AS IS CLEAR from the many insights of therapists and researchers that inform this book, psychology has produced knowledge about stepmothers that is at once illuminating and extremely specific. There is a wide range of discourses beyond psychology that, while having much to offer in the way of reframing and explaining step-realities and step-struggles, has seldom—if ever—been brought to bear on the topic. How might we bulwark the discoveries and contributions of psychology and counter both its inward orientation and the misapprehension of some therapists that we can "fix" most of the problems of stepparenting? (This bias is explored in depth in chapter 9.) Certainly, the historical and cultural pieces of the stepmothering experience, often considered by the best family practitioners in their work with stepfamilies, can help us to see contemporary stepmothers in a broader context, offering new ways to understand and perhaps resolve dilemmas that might otherwise seem purely interior or interpersonal. But other disciplines may allow us to widen our field of vision even further—into prehistory, for example, as well as into other worlds (or at least other cultures). The fields of evolutionary biology and anthropology do more than simply allow us to see stepmothering in a new way. They urge a fundamental reconsideration of what a stepmother is, and what having stepchildren means, by exploring just what might be informing our social behavior other than psychological drives or psychodynamics.
When Harvard entomologist E. O. Wilson published Sociobiology: The New Synthesis in 1975, he set off a controversy that continues to reverberate in some quarters even today. His contention that natural selection acts not just on our bodies but also on our social behaviors, attitudes, and emotions touched a nerve. By and large, the outrage stemmed from the belief that Wilson and other sociobiologists were suggesting that animal (including human) social behavior is determined by our genes. Nor did many people like the implication that behaviors—especially unsavory ones—might have been selected for because they were evolutionarily advantageous or adaptive. Wilson was not the lone proponent of sociobiology. His colleagues and collaborators included biologists, zoologists, primatologists, and anthropologists, such as Robert Trivers, William Hamilton, and Sarah Blaffer Hrdy. Of course, sociobiology was ultimately indebted to and expanding on Charles Darwin's theories. The main assertion of sociobiology was that natural selection would favor those individuals who acted to improve their fitness—their ability to survive and produce strong, healthy offspring, who would in turn survive to reproduce.
Three decades later, those who are interested in the biological underpinnings of human social behavior tend to call themselves human behavioral ecologists. Whatever name they go by, these scientists are paying more attention to context than ever before, emphasizing the complex interplay of biological, social, cultural, and ecological factors that likely underlie specific human behaviors such as taking care of our young. These scientists suggest that such practices, far from being preprogrammed by our genes, have likely been informed by millions of years of natural selection but will express themselves in different ways depending on the situation. A devoted mother bear may be assiduously maternal by letting one of her two or three cubs die, for example, rather than committing to all of them under unfavorable conditions and increasing the odds that none will survive. The main conceptual underpinnings of behavioral ecology and sociobiology—concepts such as fitness, altruism, reproductive tradeoffs and maternal retrenchment, parental investment, parent-offspring conflict, and kin selection—seem ready-made for helping us think through just why stepparenting might be at once so challenging and so widespread.
Oddly, one of the best ways to understand stepmothers, and the internal and external conflicts in which they find themselves mired, may well be to take a look at what sociobiologists and human behavioral ecologists have had to say about mothers. Even more oddly, what a few of them have had to say about mothers of species other than our own may shed the most suggestive light on the conundrums of contemporary human stepmothers. Though admittedly a circuitous path, this one does afford a uniquely comprehensive perspective, reaching back into prehistory while linking us to our closest animal relatives—as well as some that are not so close. For example, birds.
In her masterful book Mother Nature: Maternal Instincts and How They Shape the Human Species, which informs this chapter and the next in fundamental ways, sociobiologist Sarah Blaffer Hrdy calls David Lack, an adviser to the British Trust for Ornithology in the early 1940s, "the first reproductive ecologist." After World War II, Lack organized hundreds of amateur birders in Britain to help him compile information about banded swallows and robins, among other birds. They observed nests, carefully counting and weighing eggs, then continued watching as chicks hatched and fledged.
Lack wanted to know: How many eggs were produced? How many hatched? Of those that hatched, how many actually successfully fledged? And why? How to account for the discrepancies? For example, why would a mother bird lay three eggs but fledge two chicks? Or only one? Why did some bird mothers fail to rear any young at all in some breeding seasons? Lack's interest from the outset was to investigate certain assumptions about what birds "just do naturally" when it comes to parenting. When the massive amount of data was in, Lack realized that there were significant differences when it came to individual birds' breeding success: some mother birds seemed to be better at it than others. He also noted that bird mothers did not adjust their fertility to benefit the species or the group, but rather, as Hrdy puts it, "they managed their reproductive effort"—their egg laying, nest guarding, incubating, and provisioning—"so as to make the best of their own particular circumstances." Far from "greater goodists"—a term coined by scientist Helen Cronin to describe the misapprehension that evolution was about the survival of the species—these bird mothers were acting out an individual's agenda.
And it was all a great deal more complicated, Lack realized, than it might have seemed. For she who produced the most eggs in a breeding season or even over her lifetime, or attempted to incubate and rear every egg she laid, or provisioned the chicks most tirelessly, did not automatically win the evolutionary jackpot and fledge the most chicks. What made some bird mothers successful in this undertaking and others less so? How come some fledged more chicks than others? For the answers, Lack looked to the phenomenon of staggered egg laying. In species such as eagles and gulls, the females lay their eggs a day or more apart. But the mother begins to sit on her eggs as soon as they are laid, and thus the first-laid egg hatches days before the next. The inevitable consequence is that the first chick has the run of the nest—and several meals—by the time the next hatches, easily beating it out for food and thus all but guaranteeing that if provisions are in short supply, the unfortunate second-born will starve. During this struggle, mother bird will not intervene on behalf of the beleaguered younger sibling. But if there is no scarcity of food, she will take steps, aided by the simple fact of bounty, to ensure that the second sib will survive the elder's attempts to rule the roost.
By laying more than one egg, then allowing the firstborn to reduce the size of the brood if necessary, the mother bird tries to bring her family size in line with the food supply. Abundant food and happy ecological conditions mean two or more chicks; tougher circumstances ensure that there will be only one and that Mom will not deplete herself too much in her efforts to feed her young.
These mothers, it seemed to Lack, were far from birdbrained. They were hedging their bets, taking the measure of circumstances around them before deciding how the drama in the nest would unfold. Would a mother incubate all her eggs or let one fall to the side? Would she provision all the chicks, investing equally in each of them? Or would she allow the oldest to extinguish the younger one(s)? Lack's birds were, in Hrdy's words, "highly discerning mothers" (weighing their options, assessing prevailing conditions), "whose commitment to their young was contingent on circumstances."
