safety? Does it need cleaning? Is it hurt? Is it in danger?

  That all of these new features—altricial young, milk production, attentive maternal care, and intense investment in each offspring—came bundled together might seem improbable bordering on miraculous. But this bundling is in perfect accordance with something called life history theory. According to the theory, the reproductive strategies that a given species can adopt lie on a continuum. At one end of the continuum sit species like loggerhead turtles that are r-selected, meaning that their reproduction is limited by the available resources. R-selected species tend to produce precocial offspring, invest few resources in them, and provide them with little or no care. As a result, most of these offspring die young. But r-selected species produce so many offspring that only a few need to survive to keep the species going. It’s a mass-production approach to reproduction that seems terribly heartless and wasteful to us because our ancestors shifted so dramatically away from it. Cynodonts and most of their descendants follow more K-selected strategies, which you could think of as an artisanal approach to reproduction. Mothers who follow a K–selected strategy produce altricial offspring and so must devote time and energy to keeping them alive. As a result, they can’t have nearly as many of them. Instead, they lavish the few babies they have with nourishment and care to maximize their odds of surviving to adulthood. We humans, with our small numbers of desperately needy and altricial offspring who require well over a decade of parental time and energy before they reach maturity, are about as K-selected as an animal can get.

  The changes in reproductive strategies that our small, warm-blooded ancestors underwent to keep their babies alive beautifully capture the reason why a mother loggerhead could lay her eggs in the sand and then disappear without giving the proge
ny they contain a further thought while I found myself overwhelmed by anxiety and protective feelings for her hatchlings. Her chelonioidea brain simply could not conceive of love. It doesn’t have the requisite wiring, because it never needed to. But my K-selected mammalian brain comes prepared to love and dote on babies, to treat each one like a precious gem that requires abundant care and nurturing and protection.

  “Okay,” you might reasonably retort, “that would make sense if you were talking about caring for your own babies. But why on earth would your K-selected mammalian brain have prepared you to care for turtle babies?”

  This is not a bad question.

  In truth, many mammals would not care at all about turtle babies. They would be much more likely to step over them or on them, or to eat them, than to usher them to the water or heckle gulls on their behalf. These differences stem in part from how precisely tuned a species’ parental nurturing response is. All mammalian species must come prepared to care for their own babies. But the degree to which they will care for other babies varies widely. Ruminants like sheep, for example, are usually uninterested in any babies other than their own. After a newborn lamb first drops to the ground in an amniotic clump, his mother will spend the next several minutes assiduously licking him off, then nudge him to begin nursing. Their licking and nudging and nursing allows the mother and lamb to learn each other’s unique smells and to imprint upon one another. After a few hours, the imprinting window will close, and it is very difficult to get it to open again. Thereafter, the ewe will reserve all of her nurturing and milk for her own lamb and skirt away from or even butt away any other lambs who try to intrude. If a lamb is orphaned, it is unlikely to be adopted and will probably starve, even in a flock full of bulging udders. You can bet that a ewe who would complacently allow a herd-mate’s lamb to starve to death would not give a fig about a turtle hatchling.

  Compare this to the open-armed mothering that can be observed in the humble rat. Rats are devoted mothers who will work strenuously to stay close to their pups. They will cross painful electrified metal grids—the rat equivalent of walking over coals—if their babies are marooned on the other side. Mother rats will tolerate more such suffering to reach their pups than hungry rats will undergo to reach food, or thirsty rats to reach water. But perhaps more remarkably, rats will struggle and suffer even for babies that are not their own, even for babies they have never seen before.

  My colleague Stephanie Preston, a psychologist at the University of Michigan, recently unearthed a long-forgotten 1968 study by William Wilsoncroft that demonstrated this fact. Wilsoncroft and his students selected five pregnant rats for their study and taught each one that when she pressed down on a bar in her testing box, a piece of Purina rat chow would come tumbling down a nearby chute into her dish. If pregnant rats experience the same rapacious hunger I did when I was pregnant, I’m sure they were all too happy to learn this task.

  Then, after the mother rats gave birth, they were given one day to bond with and nurse their pups before the researchers whisked the pups from their nests. When the mystified mothers emerged from their empty nests to return to bar-pressing, they once again found that chow came tumbling down the chute. At least, it did after the first six bar presses. The seventh time a mother pressed the bar it was followed, not by the dry rattle of a piece of rat chow, but the soft thumping of a pink, hairless pup. Down the chute tumbled one of the mother’s lost pups, right into her dish! I leave it to you to imagine what the mothers made of this development. Two of the five immediately did what attentive mother rats do, which was to pick up the pup gently in her teeth and carry it back to the safety of the nest, some three feet away. The other three pressed the bar a few more times first and found that after each press another pup tumbled down. Soon all the mothers were on the same page—pressing the bar and toting their lost pups to their nest.

  But the experiment wasn’t over. On the thirteenth bar press, something new happened again: this time the pup who tumbled down the chute and into the cup wasn’t one of the mother’s own pups but a stranger. She had never encountered this pup before in her life. Now what? If mother rats were like ewes, the strange pups would be doomed to starve in the dish. Fortunately, mother rats take a different approach to mothering, which is a pup is a pup is a pup. None of the five so much as hesitated. They all picked up the strange pups, carried them back to the nest, and deposited them among their own pups. Then they went back to the bar and pressed again—and again and again, bringing pup after pup back to the nest, both their own pups and pups that were strangers.

