The popularity of books like Lehrer’s, however, books that reduce scientific findings to convenient bite-sized pieces, means that many readers digest half-truths as if they were whole truths. These reductive bits of partial knowledge are then repeated at cocktail parties and lunches and become part of a foggy but general idea-weather. M’s stubborn conviction that a manly feeling of entitlement is genetic is just one of countless examples of ignorance parading as knowledge. Popular science displays a deep-seated bias for establishing a simple reductive correspondence between, say, male confidence and genes or a complex illness, such as schizophrenia, and neurochemistry, in this case the neurotransmitter dopamine. Even Parkinson’s disease, an illness known to be connected to a loss of dopamine, is not cured by simply administering the missing chemical.
Steven Pinker, an evolutionary psychologist who teaches at Harvard, has published one popular book after another explaining who we human beings are. Pinker, unlike Lehrer, is an academic, a fact that gives his ideas more heft than Lehrer’s. Although he obviously wishes to appeal to a broad popular audience, all of Pinker’s books are heavily referenced. Lehrer’s generalization about dopamine and schizophrenia is documented with a single paper on the subject that offers a hypothetical scenario, not a conclusion. In his laudable desire to demonstrate that art is a form of genuine knowledge that overlaps with discoveries in science, Lehrer repeatedly turns the speculative into the known. Pinker, on the other hand, is a spokesman for evolutionary psychology, and he is aware that his work has been harshly criticized because he has engaged in open debates with some of those critics—to his credit. Nevertheless, like Lehrer, in the work he has published for mass consumption, he has consistently presented his positions as solved scientific truths and answered open questions as if they had been forever closed.
Like Galton before him, Pinker has come down firmly on the side of nature in the nature/nurture debate. In How the Mind Works, for example, the reader is told that “the biggest influence that parents have on their children is at the moment of conception.” He hastens to add that this does not mean that offspring don’t need love and protection (they should not be locked up in dark rooms), but citing the psychologist Judith Harris, he writes, “Children would turn into the same kinds of adults if you left them in their homes and social milieus but switched all the parents around.”61 This strikes me as patently false. The only way to arrive at such a conclusion is to ignore whole disciplines and dispense with volume upon volume of empirical research in child development, attachment studies, and neurobiology, as if it were so much yellowing documentation piled up for the shredding machine. In the same book, he claims that the consensus among behavioral geneticists is that “much of the variation in personality—about fifty percent—has genetic causes.”62 In The Blank Slate: The Modern Denial of Human Nature, Pinker advances a scientific version of M’s theory of male entitlement. He makes a long list of what he describes as “reliable” psychological sex differences between men and women. “Of course,” he points out, “just because many sex differences are rooted in biology does not mean that one sex is superior”63 (my italics). These differences may, however, Pinker argues, explain why women are underrepresented in certain fields, including physics and some branches of mathematics.
Pinker makes many claims for traits rooted in biology. “Biology” here is weighted toward the built-in and fixed, as opposed to the learned and changing, although he freely admits that environment and learning play a role in human development. Pinker likes to present his views as commonsense rebuttals to those intellectual snobs Americans love to hate: Marxists, radical feminists, postmodernists, and just plain old intellectuals. I never fail to be impressed by intellectuals who play the anti-intellectual card while fully enjoying their roles as “academic experts.” Pinker’s ideas influenced the now notorious remarks about women in the sciences made by the former president of Harvard, Larry Summers, in 2005. Summers is an economist, not a geneticist or psychologist, a fact that seemed to have been lost in the media discussion. After he made his public comments, he credited The Blank Slate as having influenced his remarks.64 He had obviously accepted Pinker’s argument as the state of current science on the question because he essentially regurgitated it. Summers cited “many different human attributes” that distinguish the sexes, including “height, weight, propensity for criminality,” as well as “overall I.Q.” and “mathematical ability, scientific ability.” “There is relatively clear evidence that whatever the difference in means—which can be debated—there is a difference in variability of a male and female population.”65 What does this mean?
Summers was referring to variability in Darwin’s idea of sexual selection. In order to account for animal traits that make no evolutionary sense—the gorgeous but heavy and impractical tail of the peacock, for example—Darwin surmised the reason the tail didn’t vanish through natural selection was because that beautiful tail fan is sexy to peahens. Darwin believed that in all species, including human beings, males are competitive and promiscuous and females are coy and choosy. Darwin accepted that male variability is greater than that of females, even though there was no “hard” evidence for the belief. It was founded on his observations of both animals and people. The Darwinian story has had great power, and it goes like this: Because males in every species have to fight to get the girl, sexual selection has a greater effect on males. Strong males may mate with hordes of females while loser males may mate with just a few or even none, which means the weaker males are more rigorously eliminated than weaker females, and to make this long story short, the result of all this wild male competition and promiscuity is that in the end there are more geniuses and idiots among men than among women—there is greater variation. For Darwin, variation explained why man “is more courageous, pugnacious and energetic than woman and has a more inventive genius.”66 Pinker, Summers, and a host of others may soften their rhetoric to make it more palatable for a contemporary audience, but the underlying argument is essentially unchanged.