Taking it all in, Lack struck on an idea: there was a fundamental tradeoff in the life of these avian mothers. It was Should I have more chicks and invest less in each, or have fewer chicks and go for broke each time? Lack paved the way for later scientists to explore the notion that mothers might "trade off" reproduction in the present against the possibility of doing even better in the future. This female discretion—this deciding what to do—meant a number of things. First, some mothers would be pretty good at hedging their bets, while others would fail. Such variation meant they were open to selection pressures: that is, better maternal strategists would produce young who would in turn reproduce themselves. The variation in success rates also suggested that a mother's interests were not always identical to those of her brood. Bird mothers might stand aside and complacently allow one offspring to peck its less fortunate later-born sibling to death or starve it out. Or they might rally all their energies in the service of incredibly draining efforts to ward off intruders who threaten their nestlings' lives. In short, it all depends. Nothing about mothering, Lack's work suggested, was "rotely nurturing" or "automatically maternal." These mothers were "flexible strategists" (Hrdy's term), more closely resembling film noir dames coolly assessing their options than June Cleaver. Their dedication to their offspring, their "instinct" to nurture, could not be separated from a facility for logic that might turn lethal. The charged truth that motherhood entails calculation and strategy—Is what's good for my chick going to be bad for me? Do I give this chick my all or reserve my efforts for what might be a more robust chick or, better, more plentiful conditions down the road?—seems more charged still when biologists suggest that precisely such tradeoffs inform maternal behavior in other animals as well—including bees. And humans.
Lack's strategic mothers, assessing conditions and making tradeoffs in each breeding season over a lifetime, with greater or lesser success, and adjusting their efforts to best increase their individual fitness, suggested further avenues of inquiry. Scientists now began to wonder, What are the other ways animal mothers adjust maternal investment in line with ecological conditions? And if Lack's bird mothers and other animal mothers were deciding (in some sense) how many young to care for in a given season, just as other animal mothers were also adjusting their maternal investment in line with varying and variable contexts, what to make of a species in which females would forgo motherhood? Not just for a breeding season, or even two or three either, but for their entire lives, dedicating themselves instead to the task of raising someone else's offspring. What could possibly motivate an animal to be so apparently selfless as to forgo reproduction altogether?
This was the question facing anyone with an evolutionary bent who studied honeybees, ants, and wasps, known as a group as "hymenopteran social insects." Honeybees, living in what appears to be a kind of utopia (biologists call their living arrangements "eusocial," or "perfectly social"), seem to be the ultimate daycare providers—tireless and self-abnegating—or the devoted stepmothers of our dreams. Toiling in the service of the queen bee, they busily tend to her young rather than having their own. Why?
It seemed to fly in the face of Darwinian evolutionary thinking, an exception to the rule of individual fitness, until a scientist named William Hamilton proposed a theory about just what might be going on in these highly cooperative breeding colonies, "where only one in tens of thousands of females ever becomes a mother herself." Such insects, Hamilton asserted, care for the queen's offspring rather than their own because they are extraordinarily closely related to her. So closely, in fact, that they would be less related to their own offspring than they are to hers. Chicago Zoological Society biologist and primatologist Dan Wharton explained to me how this bizarre (to us) situation comes about: "Among honeybees, females have two sets of chromosomes (diploid) while males have just one (haploid), resulting in haplodiploid reproduction. And in such haplodiploid-reproducing organisms, two sisters with the same father have more common genetic material than mothers and their own offspring." In other words, when it comes to Hamilton's bees, what seems like the ultimate in self-sacrifice is actually keenly self-serving.
With such creatures in mind, Hamilton argued that the notion of fitness should be expanded to include not just the individual but also his or her closest genetic relatives. In other words, Lack had been right that it was about the individual rather than the group, but sometimes, as in the case of these honeybees, the group was actually a closely related extension of the self. "Inclusive fitness," Hamilton suggested, was the individual's fitness plus the fitness of his or her closest kin sharing genes by common descent. Altruism would evolve, Hamilton said, when its cost to the giver (C) was less than the fitness benefits (B) obtained by helping another individual related by r, a letter designating the proportion of genes the two individuals shared by common descent. The phenomenon—often termed "kin selection" and expressed in the formula C < Br—"underlies the evolution of helping behavior in all social creatures," Hrdy writes. It also explains the universal human pattern of favoring kin over non-kin.
Behavioral ecologists are quick to point out that they are not claiming that there is a gene, or even a set of genes, that influences people to prefer kin to non-kin, only that, among animals (including humans), the preference seems to be universal. Initial experiments with jewel wasps and other insects proved that inclusive fitness was real; later studies of humans seem to prove the universality of kin selection as well. But how might kin selection actually work? Hrdy suggests that "in humans we can only assume that our powerful predisposition to prefer our own kin derives from very ancient emotional and cognitive systems, such as learning to recognize people familiar from a very early age and having a lower threshold for altruism in our behavior toward them. This is the simplest explanation for our similarities with other social creatures in this respect."
According to human behavioral ecologists and evolutionary biologists, then, we live in a "kin über alles" world. We will do more for our kin than for our non-kin, with the reverse being true as well. Which begs the question, What, exactly, is kin? What is a cost? And how, precisely, are we to define "benefit"?
William Hamilton got a renegade sociobiologist named Robert Trivers thinking. If inclusive fitness explained how shared genetic material might lead to cooperation and altruism between close relatives having common agendas, could it also explain differences in agendas between closely related individuals? Mothers and their offspring, Trivers noted, are not genetically identical. Was it not reasonable, then, to suppose—based on the theory of kin selection or inclusive fitness, as well as Lack's observations—that a mother's interest is not always identical to that of her offspring? From the perspective of the offspring, the same might be said as well. A baby of any species, for example, is related to itself 100 percent. But it shares only half its genes with its mother and half with subsequent offspring, if all have the same father. If they have different fathers, the degree of relatedness is 25 percent. Yet the mother, Trivers noted, is equally related to all her offspring. And so it is inevitable that the relations between mother and offspring, and offspring and offspring, should be not only cooperative, but also conflictual. In short, the wants and needs of mothers and their children do not perfectly coincide. Logical and reasoned as this observation sounds, its implications are profoundly subversive of our dearly held notion that mother and child live in a kind of mutually agreeable symbiosis.
Au contraire, as Lack taught Trivers and others who came after him: reproductive effort—gestation, delivery, provisioning—is costly and depleting. Any effort a mother puts into one offspring detracts from the effort she can put into another. It also detracts from her ability to have more offspring herself. Trivers had a theory about that, too, one he called parental investment. Parental investment, Trivers asserted in 1972, is anything that a parent does to promote the survival of an offspring that also detracts from the parent's ability to invest in another offspring. Now, with Hamilton's insights about kin selection in mind, and the notion of potential conflict underscored, the question became, How much and for how long should a mother care for her offspring? When did this tiny, dependent being become less an extension of her own agenda and more of a drag against it? Trivers wrote, "Parent and offspring are expected to disagree over how long the period of parental investment should last, over the amount of parental investment that should be given, and over the altruistic and egoistic tendencies of the offspring"
To make this theoretical argument more concrete, Sarah Hrdy explains how the phenomenon of weaning exemplifies the way Trivers sought to reframe family members as at once cooperative and competitive: "Weaning conflicts epitomize for Trivers the disagreement over how much and for how long a mother should provision her offspring ... Just after birth, when suckling is essential for her infant's survival, a mother and baby are likely to be of one opinion...[but later] the infant is more motivated to suckle than the mother is to provide additional nourishment."
