MOST OF THE PAPERS that flowed from the Minnesota Twin project in the late eighties appeared in professional journals of the psychology field. While these periodicals were respected, the time had come to break out of the hermetic world of psychology and put forth a broad summary of the Minnesota findings in a publication that covered important advances in all the sciences. In the United States, the premier venue for such reports was Science magazine. Bouchard had met the editor, Daniel Koshland, at a conference in 1984, when Koshland was a biochemist at Berkeley. They had had a conversation about the Minnesota project and Bouchard had obliged Koshland’s request to be kept informed about the twin research. In 1989, four years after becoming editor of Science, Koshland approached Bouchard about writing a paper that would summarize his results to date. Bouchard was delighted.
The paper, published in 1990, shows none of the reticence of the earlier papers and starts off with a trumpet blast about the finding most likely to ignite controversy, the high heritability of I.Q. The figure was slightly lower than the earlier one, .70, but still high enough to alarm the antigenes holdouts. The paper went on to summarize Minnesota’s other findings, concluding with a body blow to the environmentalists: On a number of measures of personality, temperament, interest, and attitudes, the twins reared apart measured about the same as twins reared together.
Having set forth the explosive implication that rearing environments apparently made little difference in personality formation, the authors moved quickly to soften their claims. Within the paper’s initial abstract, they suggest an explanation sure to be more palatable to traditional environmentalists. “It is a plausible hypothesis that genetic differences affect psychological differences largely indirectly, by influencing the effective environment of the developing child.” This was a puzzling disclaimer since the entire study was repeatedly showing the weakness of the environment in development compared with genetic endowment and might be seen as a strained effort to assure the hardliners that their cherished environment was still important (if only to transmit genetic effects).
In pointing out that their heritability figure for intelligence of .70 was somewhat higher than the earlier studies, the paper saw an explanation in that those studies primarily involved adolescents, whereas the Minnesota twins were closer to middle-aged. Other research had shown that heritability of most traits increases with age—that is, twins grow more alike as they grow older (a surprising statistic in light of the increased opportunity for environmental factors to work their effects)—so that the Minnesota I.Q. finding was not really inconsistent with prior studies.
As always with such papers, the Minnesota report in Science naturally went into detail about the study’s methodology and offered mean figures on the degree of separation and age at reunion, among others. Because of the informed-consent agreement, which promised the twins anonymity, the article provided no biographical information about individual twins, either anecdotal similarities or specifics about time of separation or age at reunion, or any information that might be used to identify a particular pair.
The core of the paper was a table that listed all of the traits examined with the percentages of correlation of the MZAs and the MZTs. The MZA correlation figures ranged from .96 for finger-ridge count to a .33 mean for social closeness. In other words, of the twenty-eight categories listed, including both physical and personality characteristics, every figure showed at least some degree of genetic influence. Most of the figures clustered around the more than merely significant 50 percent area.
In their conclusions Bouchard and his colleagues stated that the evidence indicated that parents might be able to increase the rate at which their children develop cognitive skills, but they will have “relatively little influence on the ultimate level attained.” Later, more diplomatically, they said: “The remarkable similarity in MZA twins in social attitudes (for example, traditionalism and religiosity) does not show that parents cannot influence those traits but simply that this does not tend to happen in most families.”
With that caveat Bouchard held out a less frightening alternative than powerful genes: ineffectual parents. If children do not turn out as we would wish, we would rather hear that the fault lies with their parents, whom we can improve, than with the genes about which we can do little. It is with asides like this that the Minnesota group revealed its awareness of the affront their findings would be to the cadres of psychologists who had based their therapies and problem-solving strategies on environmental assumptions this study was now demolishing.
In the paper’s principal conclusion, however, that in every trait investigated genes prove to be an important source of variation, they sounded a strident note: “This fact need no longer be subject to debate; rather it’s time instead to consider its implications.”
The paper ruminated about an evolutionary explanation for the high degree of variation among humans, the apparent fact that newborn babies are already different from each other, before the environment has had a chance to work its influences. The paper cited one theory that says there is no point to these individual differences and considers them “evolutionary debris.” Another believes them to have an adaptive function that has been selected for. Many Darwinians consider the small differences the Minnesotans were measuring, the variations that make humans more interesting than fruit flies, to be the engine that drives evolution. This is hard to digest in that it suggests that if you and your sister are very different, one of you may be launching a new direction for the entire species.
The Minnesota writers left it to the evolutionary theorists to make sense of the human-difference phenomenon but said that a species that was genetically uniform would have created a very different society from ours; whatever the origin of human variation, it “is now a salient and essential feature of the human condition.” Not to mention the basis of every novel, play, poem, opera, and sitcom ever written.
