“Some of these stories are closer to my own life than others are, but not one of them is as close as people seem to think.” Alice Murno, from the intro to Moons of Jupiter

"Talent hits a target no one else can hit; genius hits a target no one else can see." Arthur Schopenhauer

“Why does everything you know, and everything you’ve learned, confirm you in what you believed before? Whereas in my case, what I grew up with, and what I thought I believed, is chipped away a little and a little, a fragment then a piece and then a piece more. With every month that passes, the corners are knocked off the certainties of this world: and the next world too. Show me where it says, in the Bible, ‘Purgatory.’ Show me where it says ‘relics, monks, nuns.’ Show me where it says ‘Pope.’” –Thomas Cromwell imagines asking Thomas More—Wolf Hall by Hilary Mantel

My favorite posts to get started: The Self-Righteousness Instinct, Sabbath Says, Encounters, Inc., and What Makes "Wolf Hall" so Great?.

Sunday, February 3, 2013

The Feminist Sociobiologist: An Appreciation of Sarah Blaffer Hrdy Disguised as a Review of “Mothers and Others: The Evolutionary Origins of Mutual Understanding”

           One way to think of the job of anthropologists studying human evolution is to divide it into two basic components: the first is to arrive at a comprehensive and precise catalogue of the features and behaviors that make humans different from the species most closely related to us, and the second is to arrange all these differences in order of their emergence in our ancestral line. Knowing what came first is essential—though not sufficient—to the task of distinguishing between causes and effects. For instance, humans have brains that are significantly larger than those of any other primate, and we use these brains to fashion tools that are far more elaborate than the stones, sticks, leaves, and sponges used by other apes. Humans are also the only living ape that routinely walks upright on two legs. Since most of us probably give pride of place in the hierarchy of our species’ idiosyncrasies to our intelligence, we can sympathize with early Darwinian thinkers who felt sure brain expansion must have been what started our ancestors down their unique trajectory, making possible the development of increasingly complex tools, which in turn made having our hands liberated from locomotion duty ever more advantageous.
This hypothetical sequence, however, was dashed rather dramatically with the discovery in 1974 of Lucy, the 3.2 million-year-old skeleton of an Australopithecus Afarensis, in Ethiopia. Lucy resembles a chimpanzee in most respects, including cranial capacity, except that her bones have all the hallmarks of a creature with a bipedal gait. Anthropologists like to joke that Lucy proved butts were more important to our evolution than brains. But, though intelligence wasn’t the first of our distinctive traits to evolve, most scientists still believe it was the deciding factor behind our current dominance. At least for now, humans go into the jungle and build zoos and research facilities to study apes, not the other way around. Other apes certainly can’t compete with humans in terms of sheer numbers. Still, intelligence is a catch-all term. We must ask what exactly it is that our bigger brains can do better than those of our phylogenetic cousins.
A couple decades ago, that key capacity was thought to be language, which makes symbolic thought possible. Or is it symbolic thought that makes language possible? Either way, though a handful of ape prodigies have amassed some high vocabulary scores in labs where they’ve been taught to use pictographs or sign language, human three-year-olds accomplish similar feats as a routine part of their development. As primatologist and sociobiologist (one of the few who unabashedly uses that term for her field) Sarah Blaffer Hrdy explains in her 2009 book Mothers and Others: The Evolutionary Origins of Mutual Understanding, human language relies on abilities and interests aside from a mere reporting on the state of the outside world, beyond simply matching objects or actions with symbolic labels. Honeybees signal the location of food with their dances, vervet monkeys have distinct signals for attacks by flying versus ground-approaching predators, and the list goes on. Where humans excel when it comes to language is not just in the realm of versatility, but also in our desire to bond through these communicative efforts. Hrdy writes,
The open-ended qualities of language go beyond signaling. The impetus for language has to do with wanting to “tell” someone else what is on our minds and learn what is on theirs. The desire to psychologically connect with others had to evolve before language. (38)
The question Hrdy attempts to answer in Mothers and Others—the difference between humans and other apes she wants to place within a theoretical sequence of evolutionary developments—is how we evolved to be so docile, tolerant, and nice as to be able to cram ourselves by the dozens into tight spaces like airplanes without conflict. “I cannot help wondering,” she recalls having thought in a plane preparing for flight,
what would happen if my fellow human passengers suddenly morphed into another species of ape. What if I were traveling with a planeload of chimpanzees? Any of us would be lucky to disembark with all ten fingers and toes still attached, with the baby still breathing and unmaimed. Bloody earlobes and other appendages would litter the aisles. Compressing so many highly impulsive strangers into a tight space would be a recipe for mayhem. (3)
Over the past decade, the human capacity for cooperation, and even for altruism, has been at the center of evolutionary theorizing. Some clever experiments in the field of economic game theory have revealed several scenarios in which humans can be counted on to act against their own interest. What survival and reproductive advantages could possibly accrue to creatures given to acting for the benefit of others?