Across cultures and species, weaning is indeed accompanied by epic tantrums and titanic battles of will. Primatologists report screeching fits, angry displays, and even depression among baboons and chimps being weaned. These infants' objections to no longer being allowed to nurse were so reliable and consistent that Trivers actually advised fieldworkers attempting to locate baboons on the savannas of Africa in the early morning to listen for the weaned baboons' screaming. In human societies characterized by prolonged nursing (or in societies with foreshortened nursing periods, such as our own) such problems arise as well. When !Kung mothers are pregnant (the !Kung are hunter-gatherers who live in the Kalahari Desert of Botswana), they tell their three- and four-year-old children, "You can't nurse anymore. If you do, you will die." The !Kung children whine and throw fits, insisting that they still want to breastfeed. Many !Kung three- and four-year-olds go to live with relatives in another camp during this contentious period, so great are the stresses on mother and child alike. Indeed, most !Kung carry the memory of their weaning with them into adulthood. In Westernized cultures, we might hide our breasts from, or simply attempt to distract, a toddler who still wants to nurse, or we might encourage a diet of "solids" beginning at six months of age, accelerating a process that in other cultures might take years, so that weaning can be accomplished by the comparatively early age of eight or nine months, or perhaps a year.
"Sleep training" is another issue over which mothers and infants in Western, industrialized cultures will likely come into the kind of early, direct, and dramatic conflict that Trivers had in mind. At a certain point, those of us who eschew the notion of the family bed decide to up our expectations of an infant who has been hard-wired by eons of evolution to fear being left alone. Into the crib baby goes, to "learn to fall asleep on his or her own." Baby wants and needs to be held (in order to feel secure); mother and father want and need to sleep (in order to function). Hours of crying may ensue, for days on end, depending on the temperament of the baby and the resolution of the parents. This ordeal can be exceedingly stressful (one mother told me that she developed shingles from the stress of sleep training her infant), but our ambivalence and misery as we leave our children screaming in their nurseries does not change the fact that our needs and theirs come into fundamental opposition over the issue.
These different strategies to negotiate infant dependency, and our feeling that we need to resort to them, dramatize the ways in which, as Trivers pointed out, mothers and children might find themselves at cross-purposes. And if something as basic as nourishing a child or reassuring him when he is (arguably) in distress and fearing that he has been abandoned, can be a site of such conflict and disagreement; if mother and baby are two genetically nonidentical individuals with agendas that are not always perfectly coordinated; if the relation between mother and child is not just one of synchronized, gentle, and loving interdependence but also one of occasional but very real struggle—what, then, might the relation between stepmother and a child not her own be? Suddenly, Lack's strategic avian moms, ever mindful of potentially perilous food scarcities, bring to mind those humans (fantastical or real) who might lead children deep into the dark forest to "chop wood" during a harvest failure, abandoning them there so that they no longer continue to empty the family larder.
Comparing birds and humans might seem specious, but it is not entirely without precedent—or rationale. Stephen Emlen, a behavioral ecologist at Cornell University with a special interest in human families, convincingly argues that we might learn more about ourselves from our feathered friends than from our hairy cousins. Primates, he concedes, certainly resemble us when it comes to cognition and mental capabilities, with their tool use, problem solving, and knack for learning sign language. But in the arena of families, there are more differences than similarities between us and our close simian relatives. For example, "chimpanzees live in troops where males do not help raise offspring, while gorillas and hamadryas baboons live in extended 'harems' of several unrelated females and a dominant male," primate expert Dan Wharton told me. Birds, by contrast, form mostly monogamous pair bonds, sometimes mating for life. Male birds play an active and engaged role in parental care. And some birds even live in "communities." What do all these similarities mean? That birds are uniquely instructive in thinking through what we ourselves do, some ornithologists and evolutionary biologists suggest. "Animals that live in very similar types of societies will have had long evolutionary histories of encountering the same types of social choices, and therefore will have developed very similar rules for how to behave," Emlen explains.
One particular "community" of birds piqued Emlen's interest several decades ago. He had heard tales of the white-fronted bee-eaters of Kenya, keenly social creatures living peacefully and altruistically in apparently utopian groups of three hundred or more. Sharing, caring, and selflessness, it seemed, were the norm. During food shortages, for example, these birds shared with their neighbors. Females and males split child-care duties and were monogamous 85 percent of the time (about the same as humans, Emlen notes). And grown offspring often stayed on to "help at the nest," assisting in the rearing of their younger sibs. Remarkably, they even "babysat" for neighbors. "The reason I went after Bee Eaters," Emlen explains, "is they were seen to have complex, nonfamily helping" This, of course, flew in the face of evolutionary theory, with its emphasis on individual fitness and kin selection.
What in the world was going on with the bee-eaters? How did all this helping others, nonrelatives at that, make sense? A sociobiologist through and through, Emlen thought he might just find in Kenya an exception to Hamilton's Rule about putting kin first. Perhaps, he hypothesized, this was an instance where another theory of evolutionary biology, "reciprocal altruism," might come into play. Reciprocal altruism occurs when someone performs a favor for a nonrelative, with the expectation that the act of generosity will be returned in kind someday. If it is not, no more altruism will be forthcoming from the spurned individual, and a social bridge will have been burned. Such behaviors have been observed in male olive baboons trying to build coalitions during aggressive interactions with other males, as well as among female vervet monkeys and among male lions attempting to overtake a pride. Were white-fronted bee-eaters doing something similar? What Emlen ultimately discovered was surprising—and, for stepfamilies, perhaps also surprisingly relevant.
Peyton Place in Kenya: Conflict, Cooperation, and Kin Selection
After thousands of hours of field observation on slippery mud banks in Kenya, Emlen realized that the white-fronted bee-eaters were not the exception to the evolutionary rule; instead, they were the rule. That is, they actually lived not in close quarters with strangers, but in extended, multigenerational families. Like Hamilton's bees, they were helping their relatives, and so helping themselves. Ostensibly self-sacrificing behaviors turned out to be, once again, fundamentally self-serving. Take, for example, those grown offspring helping at the nests of neighbors. As it turns out, they were aiding relatively close kin, and so improving their own fitness. If their own nests failed—if, say, the eggs were eaten by a predator—they might switch over to the nest of a sister and brother-in-law, aunt and uncle, or their own parents. Eventually, Emlen was able to use Hamilton's theory of kin selection to predict who would help out whom. "If a nest failed," he explains, "I should be able to predict the number two backup that gets the help" based on the percentage of shared genetic material. And, indeed, he was able to do so. Natural selection, it seemed, had done its job over the millennia, such that the birds had internalized complex "decision rules" for weighing the relative importance and closeness of different kin, and thus the potential genetic payoff for helping them.