In 1948, the biologist Angus Bateman published a paper on Drosophila melanogaster, in which he proved that even the humble fruit fly faithfully embodied the rules of sexual selection. The scientist found “sexual selection more effective in males than in females.”67 In his discussion he broadens the scope of his findings: “This would explain why in unisexual [one sex or the other, not both sexes in one] organisms there is nearly always a combination of an undiscriminating eagerness in the males and a discriminating passivity in the females.”68 The Bateman paper did not truly take wing, so to speak, until 1972, when the Harvard biologist Robert Trivers cited it as key evidence for his paper “Parental Investment and Sexual Selection.” Trivers retold the sexual selection story, emphasizing a point Bateman had made in his 1948 paper: Because a female’s reproduction is limited by the number of eggs she makes during her cycle, once she has been impregnated by a single sperm, she doesn’t need to mate anymore. The male, however, unburdened by expensive eggs and loaded up with cheap sperm, can fly off merrily to his next conquest.69 The Bateman study has been cited a couple of thousand times in the literature and became vital to the argument about variance. Sexual selection means that men occupy the exceptional poles—the dumbest of the two sexes, but also the smartest. Passive, slow, weighed down by pregnancy and nurturing, we women founder somewhere in the fair-to-middling range.
But the Bateman tale may be fairytale. In 2012, Patricia Adair Gowaty and two of her colleagues at UCLA replicated Bateman’s experiment. Their paper, “No Evidence of Sexual Selection in a Repetition of Bateman’s Classic Study of Drosophila Melanogaster,” demonstrated that Bateman’s methodology was seriously flawed and that there is no way to reach his conclusion from the evidence.70 In recent years, more and more female “promiscuity” in different species has come to light. Gowaty’s study of bluebirds demonstrated considerable “extra-pair copulations” among females.71 Male antler flies are choosier than their female counterparts.72 The sex roles o
f two-spotted goby, a species of marine fish, depend on when they mate during their short breeding season. Late in the season, females compete intensely with other females for males.73 The bucktooth parrotfish, on the other hand, have a harem system, one male to a bevy of females. If the male is killed, one of the females conveniently turns into a male.74 The female bronze-wing jacana is 60 percent larger than the male, beautifully colored, and polyandrous. One female mates with many male birds, and it is the male bird that guards the nest and nurtures the offspring.75
The primatologist Sarah Blaffer Hrdy has been arguing since the 1980s that the classic version of sexual selection is wrong. In an essay published in 1986, “Empathy, Polyandry, and the Myth of the Coy Female,” she argues, “Indeed on the basis of what I believe today, I would argue that a polyandrous component is at the core of the breeding systems of most troop-dwelling primates: females mate with many males, each of whom may contribute a little bit toward the survival of offspring.” She offers as one example the fact that the multiple male consorts of a female savanna baboon develop protective relations toward her offspring.76 Hrdy has also reconfigured ideas about the social organization of those early hunting-and-gathering humans that play such a big role in evolutionary psychology. In Mothers and Others, she argues that a single woman could not possibly raise a child alone in that harsh habitat. Siblings, uncles, grandmothers, fathers, and others had to lend a helping hand in childcare or the children would have died.77
A frequent response to the astounding variety in animal mating habits is to regard each one as another exception to the wider rule. But how many exceptions are needed to overturn a rule? As the zoologist Michel Ohmer points out, “All one needs to do is scan the literature, and hundreds of articles depicting sex role reversal, female competition, male choice, and costly female ornaments, all of which go against classic theory, appear.”78 The failure to replicate Bateman’s results and the exposure of his flawed methods cast doubt on a pivotal study, as do the increasing numbers of species who seem not to follow the old rules. There is good reason to be skeptical of this evolutionary fable with its perpetually tumescent male and shrinking female and begin to think of varieties rather than poles of reproductive strategies among species.
Was Bateman acting in bad faith, fixing his results to fit the theory? I doubt it. What is most interesting about Bateman’s flawed science may be that it demonstrates a crucial aspect of perception itself, which is now an intense subject of scientific research. There have been many errors such as Bateman’s in the history of science, simply because people often see what they expect to see. Although a version of this idea has been traced back to Ptolemy, and Descartes maintained that habit played an important role in how we perceive the world, it is usually credited to Hermann von Helmholtz, the nineteenth-century biophysicist, who argued that unconscious inference (unbewusster Schluss) is at work in perception. Helmholtz’s idea, which influenced Freud, was ignored for well over a century, but it has seen a lively comeback in contemporary neuroscience.