Sarah Blaffer Hrdy as allomother
When it comes to economic exchanges, of course, human thinking isn’t tied to the here-and-now the way the thinking of other animals tends to be. To explain why humans might, say, forgo a small payment in exchange for the opportunity to punish a trading partner for withholding a larger, fairer payment, many behavioral scientists point out that humans seldom think in terms of one-off deals. Any human living in a society of other humans needs to protect his or her reputation for not being someone who abides cheating. Experimental settings are well and good, but throughout human evolutionary history individuals could never have been sure they wouldn’t encounter exchange partners a second or third time in the future. It so happens that one of the dominant theories to explain ape intelligence relies on the need for individuals within somewhat stable societies to track who owes whom favors, who is subordinate to whom, and who can successfully deceive whom. This “Machiavellian intelligence” hypothesis explains the cleverness of humans and other apes as the outcome of countless generations vying for status and reproductive opportunities in intensely competitive social groups.
One of the difficulties in trying to account for the evolution of intelligence is that its advantages seem like such a no-brainer. Isn’t it always better to be smarter? But, as Hrdy points out, the Machiavellian intelligence hypothesis runs into a serious problem. Social competition may have been an important factor in making primates brainer than other mammals, but it can’t explain why humans are brainer than other apes. She writes,
We still have to explain why humans are so much better than chimpanzees at conceptualizing what others are thinking, why we are born innately eager to interpret their motives, feelings, and intentions as well as care about their affective states and moods—in short, why humans are so well equipped for mutual understanding. Chimpanzees, after all, are at least as socially competitive as humans are. (46)
Meltzoff's famous experiment
To bolster this point, Hrdy cites research showing that infant chimps have some dazzling social abilities once thought to belong solely to humans. In 1977, developmental psychologist Andrew Meltzoff published his finding that newborn humans mirror the facial expressions of adults they engage with. It was thought that this tendency in humans relied on some neurological structures unique to our lineage which provided the raw material for the evolution of our incomparable social intelligence. But then in 1996 primatologist Masako Myowa replicated Meltzoff’s findings with infant chimps. This and other research suggests that other apes have probably had much the same raw material for natural selection to act on. Yet, whereas the imitative and empathic skills flourish in maturing humans, they seem to atrophy in apes. Hrdy explains,
Myowa's replication with a chimp
Even though other primates are turning out to be far better at reading intentions than primatologists initially realized, early flickerings of empathic interest—what might even be termed tentative quests for intersubjective engagement—fade away instead of developing and intensifying as they do in human children. (58)
So the question of what happened in human evolution to make us so different remains.
