Many of us have been curious as to why some of us are straight or gay; "Why are some of us attracted to the opposite sex?" "Why are some men attracted to men?" "Why are some women attracted to women?" Currently, we don't know why we vary in sexual orientation, but science suggests being gay at least is partly genetic, rather than a lifestyle choice.

In AsapSCIENCE's latest video, "Does Everybody Have A Gay Gene," Mitchell Moffit and Gregory Brown explain genetics and epigenetic factors — the study of how the environment can chemically modify our genes — can be used to prove that being gay is not a choice.

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A 2016 study, published in the Archives of Sexual Behavior, found linkages in a specific region of the X chromosome labelled Xq28 and in another region of chromosome 8, known as 8q12, in over 400 gay siblings. Traits like hair color, height and intelligence varied between each brothers in a pair and between all groups of brothers. In other words, any single nucleotide polymorphisms (SNPs) — differences on a single letter in the genetic code — found in the same genetic locations across the group would likely be associated with sexual orientation.

The region on the X chromosome, Xq28, was previously identified in 1993 by Dean Hamer of the US National Institutes of Health in Bethesda, Maryland. However, there needs to be more work done to determine the specific genes involved and how they work, including if there are equivalent genes in women. The study provides researchers with the potential to narrow down fewer genes linked to sexual preference.

The belief that homosexuality is genetic can create a paradox. For example, homosexuals have 80 percent fewer children than heterosexuals, which suggests the genes would not be passed down and would eventually die out.

Enter epigenetics.

A 2015 study published in Science used epigenetics to propose that everyone has a gay gene, but it's contingent on whether the attachment of a methyl group to specific regions of DNA is triggered and turned on. Upon analyzing gay and straight male twins, researchers found a specific methylation pattern was closely linked to sexual orientation. The model was able to predict the sexuality of men with 70 percent accuracy.

However, a caveat of the study is its small sample size, which means there is not too much power to make such a claim. Evidently, there were certain correlations, but a predicting model may not yet be an actual reality. Larger studies are needed to replicate these findings if valid.

A specific gay gene has not been found, but there's scientific data that suggests sexual orientation is linked to genetics on a molecular level. Previous research has found giving birth to a son increases the odds of homosexuality in the next son by 33 percent. Scientists believe a woman's body adjusts the androgen level in her womb as she has more sons, and the androgens interact with genes to produce homosexuality.

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The scientific community still has a long way to go when it comes to studying the causes of homosexuality. Currently, most research only focuses on gay men and neglect other groups, like lesbians. Further research on the genetic and epigenetic factors of homosexuality could help reduce homophobic laws around the world by proving it's not a lifestyle choice.

Science is working on proving the biology of homosexuality, but it also raises the question, does it matter if someone is straight or gay?

See Also:

Why Discrimination Against Gays Is A Global Health Hazard

Heterosexual Providers Found To Hold Bias On Sexual Orientation