After a major scientific study found there is not a singular genetic marker for homosexualty, a Catholic theologian explained that the findings are fully in accord with Catholic teaching.

The study was published Aug. 30 in Science. It examined data from several large genetic databanks in multiple countries, and surveyed nearly half a million people about their sexual partners and preferences. Previous studies on the matter have only examined sample groups of hundreds of people.

"From a genetic standpoint, there is no single [genetic distinction] from opposite-sex to same-sex sexual behaviors," said Andrea Ganna, a geneticist at Finland's Institute of Molecular Medicine, and the study's lead author.

Speaking to Scientific American, Eric Vilain, a geneticist at Children's National Health System in Washington, D.C., called the study's result "the end of the 'gay gene'" theory.

In recent decades, many of those involved in the LGBT movement have advanced the argument that sexual orientation is genetically determined, and that people who experienced same-sex attraction are born with a fixed orientation.

In a June interview, Fr. James Martin SJ, author of "Building a Bridge: How the Catholic Church and the LGBT Community Can Enter into a Relationship of Respect, Compassion, and Sensitivity," said that "most reputable psychologists, psychiatrists, biologists, social scientists say that people are simply born this way." 

In a commentary published along with the study, Oxford University geneticist Melinda Mills noted an "inclination to reduce sexuality to genetic determinism" in support of sociological or ideological positions.

"Attributing same-sex orientation to genetics could enhance civil rights or reduce stigma," she wrote. "Conversely, there are fears it provides a tool for intervention or 'cure.'"

Still, Mills said the results of the study show that the use of genetics to predict same-sex attraction, or to change it through some kind of gene editing, is "wholly and unreservedly impossible."

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Commenting on the report Friday, Martin told CNA that "the study shows that a variety of factors, including genetic factors, influence human sexuality." 

"For me, the most helpful quote came from a geneticist who was one of the lead researchers, who talked about how 'natural' homosexuality is," Martin said, quoting Dr. Benjamin Neale of MIT.

Neale told the New York Times that same-sex behavior is "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."  

"That seems to sum up the results of the study accurately," said Martin.

The research showed five distinct genetic data points which appear common among individuals who reported at least one same-sex encounter. Two of these markers appear linked to hormones and smell, factors in sexual attraction. 

But the five markers together explained less than 1% of differences in sexual activity among the population, the results found.

"Although they did find particular genetic loci associated with same-sex behavior," Mills said, "when they combine the effects of these loci together into one comprehensive score, the effects are so small, under 1%, that this genetic score cannot in any way be used to predict same-sex sexual behavior of an individual."

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Noting that the study results highlight considerable differences by generation and the influence of cultural norms on sexual behavior, Mills concluded that future research was best focused on "how genetic predispositions are altered by environmental factors."

"Once again it's also important that we listen to the lived experience of LGBT people, as we minister to them in the church," Martin said.

Dr. Kevin Miller, assistant professor of theology at Franciscan University in Steubenville, Ohio, told CNA that the results are in accord with the Church's existing teaching about homosexualtiy.

"The Catechism treats homosexuality in nos. 2357-2359. Early in this treatment we read that its 'psychological genesis remains largely unexplained.' The new study does not change this."

The study draws a distinction between people who engage in homosexual acts and those who identified as "gay" or "homosexual," a distinction Miller noted was already central to the Church's teachings.

The Catechism teaches that homosexual acts are "intrinsically disordered" and "under no circumstances can they be approved." This is because, Miller said, only sexual acts oriented by their nature to the possibility of procreation and set within marriage are "compatible with the essential moral virtue of chastity and – as St. John Paul II emphasized in both his pre-papal and papal writings – love.". 

"Any others are – independent of the subjective dispositions of those who take part in them – objectively hedonistic and selfish, rather than authentically loving. Obviously there are many types of sexual acts that could fall into this category - homosexual acts are by no means the only type."

Homosexual tendency or inclination, often called same-sex attraction, is defined by the Catechism as "objectively disordered," Miller said. This is because a desire which, if acted on, would lead to immoral acts is by its nature disordered, he said. 

But, Miller noted, the desire or inclination itself is not "morally wrong," since a person does not choose to have an inclination or exercise their free will over having it.

Central to understanding the distinction between sexual inclinations and acts, Miller said, is that all sexual acts are freely chosen; even if a person has an interior disposition toward engaging in homosexual acts, they have the same freedom to pursue them or not as a person inclined towards immoral acts with someone of the opposite sex.

"One can see that in this explanation of the Church's teaching, there is no reference of any sort to the cause of the homosexual tendency or disposition. This is simply irrelevant to the analysis of the moral goodness or evil of homosexual acts, and of the ordered or disordered character of the homosexual tendency or disposition."

Miller explained that the origin of a person's sexual orientation, whether biological, environmental, or experiential, had no bearing on what the Church teaches about the morality of acting on a particular sexual urge. 

"These teachings do not depend on any assumption regarding the cause of the tendency or inclination," he said.

"Even if it could be shown that a homosexual tendency or orientation is wholly biologically determined, this would not affect at all the logic underlying the Church's teaching."