Mothers and Others

by Sarah Blaffer Hrdy

  Right from the outset, then, brains of potential caregivers can be different. Such differences are likely to be further magnified by variation in caretaking opportunities, life experiences, and specific behaviors. A behavior known as placentophagia, placenta-eating, provides a case in point.

  CONSUMING QUESTIONS

  The placenta is an endocrine organ that synthesizes various hormones, including several steroids. At birth, both the “afterbirth” and the accompanying amniotic fluid are awash in opioid analgesics. Some scientists speculate that mothers giving birth to litters eagerly lick off amniotic fluid from each pup during short breaks in the delivery process and consume the liverlike placenta as a means of self-medicating. This is not just a matter of good house- (or, more precisely, den-) keeping. The mother’s anesthetizing cocktail eases the pain of birth and keeps her calm and on task. For even though birth in other mammals is not as tight a squeeze as it is in humans, it still hurts. A dog, for example, may give a little “yelp” as each pup emerges. The same regions of the brain that influence maternal behaviors also influence whether a mother consumes the afterbirth.

  The act of eating the placenta can in turn accelerate the onset of maternal behaviors.14 This is why it is worth noting just which individuals are interested in eating the placenta. In species with a lot of nonmaternal caregiving, such as marmosets and some hamsters, males as well as females, and in some cases prereproductives of both sexes, are as eager to eat placentas as mothers are, yet these juveniles and males have no need to dull birth pangs. I still recall how stunned I was when the primatologist Jeff French showed a video clip of birth among Brazilian bare-eared marmosets (Callithrix argentata). At first I had trouble comprehending the actions of the struggling bodies on the screen. As the first of two babies emerged from his mother’s birth canal, a fierce tug-of-war was going on between the mother and an adult male who was trying to wrest control of the emerging baby. Then, after the second baby, as the placenta emerged, the male was vying with the mother for that as well, eager to have the first bite.15

  Placentophagia has been particularly well studied among the Djungarian hamsters (Phodopus campbelli) that the Canadian biologist Katherine Wynne-Edwards brought back from Mongolia so she could study them in her lab. The male in these hamsters, and sometimes prereproductive juveniles as well, serve as midwives, mechanically assisting the female as she gives birth. When on hand, these midwives may also greedily eat the placenta. By contrast, sheep, which lack allomaternal care by fathers or by anyone else, are repulsed by the smell of amniotic fluid and will not go near a placenta unless they have just given birth. In that case, rather magically, and for a brief period only, the newly delivered mother will find the smell and taste of the placenta and the amniotic fluid still coating it absolutely irresistible.

  In other words, it is not just babies that can be sensory traps. The chemical paraphernalia that accompany them into the world can be cues every bit as potent, providing their consumers with extra doses of nurture-promoting molecules.16 Placentophagia on the part of new mothers occurs nearly universally across carnivorous and herbivorous mammals with only a few exceptions, such as camilids and marine mammals. Across primates, however, the distribution of placenta-eating mothers is more sporadic, especially in the Great Apes. A new mother chimpanzee or gorilla will sometimes consume the placenta right after birth, even before she picks up the newborn lying beside her. At other times the mother will ignore the afterbirth, perhaps leaving it behind in the makeshift nest where she delivered her baby or, seemingly oblivious to it, dragging the placenta along behind her, still attached to her infant by the umbilical cord.

  Nonhuman ape mothers lack the fixed action patterns around the time of birth that are seen in other mammals like mice or dogs. Responses are even less automatic among humans. There are virtually no traditional societies in which mothers routinely eat the placenta. Even among people starved for protein, where meat of any kind is a highly desired commodity (as is the case among the Eipo of highland New Guinea and among Australian Aborigines) placentas are not eaten. Typically, the afterbirth is buried or otherwise discarded, sometimes with a special ceremony or other ritual treatment. Ironically, most reports of placentophagia in humans come from New Age parents, who mistakenly imagine they are reverting to a more traditional or “natural” mode of childbirth.17 Clearly, though, the custom is only natural if people are emulating prehuman rather than human ancestors.

