Opinion | What Genetics Is Teaching Us About Sexuality


As researchers in biology and sociology who are also gay men, we have long wondered (and debated) whether sexual orientation has any biological basis. We followed the ascent in the 1990s of the “gay gene” finding — which claimed that male sexual orientation was linked to specific DNA markers — and then watched as that result was called into question. We have wondered whether the two of us, who differ in so many ways, could really trace our common identity to a shared biology.

New data are finally giving us answers.

A study published today in Science looked at the DNA and sexual behavior of nearly 500,000 people. It found that the sex of your sexual partners is, in fact, influenced by your genes. But it also found that it was not possible to predict your sexual behavior from your DNA alone. The study suggested, in other words, that while biology shapes our most intimate selves, it does so in tandem with our personal histories — with the idiosyncratic selves that unfold in a larger cultural and social context.

The researchers, who included one of us (Dr. Wedow), analyzed the genetic markers of people who responded to the question “Have you ever had sex with someone of the same sex?” From these data, the researchers estimated that genetic differences account for roughly one-third of the variation in same-sex behavior. The study also identified several DNA sequence variants associated with having had a same-sex experience.

So, yes, your sex life is influenced by your genes.

This conclusion fits with our personal experiences and intuitions. Sexual desire is typically stable, something we often are aware of from our first longings. Furthermore, one of the several DNA variants identified in today’s study is involved in gonad development, which accords with previous research that links sexual orientation to hormone exposure.

But the study’s findings also complicate the relationship between genetics and sexuality.

For one thing, the results make clear that there is no single biology of sexual behavior. It turns out, for example, that the genes influencing same-sex behavior in females are often different from those that shape behavior in males. It also turns out that the genes associated with having occasional same-sex experiences are unlinked to having exclusively same-sex experiences.

In addition, people who only occasionally have same-sex partners tend to have genetic variants associated with having more sexual partners overall, and with personality traits like “openness to new experience.” In contrast, the study found that exclusively same-sex behavior had little correlation with the biology of personality. For some people, same-sex behavior may be a form of exploration. For many others, it is not.

Researchers since the 1940s have described sexual orientation as a single trait that exists on a scale, ranging from “exclusively heterosexual” to “exclusively homosexual.” But today’s study suggests that sexuality is more diverse than that — many different things, rather than one thing in greater or lesser degrees.

Although valuable, the study does have limits. The sample size is enormous by historical standards, but the sample still excludes most minority groups. This not only impairs our ability to make generalizations across people with different ancestries, it also overlooks the cultural variation within and among groups.

Similarly, the study examines only the binary distinction between same-sex and opposite-sex behavior; it does not examine gender (as opposed to biological sex) or the many other varieties of sexual interest. In order to advance science for everyone, we need studies that explore the full diversity of genetics and experience.

It’s also important not to overstate the role of genes. The study found that genetically related people tend to be similar in their behavior, which tells us that sexuality has influences buried somewhere in the DNA. But when the researchers tried to add up the contributions of each DNA variant they examined, they could predict less than 1 percent of the variation among study participants.

So researchers could never predict sexual behavior from DNA alone. In fact, we’ve known this for a while. Even if you have a homosexual identical twin — someone who shares all of your DNA — you are still more likely to be straight than gay.

Many people are wary of genetic research into sexuality because they fear that scientific findings could be used to advance discrimination. They worry that people will attempt to eliminate same-sex behavior using gene-editing technologies like CRISPR or by screening embryos. But the genetic science of sexuality shows us that neither effort would work.

We must also recognize that bigotry needs no data. No facts will sway those who want to police the intimacies of consenting adults. Rather than consign ourselves to ignorance out of fear, we should use these powerful new data ethically and thoughtfully to arrive at a fuller understanding of who we are.

It’s prejudice, not knowledge, that threatens us.

Steven M. Phelps is a professor of integrative biology and the director of the Center for Brain, Behavior and Evolution at the University of Texas at Austin. Robbee Wedow is a research fellow at the Broad Institute of M.I.T. and Harvard, and a research fellow in the department of sociology at Harvard.

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