Homosexuality: Inborn or Learned Behavior? (2)

In our previous article on this topic we saw how researchers at the Karolinska Institutet in Sweden found that testosterone compounds found in male sweat were attractive to both heterosexual females and homosexual males. Conversely, estrogen compounds found in female urine were attractive to heterosexual males, but not homosexual males.

Dean Hamer, a geneticist from the National Institutes of Health in Bethesda, Maryland concluded that “this is one more line of evidence that there’s a biological substring for sexual preference”. In short, when homosexual men inhaled the odor of male sweat, the region of their brain that governs sexual response reacted in a similar way to that of heterosexual women.

Hamer claimed that these results show a link between brain activity and sexual orientation. Many studies have found similar results. For instance, the Monell Chemical Senses Center in Philadelphia, Pennsylvania found that gay men preferred the smell of other gay men, while both straight males and females like the scent of gay males the least. These studies support the hypothesis that homosexuality has a genetic rather than a learned basis.

Interestingly, individuals with homosexual orientations were found in another study to have almost a 40% chance of being left-handed or ambidextrous, far higher than the general population. Around 12% of 20-year-olds in the US are left-handed so the preponderance of left-handed homosexual individuals is also suggestive of a genetic-based origin.

Twin studies also support a biological basis for the presence of homosexuality. Identical twins are more likely to be of the same sexual orientation (either heterosexual or homosexual) than non-identical twins, or other natural siblings.

Other studies have indicated that the presence of older brothers in the family increases a male’s chances of being homosexual. The presence of female siblings has no effect. However, each additional older brother increases the odds of a homosexual orientation by almost one third.

Clearly, the factors that influence sexual orientation are not simple. Both biological and environmental aspects play important roles in our basic sexual preferences. Further studies will no doubt shed light on this complex issue.

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