Many Genes Influence Same-Sex Sexuality, Not a Single
‘Gay Gene’
By Pam Belluck
Aug. 29, 2019
[[Two points of commentary. 1. Shock! Surprise! Astonishment! But
it has been long known that man y traits depend upon interaction of many genes.
Wikipedia:
Often different genes can
interact in a way that influences the same trait. In the Blue-eyed Mary (Omphalodes verna),
for example, there exists a gene with alleles that determine the color of
flowers: blue or magenta. Another gene, however, controls whether the flowers
have color at all or are white. When a plant has two copies of this white
allele, its flowers are white—regardless of whether the first gene has blue or
magenta alleles. This interaction between genes is called epistasis, with the second gene epistatic to
the first.[43]
Many traits are not discrete features (e.g. purple or white
flowers) but are instead continuous features (e.g. human height and skin color). These complex traits are products of many genes.[44] The influence of these genes
is mediated, to varying degrees, by the environment an organism has
experienced. The degree to which an organism's genes contribute to a complex
trait is called heritability.[45] Measurement of the
heritability of a trait is relative—in a more variable environment, the
environment has a bigger influence on the total variation of the trait. For
example, human height is a trait with complex causes. It has a heritability of
89% in the United States. In Nigeria, however, where people experience a more
variable access to good nutrition and health care, height has a heritability of only
62%.
2. The most important conclusion is that now a case for genetic
determinism of sexual orientation is impossible to make..]]
How do genes influence our sexuality? The question has long been
fraught with controversy.
An ambitious new study —
the largest ever to analyze the genetics of same-sex sexual behavior — found
that genetics does play a role, responsible for perhaps a third of the
influence on whether someone has same-sex sex. The influence comes not from one
gene but many, each with a tiny effect — and the rest of the explanation
includes social or environmental factors — making it impossible to use genes to
predict someone’s sexuality.
“I hope that the science can be used to educate people a little
bit more about how natural and normal same-sex behavior is,” said Benjamin
Neale, a geneticist at the Broad Institute of M.I.T. and Harvard and one of the
lead researchers on the international team. “It’s written into our genes and
it’s part of our environment. This is part of our species and it’s part of who
we are.”
The study of nearly half a million people, funded by the
National Institutes of Health and other agencies, found differences in the
genetic details of same-sex behavior in men and women. The research also
suggests the genetics of same-sex sexual behavior shares some correlation with
genes involved in some mental health issues and personality traits — although
the authors said that overlap could simply reflect the stress of enduring
societal prejudice.
Even before its publication Thursday in the journal Science, the
study has generated debate and concern, including within the renowned Broad
Institute itself. Several scientists who are part of the L.G.B.T.Q. community
there said they were worried the findings could give ammunition to people who
seek to use science to bolster biases and discrimination against gay people.
One concern is that evidence that genes influence same-sex
behavior could cause anti-gay activists to call for gene editing or embryo
selection, even if that would be technically impossible. Another fear is that
evidence that genes play only a partial role could embolden people who insist
being gay is a choice and who advocate tactics like conversion therapy.
“I deeply disagree about publishing this,” said Steven Reilly, a
geneticist and postdoctoral researcher who is on the steering committee of the
institute’s L.G.B.T.Q. affinity group, Out@Broad. “It seems like something that
could easily be misconstrued,” he said, adding, “In a world without any
discrimination, understanding human behavior is a noble goal, but we don’t live
in that world.”
Discussions between Dr. Neale’s team and colleagues who
questioned the research continued for months. Dr. Neale said the team, which
included psychologists and sociologists, used suggestions from those colleagues
and outside L.G.B.T.Q. groups to clarify wording and highlight caveats.
“I definitely heard from people who were kind of ‘why do this at
all,’ and so there was some resistance there,” said Dr. Neale, who is gay.