            Sarah Blaffer Hrdy exemplifies a rare, possibly unique, blend of scientific rigor and humanistic sensitivity—the vision of a great scientist and the fine observation of a novelist (or the vision of a great novelist and fine observation of a scientist). Reading her 1999 book, Mother Nature: A History of Mothers, Infants, and Natural Selection, was a watershed experience for me. In going beyond the realm of the literate into that of the literary while hewing closely to strict epistemic principle, she may surpass the accomplishments of even such great figures as Richard Dawkins and Stephen Jay Gould. In fact, since Mother Nature was one of the books through which I was introduced to sociobiology—more commonly known today as evolutionary psychology—I was a bit baffled at first by much of the criticism leveled against the field by Gould and others who claimed it was founded on overly simplistic premises and often produced theories that were politically reactionary.
            The theme to which Hrdy continually returns is the too-frequently overlooked role of women and their struggles in those hypothetical evolutionary sequences anthropologists string together. For inspiration in her battle against facile biological theories whose sole purpose is to provide a cheap rationale for the political status quo, she turned, not to a scientist, but a novelist. The man single-most responsible for the misapplication of Darwin’s theory of natural selection to the justification of human societal hierarchies was the philosopher Herbert Spencer, in whose eyes women were no more than what Hrdy characterizes as “Breeding Machines.” Spencer and his fellow evolutionists in the Victorian age, she explains in Mother Nature,

Herbert Spencer, coiner of the phrase "Survival of the fittest"
took for granted that being female forestalled women from evolving “the power of abstract reasoning and that most abstract of emotions, the sentiment of justice.” Predestined to be mothers, women were born to be passive and noncompetitive, intuitive rather than logical. Misinterpretations of the evidence regarding women’s intelligence were cleared up early in the twentieth century. More basic difficulties having to do with this overly narrow definition of female nature were incorporated into Darwinism proper and linger to the present day. (17)
Many women over the generations have been unable to envision a remedy for this bias in biology. Hrdy describes the reaction of a literary giant whose lead many have followed.
For Virginia Woolf, the biases were unforgivable. She rejected science outright. “Science, it would seem, in not sexless; she is a man, a father, and infected too,” Woolf warned back in 1938. Her diagnosis was accepted and passed on from woman to woman. It is still taught today in university courses. Such charges reinforce the alienation many women, especially feminists, feel toward evolutionary theory and fields like sociobiology. (xvii)
            But another literary luminary much closer to the advent of evolutionary thinking had a more constructive, and combative, response to short-sighted male biologists. And it is to her that Hrdy looks for inspiration. “I fall in Eliot’s camp,” she writes, “aware of the many sources of bias, but nevertheless impressed by the strength of science as a way of knowing” (xviii). She explains that George Eliot,
whose real name was Mary Ann Evans, recognized that her own experiences, frustrations, and desires did not fit within the narrow stereotypes scientists then prescribed for her sex. “I need not crush myself… within a mould of theory called Nature!” she wrote. Eliot’s primary interest was always human nature as it could be revealed through rational study. Thus she was already reading an advance copy of On the Origin of Species on November 24, 1859, the day Darwin’s book was published. For her, “Science has no sex… the mere knowing and reasoning faculties, if they act correctly, must go through the same process and arrive at the same result.” (xvii)
George Eliot (Mary Ann Evans)
Eliot’s distaste for Spencer’s idea that women’s bodies were designed to divert resources away from the brain to the womb was as personal as it was intellectual. She had in fact met and quickly fallen in love with Spencer in 1851. She went on to send him a proposal which he rejected on eugenic grounds: “…as far as posterity is concerned,” Hrdy quotes, “a cultivated intelligence based upon a bad physique is of little worth, seeing that its descendants will die out in a generation or two.” Eliot’s retort came in the form of a literary caricature—though Spencer already seems a bit like his own caricature. Hrdy writes,
In her first major novel, Adam Bede (read by Darwin as he relaxed after the exertions of preparing Origin for publication), Eliot put Spencer’s views concerning the diversion of somatic energy into reproduction in the mouth of a pedantic and blatantly misogynist old schoolmaster, Mr. Bartle: “That’s the way with these women—they’ve got no head-pieces to nourish, and so their food all runs either to fat or brats.” (17)
            A mother of three and an Emeritus Professor of Anthropology at the University of California, Davis, Hrdy is eloquent on the need for intelligence—and lots of familial and societal support—if one is to balance duties and ambitions like her own. Her first contribution to ethology came when she realized that the infanticide among hanuman langurs, which she’d gone to Mount Abu in Rajasthan, India to study at age 26 for her doctoral thesis, had nothing to do with overpopulation, as many suspected. Instead, the pattern she observed was that whenever an outside male deposed a group’s main breeder he immediately began exterminating all of the prior male’s offspring to induce the females to ovulate and give birth again—this time to the new male’s offspring. This was the selfish gene theory in action. But the females Hrdy was studying had an interesting response to this strategy.