Behind all writings on genetic influence over personality and behavior, there are inevitably political undercurrents, as there are with any theories that touch all humans. In scientific papers these political substrata usually push close to the surface in the broad generalizations at the end that often address implications. Saying that present-day society is a product of human variation might seem safe enough on the face of it, but the assertion is surely a red flag to some who might see a hint that our social structures are, thanks to genes, inevitable. If this implication was found, it would be branded the status-quo justifying that evolutionists have been accused of since Darwin, sometimes with good reason. The paper’s conclusion was remarkably simple: People are different, and they are different to a large degree because of genetic differences. While this would not seem to be a belligerent manifesto for revising political thought, to some it was just that and they marshaled their forces to combat it.
INITIALLY, HOWEVER, the response to the Science article was muted, with the magazine publishing only two critical letters. One was from an M.I.T. mathematics professor, Richard Dudley, who objected to the assumption of randomly varying environments for the MZAs, noting that in earlier reared-apart twin studies “some had even gone to the same school.” He felt, therefore, that without precise measures of the rearing environments, generalizations about genetic influences on I.Q. to the populations at large could not be made.
It seemed odd that a professor at a university who presumably faced numbers of students for long enough periods to become acquainted with them to a degree (or that anyone, for that matter, who has ever been in a class with a group of students, as everyone has) would not accept as self-evident that within any environment—family, classroom, workplace—individuals will reveal differences in intelligence that remain more or less constant, that are not brought closer together by the educational process. But Dudley was suggesting that the high I.Q. correlations between Bouchard’s separated twins might be explained by their attending similar—perhaps (good grief) the same—school.
Critics of twin studies who used thi
s argument were clearly trying to leave the door open, not for improvement in the least gifted kids in an M.I.T. class, but for improvement for the least gifted kids at the lower end of American society. Underlying the point made by Dudley and many others, that I.Q. can be raised by the right environment, is a resistance to the existence of such a condition as “smart” or “stupid”; there are only good or bad environments. Although Dudley had not explicitly mentioned the underclass, Bouchard and his colleagues answered him as if he had. They quoted the warning in their paper about generalizing too broadly from their research:
Since only a few of the MZA twins were reared in real poverty or by illiterate parents and none were retarded, this heritability estimate [of I.Q.] should not be extrapolated to the extremes of environmental disadvantage still encountered in society.… These findings do not imply that traits like I.Q. cannot be enhanced.… The present findings, therefore, do not define nor limit what might be conceivably achieved in an optimal environment.
As if this weren’t sufficient obeisance to the environmentalists, the Minnesota team went on to state flat-footedly: “There is little doubt that I.Q. is malleable.”
But the Minnesota I.Q. heritability figures—.75 for MZAs, .70 for all twins—were there for everyone to see. For all their concessions to those who still insisted that environment played an important role in I.Q., the Minnesota subtext was that, yes, environment can affect I.Q., but most of the time it doesn’t.
In a later paper Bouchard made a point about genes and I.Q. that had been more fully developed by Harvard’s Richard J. Herrnstein, who later coauthored The Bell Curve, and before him, by psychologist Gerald Hirsch—a point that had caused furious protest. As society draws closer to the nation’s egalitarian ideal, they said, in which schools become of uniform quality, home environments are all healthy and substantial, and everyone has a just share of the nation’s bounty, the genetic effects on young people’s development will increase, rather than decrease. This would be because the wide range of environments now existing will be leveled, homogenized, equalized—leaving genes the only variable. Some might argue, and the Minnesota findings implied, that for large portions of the population, this had already happened.
The other letter raised the familiar criticism that the random environments of the study’s separated twins were broad enough to show effects on gene expression. Yes, the critics said, the environments were different, but not different enough to show the environment’s power over genes. The opponents would point to environmentally induced alterations in gene expression of other species, which clearly demonstrated that gene expression can be enhanced or diminished by varying environments.
The Minnesota geneticists responded that the evidence showed that, in general, genes acted “independently of the environment” as long as the environment fell within a normal range—that is, no droughts or toxic fumes. Vague and unscientific as the concept of “normal range of environment” sounded, there appeared to be no other way to express a condition crucial to the entire study of genetics and that would be the crux of the later dispute triggered by The Bell Curve in which critics disagreed heatedly with the authors over the point at which an environment becomes “abnormal” and interfered with development.
With humans the assumption is that a certain minimal level of shelter, diet, and nurturing places the developing child within the normal range of environment, the range in which the genome would express itself as nature intended. On the other hand, a child who has been beaten, starved, or chained in a closet clearly fell outside the normal range and, developmentally speaking, all bets were off. Infant Romanian orphans warehoused in subhuman conditions and others brutalized in early life are known to have suffered permanent neurological damage. Not only their bodies but their behavior can be permanently altered. But the evidence has not shown that negative, but less-than-brutal, experience will also cause permanent changes, just to a lesser degree. The environment must push genes pretty far before they react with any changes whatsoever in the organism. Jerome Kagan’s work with Guatemalan infants, to be discussed in chapter 8, is just one vivid demonstration of the genome’s power to overcome adverse conditions.