Simply put, an observer’s perceptions are unconsciously shaped by his earlier perceptions. We have the visual equipment to see, but we also learn to see and read the world through our experiences in it. Helmholtz stresses that there are many “illustrations of fixed and inevitable associations of ideas due to frequent repetition,” some of which are purely conventional—the letters of a word in relation to its sound and meaning, for example. Helmholtz’s insight that “experience, training, and habit” unconsciously influence our perceptions is now widely accepted.79 In an article in Frontiers in Human Neuroscience, Peggy Seriès and Aaron Seitz summarize the research: “Our perceptions are strongly shaped by our expectations. In ambiguous situations, knowledge of the world guides our interpretation of the sensory information and helps us recognize objects and people quickly and accurately, although sometimes leading to illusions.”80 Bateman may well have seen male eagerness and female passivity among his buzzing flies. It was, I suspect, what he expected to see.
Heritability and Twin Tales
When I was eighteen, I was in the act of turning away from the mirror, and I suddenly caught a glimpse of my father’s face in my own. I have seen my mother, too, especially now as I grow older. Every once in a while she shines out at me in the reflection of my own older countenance. It goes without saying that we are not self-created, and if we have children we leave something of ourselves in them. It also goes without saying that long before the discipline we now call genetics, it was obvious that we inherited certain features from our parents, features that may be visibly present in us. Just because the relationship between genotype and phenotype is not that of a perfect blueprint or code doesn’t mean George won’t get a nose that may look strikingly like his Aunt Zelda’s. Moreover, many of us have found ourselves “acting” like one of our parents and then catching ourselves doing it, as in, Oh my God, that’s just what my mother used to say (or do). It makes sense to talk about these traits as “inherited” or “heritable.” A heritable trait is simply a trait in an offspring that resembles the corresponding trait in a parent, but that correspondence does not have to be genetic. Rich children are usually born of rich parents, but that does not mean wealth has genetic causes. And what about behaviors? Do I walk like my mother because I grew up with my mother and watched her walk and gesture for years or because I have an inborn proclivity to walk that way?
Behavioral geneticists try to untangle that question, never in a single person but in populations. They arrive at heritability percentages in those groups through statistical analyses of correlations. They measure variation in genetic similarity. The difference in “variability” Summers mentioned in relation to sex, therefore, is a statistical measurement, something an economist would understand well. The gold standard for such measurements are identical (monozygotic) twins as opposed to fraternal (dizygotic) twins because the former have the same genetic material as each other and the latter do not. If twins grow up together, they are believed to share the same “environment” as well as the same (or different) genes. When there are similarities between identical twins who share 100 percent of their genes and who grew up in a shared environment, as opposed to fraternal twins who do not share all the same genes but also grew up together, then the argument goes that the similarity between the identical twins can be attributed to genes. Therefore, through a series of calculations, it is possible to come up with a general number between 0 and 1 of what percentage, to put it crudely, is “nature” and what is “nurture.” Or, to be more exact: these numbers are intended to represent the proportion of phenotypic variance in a given population due to genetic variance. A heritable score of .50 means that half the variation in the distribution of a trait in the population the scientists tested is correlated with “biology” and half with “environmental” factors.
Everyone has read pleasing stories about separated identical twins, who, when reunited years later, turn out to both love the color red, sing Verdi in the shower, and buy the same brand of toothpaste. “Two middle-aged male identical twins, separated for a good portion of their lives, both worked as telephone linemen and both had wirehaired fox terriers named Trixie.”81 This story appears in a book called Born That Way (1998) by the journalist William Wright. Although unable to explain how genes determine job choice and dog naming, Wright is persuaded that they are hard at work. The twins appear to confirm the idea that what really matters in life is your parents’ genes—“the moment of conception”—not how you were brought up.
As with many twin studies that claim to track “separated” twins, these identical twins had spent time together and already knew each other. Had one lived in Tanzania and the other in Sweden, the chances of either of them having terriers named Trixie would arguably have been very low. The unstated time these twins did spend together may have been decisive when it came to jobs and dogs. I don’t know. The rhetorical device used here is important, however. The twins may diverge from each other in many ways, may have
different tastes and habits in other matters, but citing two remarkable likenesses achieves its goal: they’re the same and they were raised apart! What I do know is that such coincidences do not tell us much about human development, and the statistics of behavioral genetics tell us nothing about a single pair of twins.
Scientists have to make a blanket assumption that all twins who grow up in the same house with the same parents have the same “environment,” even though that may not be true. Behavioral geneticists would argue that for their purposes it is broadly true. Individual cases do not matter. In a textbook chapter on the subject, the authors articulate the ambiguities involved in measurements of heritability:
In most studies in behavioral genetics the effects of gene-environment correlation and gene-environment interaction cannot be estimated separately and are included within the estimate of heritability. This means that even when a trait is highly heritable, environmental influences may still be important in mediating the effects of the genes on behavior. For example, in the case of gene-environmental correlation, if exposure to friendly company were correlated with a person’s genotype, sociability could be found to be heritable even though it may have arisen as a result of increased exposure to company.82