In the early 1970s, it was still widely assumed by Darwinians that females were sexually passive and “coy.” Female langurs were anything but. When bands of roving males approached the troop, females would solicit them or actually leave their troop to go in search of them. On occasion, a female mated with invaders even though she was already pregnant and not ovulating (something else nonhuman primates were not supposed to do). Hence, I speculated that mothers were mating with outside males who might take over her troop one day. By casting wide the web of possible paternity, mothers could increase the prospects of future survival of offspring, since males almost never attack infants carried by females that, in the biblical sense of the word, they have “known.” Males use past relations with the mother as a cue to attack or tolerate her infant. (35)
Hrdy would go on to discover this was just one of myriad strategies primate females use to get their genes into future generations. The days of seeing females as passive vehicles while the males duke it out for evolutionary supremacy were now numbered.
            I’ll never forget the Young-Goodman-Brown experience of reading the twelfth chapter of Mother Nature, titled “Unnatural Mothers,” and covering an impressive variety of evidence sources that simply devastates any notion of women as nurturing automatons, evolved for the sole purpose of serving as loving mothers. The verdict researchers arrive at whenever they take an honest look into the practices of women with newborns is that care is contingent. To give just one example, Hrdy cites the history of one of the earliest foundling homes in the world, the “Hospital of the Innocents” in Florence.
Founded in 1419, with assistance from the silk guilds, the Ospedale delgi Innocenti was completed in 1445. Ninety foundlings were left there the first year. By 1539 (a famine year), 961 babies were left. Eventually five thousand infants a year poured in from all corners of Tuscany. (299)
What this means is that a troubling number of new mothers were realizing they couldn't care for their infants. Unfortunately, newborns without direct parental care seldom fare well. “Of 15,000 babies left at the Innocenti between 1755 and 1773,” Hrdy reports, “two thirds died before reaching their first birthday” (299). And there were fifteen other foundling homes in the Grand Duchy of Tuscany at the time.
            The chapter amounts to a worldwide tour of infant abandonment, exposure, or killing. (I remember having a nightmare after reading it about being off-balance and unable to set a foot down without stepping on a dead baby.) Researchers studying sudden infant death syndrome in London set up hidden cameras to monitor mothers interacting with babies but ended up videotaping them trying to smother them. Cases like this have made it necessary for psychiatrists to warn doctors studying the phenomenon “that some undeterminable portion of SIDS cases might be infanticides” (292). Why do so many mothers abandon or kill their babies? Turning to the ethnographic data, Hrdy explains,
Unusually detailed information was available for some dozen societies. At a gross level, the answer was obvious. Mothers kill their own infants where other forms of birth control are unavailable. Mothers were unwilling to commit themselves and had no way to delegate care of the unwanted infant to others—kin, strangers, or institutions. History and ecological constraints interact in complex ways to produce different solutions to unwanted births. (296)
Many scholars see the contingent nature of maternal care as evidence that motherhood is nothing but a social construct. Consistent with the blank-slate view of human nature, this theory holds that every aspect of child-rearing, whether pertaining to the roles of mothers or fathers, is determined solely by culture and therefore must be learned. Others, who simply can’t let go of the idea of women as virtuous vessels, suggest that these women, as numerous as they are, must all be deranged.