The susceptibility of behavioral genes to environmental pressures has not been shown to be a continuum on which life experience can bring about degrees of permanent neurological change. The exceptions that result from extreme environments do no damage to the normal-range concept, which remains a potent and meaningful factor in appraising genetic expression. Most professionals in the field understand this and accept the validity of the concept when discussing gene action. For humans and many other species there is a wide range of environments that permit the genes to produce their preordained results without significant alteration. The lack of scientific precision to the words normal range, however, carries a sense of vagueness and provides opponents with a handy weapon for criticisms and claims of “fatal flaws”—not just in twin studies but in all of behavioral genetics. Yes, the environment can thwart genetic expression; that it rarely does is a point the critics like to overlook as they trot out their shopworn examples of environmentally altered genetic effects.
SIX
TWO DOGS NAMED TOY
WITH THE PUBLICATION of the Science article in October 1990, the Minnesota Twin Study was solidly on the scientific map and the environment-is-everything dogma had been dealt a mighty blow. Bouchard’s twins had provided statistical evidence, compelling to all but a few environmental diehards, of a genetic component to personality and behavior. He and his research team had been looking for signs of inherited traits, and they had found them—everywhere they looked. The notion of nature or nurture—which more and more people were increasingly realizing was a bogus dilemma—had been changed to nature and nurture, or, as the Minnesota group preferred to say, nature through nurture.
What the Minnesota group had produced were percentages of genetic contribution that were expressed in figures of heritability. This is very specific, and to outsiders a confusing term, meaning the percentage of variation of a trait within a given population that is due to genes. It is an estimate of the genetic contribution to a particular trait for the group measured—a group average, in effect—and does not necessarily say anything about an individual in the group.1 Because the sample was substantial in this case, the figures had a high degree of accuracy for groups but not for individuals. It is ironic, therefore, in a study scrupulously avoiding generalizing to individuals, some of the most interesting data that was turned up—stumbled upon, rather—concerned the amazing similarities between individuals.
It should be emphasized that a number of striking and unusual behavior forms turned up that were not found in both twins. This is simply evidence that MZAs and MZTs do not share all traits and qualities, a proposition no one has ever made, least of all the Minnesota group. Such twin inconsistencies, even in unusual traits, takes little away from the potential significance of the large numbers of tastes, habits, and quirks found in both members of a twin pair.
One of the most interesting pairs of twins to undergo the week of tests at Minnesota were two Englishwomen, Daphne Goodship and Barbara Herbert. Their mother was an unmarried Finnish exchange student who was living in England in 1939 when she gave birth to the twins. Before returning to Finland immediately after the birth, the young woman put them up for adoption. The sisters were raised by two unconnected English families and did not meet again until shortly before their fortieth birthday.
What makes their story unusual is that the two adopting families were of different social classes, answering a frequent complaint of the critics that the social-economic level of the “separate” homes are similar enough to explain the parallels. Barbara grew up the daughter of a municipal gardener, a British groundskeeper in a public park. The adoptive father of the other twin, Daphne, was a well-paid metallurgist who lavished on his daughter the comforts and privileges of an upper-middle-class rearing—private schools, cultural events, and vacation trips ab
road. While such disparate childhoods would seem to augur a matching set of before-and-after Liza Doolittles, it did not turn out that way. The two women were more similar than most sisters growing up in the same home.
When the genetically identical women arrived in Minneapolis, the university staff was immediately struck by a shared idiosyncrasy: They laughed constantly. No matter how innocuous an interview question or routine an observation, it would send them both into peals of laughter, laughter that at times was difficult to subdue. Just when the merriment seemed to have subsided, they would go off again. Staff members dubbed them the giggle twins. Because an exchange of glances usually preceded the eruptions, it appeared they shared some secret joke, or perhaps found the Minnesota Twin Study the funniest experience of their lives. But it was learned that both women had been laughers for years before they met, and they admitted that in their pre-reunion lives they both knew no one who laughed as much as they did.
When the twins were not cracking up, they were cheerful to the point of giddiness. They were also enthusiastic pranksters. Walking across the Minnesota campus with Bouchard, they suddenly decided to pelt him with snowballs, shrieking as they forced the distinguished scientist to shield his eyeglasses from their blitz. While not exactly a behavioral oddity, it is unlikely that many forty-year-old women would do it, even if prompted by their sister’s tossing the first ball. Later in the week during an interview together—a videotaped record of the twins interacting—they pulled another stunt. They announced that they had both wanted to become opera singers. Since neither could hold a tune, they thought this a fine joke but quickly admitted their hoax. While cute, it is not everyone’s humor.
In all the physiological tests—brain waves, heart, and so on—they responded almost identically to stimuli, needles jumping as with the same person being retested. Both had a slight heart murmur and the thyroid glands of each was a shade larger than normal. Both were attractive women, both five feet three inches tall; while they looked alike, they could be told apart without difficulty. Both had been born with crooked little fingers, a malformation that made piano playing and touch-typing impossible.
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