  COMMODITIES IN THEIR OWN RIGHT

  Whether or not they eat the placenta, many primates are sensitive to infant cues and alert to their well-being. Even the most aloof male will rush to protect a threatened infant. Yet group members are not equally likely to seek to get their hands on or actually hold babies. In the next chapter, we will see how among langur monkeys it is the mother’s older female kin who are the most intrepid and determined in defending babies. Yet these same old females exhibit little interest in holding the babies they protect. Rather, it is the prereproductive juvenile and subadult females, those most in need of babies to practice with in advance of becoming mothers, who are most eager to touch, take, and carry infants. Young females go to the most trouble to keep babies content and quiet. More experienced adult females will occasionally take a baby and hold it for a few minutes, but they seem relatively blasé about the baby’s complaints. Younger, prereproductive females are more attentive and seem more concerned lest their charge’s cries attract a competing allomother. These immatures strive harder to keep their charges all to themselves and hold them the most number of minutes.18 That said, virtually all primate females find babies at least initially attractive and are eager for a closer look.

  This is certainly the case among savanna baboons. These mothers are exclusive caretakers of their infants during the first weeks of life, carrying them 100 percent of the time. Nevertheless, newborns attract intense interest from other females. Juveniles, subadults, and adults seek to sniff, inspect, and, if they possibly can, get their hands on the new baby. They persist in spite of the baboon mother’s possessive oversight, the tone of which can be summed up as “Touch maybe, if you must, but unless you happen to be much, much more dominant than me, don’t you dare take.” The only exceptions to this rule are low-ranking mothers who simply are not always able to assert their “parental rights,” as the Amboseli baboon researcher Jeanne Altmann puts it. In these circumstances, a dominant animal may forcibly kidnap a baby, which she then may or may not return.19 In species of cercopithecine monkeys with rigid dominance hierarchies, such kidnappings can have disastrous results if a nonlactating female refuses to give the baby back; in a few cases, infants have starved to death. The threat of kidnap is one reason mothers in species with rigid female dominance hierarchies (like baboons or rhesus macaques) are so unwilling to give up their infants. In species with more relaxed hierarchies, such as langurs, there is no such thing as a within-group kidnapping. Mothers can always get their babies back.20

  From the savannas of Africa to the forests of southern Mexico, baby monkeys are so attractive that little baboons and spider monkeys become commodities in a bustling simian marketplace. According to primatologists Peter Henzi and Louise Barrett, females essentially bargain for the right to touch babies. Adult female baboons who do not currently have an infant of their own provide many minutes of nonreciprocated grooming in exchange for being able to briefly touch another female’s three-month-old or younger infant. The younger the infant and the fewer other infants there are in the group at the time, the more attractive a specific infant tends to be. In line with conventional marketplace rules of supply-and-demand, the rarer the baby, the more minutes of grooming—or in the case of the New World spider monkeys, who rarely groom but hug instead, the more social massaging—is required for access. As Henzi and Barrett put it: “Grooming bout duration (the baboon price ‘paid’ for handling) was inversely related to the number of infants present in the group.”21

  Why strive so hard for access? Part of the answer is the need f
or experience. Far from automatic, competent caretaking requires practice. Lack of experience is a big factor in the extremely high mortality rates for firstborn infants recorded in every primate species for which we have data.22 This penalty for being born to a first-time (primiparous) mother may be especially high in species with a touch-but-don’t-take policy. We know from long-term records for the savanna baboons at Amboseli that infants of experienced mothers are twice as likely to survive as are those of primiparas (63 percent survival rate vs. 29 percent).23

  In infant-sharing species such as langurs, mothers may be reluctant to give up infants to very young females (under 13 months of age themselves), but as they age, and especially as they become more competent caretakers, prereproductive females get more access. Developmental age is clearly a factor in competence, but practice matters as well, including among females who have given birth before. Even experienced mothers benefit from brief refresher courses with borrowed babies, especially if they are pregnant and need a bit of priming to ensure that they respond appropriately as soon as their new baby emerges.24

