Dr. Dennis McFadden was a faculty member at University of Texas at Austin’s Department of Psychology from 1967 until his retirement as Professor Emeritus in early 2011. He has published over 100 research papers and two books on various topics on hearing. His groundbreaking research discovered subtle variations in the inner ears of lesbians and bisexual women, demonstrating that they may have been masculinized by prenatal exposure to male sex hormones. Dr. McFadden graduated from Indiana University in 1967.

When is a person’s sexual orientation established?

Sexual orientation is determined, whether it is heterosexual or homosexual, at the time of birth or certainly very soon thereafter.

How did you discover that there were both sex and sexual orientation differences associated with hearing?

The oto-acoustic emissions* that we measured in opposite sex twins, the females that had male co-twins were actually like those of other males. It was not like those of females. That was rather perplexing. And part of the reason it’s perplexing is we know from other evidence that oto-acoustic emissions are reasonably stable through life, so the emissions that you measure in young adults are very representative of what they had at birth.

So, why should a newborn female who had a male co-twin have weak oto-acoustic emissions? Oto-acoustic emissions that look like those of males rather than those of other females?

Well, it turns out that in the literature on hormone effects, there is any number of examples in non-humans on effects that are just like this. What happens is that the females get exposed to the androgens, male sex hormones, that are produced by the male fetuses that they are sharing the intrauterine environment with, and these females get masculinized on various traits and measures because of that exposure.

So, the question was, is it possible that our opposite sex twins are females who have male co-twins might have weak masculine-like oto-acoustic emissions because they got exposed to the androgens being produced by their co-twin brothers? I don’t have any direct evidence for that, but I do know that these women are also masculinized in a number of different characteristics. There are differences in dentition, the way the teeth fit into the jaw, marked sex differences in that. And females with male co-twins have dentition that’s like that of males, not like that of females. And there are a couple of other measures that were like our oto-acoustic emission — masculinized.

What made you decide to study oto-acoustic emissions in lesbians?

It occurred to me that perhaps non-heterosexuals also would show some differences in their oto-acoustic emissions. So, we started another study in which we measured oto-acoustic emissions in heterosexuals and non-heterosexuals and, sure enough, what we found was that homosexual and bisexual females have oto-acoustic emissions that are shifted in the male direction. They are masculinized. We don’t know what prenatal mechanisms exactly are responsible for that masculinization. But, we are reasonably confident that it is prenatal because we know from other measures of oto-acoustic emissions that the oto-acoustic emissions that are present in young adults, which is what we measured, are very representative of what exists in newborns. So, the implication was pretty strong that somehow homosexual and bisexual females are getting exposed to higher than normal levels of androgens than was true for typical females. And, this was going on during prenatal development.

Does sexual orientation have biological origins?

Any human behavior as complex as sexual behavior is bound to have multiple contributing components to it. There are going to be some environmental, experiential contributions, and there are going to be some physiological, biological contributions. My belief is it is the latter — the physiological, biological contributions are overwhelmingly stronger for most non-heterosexuals than are the other contributions.

What is your opinion of so-called “ex-gay” programs?

It’s very unlikely that you can develop any kind of a training program that is going to change someone from being a non-heterosexual to a heterosexual. Just think about it, what kind of training would you have to change a heterosexual into a non-heterosexual. It’s just not scientifically very appealing. It’s just seems quite nonsensical.

Are there biological markers for sexual orientation other than oto-acoustic emissions?

Our auditory research is just one example of studies that have shown physiological measures that appear to be innately different in heterosexuals and non-heterosexuals. For example, handedness. Homosexual males and homosexual females are much more likely to be left handed then are heterosexuals. Puberty has an earlier onset, about three months earlier in homosexual males then in heterosexual males. Homosexual males at birth tend to weigh less but have heavier placentas than do heterosexuals. And finally, there is the fraternal birth order effect, which is remarkably compelling — the fact that the chance of any male being homosexual goes up by about a third for every additional older brother that he has born to that same mother.

* Oto-acoustic emissions are weak sounds produced by the ear’s cochlea; they may be spontaneous or they may be evoked by clicks.
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