Daly and Wilson
            Hrdy demolishes both the purely social constructivist view and the suggestion of pathology. And her account of the factors that lead women to infanticide goes to the heart of her arguments about the centrality of female intelligence in the history of human evolution. Citing the pioneering work of evolutionary psychologists Martin Daly and MargoWilson, Hrdy writes,
How a mother, particularly a very young mother, treats one infant turns out to be a poor predictor of how she might treat another one born when she is older, or faced with improved circumstances. Even with culture held constant, observing modern Western women all inculcated with more or less the same post-Enlightenment values, maternal age turned out to be a better predictor of how effective a mother would be than specific personality traits or attitudes. Older women describe motherhood as more meaningful, are more likely to sacrifice themselves on behalf of a needy child, and mourn lost pregnancies more than do younger women. (314)
The takeaway is that a woman, to reproduce successfully, must assess her circumstances, including the level of support she can count on from kin, dads, and society. If she lacks the resources or the support necessary to raise the child, she may have to make a hard decision. But making that decision in the present unfavorable circumstances in no way precludes her from making the most of future opportunities to give birth to other children and raise them to reproductive age.
            Hrdy goes on to describe an experimental intervention that took place in a hospital located across the street from a foundling home in 17th century France. The Hospice des Enfants Assistes cared for indigent women and assisted them during childbirth. It was the only place where poor women could legally abandon their babies. What the French reformers did was tell a subset of the new mothers that they had to stay with their newborns for eight days after birth.
Under this “experimental” regimen, the proportion of destitute mothers who subsequently abandoned their babies dropped from 24 to 10 percent. Neither cultural concepts about babies nor their economic circumstances had changed. What changed was the degree to which they had become attached to their breast-feeding infants. It was as though their decision to abandon their babies and their attachment to their babies operated as two different systems. (315)

Following the originator of attachment theory, John Bowlby, who set out to integrate psychiatry and developmental psychology into an evolutionary framework, Hrdy points out that the emotions underlying the bond between mothers and infants (and fathers and infants too) are as universal as they are consequential. Indeed, the mothers who are forced to abandon their infants have to be savvy enough to realize they have to do so before these emotions are engaged or they will be unable to go through with the deed.

Part one of the attachment series
            Female strategy plays a crucial role in reproductive outcomes in several domains beyond the choice of whether or not to care for infants. Women must form bonds with other women for support, procure the protection of men (usually from other men), and lay the groundwork for their children’s own future reproductive success. And that’s just what women have to do before choosing a mate—a task that involves striking a balance between good genes and a high level of devotion—getting pregnant, and bringing the baby to term. The demographic transition that occurs when an agrarian society becomes increasingly industrialized is characterized at first by huge population increases as infant mortality drops but then levels off as women gain more control over their life trajectories. Here again, the choices women tend to make are at odds with Victorian (and modern evangelical) conceptions of their natural proclivities. Hrdy writes,
Since, formerly, status and well-being tended to be correlated with reproductive success, it is not surprising that mothers, especially those in higher social ranks, put the basics first. When confronted with a choice between striving for status and striving for children, mothers gave priority to status and “cultural success” ahead of a desire for many children. (366)
And then of course come all the important tasks and decisions associated with actually raising any children the women eventually do give birth to. One of the basic skill sets women have to master to be successful mothers is making and maintaining friendships; they must be socially savvy because more than with any other ape the support of helpers, what Hrdy calls allomothers, will determine the fate of their offspring.
            Mother Nature is a massive work—541pages before the endnotes—exploring motherhood through the lens of sociobiology and attachment theory. Mothers and Others is leaner, coming in at just under 300 pages, because its focus is narrower. Hrdy feels that in attempting to account for humans’ prosocial impulses over the past decade, the role of women and motherhood has once again been scanted. She points to the prevalence of theories focusing on competition between groups, with the edge going to those made up of the most cooperative and cohesive members. Such theories once again give the leading role to males and their conflicts, leaving half the species out of the story—unless that other half’s only role is to tend to the children and forage for food while the “band of brothers” is out heroically securing borders.