But that wasn't all. The bee-eaters' "peaceful society" was something else altogether. Instead of being cooperative, caring, and devoid of conflict, it was a kind of avian Peyton Place, described by one nature writer as "a swirling soap opera of love, deceit, harassment, divorce, and adultery." Emlen, his wife, and their assistants, who had begun to recognize specific birds and keep track of precisely what they were up to day in and day out, were eventually struck by how "human" they sometimes seemed in their courting, trespassing, and sneaking off to achieve an "extra-pair copulation" far from home. And although it was true that grown offspring often stayed "home" with their parents, rather than move to their own nearby "apartments" built in adjacent mud banks, even this started to look more complex than it had at first. Sometimes parents actually aggressively pressured their young into coming back home once they'd moved out—for entirely self-serving reasons. For example, one day Emlen noticed a father "greeting" his son over and over again at the entrance to the son's nest. The greeting went on for so long and was so persistent that it had the effect of preventing the son from going into the nest for quite some time. Significantly, the son's mate was inside sitting on their clutch of eggs, and he couldn't get inside to feed her.
Over the course of his observations, Emlen realized that with this kind of coercion, parents could actually increase the likelihood that their own offspring's nests would fail. And—voilà!—the offspring would come back "home" to help Mom and Dad with their child-rearing duties. Dad had seen to it that those most closely related to him—his own offspring—had a better chance of fledging than those less closely related to him—the offspring of his offspring. And he had his nearest and dearest older kids as ultrareliable "helpers at the nest." There was something in it for these grown offspring, too, of course. After all, if you're not raising your own kids, the next best thing is to raise your siblings, with whom you share 50 percent of your genes.
It didn't always work out so well, however. Emlen discovered that the busy bee-eaters had one more thing in common with humans. Pairs that were unsuccessful in their reproductive attempts had higher probabilities of what he and many ornithologists actually term "divorce." And in the event of a nest failure and subsequent breakup, they were likely to re-pair, choosing new mates. Emlen observed very closely when long-term bee-eater mates split up and chose new partners. What would happen? he wondered. Would everyone get along, or would there be tensions when a feathered stepparent came on the scene? Would the offspring from the original pair bond stay, or would they go? Based on Hamilton's Rule, Emlen had a hunch, and what he discovered did, in fact, jibe with the theory of inclusive fitness.
The bee-eater offspring of an original pair were much less likely to help raise hatchlings of one of their own parents and a stepparent than they were to tend to the chicks of both their parents. Consequently, the chances that they would disperse and go help at the nest of others in their extended family increased whenever a stepparent showed up. Emlen wasn't surprised: the offspring with a parent and stepparent shared the same amount of genetic material with a niece and nephew as with its half sibling (25 percent), making a move that much more likely. Nor was Emlen surprised to see that the likelihood of leaving the nest of the parent and stepparent for good increased. "The kids from the first pairing say, 'Thank you, no. I'm doing much less, provisioning much less. I'm going to spend much more time over there with my other family members," Emlen explains. Finally, when a new mate first came on the scene, tension and aggression shot up—for very specific reasons. "Sometimes, there is great interest between the son and his stepmother, while there had been none between the son and his mother, and great aggression as the father attacks the son, as the father guards the mate," Emlen observes.
But what does this all mean for humans? An adaptationist through and through, Emlen believes that the answer is, quite a lot. Being subject to selection pressures and having similar predilections (more or less monogamous, long-term pair bonds, divorce and re-partnering, shared care for offspring, and an evolutionary history of living in extended families), humans, he argues, have developed similar "decision rules"—those unconscious strategies that guide us in our social behavior. For Emlen, the bee-eaters are a lens of sorts, a lens onto a broad, comparative evolutionary view of families and family issues. In all stepfamilies, he suggests, we are likely to see much of what we see among white-fronted bee-eater families in Kenya: early dispersal (or "leaving the nest") for stepchildren; increased conflict and sexual tension in stepfamily households; and a preference for one's own kids, one's own parents, and one's full siblings. None of this is particularly savory, but neither is it terribly controversial. Based on studies and clinical work, a number of sociologists and psychologists have drawn many of the same conclusions Emlen has. Still, Emlen is quick to point out that none of these problems or conflicts is "genetically determined" or inevitable. Asked whether environment and culture play "second fiddle" to genetics, his answer is a resounding no. "Both genetics and environment are major fiddles," he insists. "There is no disagreement that most human behavior is strongly influenced by culture and environment. But there are biological underpinnings as well, and these underpinnings—our inherited predispositions—play a more important role in shaping our social interactions than previously realized." How so, exactly?
A particularly elegant study conducted by behavioral ecologists William Jankowiak and Monique Diderich among polygynous Mormon families in the year 2000 nicely illustrates Emlen's point about the importance of biology in guiding our social behavior and shaping our feelings. Jankowiak and Diderich studied interactions and perceptions of closeness between full and half siblings in a Mormon community they call Angel Park. This particular community is unique even among Mormon polygynous communities in that the preferred ideal, relentlessly promoted in sermons, Sunday school lessons, and high school classes, as well as at home, is to live together in one "united and harmonious household" of one father, several wives, and their collective offspring. To this end, genetic differences in the polygynous family households of Angel Park are consistently and intentionally downplayed, while an ethos of family is emphasized. Kids of different co-wives live and play in common areas and are consistently told "we are all true brothers and sisters." This made Angel Park an ideal setting for exploring just how much genetic relatedness matters. Do people really feel as close and as attached to their half siblings as they do to their full ones? Will they bend over backward for half siblings as they will for blood kin? Put another way, is the degree of sibling solidarity in Angel Park (and perhaps in general) about biological kinship? Or, as sociologists and psychologists suggest, might other factors, such as being raised together and being close in age, play more of a role in establishing closeness?
For Jankowiak and Diderich, the big question was, Can people who are not related learn to love each other as if they are, with constant proximity and under ideally supportive conditions? It is not difficult to see just how relevant and instructive such questions—and answers—might be for stepfamilies, where unrelated stepsiblings, half siblings, and full siblings, as well as an adult to whom they are not related, may reside together, feeling compelled, to some extent, to "blend."