  Among infant-sharing species, access to babies and opportunities to practice holding babies are a routine part of a maturing female’s life, with the result that by the time she first gives birth she is well versed in how to hold a baby and keep it comfortable and content.25 Practice is so important that, in situations where no new babies are present in a female’s own troop, an inexperienced young female may feel compelled by baby-lust to make a risky foray into a neighboring troop to try to steal one. In most cases the darting interloper is chased away, but very, very occasionally a langur succeeds in taking a new baby from a female in another troop.

  The magnetic attraction of neonates incites spirited competition between inexperienced young langur allomothers to get hold of the newest arrival, especially when babies are scarce. An allomother will run off three-legged, holding her prize with one arm against her body, stopping every so often to pat and cajole it so as to cut down on the baby’s whining. It’s as if the nursemaid recognizes that the cries might attract a competing caregiver. They remind me of Gollum in The Lord of the Rings, obsessively eager to hold tight to his “precious.”

  NATAL ATTRACTIONS

  Once natural selection starts to favor parents and alloparents who are responsive to babies, this changes the playing field for the infants themselves. Wherever babies who attract the most care are most likely to survive, natural selection is going to favor those who broadcast even more appealing cues or whose attractive signals are broadcast further. After all, other immatures may be competing for allomaternal attention as well. Thus maternal or allomaternal biases in favor of the youngest and most vulnerable immatures produces selection for traits that accentuate “babiness,” rendering immatures cuter and cuddlier still, more delectable to protect or hold.

  A self-reinforcing evolutionary process produces parents and alloparents who are more sensitive to infantile signals and babies who are better at emitting them. Such processes have certainly been at work in humans, as evidenced by recent neurophysiological research at Oxford University. Twelve adults, three of them parents, nine of them childless, were shown portraits of unfamiliar infants. Within a seventh of a second, brain scans detected specific neural signatures in the medial orbitofrontal cortex, a region of the brain implicated in monitoring, learning, and remembering rewarding experiences.26 The response was quite different from the signature produced when the same people looked at the faces of other adults, and occurred far too fast to be conscious.

  The media went wild. One headline read: “Neural Basis for Parental Instinct Found.” Yet only three of the study subjects had actually been parents. Magnetoencephalographic scans of the remaining nine nonparents revealed the same highly specific brain activity. Hence, this near-immediate response to a baby’s face was a generalized reaction found in parents and nonparents alike. I predict that similar neural signatures will also be found in other primates exposed to infantile traits. By then I hope the headlines read: “Neural Basis for Alloparental Responses Confirmed.”

  Most primates are born looking very different from adults. Even in rhesus macaques or savanna baboons, among whom mothers do not allow other group members to take their newborns, babies wear black natal coats accessorized by bright pink skin around their ears, feet, and rump, as if to reinforce the brand “Really New Baby.” (I have even wondered if perhaps the recently reported preference for the color pink found in women but not in men might not be a leftover maternal response to infant coloration in primates.)27 In infant-sharing species where several new babies are simultaneously available, as when births are clustered in one season, there is going to be intense competition between babies to attract the attention of caretakers. The outcome can be spectacular.28

