Dr. Kerby Anderson, national director of Probe Ministries [source article] explains why:

At this point in our discussion, we need to consider the claim made by some homosexuals that, “God made me gay.” Is this true? Is there a biological basis to homosexuality? For the remainder of this essay, we will consider the evidence usually cited. Simon LeVay (a neuroscientist at the Salk Institute) has argued that homosexuals and heterosexuals have notable differences in the structure of their brains. In 1991, he studied 41 cadavers and found that a specific portion of the hypothalamus (the area that governs sexual activity) was consistently smaller in homosexuals than in heterosexuals. He therefore argued that there is a distinct physiological component to sexual orientation. There are numerous problems with the study. First, there was considerable range in the size of the hypothalamic region. In a few homosexual men, this region was the same size as that of the heterosexuals, and in a few heterosexuals this region was a small as that of a homosexual.

Second is the chicken and egg problem. When there is a difference in brain structure, is the difference the result of sexual orientation or is it the cause of sexual orientation? Researchers, for example, have found that when people who become blind begin to learn Braille, the area of the brain controlling the reading finger actual grows larger. Third, Simon LeVay later had to admit that he didn’t know the sexual orientation of some of the cadavers in the study. He acknowledged that he wasn’t sure if the heterosexual males in the study were actually heterosexual. Since some of those he identified as “heterosexual” died of AIDS, critics raised doubts about the accuracy of his study.

In December 1991, Michael Bailey and Richard Pillard published a study of homosexuality in twins. They surveyed homosexual men about their brothers and found statistics they believed proved that sexual orientation is biological. Of the homosexuals who had identical twin brothers, 52 percent of those twins were also homosexual, 22 percent of those who had fraternal twins said that their twin was gay, and only 11 percent of those who had an adopted sibling said their adopted brothers were also homosexual. They attributed the differences in those percentages to the differences in genetic material shared.

Though this study has also been touted as proving a genetic basis to homosexuality, there are significant problems. First, the theory is not new. It was first proposed in 1952. Since that time, three other separate research studies come to very different conclusions. Therefore, the conclusions of the Bailey-Pillard study should be considered in the light of other contrary studies. Second, most published reports did not mention that only 9 percent of the non- twin brothers of homosexuals were homosexuals. Fraternal twins share no more genetic material than non-twin brothers, yet homosexuals are more than twice as likely to share their sexual orientation with a fraternal twin than with a non-twin brother. Whatever the reason, the answer cannot be genetic.

Third, why aren’t nearly all identical twin brothers of homosexuals also homosexual? In other words, if biology is determinative, why are nearly half the identical twins not homosexual? Dr. Bailey admitted that there “must be something in the environment to yield the discordant twins.” And that is precisely the point; there is something (perhaps everything) in the environment to explain sexual orientation. These are two studies usually cited as evidence of a biological basis for homosexuality. Next we will consider a third study often cited to prove the claim that “God made me gay.”

Now let’s look at another study often cited as proof of this claim. This study is often called the “gay gene” study. In 1993, a team of researchers led by Dr. Dean Hamer announced “preliminary” findings from research into the connection between homosexuality and genetic inheritance. In a sample of 76 homosexual males, the researchers found a statistically higher incidence of homosexuality in their male relatives (brothers, uncles) on their mother’s side of the family. This suggested a possible inherited link through the X chromosome. A follow-up study of 40 pairs of homosexual brothers found that 33 shared a variation in a small section of the X chromosome. Although this study was promoted by the press as evidence of the discovery of a gay gene, some of the same concerns raised with the previous two studies apply here. First, the findings involve a limited sample size and are therefore sketchy. Even the researchers acknowledged that these were “preliminary” findings. In addition to the sample size being small, there was no control testing done for heterosexual brothers. Another major issue raised by critics of the study concerned the lack of sufficient research done on the social histories of the families involved.

Second, similarity does not prove cause. Just because 33 pairs of homosexual brothers share a genetic variation doesn’t mean that variation causes homosexuality. And what about the other 7 pairs that did not show the variation but were homosexuals?

Finally, research bias may again be an issue. Dr. Hamer and at least one of his other team members are homosexual. It appears that this was deliberately kept from the press and was only revealed later. Dr. Hamer it turns out is not merely an objective observer. He has presented himself as an expert witness on homosexuality, and he has stated that he hopes his research would give comfort to men feeling guilty about their homosexuality.

By the way, this was a problem in every one of the studies we have mentioned in our discussion. For example, Dr. Simon LeVay said that he was driven to study the potential physiological roots of homosexuality after his homosexual lover died of AIDS. He even admitted that if he failed to find a genetic cause for homosexuality that he might walk away from science altogether. Later he did just that by moving to West Hollywood to open up a small, unaccredited “study center” focusing on homosexuality.

Each of these three studies looking for a biological cause for homosexuality has its flaws. Does that mean that there is no physiological component to homosexuality? Not at all. Actually, it is probably too early to say conclusively. Scientists may indeed discover a clear biological predisposition to sexual orientation. But a predisposition is not the same as a determination. Some people may inherit a predisposition for anger, depression, or alcoholism, yet we do not condone these behaviors. And even if violence, depression, or alcoholism were proven to be inborn (determined by genetic material), would we accept them as normal and refuse to treat them? Of course not. The Bible has clear statements about such things as anger and alcoholism. Likewise, the Bible has clear statements about homosexuality.