Focusing on thirty-two polygynous families, the study authors spoke to seventy individuals total, all with full and half siblings living in the community. They used a number of measures to assess perceptions of "closeness" and feelings of solidarity. Young kids were asked to "draw a picture of your family," on the theory that excluding someone from the drawing would be a strong indicator of negative feelings. If these young children resided in a home with two or more infants, they were also asked, "Who is your favorite baby?" Then they were asked, "Is that your birth mother's baby, or the baby of one of your other mothers?" Adults were asked whether they had recently loaned a brother or sister money. With outsize families the norm, there are perpetual cash shortages in Angel Park; this means loans are both necessary and carefully allocated. Researchers also asked the adults whether they had recently asked a sibling to babysit. With so many children around, providing child care is a significant and much-appreciated favor, neither requested nor conferred lightly. If the answers to these questions about loans and babysitting were yes, the respondents were further asked, "Was it a sibling through your birth mother, or another mother?" Finally, the authors analyzed who went to whose birthday parties and wedding receptions. Was attendance skewed more toward full siblings, they wondered, or split evenly between half and full sibs?
When the data was collected and analyzed, it revealed a dramatic difference in emotional closeness, degree of loyalty, and affection between full siblings and half siblings. Overwhelmingly, Jankowiak and Diderich found, there was more affection and attachment to full siblings, and a remarkably increased willingness to put oneself out for them. This held true despite the force of religious ideals, regardless of similarity in age, and notwithstanding the continued close physical proximity of half siblings as they had grown up.
This preference—a strong partiality for those who are closest kin—was revealed in at least two additional ways the authors had at first not thought to measure, but observed in the course of their interviews and other work in the community. First, if the father of a polygynous family was alive, adult siblings would meet at his home for weekly family dinners. But after his death, something interesting happened, and it happened quickly: half siblings dispersed, not unlike white-fronted bee-eater step-offspring abandoning the nest, and these family gatherings rearranged themselves in accordance with full blood ties, with the birth mother taking the dead father's place at the center of the family, if not at the head of the table. Second, virtually all the adults interviewed remembered at least an incident or two in which they had perceived that one of their father's co-wives had shown a preference for her own child over him or her. For example, they recalled a co-mother bending the house rules for her own child or giving her own child a bigger piece of cake. "Perception" is the key word here, and it is remarkable indeed that such perceptions can take root and bloom in an environment that has dedicated itself to their extinction, to promoting the notion of co-mothers and biological mothers loving children just the same, and biological and nonbiological ties being equivalent. What, we might wonder, would be the perceptions of children growing up in a culture that promulgates precisely the opposite?
The study authors concluded, with understatement, that "there is a pronounced clustering of feelings and affection in Angel Park that is consistent with inclusive fitness theory." Even in an environment where non-blood relatives and half siblings are encouraged to feel "just like kin," where this ideal is promoted tirelessly and kids grow up in close proximity from birth, in the end relatedness matters. Well might we want to share these findings with anyone who judges us wanting when our stepfamilies "fail" to "blend."
Like the white-fronted bee-eaters and the Mormons of Angel Park, stepfamily members, while capable of great affection for those less related to them, nonetheless seem to be wired to feel closest to their own. For example, in a 1981 national survey of U.S. children ages eleven to sixteen, participants were asked, "Whom do you consider a member of your family?" Thirty-one percent of the stepchildren did not consider their residential stepparent a family member, and 41 percent of them did not mention their stepsiblings.
"His kids aren't coming for the holidays?" relatives, friends, and even acquaintances may ask, aghast. Or, "Why on earth hasn't your stepson come down from college to see the new baby yet?" The implication is that something isn't right, and the unmistakable insinuation, in many cases, is that the stepmother must be doing something wrong. She is failing at her culturally designated role as "family carpenter" or falling short in the "warm and maternal" department where her stepkids are concerned. The simple fact of the matter, confirmed in numerous studies, is that stepfamilies (as we saw in chapter 4) are different from first families. To reiterate a point that seems difficult for outsiders and sometimes stepmothers themselves to accept, they are less cohesive. And there is little empirical evidence for the assumption that they tend to become closer or more cohesive over time. The even bigger news is that as disorienting as this may seem to the uninitiated and to those who try to use a first-family map to understand the topography of stepfamilies, they often function just fine that way.
Residential stepfamilies can have a college dorm/roommate feel that is likely to throw those who equate "family" with synchronized, super-close first-family dynamics. Stepfamily members—particularly when both members of the couple bring kids of their own—might eat at different times, put up two different Christmas trees, even elect not to take all their vacations together (all practices described by people I interviewed). When kids are older and not living together, even less "bondedness" is the rule. Some of the stepfamilies with adult children I interviewed went months without seeing one another, as holidays did not provide an automatic pretext for getting together. With obligations to so many people, there was no assumption that Thanksgiving, for example, meant "all together now."
As off-putting and "wrong" as some first families might find such a reality, it may well be this very lack of proximity and closeness that allows stepfamilies to jell in their own way and to foster positive relationships. A number of researchers have noted that in stepfamilies, respectful behavior, flexibility, and lower levels of cohesion are not only more normal but also more adaptive, and so more predictive of a good outcome, than "tight-knit-ness." If the unrealistic yet unrelenting fantasies of uninformed outsiders about how things "should" be in our stepfamilies have become our burden, there is solace in the unlikely facts gleaned from evolutionary biology—from Angel Park and the Kenyan mud banks—worlds at once utterly apart from and unexpectedly adjacent to our own.
If Emlen was interested in how family life in general and stepparenting in particular played out among his avian cohort, as well as among other animals including humans, a number of other biologists have been interested in why. Why does stepparenting happen in the animal world at all? Why would any creature—an anemone fish or a baboon or a yellow-headed blackbird or a white-fronted bee-eater (all of whom, it turns out, exhibit stepparental behaviors)—do anything so apparently altruistic?
Maybe, the early thinking on the topic went, they wouldn't. In 1975, in a paper titled "Mountain Bluebirds: Experimental Evidence Against Altruism," ornithologist Harry Power asserted that the presence or absence of what he termed "true altruism"—"the promotion of others' reproductive success while reducing one's own inclusive fitness"—could be gauged by how these birds behaved toward the offspring of others. He removed male and female mountain bluebirds from pairs during the nesting phase; the newly single birds found replacement mates. However, most of these replacement mates did not help in the raising of their step-offspring. This was an obvious outcome, Power suggested: an effort to raise someone else's offspring contributes to the proliferation of the genes of rivals rather the genes conducive to the development of altruism. Basically, Power asserted, stepparental "selflessness" makes no adaptive sense.
Like so many scientists whose work has a marked impact, Power raised as many questions as he answered. Ten years after he wrote his paper, another ornithologist, Sievert Rohwer, disputed its findings as well as its conclusions. After reviewing the literature on how birds behave toward the previously sired offspring of their new consorts, he discovered that avian stepparental care was not at all rare. Remarkably, among Cooper's hawks, peregrine falcons, western gulls, sandhill cranes, and Australian ravens, for example, females would actually incubate eggs and then raise young not their own. And males of a number of species, including hawks, gulls, chickadees, yellow-bellied sapsuckers, purple martins, and cactus wrens, ran the gamut from provisioning and guarding the incubating female to defending and feeding the brooded young, or even raising them altogether.
