The Biological Basis of Sexual Orientation
Trey (center), with husband Guy (right) and daughter Emma
By Warren "Trey" C. Lathe, III, M.S.
Originally given at the Sunstone Symposium, August, 1996 in Salt Lake City. Trey was then a Ph.D. Candidate in Molecular Biology and
Genetics, University Of Rochester.
Recently LDS Social Services has put out a pamphlet that puts forth a very simple explanation for a very complex human behavior. It puts forth a dichotomy that is false. It puts forth a dichotomy that is an "either" or an "or" proposition. And, it puts forth a treatment plan that is based upon this simple and false dichotomy.
I have come here today because I am concerned for three reasons: First: I am a believing convert to the Mormon church and unrepentant in that. Second: I am a gay male who has gone through LDS Social Services therapy and knows the destructive and debilitating effect it can have on a man's spirituality. And, third: I am a molecular biologist who is concerned that LDS Social Services' approach is both unprofessional and lacking in the understanding of even basic science.
I am going to speak to you today as a molecular biologist and as someone who sees the world as such. The two points I want to make today is that first, modern research points to the fact, ignored by the Social Services pamphlet, that sexual orientation is biologically and genetically determined. The second point is that what this means is not what most people think it means. It is not a simple dichotomy of "either" or "or" / Nature or nurture. It is much more complex than that. Biology and human behavior can never, ever, be reduced to an "either/or" proposition.
Let me explain to you first why modern research has come to accept that sexual orientation (I speak of sexual orientation, not homosexuality or heterosexuality because that is a false dichotomy, and I'll explain that
later) is believed to be that it is genetically and biologically innate and determined. The first is theoretical. Theoretically it is expected to be so.
Let me walk you through a thought experiment. If you take a population of sexually reproducing organisms with two genders and in that population all the individuals are ambisexual (a term I made up meaning having no sexual orientation whatsoever), in those individuals, only half of their matings will be successful. If in this population of individuals of ambisexual organisms, you introduce one individual that has a mutation that makes them sexually oriented to only one gender, then every one of that individual's matings will be successful. Over time what happens in a population, a finite population of such organisms, is that that organism's offspring will soon overtake the others and the entire population will be innately sexually oriented.
Another thought in that same thought experiment is to take a population of environmentally determined individuals where in some environments they are heterosexual and in some environments they are homosexual. Again, you can introduce one single individual with one single mutation that makes them innately and irretrievably oriented to only one gender, then sooner or later that population will be innately so. Because almost all the matings of that individual will be successful and all its offspring will carry that gene.
There is a basic mathematics population genetics model that every biology student learns. If you take a population and mathematically model it with several versions of a gene (alleles), some of the individuals, if they have offspring, will pass on the gene that gives them 50% male and 50% of their offspring as female and some individuals will have versions of that gene that give them 90% female and 10% of their offspring will be male. What you end up with is that the alleles of those genes work themselves through time over a population, that even if those different genes exist, the entire population will always end up as one half male and one half female.
Now, the reason I bring this up, because it has nothing to do with sexual orientation, is that no matter what population you start out with, all the organisms, end up to be innately sexually oriented. Now once you have such innate, genetic sexual orientation, there are several explanations why homosexuality or bisexuality, or some combination thereof, could be maintained. It could be that the mutation rate that makes a male oriented to a male is higher than the strength of the selection against it in the population, thus maintaining it at a low percentage. It could be a polygenic trait where there are many genes, and many versions of the alleles of that gene that affect the trait. And most combinations of those are advantageous. But, the rare combination causes the individual, or several individuals to be homosexual or such, and that even though that might be considered to be a disadvantage, the advantages of most of the combinations is so overwhelming that it will still persist.
A third explanation is called kin selection. It is a widely seen phenomenon in birds, insects, mammals and in many other organisms. It can sometimes be advantageous for some individuals to forego reproduction for either all or for some of its lifetime in order to assist their kin to do so. By helping their kin, either their siblings, cousins, or parents to survive and reproduce, they are actually passing on their own genes because their kin are carrying the same genes that they are, including the one that causes them to be non-reproducing, or homosexual in this case.
It is probably most likely that all three of these explanations explain homosexuality from a genetic/biologic point of view.
Now, what we see theoretically, is it true in nature? Well, yes, it is. The fact that sexual desire and orientation have a biological origin in gendered organisms is well substantiated in experiments physiologic, genetic and molecular. It has been found true in a disparate range of organisms from flies to mice. Physiological differences in rats and flies and genetic evidence in flies has shown conclusively that sexual orientation is of biological origin. A recent study in Drosophila (the fruit fly) shows that a mis-expression of a gene, called "near the white gene" (because it has other effects), causes male flies to mate with other male flies. The converse is true, that a full expression of this gene causes innate sexual orientation. There is no doubt that sexual orientation in flies and other organisms is genetically determined and thus biological in its origins. This research in organisms and other animals suggests that what we expect theoretically is actually true in nature.
Now it is not always true that what we see in animals is also true in the animal we call human. But, there are two reasons that we might expect that to be true. One is that if we expect it theoretically and then see it in other populations we can reasonably expect to see it in humans. Secondly, if a trait is fundamental, it is expected to be shared among a disparate group of organisms.