            Hrdy doesn’t weigh in directly on the growing controversy over whether group selection has operated as a significant force in human evolution. The problem she sees with intertribal warfare as an explanation for human generosity and empathy is that the timing isn’t right. What Hrdy is after are the selection pressures that led to the evolution of what she calls “emotionally modern humans,” the “people preadapted to get along with one another even when crowded together on an airplane” (66). And she argues that humans must have been emotionally modern before they could have further evolved to be cognitively modern. “Brains require care more than caring requires brains” (176). Her point is that bonds of mutual interest and concern came before language and the capacity for runaway inventiveness. Humans, Hrdy maintains, would have had to begin forming these bonds long before the effects of warfare were felt.
Apart from periodic increases in unusually rich locales, most Pleistocene humans lived at low population densities. The emergence of human mind reading and gift-giving almost certainly preceded the geographic spread of a species whose numbers did not begin to really expand until the past 70,000 years. With increasing population density (made possible, I would argue, because they were already good at cooperating), growing pressure on resources, and social stratification, there is little doubt that groups with greater internal cohesion would prevail over less cooperative groups. But what was the initial payoff? How could hypersocial apes evolve in the first place? (29)
In other words, what was it that took inborn capacities like mirroring an adult’s facial expressions, present in both human and chimp infants, and through generations of natural selection developed them into the intersubjective tendencies displayed by humans today?
            Like so many other anthropologists before her, Hrdy begins her attempt to answer this question by pointing to a trait present in humans but absent in our fellow apes. “Under natural conditions,” she writes, “an orangutan, chimpanzee, or gorilla baby nurses for four to seven years and at the outset is inseparable from his mother, remaining in intimate front-to-front contact 100 percent of the day and night” (68). But humans allow others to participate in the care of their babies almost immediately after giving birth to them. Who besides Sarah Blaffer Hrdy would have noticed this difference, or given it more than a passing thought? (Actually, there are quite a few candidates among anthropologists—Kristen Hawkes for instance.) Ape mothers remain in constant contact with their infants, whereas human mothers often hand over their babies to other women to hold as soon as they emerge from the womb. The difference goes far beyond physical contact. Humans are what Hrdy calls “cooperative breeders,” meaning a child will in effect have several parents aside from the primary one. Help from alloparents opens the way for an increasingly lengthy development, which is important because the more complex the trait—and human social intelligence is about as complex as they come—the longer it takes to develop in maturing individuals. Hrdy writes,
One widely accepted tenet of life history theory is that, across species, those with bigger babies relative to the mother’s body size will also tend to exhibit longer intervals between births because the more babies cost the mother to produce, the longer she will need to recoup before reproducing again. Yet humans—like marmosets—provide a paradoxical exception to this rule. Humans, who of all the apes produce the largest, slowest-maturing, and most costly babies, also breed the fastest. (101)
Those marmosets turn out to be central to Hrdy’s argument because, along with their cousins in the family Callitrichidae, the tamarins, they make up almost the totality of the primate species whom she classifies as “full-fledged cooperative breeders” (92). This and other similarities between humans and marmosets and tamarins have long been overlooked because anthropologists have understandably been focused on the great apes, as well as other common research subjects like baboons and macaques.