“Personally, I’m still concerned that it’s going to be deliberately misused to
advance agendas of hate, but I do believe that the sort of proactive way we’ve
approached this and a lot of the community engagement aspects that we’ve tried
were important.”
The moment the study was published online Thursday afternoon,
the Broad Institute took the unusual step of posting essays by
Dr. Reilly and others who raised questions about the ethics, science and social
implications of the project.
“As a queer person and a geneticist, I struggle to understand
the motivations behind a genome-wide association study for non-heterosexual
behavior,” wrote Joe Vitti, a postdoctoral researcher at the Broad Institute,
in one essay. “I have yet to see a compelling argument that the potential
benefits of this study outweigh its potential harms.”
In a way, the range of opinions by scientists who also identify
as L.G.B.T.Q. underscores a central finding of the study: Same-sex sexuality is
complicated.
The study analyzed the genetic data of 408,000 men and women
from a large British database, the U.K. Biobank, who answered extensive health
and behavior questions between 2006 and 2010, when they were between the ages
of 40 and 69. The researchers also used data from nearly 70,000 customers of
the genetic testing service 23andMe, who were 51 years old on average, mostly
American, and had answered survey questions about sexual orientation. All were
of white European descent, one of several factors that the authors note limit
their study’s generalizability. Trans people were not included.
The researchers mainly focused on answers to one question:
whether someone ever had sex with a same-sex partner, even once.
A much higher proportion of the 23andMe sample — about 19
percent compared to about 3 percent of the Biobank sample — reported a same-sex
sexual experience, a difference possibly related to cultural factors or because
the specific 23andMe sexual orientation survey might attract more L.G.B.T.Q.
participants.
Despite its limitations, the research was much larger and more
varied than previous studies,
which generally focused on gay men, often those who were twins or were
otherwise related.
“Just the fact that they look at women is hooray,” said Melinda
Mills, a professor of sociology at the University of Oxford, who wrote a commentary that Science
published alongside the study.
There might be thousands of genes influencing same-sex sexual
behavior, each playing a small role, scientists believe. The new study found
that all genetic effects likely account for about 32 percent of whether someone
will have same-sex sex.
Using a big-data technique called genome-wide association, the
researchers estimated that common genetic variants — single-letter differences
in DNA sequences — account for between 8 percent and 25 percent of same-sex
sexual behavior. The rest of the 32 percent might involve genetic effects they
could not measure, they said.
Researchers specifically identified five genetic variants
present in people’s full genomes that appear to be involved. Those five
comprise less than 1 percent of the genetic influences, they said.
And when the scientists tried to use genetic markers to predict
how people in unrelated data sets reported their sexual behavior, it turned out
to be too little genetic information to allow such prediction.
“Because we expect the sum of the effects that we observe will
vary as a function of society and over time, it will be basically impossible to
predict one’s sexual activity or orientation just from genetics,” said Andrea
Ganna, the study’s first author, whose affiliations include the Institute of
Molecular Medicine in Finland.
While many genetic variants tend to have the same effect in both
men and women, Dr. Mills said, two of the five variants the team found were
discovered only in males and one was discovered only in females. One of the
male variants might be related to sense of smell, which is involved in sexual
attraction, the researchers report. The other male variant is associated with
male pattern balding and sits near genes involved in male sex determination.
Steven
Reilly, a geneticist on the steering committee of the Broad Institute’s
L.G.B.T.Q. affinity group, said of the study, “It seems like something that
could easily be misconstrued or it seems problematic.”Kayana Szymczak for The
New York Times
In a finding that could be especially sensitive, the researchers
found that whether someone ever engaged in same-sex sexual behavior showed
genetic correlations with mental health issues, like major depressive disorder
or schizophrenia, and with traits like risk-taking, cannabis use, openness to
experience and loneliness.
They emphasized that the study does not suggest that same-sex
sexual behavior causes or is caused by these conditions or characteristics, and
that depression or bipolar disorder could be fueled by prejudicial social
experiences.