Let me give you a very basic example. There is a protein in all organisms called a "histone" protein. This protein basically binds up your chromosomes into DNA. It is fundamental. There is less than one half of one tenth of one percent of difference between a yeast histone protein and human histone protein. A trait that is fundamental is expected to be shared. A trait such as sexual orientation, which we theoretically believe to be fundamental is expect to be shared. We are now seeing this in humans.
There are physiological differences that recent research has found. Let me quote a common one, Levay's study of the anterior hypothalamus. It is important because, unlike some earlier studies, it looked at a part of the brain that is known to have a function in sexual desire. The difference found between in Levay's work, a difference between the size of the anterior hypothalamus between homosexual and heterosexual men, is statistically significant. The work is not without its weaknesses, of course. All homosexual men in his study died of AIDS. The disease could have had, though not shown to have, an effect on the brain's physiology. There are also some concerns that it is not the physiologic differences as the cause of the behavior, but the behavior as the cause of physiological difference.
I am not bringing these evidences up as proof. Science rarely works by proof. It works by a preponderance of evidence in most times, as I have distressingly learned in my research.
Secondly, twin studies. An early twin study in 1956 showed a 100% concordance with the rate of identical twins and a 15% for fraternal twins and homosexuality. This study was admittedly weak, but recent studies by Bailey et al., suggest that indeed there is a correlation between homosexuality and relatedness. They found that 50% of all identical twins shared homosexuality. If they were fraternal, the percentage was lower. If they were adopted, the percentage was around 5%. Again twin studies do not prove, but point to the idea that homosexuality is biological in origin.
Recent studies in genetic linkage in humans have shown more conclusively that homosexuality is biological in origin. And sexuality in general. Hamer recently did a study, reported in SCIENCE in 1993, that there is a linkage on the X chromosome for male sexual orientation. Further studies, in his lab have shown the same for female sexual orientation. A recent paper, in 1995, for Turner collaborated Hamer's evidence. A soon to be published paper (in 1997) Hamer et al., will also show a definite linkage for some individuals, a definite genetic origin for homosexuality.
Now, what does this mean? I am, as a biologist, convinced that sexual orientation is of biological origin. But, this is not what most people think in the popular image of biology or the public debate going on today. It is not an ON/OFF, nature/nurture, gene/no gene event. Even if something is biologic and genetic, it is never determined. Biologists who use all these terms: genotype, phenotype, penetrance, overdominance, underdominance, pleotropy, polygenic . . . . Genetic makeup of human beings is never a simple ON/OFF explanation.
There are diseases that are caused by a mutation in a gene. But, there is something called "penetrance" and sometimes even the mutation does not penetrate to the phenotype (what you see). Let me give a very simplistic analogy. Today we look out at this audience and we see a range of hair color that ranges from blonde to white to black. That range is extreme. Hair color is determined by so many different genes, by pigments, by regulation of pigments, by the very surface of the hair, that we can never tell you what will make a blonde person and what will make a dark haired person. Hair color is also not so easily categorized. You can not say that someone is necessarily blonde because they might be born a towhead, but grow up to be brunette. Someone who has black hair today might be gray tomorrow.
Hair color is not a simple dichotomy. Something as simple as hair color being so complex, you would expect human behavior to be the same. It is of biological origin. But, it is not necessarily the same in every individual. There will be individuals who are innately and irretrievably heterosexual. There will be individuals who are innately and irretrievably homosexual. There will be individuals who are innately and irretrievably bisexual. And, there will be individuals who can change. This is because, even if
something is of biologic origin, it is always complex.
In conclusion, I would like to say that the fact that sexual orientation is of biological and innate origin in humans is highly relevant in the ongoing discussion to the church's response to its homosexual brothers and sisters. Some in the church would suggest it is not. Orson Scott Card, a man I respect, and whose writings I love, unfortunately, wrote in an article titled, The Hypocrites of Homosexuality: "the argument by the hypocrites of homosexuality that homosexual tendencies are genetically ingrained in some
individuals is almost laughably irrelevant."
It would be laughably irrelevant if the actions of the church and its therapists in the past and continuing present hadn't made it so solemnly relevant. It would be laughably irrelevant if the LDS SS and other church counselors hadn't put hundreds of men through tortuous electric shock and aversion therapies to change these children of God. It would be laughably irrelevant if it doesn't force thousands of young men and women through years of fruitless and spiritually debilitating reparative counseling and encourage thousands of men and women into marriage as therapy. I am here to say it is highly relevant whether it is of biological origin or not. Using a simplistic notion, a false dichotomy and then basing a therapy upon that can only hurt and not help the individuals and children of God.
In an earlier talk at Sunstone, Melissa Wunderly said something that is very true for me. She said that "style is how we make it through this world and accomplish things in a world of unknowns."
All I ask of LDS Social Services and the church, is that they realize this: that we are living in a world of a thousand unknowns; that we are living in a world where things are never an "either/or" proposition; and each individual is unique and needs to be treated as such. If the church or social services does not do this, then they bring themselves to hurting the children of God.