From birth, babies are tuned in to auditory stimuli that sound like words and to visual stimuli that look like faces. They study the faces of the people they encounter and quickly learn to recognize the ones who keep turning up. Before they are halfway through their first year, they are behaving differently—and appropriately—with the various people in their lives. With a depressed person the baby is subdued, with a cheerful person the baby is lively. From Mommy, the baby expects food and comfort; from older siblings the baby looks for entertainment. These different responses to different people are superimposed upon, or averaged in with, underlying behavioral predispositions. A baby born with a stolid temperament will be less lively with every social partner than one born with an exuberant temperament. We know next to nothing about how genes produce such effects.
At one year of age, the relationship system is operating on all cylinders—the baby’s mind already contains an extensive people-information lexicon—and the language system is just beginning to roll. The socialization system has made a start at categorizing people and at calculating central tendencies (prototypes) for the members of these social categories, but at this point babies still have no idea which category they themselves belong in.
They start to figure it out when they’re around two years old. By age three, children know that they are children, not grownups, and they know whether they are girls or boys. Once they’ve categorized themselves, children begin to conform to the norms of their own social category and to favor that category over others. But self-categorization depends on context. A child may categorize herself with the girls (versus the boys) in some situations, with the children (versus the adults) in others, and as a member of her race or religion or team in still others. Part of getting older is the need to adapt to changes in self-categorization. When an individual stops categorizing herself as a child and starts categorizing herself as a teenager, she has to adjust her behavior to a whole new set of norms. Later, when she starts categorizing herself as a grownup, the norms will change again, to the immense relief of her parents.
The effect of socialization is that children become more similar to their same-sex peers in behavior—some kinds of behavior, at least. That is why behavioral geneticists occasionally find nongenetic similarities between twins or siblings—similarities that can be attributed to “shared environment.” The environment they share is a culture or subculture: the culture of the neighborhood, school, social class, or ethnic group that siblings who grow up together have in common. Small subcultural effects are sometimes found for personality and intelligence; larger effects are found for things like delinquency and accents. Siblings almost always speak with the same accent, and it doesn’t necessarily match that of their parents.5
I have been quoted as saying that children are socialized by their peers. In a sense that is correct, but they aren’t socialized by interactions with their peers or by relationships with their peers. What causes them to become more like their same-sex peers is their identification with a particular social category and their own effort (motivated by the socialization system) to tailor their behavior to that of the prototypical member of that social category. Interaction with peers gives them useful feedback on how well they are doing the tailoring, but if need be they can do these things without any interaction at all.
Social categorization defines for children who their allies are and also who their rivals are. They want to be part of a group and to do what the other members do, but at the same time they want to be better than the other members of their group—they seek high status. The existence of these two conflicting motives is a clue that more than one mental system is involved. The motivation to compete is provided by the status system. Little boys vie for status by trying out for the position of alpha male. In play they get an idea of how strong they are relative to other boys their age.
But humans compete in many arenas; information obtained solely through contests of strength is not enough. One reason the status system is slow to get moving is that much of its input is provided by the mindreading mechanism, which is capable of doing some impressive things by the age of four but takes many more years to become good at its job. Though the mind reading mechanism evolved to serve the relationship system and continues to do so, it also provides important information to the status system: information on how the self is regarded by other people. Information on how the self compares, in the eyes of other people, with other girls or boys or other children or teenagers—the others with whom the self is vying for status.
The information keeps coming in. At least through adolescence and probably well into adulthood, people are capable of modifying their behavioral strategies on the basis of new information. I can’t outdo my rivals by overpowering them? Then let me try something else. Maybe I can be the funniest, or the smartest, or the one who is best at identifying plants or hitting a golf ball. I can’t be the prettiest? Then maybe I can be the nicest, and if that doesn’t work either, maybe I should try being the nastiest. Humans have many ways of finding something to be good at, but the limits put on them by their genes and their environment make some choices impractical, and some individuals are constrained to pick from a smaller menu than others. Shakespeare’s Richard III is physically deformed and Shakespeare has him explain himself like this: “Therefore, since I cannot prove a lover…I am determined to prove a villain.”6
Peers are as important for the status system as they are for the socialization system, but for different reasons. To the status system, the child’s same-sex peers are his rivals, and one of the things he has to do is figure out how he compares with them. But the information that tells him how he compares with them needn’t come only from peers: it can come from anyone in his community, the more information the better. I suspect that information provided by close relatives is discounted because it is likely to be inaccurate and biased, but even if it is given equal weight it isn’t going to count for much in the long run, because as children get older they spend more and more of their time with nonrelatives.
Personality varies in part because people have different genes, in part because even people with the same genes have slightly different brains, in part because even people with the same genes have different social experiences, and in part because variation and division of labor are emergent properties of human groups.