Golden Lion Tamarins, by Sarah Landry
            Callitrichidae, it so happens, engage in some uncannily human-like behaviors. Plenty of primate babies wail and shriek when they’re in distress, but infants who are frequently not in direct contact with their mothers would have to find a way to engage with them, as well as other potential caregivers, even when they aren’t in any trouble. “The repetitive, rhythmical vocalizations known as babbling,” Hrdy points out, “provided a particularly elaborate way to accomplish this” (122). But humans aren’t the only primates that babble “if by babble we mean repetitive strings of adultlike vocalizations uttered without vocal referents”; marmosets and tamarins do it too. Some of the other human-like patterns aren’t as cute though. Hrdy writes,
Shared care and provisioning clearly enhances maternal reproductive success, but there is also a dark side to such dependence. Not only are dominant females (especially pregnant ones) highly infanticidal, eliminating babies produced by competing breeders, but tamarin mothers short on help may abandon their own young, bailing out at birth by failing to pick up neonates when they fall to the ground or forcing clinging newborns off their bodies, sometimes even chewing on their hands or feet. (99)
It seems that the more cooperative infant care tends to be for a given species the more conditional it is—the more likely it will be refused when the necessary support of others can’t be counted on.
Kristen Hawkes
            Hrdy’s cooperative breeding hypothesis is an outgrowth of George Williams and Kristen Hawkes’s so-called “Grandmother Hypothesis.” For Hawkes, the important difference between humans and apes is that human females go on living for decades after menopause, whereas very few female apes—or any other mammals for that matter—live past their reproductive years. Hawkes hypothesized that the help of grandmothers made it possible for ever longer periods of dependent development for children, which in turn made it possible for the incomparable social intelligence of humans to evolve. Until recently, though, this theory had been unconvincing to anthropologists because a renowned compendium of data compiled by George Peter Murdock in his Ethnographic Atlas revealed that there was a strong trend toward patrilocal residence patterns in all the societies that had been studied. Since grandmothers are thought to be much more likely to help care for their daughters’ children than their sons’—owing to paternity uncertainty—the fact that most humans raise their children far from maternal grandmothers made any evolutionary role for them unlikely.
But then in 2004 anthropologist Helen Alvarez reexamined Murdock’s analysis of residence patterns and concluded that pronouncements about widespread patrilocality were based on a great deal of guesswork. After eliminating societies for which too little evidence existed to determine the nature of their residence practices, Alvarez calculated that the majority of the remaining societies were bilocal, which means couples move back and forth between the mother’s and the father’s groups. Citing “The Alvarez Corrective” and other evidence, Hrdy concludes,
Instead of some highly conserved tendency, the cross-cultural prevalence of patrilocal residence patterns looks less like an evolved human universal than a more recent adaptation to post-Pleistocene conditions, as hunters moved into northern climes where women could no longer gather wild plants year-round or as groups settled into circumscribed areas. (246)
But Hrdy extends the cast of alloparents to include a mother’s preadult daughters, as well as fathers and their extended families, although the male contribution is highly variable across cultures (and variable too of course among individual men).
            With the observation that human infants rely on multiple caregivers throughout development, Hrdy suggests the mystery of why selection favored the retention and elaboration of mind reading skills in humans but not in other apes can be solved by considering the life-and-death stakes for human babies trying to understand the intentions of mothers and others. She writes,
Babies passed around in this way would need to exercise a different skill set in order to monitor their mothers’ whereabouts. As part of the normal activity of maintaining contact both with their mothers and with sympathetic alloparents, they would find themselves looking for faces, staring at them, and trying to read what they reveal. (121)
Mothers, of course, would also have to be able to read the intentions of others whom they might consider handing their babies over to. So the selection pressure occurs on both sides of the generational divide. And now that she’s proposed her candidate for the single most pivotal transition in human evolution Hrdy’s next task is to place it in a sequence of other important evolutionary developments.
