One and the Same (28 page)

The credence he gives to gender stereotypes may make some people bristle. I was raised by a feminist who would strongly object to the premise that one kind of behavior is “normal” for boys or girls, but Bailey unapologetically contends that stereotypes have emerged because they're based in truth. “I've only met a few discordant twin pairs in the flesh—that is, meeting both the gay twin and the straight twin—and the ones whom I met are somewhat consistent with that picture even in adulthood: You can tell them apart. The gay one seems gayer than the straight one. There's a lot of skeptics who say, ‘Well, is the straight one really straight?' and I don't doubt there are cases where he's not. But usually I suspect he is.”

Bailey believes “gender nonconforming” behavior is a clue to the fact that homosexuality is ingrained early on—not “learned” or “acquired” later. “I've had several mothers who've seen articles about my research, contacted me, and said they have identical twin pairs in which one twin from early on is totally feminine, wants to be a girl, where his identical twin brother is a typical boy. I feel confident that when these children become adults, the very feminine one is going to be a gay man and the other twin is going to be a straight man. So what kind of things can make twins like that? The mothers deny that they're treating each child differently. … So I've always suspected that the cause of this difference is some sort of innate environmental influence. It means that it's not caused by social treatment, but it is
within
the individuals, that this difference was probably present at birth. Now what kind of things can cause differences like that before birth? I'm very curious; I think it's a huge, important question, but I don't have many good ideas. I think that this is one of the key questions in psychology and biology. We know that profound biological differences can arise in twins before birth.” (These differences can be caused by a disparity in circulation and oxygenation, infectious agents, drugs, chemicals, trauma in utero. Some variations in identical twins—such as their fingerprints, which aren't the same—are explained by conditions in the womb and the position of the fetuses.)

So, whether the concordance rates between identical twins are 50 percent or 20 percent, the bottom line seems to be that, when it comes to homosexuality, it's not genetics.

Bailey corrected me: “You can't say, ‘It's not genetics.' You can say, ‘It's not
completely
genetics. If it was completely genetics, identical twins would always be alike.”

Can you then say “It's not nurture”?

“I would say, ‘It's not nurture in the case of men,'” Bailey replied. “We have been doing research on sexual orientation and sexual arousal, and I think for men, sexual orientation is precisely a directed sexual arousal pattern: Men are gay because they get more sexually
aroused by men than by women. Women get sexually aroused by both men and women, no matter what their sexual orientation. It's possible that women don't have a sexual orientation, although they clearly have strong preferences for one sex or another, but it's not clear that it's caused by anything that is like what causes men to have preferences. It's a hot topic now in psychology that women are more flexible in their sexuality, that they're more changeable in their lifespan. … So it's very plausible to me that there is a role for nurture in sexual preference. Our results also suggest that there's a role for genes, as well.”

Vilain says his biggest obstacle in continuing the research now is gathering enough twins and enough financial support. “I think there is some reluctance to fund this issue,” he says.

Because people are politically invested in the findings?

“Right. Some gay activists say it's wonderful that you found something genetic, because it proves sexuality is involuntary, and so gays should have the same civil rights. Others say that sets up the stage for selective abortions. And now what we're looking at is even a little more complicated, because if it
is
environment changing biology, it's the nature/nurture debate at its worst.”

But I thought the “environment” that researchers are investigating does not mean “Your mom overprotected you, which made you gay.”

“It's not,” Vilain replies hesitatingly, “but I don't know that for a fact. It could be a little bit.”

Even something like a hovering mother could impact the genome?

“Well, the mouse study of the mother's grooming
did
impact the genome,” he points out, referring to the Canadian rat study.

I'm curious as to what he thinks the implications would be if he finds “the answer” as to which genes—or which epigenetic events—”cause” homosexuality.

“First of all it would be fascinating to show for the first time that
there is, in humans, an epigenetic influence in behavior. This behavior—whom we're attracted to—is fundamental behavior, essential for human survival. It's also a very dichotomous behavior: You're either attracted to males or to females. As a biologist, I think it would be a fascinating finding. Hopefully it will tell us which part of the genome is implicated. Whether I want it or not, there will be social implications. Even the way we look at evolution. People ask, ‘Why does the gay gene survive?' Well, I don't know why it stays on. Maybe this will give us a clue. There are all sorts of ideas out there why it keeps popping up in each generation. … Other social consequences? I really think it's going to go in all directions. And people are going to take what they want to hear.”

Vilain's intuition is that the environmental catalyst for homosexuality does occur before birth, not after, for the same reason Bailey cited: that gay boys seem feminine so early on. “The only reason why I think it's more likely to be prenatal than it is to be postnatal is because of children who are highly gender nonconforming,” Vilain tells me. “We know that these children become gay. It's very highly predictive. And in all the cases that I know of and all the cases that have been studied, it's not like the homosexuals' environment has been different from their brothers' and sisters'; it's really not. So something is going on very early on—as early on as age three. So that's why my hunch—I can't prove it, but my hunch is it's prenatal.”

In February 2008, a new study peeled back another layer to reveal why identical twins might differ in health: Their DNA isn't as alike as we thought. Scientists at the University of Alabama at Birmingham and at universities in Sweden and the Netherlands found “copy number variations” in twins—meaning that one twin might be missing a segment of DNA or might have
more
copies of that segment than his or her twin. It's possible that these disparities are to blame when one twin gets a disorder and the other doesn't. Jan Dumanski, a coauthor of the study, told the
New York Times
, “When we started this study, people were expecting that only epigenetics would differ greatly
between twins. … But what we found are changes on the genetic level, the DNA sequence itself.”