Identical twins have different social experiences because the members of their community see them as unique individuals. They may differ initially only because of developmental noise, but people who know them pick up on these little differences and use them to distinguish the twins. That’s one of the jobs of the relationship system: to keep individuals straight, to tell them apart. If I’m mad at Shawn I don’t want to make the mistake of punching Jonathan in the nose, so I keep a separate page in my people-information lexicon for each of them. The status system in Shawn’s mind tries to read what my lexicon says about Shawn, and the status system in Jonathan’s mind tries to read what my lexicon says about Jonathan. Since I hold different opinions of Shawn and Jonathan, their status systems will receive different input. They’ll receive different input from everyone who knows them. The self-knowledge Shawn acquires will differ from the self-knowledge Jonathan acquires.
Division of labor is an emergent property in human groups, just as it is in ant nests. While the socialization system is motivating the child to conform—“I do what the others do”—the status system is motivating the child to find something to be best in, perhaps something no one else is doing—“I do what they don’t do.”
All these things create or widen behavioral differences between identical twins. Such differences, if they are persistent, are both the cause and the result of differences in the brain. Behaving differently causes different synapses to form and different genes to be expressed, and these changes in the brain cause the behaviors to persist.
Each of the three systems I have described gives people a way of adjusting to or making use of a particular aspect of their soc
ial environment. Nature—that is, evolution—has endowed humans with dispositions which fit them for society. These dispositions enable people to behave appropriately in different social contexts and with different social partners. People make long-term adjustments in behavior that adapt them to their culture; thus they become more alike in some ways. People also find different ways of competing with their rivals; thus they become less alike in other ways. The result is that no two people have the same personality. No two are alike.
Nero Wolfe relies on the members of the local constabulary to haul the perpetrators off to jail, but otherwise he has little use for them. Like most fictional detectives who are not themselves cops, he harbors a fine disdain for the people who are officially charged by the society with the duty of identifying and nabbing perpetrators. He sees cops as close-minded, unidirectional in their thinking, and prone to settling prematurely on the easiest solution and confining their investigation to attempts to prove it.
Admittedly, I have done my share of throwing brickbats at the professionals, but I don’t want to leave you with the impression that I think most of them are clueless. On the contrary, the professionals have provided every single one of the clues. The clues, however, came from many different sources—not just from evolutionary psychology and behavioral genetics but from social psychology, developmental psychology, psycholinguistics, neurophysiology, anthropology, primatology, and entomology. The academic world, like the human mind, is made up of specialists. I’ve found that the most important advantage in not being a member of that world is the freedom not to specialize. Specialists view their field through a magnifying glass: they see very small details in a very small area. There are occasions when a jack of all trades like me can come in handy.
It is not specialization per se, however, that has caused so many academic psychologists to waste their time (and ours) chasing red herrings. It’s mostly that they don’t know enough about one particular area: behavioral genetics. Academics who are not themselves behavioral geneticists are apt to turn up their noses at it. This has been true since the late 1940s, when it became socially unacceptable even to hint that some of the differences among people might have a genetic basis. Despite the fact that the word “genes” can now be spoken aloud in polite company, most academic psychologists remain willfully ignorant of the methods and findings of behavioral genetics. They reveal their ignorance every time they open their mouths to say something about the length and width of a rectangle.
It is impossible to figure out what the environment does without taking into account what the genes do. It’s like trying to figure out how much you’ve earned by looking at how much money you have at the end of the year, without considering your assets and debts at the beginning of the year. All research that looks at individual differences has to have some way of controlling for the effects of genes—otherwise the results are meaningless. Regrettably, most research on individual differences does not meet this standard. People take such research seriously because the results confirm what they already believe and because there is so much of it. But no matter how high you pile it, worthless research is still worthless research. And theories based on worthless research are worthless theories.
Let me give you an example. In 1991, two developmentalists and an anthropologist—Jay Belsky, Laurence Steinberg, and Patricia Draper—proposed an “evolutionary theory” of female mating strategy.7 They reasoned that there is no one best mating strategy for human females, and that evolution has therefore endowed females with two alternative strategies, short-term and long-term. Which one will a given individual adopt? According to this theory, it depends on the family environment she experienced in infancy and early childhood. Girls who spent those early years in stressful environments—homes without fathers, or homes in which the parents got along poorly—will tend to adopt a short-term mating strategy: reach sexual maturity early, find a guy, jump into bed with him, kiss him good-bye, and find another guy. Girls reared in homes with nice, steady dads, on the other hand, will tend to adopt a long-term mating strategy: mature late, be choosy about whom to have sex with, find a guy just like dear old Dad, and stick with him.