  Like other primates, humans find babies irresistible. The discovery of this innate human attraction to infantile traits was one of the early triumphs of ethology, and this attraction continues to provide an important source of revenue for Walt Disney and Madison Avenue. As early as the 1950s, Konrad Lorenz identified a suite of traits contributing to the perception of infants as adorable, what he called kindchenschema (infant schema). These include a relatively large head; large, low-lying eyes; and pudgy cheeks. Together with short, thick extremities and clumsy, gamboling movements, such infantile features render baby animals luscious and irresistibly appealing. Infantilized dog breeds (like pug-nosed Pekinese) and manufactured baby dolls exploit these innate responses. Even though humans are universally responsive to infant cues, the thresholds for responding vary with the receiver’s age, sex, and experience (both past and recent) with babies. Thirty years after Lorenz published this diagram, the ethologist Thomas Alley asked 120 childless undergraduates to examine drawings of children that differed in size and in how immature the proportions seemed. For both sexes the “mean cuddliness rating” decreased with perceived age, but subjects with younger siblings proved most responsive. Even though women were on average significantly more protective than men were, both sexes became responsive to infants after prolonged exposure. Given such propensities, it is perhaps not surprising that so many members of our species become attached to puppies and other pets with babylike attributes. U.S. pet owners spend some $41 billion a year on the purchase, grooming, boarding, feeding, and veterinary care of their dogs, cats, and other miscellaneous pets. Based on a 2004 survey by the American Pet Products Manufacturers Association, one third of such small animal owners specifically say that they consider their pets as immature family members. (Lorenz 1950, rpt. 1971:155)

  Among some of the infant-sharing primates where allomaternal care of infants is beneficial to their mothers and where infants are in competition with other infants born around the same time to attract this care, neonatal coats have evolved to be more than just distinctive; they are positively flamboyant, visible to would-be caregivers from far away. But since birds of prey, often the biggest predators upon arboreal monkeys, have excellent color vision, flamboyant natal coats are visible to them as well. From high above the forest, these raptors can also pick up the message “New baby on board,” suggesting that the advantages to infants from being desirable commodities must have been great enough to outweigh this extra risk.

  Within the far-flung subfamily Colobinae, infant-sharing species across Africa, Asia, Southeast Asia, Borneo, and Sumatra have evolved a diverse wardrobe of natal coats. Ebony langurs from Java, dusky leaf monkeys from Malaya, and silver leaf monkeys from Borneo are all born bright orange, reflecting the sunlight like spun gold. Sumatran mitered leaf monkeys are born white with a dark stripe down the back crisscrossed by another stripe across the shoulders, while Bornean proboscis monkeys are born with robin’s-egg-blue faces and distinctive, upturned blue noses. African black-and-white colobus babies are born covered in snowy white fur. Are these monkeys really so different from the dowdy jeans-wearing parents in Harvard Square who squire about children wearing brightly colored designer outfits?

 
Locale to locale, Mother Nature had to make do with the genetic materials she had at hand, but wherever benefits outweighed the costs, natural selection favored the production of infants that advertised their status as really new babies, helping to ensure their care. Over the hundreds of thousands of years it took to evolve flamboyant natal coats, attracting allomothers must have been sufficiently important to parental reproductive success to make this a good bet despite the increased predation risks.

  But wait, some primate-savvy reader might say. Given how especially important alloparents are to callitrichids, why is it that marmoset and tamarin infants arrive in the world dressed so much like their grown-up parents? Baby golden lion tamarins, for example, are born the same color as their parents, distinguished only by a contrasting black stripe down the middle of their forehead. Such drabness seems to challenge the hypothesis that reliance on shared care favors the evolution of fancy natal coats. Rather than brightly broadcasting their neonativity, babies whose survival will depend absolutely on allomaternal attention wear uniforms that blend discreetly into the fur of the adult to whose back they cling. One possible explanation is that marmoset babies do not have to compete for alloparental attentions as much, since ordinarily only one mother is producing at a time. Alternatively, such seeming anomalies may be reminders of the constraints past evolutionary history places on natural selection. Rather than devising the perfect solution in the most efficient possible way, Old Mother Nature had to make do with what she had on hand, the ingredients in her cupboard left over from previous creations, a matter of phylogeny.

  In some infant-sharing monkeys there has been selection on infants to attract allomaternal attentions by evolving distinctive natal coats visible at a distance. These black-and-white colobus monkey babies arrive in the world snow-white, then gradually over the first months of life morph into the black-and-white dress of adults. As far as allomothers are concerned, the younger the baby, the more powerful the stimulus. Gradual loss of the natal coat coincides with declining allomaternal interest. (Noel Rowe/All The World’s Primates)