Without a doubt, highly complex coevolutionary processes were involved in the evolution of extended lifespans, prolonged childhoods, and bigger brains. What I want to stress here, however, is that cooperative breeding was the pre-existing condition that permitted the evolution of these traits in the hominin line. Creatures may not need big brains to evolve cooperative breeding, but hominins needed shared care and provisioning to evolve big brains. Cooperative breeding had to come first. (277)

Flipping through Mother Nature, a book I first read over ten years ago, I can feel some of the excitement I must have experienced as a young student of behavioral science, having graduated from the pseudoscience of Freud and Jung to the more disciplined—and in its way far more compelling—efforts of John Bowlby, on a path, I was sure, to becoming a novelist, and now setting off into this newly emerging field with the help of a great scientist who saw the value of incorporating literature and art into her arguments, not merely as incidental illustrations retrofitted to recently proposed principles, but as sources of data in their own right, and even as inspiration potentially lighting the way to future discovery. To perceive, to comprehend, we must first imagine. And stretching the mind to dimensions never before imagined is what art is all about.
Yet there is an inescapable drawback to massive books like Mother Nature—for writers and readers alikewhich is that any effort to grasp and convey such a massive array of findings and theories comes with the risk of casual distortion since the minutiae mastered by the experts in any subdiscipline will almost inevitably be heeded insufficiently in the attempt to conscript what appear to be basic points in the service of a broader perspective. Even more discouraging is the assurance that any intricate tapestry woven of myriad empirical threads will inevitably be unraveled by ongoing research. Your tapestry is really a snapshot taken from a distance of a field in flux, and no sooner does the shutter close than the beast continues along the path of its stubbornly unpredictable evolution.
Kim Hill
When Mothers and Others was published just four years ago in 2009, for instance, reasoning based on the theory of kin selection led most anthropologists to assume, as Hrdy states, that “forager communities are composed of flexible assemblages of close and more distant blood relations and kin by marriage” (132).  This assumption seems to have been central to the thinking that led to the principal theory she lays out in the book, as she explains that “in foraging contexts the majority of children alloparents provision are likely to be cousins, nephews, and nieces rather than unrelated children” (158). But as theories evolve old assumptions come under new scrutiny, and in an article published in the journal Science in March of 2011 anthropologist Kim Hill and his colleagues report that after analyzing the residence and relationship patterns of 32 modern foraging societies their conclusion is that “most individuals in residential groups are genetically unrelated” (1286). In science, two years can make a big difference. This same study does, however, bolster a different pillar of Hrdy’s argument by demonstrating that men relocate to their wives’ groups as often as women relocate to their husbands’, lending further support to Alvarez’s corrective of Murdock’s data.  
Even if every last piece of evidence she marshals in her case for how pivotal the transition to cooperative breeding was in the evolution of mutual understanding in humans is overturned, Hrdy’s painstaking efforts to develop her theory and lay it out so comprehensively, so compellingly, and so artfully, will not have been wasted. Darwin once wrote that “all observation must be for or against some view to be of any service,” but many scientists, trained as they are to keep their eyes on the data and to avoid the temptation of building grand edifices on foundations of inference and speculation, look askance at colleagues who dare to comment publically on fields outside their specialties, especially in cases like Jared Diamond’s where their efforts end up winning them Pulitzers and guaranteed audiences for their future works.
Mutual gazing in gorillas (de Waal's FB page)
But what use are legions of researchers with specialized knowledge hermetically partitioned by narrowly focused journals and conferences of experts with homogenous interests? Science is contentious by nature, so whenever a book gains notoriety with a nonscientific audience we can count on groaning from the author’s colleagues as they rush to assure us what we’ve read is a misrepresentation of their field. But stand-alone findings, no matter how numerous, no matter how central they are to researchers’ daily concerns, can’t compete with the grand holistic visions of the Diamonds, Hrdys, or Wilsons, imperfect and provisional as they must be, when it comes to inspiring the next generation of scientists. Nor can any number of correlation coefficients or regression analyses spark anything like the same sense of wonder that comes from even a glimmer of understanding about how a new discovery fits within, and possibly transforms, our conception of life and the universe in which it evolved. The trick, I think, is to read and ponder books like the ones Sarah Blaffer Hrdy writes as soon as they’re published—but to be prepared all the while, as soon as you’re finished reading them, to read and ponder the next one, and the one after that.