Many evolutionary psychologists found this theory appealing, especially the part about the effects of a fatherless home. The reasoning made sense to them. If you live in an environment where security is nonexistent, why waste time waiting for it? Reproduce while you can. It’s a theory that seemed to explain how girls adapt to the harsh or benign realities of their environment, and there were plenty of data to support it. Girls reared in fatherless or troubled homes do reach puberty earlier, on average. They do have sex earlier. They do have more sexual partners and more broken relationships.8
The believers in this theory were willing to admit that genetic factors play a role in determining rate of sexual maturation and age at puberty; it has long been known that women who matured early are likely to have daughters who mature early. The believers were also willing to admit that girls who mature early are more likely to have sex early. But it couldn’t just be heredity, they reasoned, because the “effects” of a fatherless or troubled home were still detectable even after researchers controlled for the age at which the subjects’ mothers reached puberty.9
But girls inherit behavioral predispositions, as well as physical traits, from their mothers. And what about their fathers? Don’t girls inherit anything from their fathers?
Certainly they do. A group of medical geneticists recently identified a gene that girls inherit from their fathers (it’s on the X chromosome) and that has psychological and physical effects on both sexes. Males who inherit a particular variant of this gene tend to be impulsive and aggressive and are more likely to have troubled relationships—hence, more likely to sire children who grow up fatherless. Females who inherit this gene variant tend to reach sexual maturity earlier, begin having sex earlier, and have more sexual partners. The researchers who did this study looked at only a single gene; there must be other genes involved as well. But the study showed that genetic explanations of the “father absence effect” are plausible.10
The problem with the “evolutionary theory” of female mating strategy proposed by Belsky, Steinberg, and Draper is that it was based on the wrong kind of research. Individual differences in girls’ physical maturation and sexual activity were attributed to their home environment in early childhood, but the method used by the researchers provided no way of establishing that the differences they found were indeed due to the home environment and not to genetic differences among their subjects. The researchers should have looked at pairs of twins or siblings reared in the same home, to see if the home environment had similar effects on both siblings. They didn’t do this; they looked at only one subject per home. It was a behavioral geneticist, David Rowe, who finally did the right kind of research. Rowe found that environmental factors do play a small role in the age of onset of sexual activity, but his evidence suggests that these factors operate during the teen years, not in early childhood, and involve cultural or subcultural influences—the environment shared by siblings outside the home.11
This was not the only case in which lack of knowledge of behavioral genetics, and the seductive use of the word “evolutionary,” led evolutionary psychologists astray. Another example is the birth order theory presented by Frank Sulloway in his book Born to Rebel. Sulloway claimed that his explanation of the personality differences between siblings was an evolutionary theory and many evolutionary psychologists embraced it. They accepted his misinterpretation of the behavioral genetic evidence—the notion that growing up together makes siblings less alike—because they liked his Darwinian-sounding story of why siblings become less alike: it’s because they compete with each other. But the evidence I told you about in chapter 4 shows that growing up together is not responsible for sibling differences; nor is competing with each other. Environmental effects on personality are about the same in magnitude, whether siblings grow up together or apart and whether they compete or co
operate.
As you know, I’m not a behavioral geneticist myself; my interest is in the environment, not in genes. But I have come to the conclusion that current theories of environment are wrong, and that most of them are wrong because the theorists have not paid adequate attention to genetic factors. They have failed to use research methods capable of assessing the contributions of genes, and they have failed to understand—or even to attempt to understand—the results of research that did use such methods.
Since the late 1940s, theorists and researchers in most areas of psychology have persistently underestimated the influence of genes on behavior. When they see children with the same faults and virtues as their parents, they attribute the similarities to what the children learned from their parents. When they see children displaying the same faults and virtues at school as they do at home, they attribute the similarities to generalization—a carry over of learned behavior from the home to the school. They are wrong on both counts. Genetic influences on behavior account for most behavioral similarities between parents and children and for most of the behavioral similarities across social contexts (cultural or subcultural effects account for the remainder). Genetic influences also account for most of the continuity in personality between early childhood and adulthood. When traits show up early and persist into adulthood, it’s because of heredity, not early environment.
Don’t worry, there’s still plenty of room for environmental effects on behavior. Evolution provided the members of our species with a mind prepared from birth to collect specific kinds of information from the environment. The question is not whether young humans are responsive to their environment—of course they are! The question is, what kinds of information do they collect and what do they do with it? My answer is that they collect information of a pertinent sort, as close as possible to the time when they will be needing it (so that the information is up-to-date), and they use it in ways that make evolutionary sense. To assume that children are fashioned in such a way that their adult behavior is contingent on their experiences with their parents in the first few years of life is not just to underrate them but to underrate evolution itself. The reason why evolutionary psychologists fall prey to such ideas is that they, too, find it hard to put aside their faith in the nurture assumption.
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