Why Homosexuality is Considered to be Biologically Based

The purpose of this post is to point out the biological basis of homosexuality. For religious and political reasons this is a topic that seems to always be in hot debate. It is really nothing more than the nature nurture argument, and we find that people who are in the extremes in this argument are usually wrong.

All human traits are on two continuums. They are on a continuum for the particular trait, and they are on a nature nurture continuum. For example, for the trait sex, we have male on one side, female on the other, and intersexed individuals in the middle. In the case nature nurture, biology is the primary factor that determines sex. Sexuality is a trait like all others and is on the two continuums. It is on a continuum for the trait itself and a nature nurture continuum. The source of hot debate is that people with their own political agendas want to show that homosexuality is either all nature or all nurture. However, it is believed by the scientific community that sexuality is more biologically based than environmentally based this is not so say that environment does not play any role. Lets face it, in extreme situations like prison and some other historical situations, homosexuality is or was a consequences of environment. However, these are extreme and oppressive environments and the choice ins't/wasn't whether to be hetero or homo, but whether to have sex or not. In today's society, it is more difficult to be homosexual so I would say that not many would want to choose to be that way. Admittedly, there is a certain amount of bumper sticker logic to that statement, and I am always afraid to apply such logic to any situation. The fact is, many people choose to do things that are counter productive. I think the important thing to remember is that homosexuality is a difficult lifestyle so there must be more than simple choice involved.

I would like to apologize because this is really nothing more than a book report from here to the conclusion. I am too lazy to look through the journals on this particular topic so I am going to rely upon a text book called the Biological Psychology Seventh Edition by James W. Kalat. Second, I would like to make it clear that I am not claiming that homosexual behavior is 100% biological. My point is simply that there is a strong biological basis for homosexual behavior


Genetic Evidence
Here Kalat combines several studies into a chart on page 327 that shows the genetic basis of homosexuality. These charts show the likelihood of siblings of a twin being homosexual if one twin reported being homosexual. Notice that there is a very high likelihood for a monozygotic twin to be homosexual if one twin has reported to be homosexual.

Related to a Homosexual Man
Monozygotic Twin
52% homosexual

Dizygotic Twin
22% homosexual

Adopted Brother
11% homosexual

Related to a Homosexual Woman
Monozygotic Twin
48% homosexual

Dizygotic Twin
16% homosexual

Nontwin Sister
11% homosexual

Adopted Sister
6% homosexual

Prenatal Environment
Kalat later goes on to sight a comparative biology study where with the use of testosterone during sensitive times in pregnancy researchers were able to induce homosexual behavior in female rats. Next he mentions that there have been several studies where prenatal stress was induced to increase the likelihood of homosexuality. In the stress studies they did find that with different environmental factors it was possible to induce bisexuality versus strict homosexuality.

Differences between men and women
Finally Kalat points out that there are differences in the male and female brain. Heterosexual woman have several areas of the brain that are larger than in heterosexual men. This comparison includes the interstitial nucleus which has a relationship to sexual behavior. It has been found that homosexual men have greater similarity to heterosexual women than they do to heterosexual men in these brain areas.

Conclusion
Finally, while there is still work to be done in this area to clear up specific questions about the role of biology, it is apparent that social psychologists, sociologists, religious scholars, and others with a vested interest in disproving the biological nature of homosexuality have had little success. There is meager evidence that environment can induce bisexuality versus strict homosexuality, but it does not lessen the central idea that it is primarily nature that determines one’s propensity to engage in homosexual acts. Finally, I do not see the occasional person reporting that he or she has chosen heterosexuality over homosexuality as being evidence of the environmental nature of homosexuality. Since sexuality is on a continuum, logically those on the extreme ends will claim to have had no choice as to their sexuality while those individuals who have sexuality that is in the middle of the sexuality continuum, may report that they chose their sexuality or environment may have played a role.