“We are particularly worried that people will misrepresent our
findings about mental health,” Dr. Neale said.
“That right there is the big issue with looking for the genetics
of sexual orientation — social context could be a big part of the expression of
the trait,” said Jeremy Yoder, an assistant professor of biology at California
State University, Northridge, who is gay and follows genetic research in the
field.
Dr. Neale said increasing social acceptance might be reflected
in the fact that younger study participants were much more likely than older
ones to report same-sex sexual experiences. He and others noted that older
participants came of age when homosexual behavior was criminalized in Britain
and that for much of their life homosexuality was classified as a psychiatric
disorder.
Dr. Reilly and others said such stark differences between older
and younger participants show the trickiness of trying to draw representative
biological information from a study population so strongly influenced by
society’s changing attitudes. People steeped in a culture that demonized
same-sex encounters might only have the gumption to admit it in a study if they
were risk-takers to begin with.
Later, the researchers compared the genetic underpinnings of
whether people ever had same-sex sex with their answers to what proportion of
same-sex partners they had. They found there was little genetic correlation
between answers to the “ever-never” question and whether someone ended up
having a bisexual mix of partners, said Dr. Neale, who sees those results as a
genetic reflection of the variety of sexual orientations within the expanding
alphabet of the L.G.B.T.Q. community.
The researchers also looked at answers to other questions in the
23andMe survey, including people’s sexual identity and what gender they
fantasized about. There, they found considerable genetic overlap between those
results and whether people ever engaged in same-sex sex, suggesting that these
aspects of sexual orientation share common genetics, they said.
Dean Hamer, a former National Institutes of Health scientist who
led the first high-profile study identifying a genetic link to being
gay in 1993, said he was happy to see such a large research
effort.
“Having said that, I’d like to emphasize that it’s not a gay
gene study — it’s a study of what makes people have a single same-sex
experience or more,” said Dr. Hamer, now an author and filmmaker. The gene he
identified was on the X chromosome, one of the sex chromosomes, a location the
new study did not flag as being significant for same-sex sexual behavior.
“Of course they didn’t find a gay gene — they weren’t looking
for one,” Dr. Hamer said.
Experts widely agree that the research was conducted by
first-rate scientists.
“I kind of held my breath when I first saw the study — I
thought, oh no,” said Dr. Mills of Oxford. “But it’s the top geneticists and
some of the top social scientists in the field working on this, so if somebody
was going to do it, I’m glad they did it.”
Indeed, Dr. Neale, who also consults for several pharmaceutical
companies, said one reason his team did the study was to ensure less careful
researchers would not tackle it first, “given how sensitive and hot-button this
topic really is and how personal it is.”
Robbee Wedow, a member of the research team who also belongs to
Out@Broad, served as a kind of bridge, organizing meetings between the
researchers and their Broad Institute critics.
“I grew up in a highly religious evangelical family,” said Dr.
Wedow, a research fellow with the Broad Institute and Harvard’s sociology
department. “Being confused about not being attracted to women and being
attracted to men, being convinced it was a sin and that I would go to hell.”
For a long time, “I definitely tried to pray it away, tried to
like girls, tried to have girlfriends,” he said. “This wasn’t something I, of
all people, would have chosen. There must be some sort of biological
background.”
He concluded: “Saying ‘sorry, you can’t study this’ reinforces
it as something that should be stigmatized.”
Outside L.G.B.T.Q. groups that were consulted did not seem as
strongly concerned as some of the Out@Broad members, he said. Zeke Stokes,
chief programs officer at GLAAD, who was shown the findings several months ago,
said, “Anyone who’s L.G.B.T.Q. knows that their identity is complicated and to
have science sort of bear that out is a positive thing.”
Over all, Dr. Neale said he believes the study shows that
“diversity is a natural part of our experience and it’s a natural part of what
we see in the genetics. I find that to actually just be beautiful.”