But why? There were, after all, other options. When confronted with these offspring not their own, birds could do one of three things, Rohwer noted. They could commit infanticide, tolerate the chicks without putting forth any effort, or actively assist in rearing them. Tolerance and care, Rohwer concluded, were actually more common than infanticide. But why? Wouldn't infanticide make more sense? Primatologist Sarah Blaffer Hrdy had already argued that, among a certain type of langurs in India, invading males killed infants whenever they could. Committing infanticide, Hrdy argued, gave the new males an advantage in siring offspring of their own, since the females would ovulate soon after they ceased nursing. Confronted with infanticidal males, female langurs had developed counterstrategies, such as fighting off males and copulating with a number of males in order to confuse the issue of paternity. But ultimately, it was in the best interest of the female to reproduce again, even with the male who had killed her first infant. After all, her own reproductive fitness was at stake as well. So went the adaptive, albeit gruesome, logic behind such infanticide.
Soon biologists found a similar strategy among lions. Males who took over prides killed the cubs in order to shorten the wait until the next breeding opportunity with the females. In some sense, then, Rohwer's discoveries about stepparental behavior in birds were extremely surprising. Might such behavior, he asked, be a misdirection of parental care, and so maladaptive? In other words, was it possible that the birds just couldn't tell that the offspring were not their own? Perhaps, like unsuspecting characters in a human soap opera, they had been intentionally deceived about their parenthood by their mates. Or maybe, Rohwer hypothesized, stepparenting could actually be adaptive. It might be a mating effort, a tradeoff in the classic Lackian sense: the payoff for raising offspring not one's own was future mating opportunities with the step-offspring's genetic parent.
Once Rohwer conducted experiments with yellow-headed blackbirds which confirmed that they could, in fact, detect which offspring were their own, he came down on the side of the "stepparenting behavior as mating effort" hypothesis. A bird would invest in the young of another under very specific circumstances, Rohwer noted. In certain cases, he reasoned, tolerance and even care of the new mate's previously sired offspring was the best possible mating strategy. As with Lack's mother birds, who could be selfless or heartless by human standards when it came to investing in a particular brood in a particular season, in this case, once again, it all depended on circumstances. The factors that would make it worthwhile to invest in step-offspring were linked to specific ecological conditions.
For example, using their unconscious internalized "decision rules," the birds would make various assessments, weighing their options in ways that might, in some cases, sound familiar. Were new, unfettered mates sufficiently scarce? That is, would it take a lot of time and a big expenditure of energy to find a mate without offspring, and might the bird risk not finding one at all if it didn't pair up with this potential mate right now? Could the newly formed pair, including a mate with previously sired offspring or a clutch of eggs sired by another bird, be expected to endure relatively long-term? If there were plenty of opportunities to sire or lay eggs of one's own down the road, it could make sense to wait out a single breeding season. Did the birds tend to divorce after a nesting failure? If so, the bird would only be putting itself at a disadvantage in creating a nesting failure by killing or not provisioning the previously sired young. Would an individual who lost its young quickly return to breeding condition, or would that take a long time? In the case of it taking a long time, there would really not be much cost in waiting out the fledging of a brood not one's own. Finally, was there time left in the breeding season for another clutch? If not, then ignoring, tolerating, and even provisioning the young would not cost the stepparental bird so much.
Summarizing Rohwer's work with birds, Canadian biologists and evolutionary psychologists Martin Daly and Margo Wilson write that "in circumstances ... where breeding territories or mates are scarce, and are retained for a long time once they have been acquired ... stepparental investment is evidently the price paid for future breeding opportunities with the genetic parent." Given these specific environmental and ecological constraints, Daly and Wilson note, not only certain birds but also monogamous fish such as anemone fish, as well as some baboons, "find stepparenting an acceptable courtship experience." Then, in a rather astonishing turn, Daly and Wilson hypothesize that much the same holds true for human stepparents:
The human case seems to us analogous. Stepparents are primarily replacement mates and only secondarily replacement parents. They assume their pseudo-parental obligations in the context of a web of reciprocities with the genetic parent, who is likely to recognize more or less explicitly that the new mate's tolerance and investment constitute benefits bestowed on the genetic parent and the child, entitling the stepparent to reciprocal considerations.
With their emphasis on tradeoffs and benefits in human stepparenting, and the suggestion that this is not a selfless undertaking but something more strategic (albeit unconsciously so), Martin Daly and Margo Wilson lead us down a darker path, one that might be strewn with Hansel and Gretel's pebbles and bread crumbs, those plangent semaphores of parental neglect—and worse. The husband-and-wife team, based at McMaster University in Ontario, wanted to know whether stepchildren were, in fact, disadvantaged relative to genetic children. To find out, they trained their sights on lethal child abuse perpetrated by stepparents (actually, stepfathers—more on this later). They didn't do this because they thought that most stepparents were killers—in fact, more than 99 percent of us are not. But lethal abuse, they reasoned, while the most extreme, was also the most undeniable and verifiable indicator of bias against stepchildren. After all, virtually every case of it would be reported, making it a more reliable measure than other forms of child abuse, which tend to be vastly underreported. After pouring over statistics, studies, police reports, and child abuse registries in the United States, Canada, England, Australia, Finland, and Korea, Daly and Wilson concluded that children who lived with one genetic parent and one stepparent were much more likely to suffer the most severe forms of child maltreatment. In fact, in a 1988 article in Science, they reported that a co-residing stepparent was seventy times more likely to kill a child under two years of age than was a co-residing genetic parent.
But were these lethal effects of living with a stepparent not perhaps just byproducts of other factors associated with stepparenthood, such as poverty? Might stepparenthood itself be a mere incidental correlate of abuse, rather than a cause of it? Daly and Wilson had already thought through this objection to their findings. They had conscientiously tested for poverty and a number of other potentially confounding variables, such as differences in parental age, differences in family size, and the traits of those who become stepparents, reasoning that the abuse might be explained by the population of remarried adults potentially including disproportionate numbers of violent people. Even when controlling for these other factors, however, they found that living with a stepparent increased the risk of all abuse, and specifically lethal abuse, dramatically.
