A central tenet of modern neuroscience is that for every difference in behavior, whether between groups of people or within an individual person over time, there must be some corresponding differences in the structure or function of the brain. Accordingly, the brains of homosexuals somehow must be different from the brains of heterosexuals. Whether those differences were present at birth or acquired later in life is an important question, because if the differences are innate, then the attitudes of many people toward homosexuals could change.
Consider handedness. Historically, many societies viewed left-handers with suspicion and shunned them. This discrimination was justified as traditional and by various passages in the Bible and the Quran. However, modern societies realize that there is nothing evil, second-rate or worthy of discrimination in left-handedness. It is simply how a minority of people are born. They did not choose to be different, and they are just as powerless to make themselves like the majority as they are to change their eye color. Is homosexuality a comparable phenomenon? Many would argue that discrimination against left-handers or homosexuals is indefensible regardless of the origins of those attributes, but human prejudices are complex, and the simple reality is that many people find it easier to accept a difference that is believed to be innate than a difference that is believed to be a choice, even one made in the madness of puberty.
Many homosexuals believe that they were different from an early age and that they did not make a conscious choice to be homosexual. While this may be true, these are anecdotes, which are not convincing to science. However, research studies have shown several interesting differences between homosexuals and heterosexuals. (The following findings pertain to the averages of groups and thus will not necessarily be true of each individual person in a group.)
Although individuals vary a great deal, males and females differ, on average, in the strength of their hands, their ability to accurately throw projectiles at targets, their ability to mentally rotate complex three-dimensional objects and their ability to navigate through complex real-world environments. Interestingly, homosexual males and females are intermediate to heterosexuals on all those characteristics. That is, the average homosexual female is shifted away from the average heterosexual female and toward the average heterosexual male on all those characteristics, and the average homosexual male is shifted away from the average heterosexual male and toward the average heterosexual female on all those characteristics. Furthermore, the speech patterns of homosexual males often are characteristically different from those of heterosexual males, a small nucleus in the hypothalamus of the brain in homosexual males is intermediate in size to that in heterosexual males and females and homosexual males and females have different sleep-wake cycles than do heterosexuals.
This is a fascinating collection of behavioral and brain differences between heterosexuals and homosexuals. However, none of these findings is (yet) unambiguous evidence that homosexuality is innate. The reason is that each of these characteristics might be attributable to experience; in other words, these differences might be acquired.
Consider the case of a young boy who, for various reasons, is smaller than average, somewhat timid and somewhat introverted. Isn't it intuitive that such a boy might engage in fewer of the various athletic and rough-and-tumble activities practiced by his male peers and in more of the various social activities practiced by girls of the same age? People generally do what interests them, and what interests them generally is what they are good at.
If a person does not practice gripping objects tightly, throwing objects at other objects or people or thinking about complex objects and complex environments, then inevitably the body and brain will not be as good at those tasks as the body and brain of someone who practices them regularly. Similarly, if a boy is involved in activities that are sex-atypical for boys, such as "playing house," then that will produce a brain that is different from the typical male brain. A parallel but reversed story could be told for a young girl who is a tomboy. And it certainly is plausible that different patterns of life experience could result in different sleep patterns.
The point is that some differences in behavior or brain structure between homosexuals and heterosexuals could be acquired through differential experience and thus are not unambiguous evidence of differences existing at birth.
With that said, there are other differences between homosexuals and heterosexuals that do not appear to be acquired and thus do appear to offer strong evidence of innate differences between the two groups (again, think group averages, not individual people):
Collectively, these latter findings strongly suggest that homosexuality is connected to differences in the body and brain that existed at birth. Clearly, a person has no control over how many aunts, uncles or older brothers he has, so these differences suggest a maternal contribution that is not strictly genetic. Handedness, toy preferences and the auditory differences mentioned all are evident far earlier in life than is any awareness of sexual orientation, and thus far earlier than any possible conscious decision to live with one orientation rather than another.
As facts like these continue to accumulate and become generally known, I believe reasonable people will conclude that laws and practices discriminating against homosexuals are just as unfair as any laws and practices that discriminate against people who are left-handed, blue-eyed or dark-skinned.
This piece is a summary of a talk given recently in the Whom You Love series at Michigan State University. For more, visit WhomYouLove.com.