If epigenetics and womb environment explain why identical twins end up with divergent medical histories or sexualities, can it also explain the differences in personality?

Studies of twins reared apart, conducted at the University of Minnesota in the 1990s, found the most telling evidence for what does or does not differentiate identical twins from one another. Dr. Thomas Bouchard's team found, after exhaustive interviews with twins who had been separated early and then reunited in adulthood, that identical twins who'd grown up in different homes were just as alike as identical twins who had been raised together.
Just as alike:
similar habits, tastes, predilections, strengths, vices. Their different parents, homes, towns, schools, and luxuries had a negligible effect on who they became. Which means that identical twins are destined to turn out similarly (though not identically), no matter who their parents are. That tells us that genetics generally carry the day, or at least pack a significant punch when it comes to “every measured behavioral trait,” as Nancy Segal puts it, “such as religious interests, social attitudes, vocational interests, job satisfaction and work values. This research has truly affected the way we think about our own abilities, shortcomings and potentialities. …”

“It tells you that the
specifics
of parenting are not as important as we thought,” says Dr. Bouchard, who is now semiretired and lives part of the year in Colorado. “What's making twins similar is largely their genes. That seems to be what the data tells us. … We're not saying environment is unimportant, but, by golly, ‘environment' includes a lot of things that aren't what parents are doing.”

The idea that parenting is basically irrelevant in the end is so counterintuitive, it's difficult to absorb; Bouchard himself concedes that his team's findings have been “controversial,” especially among developmental psychologists who believe parental influence is decisive.
I'd certainly like to think my child-rearing style matters. “You are obviously important,” says Bouchard, “but the fact is, I could take a different mother and put her in your place and your kids would probably turn out the same. As long as we're taking abuse out of the equation, most mothers provide an adequate nurturing environment, and these environments are practically substitutable.”

Segal, who worked with Bouchard in Minnesota, underscores his point in her book: “Children's achievements might still be the same even if they were raised by different parents in different settings as long as their best abilities were encouraged and their emotional development supported.” She says the evidence for this theory is in the twins reared in different homes. “In my view, the most remarkable outcome of all is that, despite the many factors creating intellectual differences between twins, the intelligence test scores of identical twins still turn out to be so alike.” She adds later, “The bottom line is that living together does not make people in a family alike and that similarities are explained primarily by shared genes.”

Does this mean that DNA is destiny? In his 1997 book,
Twins: And What They Tell Us About Who We Are
, journalist Lawrence Wright captured how unsettling that idea can be. “Twins threaten us because they undermine our notion of identity. We think we are who we are because of the life we have lived. We think we shape the character and values of our children by the way we raise them. We think that we are born with the potential to be many things, and to behave in an infinite variety of ways. … But when we read about twins who have been separated at birth and reunited in middle age only to discover that in many respects they have become the same person, it suggests that life is a charade. … The science of behavioral genetics, largely through twin studies, has made a persuasive case that much of our identity is stamped on us from conception; to that extent our lives seem to be pre-chosen—all we have to do is live out the script that is written in our genes.”

Separated identical twins turn out the same not just because they
have similar traits but also because they make similar choices. Genes don't just impact how we look and act; they prompt us to
select
certain paths or behaviors. They inform whom we marry, whether we fight with them, whether we drink too much, work hard, the names we give our dogs, which raincoat we buy. The likenesses of twins are, therefore, not just wired into us but also
constructed by us
over time as we go through life making similar decisions, responding similarly to situations, people, and events, prompting similar reactions from people, which then shape those relationships similarly.

According to some experts, identical twins reared apart turn out to be
more
similar than those raised together because twins in the same household work harder to distinguish themselves. Bouchard disagrees: “I think that's wrong. Twins reared apart were
just as
alike as twins reared together, not
more
alike. And those twins who grew up under the same roof may or may not look to differentiate themselves.” He stresses that the reason identical twins reared together turn out similarly, if they do, is not necessarily because their parents treated them the same; that, in fact, twins reared in the same home will probably be treated differently depending on their personality. What's more, the term
identical
biases us in the first place. “There's a tendency for you to think you were more alike than you probably were,” he tells me.

If the similarities between me and Robin can be chalked up primarily to our genes, it seems environment is responsible for our distinctions. Environment is life experience, everything nongenetic that impacts us, including a formative friendship, a powerful teacher, a thwarted romance, a scary accident, a memorable trip—everything, in other words, but our parents. And the most critical environmental influence that differentiates twins (and, in fact, all of us) may actually be our peers.

That was the surprising thesis that Judith Rich Harris put forth in her groundbreaking 1998 book,
The Nurture Assumption
. Her basic
finding, after combing through every existing bit of research, was that peers are the missing link in understanding child development.
They
shape who we become. “Experiences in childhood and adolescent peer groups modify children's personalities in ways they will carry with them to adulthood,” Harris writes in her book, which was a 1999 Pulitzer finalist. “Children learn about themselves by comparing themselves to their groupmates. They vie for status within the group; they win or lose. They are typecast by their peers; they choose or are chosen for different niches. Identical twins do not end up with identical personalities, even if they are members of the same peer group, because they have different experiences within the group.”