  How long do you think this process went on? Ten minutes? An hour? The surprising answer is that it never did end. The ones who put a stop to the parade of pup-toting were the researchers, who after three hours of refilling the hopper with pups ended the experiment in exhaustion. During this time the supermom of the group, Rat 5, retrieved an astonishing 684 pups from the dish (although in reality it was the same set of 20 or so pups, recycled many times over). That’s a pup every fifteen seconds for three hours, without a break, carted back to the nest for a total distance of over 2,000 feet. But even the least energetic of the mothers retrieved a total of 247 pups back to the nest. Moreover, all the mothers were equally attentive when confronted with both their own and strange pups, which suggests that for some mammalian mothers, anything that trips the “baby!” alarm is a call to maternal action (even if, again, this alarm did not always sound equally urgently in all the mothers).

  This take-all-comers approach to mothering is not unique to rats. Many other group-living mammals excel in allomothering, which literally means “other mothering,” or taking care of infants other than one’s own. Allomothering can include anything from toting around other mothers’ babies to protecting them from danger to nursing them. In some cases, allomothers even foster or wholly adopt orphaned animals. Allomothers are often sisters, aunts, and other adolescent or adult female relatives, but not always. Females of many species allomother unrelated infants as well. And despite what the term implies, males also allomother, contributing to nearly every aspect of parenting other than nursing across a variety of species.

  The emergence of allomothering within a species is largely driven by the neediness of the species’ young. It’s a behavior that is at least three times more likely to arise in animals that bear altricial babies. Hence sheep, which are born woolly and able to stand and walk within minutes, do not allomother, whereas rats, which are born naked, blind, and totally helpless, do. Among the many other mammals renowned for their energetic allomothering are meerkats, seals, sea lions, jackals, wolves, domestic dogs, and lions. Consider for a moment the fact that these highly nurturant species are also all predatory carnivores. Their ferocity on the hunt makes for a striking juxtaposition with the gentleness and devotion that female jackals, wolves, and lions show not only their own but other females’ young. The same lioness who runs down and eviscerates a wildebeest one minute may well groom and nurse another female’s cubs the next. It also makes for an interesting contrast with sheep, who are often depicted as quintessentially innocent and gentle creatures but can be callous or downright cruel toward each other’s lambs. It’s a good reminder that there is nothing unnatural or even surprising about the capacities for genuine ferocity and genuine nurturing care coexisting within a single species, or a single individual.

  One spectacular demonstration of this is a Kenyan lioness dubbed Kamunyak, or “Blessed One,” who in 2001 was discovered in close proximity to an oryx calf that, to the astonishment of the locals who discovered them, was not dead. Oryxes are antelopes, which are favored prey for lions. So what was going on with Kamunyak? Nobody knows for certain, but it is thought that she may have chanced upon the calf and its mother, and the mother had bolted. Ordinarily that would have been the end of the calf. But not only did Kamunyak not attack the abandoned calf, she adopted it. For days she could be seen lying or walking by its side, occasionally even grooming it with her rough tongue. She responded atten
tively when it cried out and was fiercely protective of its safety, keeping it away from humans who ventured too close and at one point chasing off a leopard. She wouldn’t leave the calf long enough to find food for herself, so she must have been very hungry. Yet still she cared for the little calf until it ultimately met a sad end—it was killed and eaten by another lion after it ventured out of Kamunyak’s sight for a moment. By all appearances, Kamunyak grieved the death of her charge, rushing the lion who had attacked it and then, when nothing more could be done, wandering around roaring mournfully. But it wasn’t long before Kamunyak was spotted with another calf—the second of six oryxes that she would ultimately attempt to adopt. Her mothering skills improved over time; starting with her third adoptee, she briefly allowed the calves to nurse from their mothers before chasing the mothers away again.

  Although her behavior was undoubtedly unusual—visitors to her park flocked to see a lion quite literally lying down with, if not a lamb, a similarly vulnerable antelope calf—Kamunyak was no singularity. Another lioness in Uganda was recently seen toting around an antelope calf by the scruff of its neck as though it were an unusually gangly cub; later she was spotted allowing it to try (fruitlessly) to nurse. And in 2014, photographers in Botswana observed yet another lioness kill an adult female baboon that was carrying a baby at the time. The infant tried to escape but wasn’t yet strong enough to climb a nearby tree. The lioness walked over to investigate and, spotting the baby, pawed at it gently with her massive forefoot. Eventually, she picked the baby up—as though it was one of Wilsoncroft’s tumbling rat pups—and carried it a short distance away, whereupon she lay down in the shade and deposited it between her front feet. The photographers captured images of the baby trying to suckle from the lioness’s bristly chest, and of the lioness charging a male who attempted to encroach. Retrieval, caressing, nursing, defense—the full suite of mammalian mothering behaviors—were all shown by a lion for a baby baboon!