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A large study suggests that genes are connected to homosexual behavior, but also found there is no gene that makes people gay.
The study is said to be the largest of its kind. Researchers examined genetic material and information about sexual experiences from more than 470,000 adults in the United States and Britain. The findings were published in Science magazine.
The researchers found there are thousands of genetic differences linked to same-sex sexual behavior. Most have a very small effect on a person's behavior.
However, the researchers said five of the genetic markers were more strongly linked with same-sex sexual behavior. The genetic differences, or variants, were more commonly found in people who reported having had a experience at some time.
Some of the genetic variants found were present in both men and women. Two of the variants found in men were near genes involved in male hair loss and sense of smell.
About five percent of British participants and about 19 percent of U.S. persons who took part reported ever having a same-sex sexual experience. Those providing information for the study were not asked whether they identified themselves as gay or lesbian.
The research "provides the clearest glimpse yet" into the genetic reasons for same-sex sexual behavior, said study co-writer Benjamin Neale. He is a geneticist at the Broad Institute in Cambridge, Massachusetts.
But Neale also added, "We also found that it's effectively impossible to predict an individual's sexual behavior from their genome."
The researchers noted that the study centered on people's sexual behavior, and not on sexual identity. They also noted that the study only involved people whose ancestors were European. They could not answer whether similar results would be found in other groups.
The origins of same-sex behavior are unclear. Some of the strongest evidence of a genetic link comes from studies on twins. Many scientists believe that social, cultural, family and biological conditions are also involved. Some religious groups and other critics consider it a choice or a behavior that can be changed.
A Science magazine commentary notes that the five identified genetic variants had such a weak effect on behavior that using the results "for prediction, intervention or a supposed ‘cure' is wholly...impossible."
Experts not involved in the study had many reactions. Former National Institutes of Health geneticist Dean Hamer said the study confirms "that sexuality is complex and there are a lot of genes involved." But he added that the study was not "really about gay people."
"Having just a single same sex experience is completely different than actually being gay or lesbian," Hamer noted.
His research in the 1990s linked a marker on the X chromosome with male homosexuality. Later studies had similar results. The latest study, however, found no such link.
Doug Vanderlaan is a psychologist at the University of Toronto in Canada. He said the lack of information on sexual orientation is a weakness of the study.
The study was released on August 29. An international team of experts from Britain, the U.S., Europe and Australia carried out the research. They completed human genome examinations using blood samples from the UK Biobank and saliva samples from the U.S.-based ancestry company 23andMe. All samples were from individuals who had agreed to take part in the research.
I'm Anna Mateo.
Ashley Thompson adapted this story based on reports by The Associated Press and the Reuters news agency. Mario Ritter Jr. was the editor.
