Research shows that this minority orientation has the following profile:

1. The trait is a “stable bimophism.” It occurs in all human populations as two orientations, expressed behaviorally.
2. About 92% of the population has the majority orientation, and 8% has the minority orientation.
3. The historical evidence suggests that both orientations have existed for at least five millennia.
4. The minority orientation appears in all races and ethnic groups.
5. Neither orientation favors any geographical location, culture, nor any other environmental factor.
6. The trait is not a behavior, but an internal orientation. Those with the minority orientation are sometimes able to hide it in response to social coercion.
7. Clinical studies show that the minority trait is not associated with any disease and isn’t pathological in any way.
8. Neither orientation is chosen.
9. Signs of the orientation are detectable in very young children.
10. Adoption studies demonstrate that the orientation of adopted children is unrelated to the orientation of their parents, indicating that the trait isn’t the result of upbringing.
11. Identical twins have a higher than average chance of sharing the same orientation compared to pairs of randomly selected people. The average rate of this trait in the general population (called the “background rate”) is just under 8%, while the twin rate is just above 12% — more than 50% higher.
12. The minority orientation is 27% higher in the male than in the female population. Many biologically determined conditions, for reasons that science can now explain, occur more frequently in men than in women.
13. Family studies reveal that, like eye color, the minority orientation runs in families, passed down from parent to child.
14. This pattern shows a “maternal effect,” a common sign of a biological trait. The minority orientation in men appears to be passed down from the mother, pointing to the X chromosome.

All of these factors, taken together, have convinced geneticists that the trait in question is biologically determined, innate, and immutable. The minority trait just described, by the way, is left-handedness.

The above list is taken from “The Only Question that Matters,” a white paper which Chandler Burr, author of A Separate Creation: The Search for the Biological Origins of Sexual Orientation, wrote for the Liberty Education Forum. In the paper, Burr points out that the trait profile for left-handedness is “astonishingly similar” to the profile for sexual orientation. Neither trait correlates with any environmental factors. As with left-handedness, the sexual orientation of adopted children bears no relationship to that of adopted parents, clearly pointing to its biological origins. The twin studies show that twins share the trait of homosexuality more frequently than they do left-handedness, suggesting that genetics plays an even greater role in sexual orientation than in handedness.

It is sometimes asked “If sexual orientation is biological why don’t monozygotic twins (who have identical genes) always share the same sexual orientation?” Burr explains that, as with left-handedness, the biological factors for sexual orientation probably include several genetic factors which interact with other constitutional factors such as hormones and neural structure. In 2005, geneticists at the University of Illinois identified three chromosomal regions linked to sexual orientation in men.

The public policy implications of understanding that sexual orientation is constitutional are huge. As Burr notes, in the current public debate, there are three competing positions on homosexuality: 1) that it’s a “lifestyle choice” like vegetarianism, 2) that it’s a disease, like schizophrenia, and 3) that it’s a constitutional condition like left handedness. Poll after poll shows that, when Americans believe that it’s constitutional, they are far more likely to favor full equality than when they believe one of the other two possibilities.

Understanding the biological origins of sexual orientation also has powerful implications for how we view ourselves. In my work with gay men, I often find that men who believe they’re completely self-accepting still hold “less than” ideas about themselves derived from psychoanalytic models which describe homosexuality as a psychological disorder. Some men still privately tell me “It’s because I didn’t have masculine role models.” “I wasn’t loved enough by my father.” “My mother babied me too much.” “I’m gay because I’m too narcissistic.” And so on. These notions were debunked by scientific research decades ago, but they still linger in the culture.

There was a time when left handed people, too, were made to feel wrong, inferior, and disordered because of their minority orientation, but that all changed when science discredited the mythologies about the meaning of that variation. Within a few decades, we will probably have a complete map of the biological determinants of sexual orientation. As knowledge of the science becomes more widespread, perhaps more and more people will also come to accept as common sense that being gay is a minority variation like left handedness, and that, as with left handedness, it has no inherent moral or psychological meanings whatsoever.