In addition to increased frequency of lethal abuse, Daly and Wilson found that stepparents murdered their stepchildren differently than parents murdered their own children. Parents who killed their children, police reports and studies by psychologists showed, tended to be depressed. They often killed their children as they slept, by smothering or a gunshot, and frequently killed them under the delusion that they were somehow sparing the children from future hardship and suffering, rescuing them even. Such murderous parents were highly likely to kill themselves after killing the child. Stepparents, on the other hand, used what Daly and Wilson term "more assaultive means" to kill stepchildren: they tended to batter, kick, or bludgeon their victims to death. And homicidal stepparents did not kill themselves afterward. Perhaps most tellingly for their hypothesis, Daly and Wilson found that stepfathers didn't abuse and kill their own children nearly as often as they did their stepchildren.
These qualitative and quantitative differences in how stepfathers versus genetic fathers killed, and whom they killed, were dramatic and disturbing. But one of Daly and Wilson's findings is particularly notable. They discovered that, perhaps counterintuitively, the stepchildren at greatest risk of dying at the hands of their stepparents were infants. Why might this be? It was clear to them what a "difficult" older kid might do to elicit rage from a stepparent, however out of proportion and irrational that rage might be. But how on earth could a defenseless infant provoke such anger and resentment? It was here that evolutionary theory offered a way to understand something otherwise incomprehensible. Confronted with the unsettling realities of who killed and who was killed, and building on the work of Lack, Hamilton, and Trivers, Daly and Wilson eventually articulated their theory of "discriminative parental solicitude." This concept springs from Trivers's premise that parental resources are limited, as well as Hamilton's concept of kin selection. It also hinges on one of Lack's observations: in some species, birds could discern their own young, while in others they could not.
Daly and Wilson theorized, first, that successful discrimination of one's own offspring from those that are not one's own is a problem parents, particularly fathers (more on that later), have likely faced throughout our evolutionary history; and, second, that we discriminate in the degree to which we are solicitous of children: more so if they are our own, less so—perhaps not at all—if they are not. From an evolutionary perspective, given the intensive and protracted period of energy expended to raise a human child, there is nothing so mysterious about allocating one's investment to one's own offspring. Conversely, Daly and Wilson write, "indiscriminate allocation of parental benefits without regard to cues of actual parentage would be an evolutionary anomaly." Psychologists as well as biologists, Daly and Wilson go on to frame the issue in terms of feelings as well as behaviors: "If the psychological underpinnings of parental care have evolved by natural selection, we may thus anticipate that parental feeling and action will not typically be elicited by just any conspecific juvenile. Instead, care-providing animals may be expected to care selectively for young who are a) their own genetic offspring and b) able to convert that care into improved prospects for survival and reproduction."
Babies could not be more vulnerable—or more demanding. They require constant care, monitoring, attention, and interaction, and they have evolved all kinds of ways to get it. From crying to clinging to gazing at a caregiver; from ample fat stores that render them plump and hence healthy-looking (read, worth investing in) to appealing round eyes and faces that we find adorable (under the right conditions, especially), infants have, as Sarah Blaffer Hrdy points out, evolved over the millennia a number of strategies to elicit love and care from their mothers, fathers, close kin, and caregivers. In fact, research has shown that, with exposure to our infants and even those not our own, if the circumstances are right, we do tend to fall under their sway—and how. Levels of prolactin—a hormone that elicits loving feelings of bondedness—increase in both fathers and mothers when they spend continuous time with their infants, and levels of testosterone in fathers actually decline when they care for their babies for several hours at a time. Humans, it is clear, can be "primed" by both biology and culture to care for their neonates.
What, then, of Daly and Wilson's cohort, stepfathers who lethally abuse children, usually those under age two? Why might the rate of lethal assault of infants be so high compared to the rates for older children and teens? First of all, Daly and Wilson are quick to point out, these murderous stepfathers are no infanticidal male lemurs or lions. There is nothing adaptive about murdering a child: the perpetrator will not increase his fitness or even reduce his costs by killing a baby. He will end up in prison, likely for life, and incur the wrath of an entire society. Even in our evolutionary past, Daly and Wilson emphasize, it is implausible that abusing or killing stepchildren would have promoted the assailants' fitness. A preference for their own offspring, however, likely would have been highly adaptive. And so evolutionary biology offers an explanation—one that is rather circuitous—for such bewildering behavior. The conundrum of the male mammal, as so many biologists have pointed out, is internal fertilization, a phenomenon that makes it particularly difficult— The Jerry Springer Show notwithstanding—to determine paternity with a great deal of certainty. And so unlike female mammals, who know that a baby is theirs, males just might get duped into caring for a child not their own. Owing to this uncertainty, evolutionary biologists believe, men and women evolved different reproductive strategies. Females tend to invest more in care, or parental effort, while males invest more in mating effort. This typical mammalian asymmetry means that males with babies have always found themselves facing a conundrum: Should I put my faith and efforts here in these offspring, or should I sire another or even several more offspring? Should I stay (and invest) or go (and inseminate another)? Or should I stay and inseminate again?
Given the sex-specific realities and strategies of our evolutionary history, it only makes sense that males, faced with constant uncertainty about paternity, would have evolved a higher threshold for parental care—that is, more of an ability to resist the charms of an infant attempting to elicit coos, cuddles, and more depleting forms of parental care from them. A woman, on the other hand, was unlikely to be confused about whether a baby was hers, as she had gestated it in her own body and pushed it out of her birth canal. Humans are not ungulates, so there was no possibility that someone else's offspring would climb to his or her feet, sidle up to another woman, and begin to nurse. Even if women were, in our prehistoric past, occasionally of the habit to nurse the babies of others (and there is a compelling argument to be made that we were), this was likely more for snacking than to provide sustenance, and the favor was conferred upon the baby of someone closely related. Thus, in a woman's case, falling in love with an infant can only be for the good, as she can be sure that the child is her own (or closely related). But a man cannot be entirely certain that even his partner's tiny, demanding creature is his issue. A higher threshold for feeling warm and fuzzy about a stranger's infant is a kind of protection—it decreases the likelihood of falling for a baby not his own.
What Daly and Wilson have unearthed—rather than some "rationale" for lethal child abuse—is compelling and meticulously documented evidence that, given eons of selection, unrelated males have evolved what we might think of as "emotional earplugs" when faced with a crying baby's unrelenting, unremitting need. Such indifference, relative to what a mother (or confident father) might feel, means, as Hrdy has observed, that there is in turn less of a barrier guarding against all the factors that lead to infant abuse—bad judgment, rage, and frustration. Elevated rates of abuse and violence, Daly and Wilson emphasize, are best understood as "non-adaptive byproducts of lesser solicitude." Babies, who will require intensive caregiving for years on end—that is, the most investment—are at maximal risk for abuse. For Daly and Wilson, the fact that those who are the most vulnerable and needy over the long term are in the most danger is virtual proof of their hypothesis about discriminative parental solicitude and adult resentment of pseudoparental obligation. From a biosocial perspective, what might create more resentment in someone "unprimed" to provide than a being not our own, a being who demands the most protracted, intensive, and committed forms of investment?
Daly and Wilson are careful to emphasize that most stepparent-stepchild relationships are not violent or abusive in any way. (In fact, Wilson told me that she had a stepfather, "a nice, nonabusive one!") They also note that lethal abuse is the extreme manifestation of discriminative parental solicitude—commonly, more benign effects, such as a stepchild leaving home earlier than a biological child is likely to, are the strongest evidence of discrimination. "Ideally, and perhaps typically," Daly and Wilson told me, "these relationships become somewhat like friendships, with genuine mutual interest in one another's well-being. In-law relationships are potentially problematic, too, but they are not ineluctably conflictual."
Still, they insist, discriminative parental solicitude is real and is likely the root cause of fundamental differences in agendas between genetic parents and stepparents, as well as between stepparents and stepchildren—issues such as how much money to give to which children and for how long, for example. Is there anything so controversial, they want to know, about suggesting that stepparents will not often, and certainly not automatically, come to feel the same sort of love and commitment as is ordinarily felt by genetic parents? "Might it not be helpful," they wonder, "if the stepparent's ambivalent and sometimes aggrieved feelings were acknowledged as normal and if the genetic parent were encouraged to express appreciation for stepparental investment, rather than to demand it as one's due?"
Most of Daly and Wilson's work centers on stepfathers. Residential stepmothers, they point out, are statistically rarer, and so there are fewer instances of lethal abuse among them. Nevertheless, they note, stepmothers are also greatly overrepresented in child abuse statistics, and they estimate the risks of having a stepmother to be comparable to having a stepfather. As evidence, Daly and Wilson report that the American Humane Association found more abuse in stepmother homes than in stepfather homes and that homeless adolescents in New York City are disproportionately from stepmother homes. In a study of Korean schoolchildren they cite, there were identical frequencies of being beaten among those from stepmother and stepfather homes, with both rates being substantially higher than those among children who lived with two parents. All of which suggests, Daly and Wilson insist, that discriminative parental solicitude does not discriminate against women.
But if women have evolved to have a lower threshold for eliciting care—and less to fear, as it were, from babies not their own—why wouldn't this ensure that we would be better stepparents for it? Does this lower threshold fail to buffer against discriminative parental solicitude because we virtually never get a stepchild who is a baby? Perhaps. Or perhaps discriminative parental solicitude simply overrides the other predisposition: once the "courtship" component is over and "courtship effort" becomes mere everyday effort—effort directed toward a child not our own, no less, and unlikely to be a baby who has evolved a repertoire of charms to elicit commitment—all bets are off. And so, this theory goes, we discriminate—not by beating and killing, the rarest of all instances of discrimination—but by caring and giving less.
Another possibility also presents itself: that the entire notion that stepparental behavior has evolved as an adaptation for anything is wrong. Richard Prum, chair of Yale University's Department of Ecology and Evolutionary Biology, takes a dim view of the notion that natural selection is acting to produce stepparenting behaviors of any sort, suggesting, in effect, that there is no there there. An ornithologist, he told me about a fascinating, classic photo of a male cardinal perched on the side of a concrete pool, stuffing bugs into the mouth of a ... goldfish. "Why would we call that a misdirection of parental effort, or call the behavior of birds taking care of chicks not their own step parental effort that has been selected for, rather than just parental effort?" Prum asked me. The goldfish's open mouth elicited parental feeling in the male cardinal, suggesting that he had the qualities of a great dad, period. "The same qualities that make me a good father will lead me to wipe the nose of a kid I don't know on the playground," Prum explained. It's unlikely that such decisions and behaviors are subject to natural selection pressures, because, as Prum put it, "it may be that the parental behavior module in the brain cannot be so fine-tuned by natural selection." The failure of Rohwer's idea, and Daly and Wilson's, he suggests, "is to imagine that every component of phenotype is independently subject to natural selection." For evolutionary explanations of avian and human stepparental behavior to fly, it must be possible to select for specific aspects of reproductive behavior without also damaging others, and Prum, and evolutionary biologists like him, don't buy it. From their perspective, good parents will make good stepparents, and vice versa. Presuming that a stepparent who murders or abuses stepchildren can also be a parent who nurtures and loves his or her own children doesn't always make sense from an evolutionary perspective, Prum said. That's probably not how selection works. "When there is evidence of adaptive infanticide, it's not often associated with parental care," he explained. "A male lion may kill the youngest cubs when he takes over the pride, but then he provides little paternal care of his own offspring later on."
What, then, accounts for the difficulties? Nothing quite so convoluted as genes or selection or discriminative parental solicitude, according to Prum. Rather, stepfamily life is difficult because families are cultural systems. "The new parent is bringing experiences, expectations, and desires for social stability that are different," Prum said. "Plus, we're comfortable and stable in our natal families of origin and likely less so in others." Which all adds up to some degree of stepfamily tension and drama.
Daly and Wilson's reach extends to folklore as well, and with scientists' discerning eyes, they seize on an apparent paradox: although the absolute quantity of abuse perpetrated by (more numerous) stepfathers exceeds the violence by (less numerous) stepmothers, there are literally hundreds of stories in the folklore about wicked stepmothers and virtually none about wicked stepfathers. Why might this be? First, they explain that, as we saw in chapter 6, stepmothers have not always been rare. Historically, high rates of mortality in general and death during childbirth in particular meant that more stepfamilies were formed when fathers sought replacement mothers for their children. If stepmothers were common, one might surmise that mutual hostilities, as well as incidences of abuse, violence, or neglect, were likely proportionally higher than they are today.
Daly and Wilson suggest another reason for the popularity of wicked stepmother stories. If maternal death and paternal remarriage were common, they reason, the social purposes of storytellers must certainly be considered. Tales such as Cinderella and Snow White, with their vast folk traditions, were told to young children. The narrators were overwhelmingly likely to have been their mothers—mothers cognizant of the terrible possibility that they might die and leave their little listeners behind. "It is easy to imagine," Daly and Wilson explain, "why mothers might prefer stories whose subtext is, 'remember, my dears, that the worst thing imaginable would be for me to disappear and for your father to replace me,' over those that instead whispered, 'should your father ever die or leave us, it would be a terrible thing for you if I were to remarry." Human behavioral ecology suggests such fears—that those unrelated to our children might fail to put them first—are not the stuff of mere fantasy or legend, but rather based at least partly in fact. Since the beginning of time and in virtually all species, mothers have made tradeoffs, decisions, and what Hrdy terms "retrenchments in care" that might appear harsh and uncaring. If mothers can be accurately characterized as dry-eyed, strategic, and ruthless, as well as doting and devoted, what can and should we expect of stepmothers? If motherhood is "a burden seldom embraced unconditionally" (Hrdy's phrase), what might stepmotherhood be? This question suggests another one as well: if selective pressures have created a tendency to do more for our kin, how is it that, so often, so many women and their stepchildren accommodate each other so well?