Twin Studies: What Do They Show? 
By Alan P. Medinger 

The nature-nurture debate over the origins of homosexuality was fed an ample supply of grist last year with the publication of Simon LeVay's hypothalamus study and with the subsequent publication of a new study of twins. In the September, 1991, Regeneration News, we looked briefly at the hypothalamus study, and like many others, concluded that it was almost totally inconclusive. The twin study, on the other hand, appears to have much more significant implications; ones that are particularly encouraging for those who share our perspective on homosexuality. 

Briefly, a Northwestern University study by J. Michael Bailey and Richard Pillard of 56 sets of identical twins in which at least one twin was a homosexual, discovered that in 52% of the cases, the other twin was homosexual also. Among 54 sets of fraternal twins in which one was homosexual, the other was homosexual 22% of the time. They also studied adoptive brothers and there found an 11 percent correlation. 

The press, in reporting the study, immediately announced that it "implies a genetic basis for sexual orientation." A deeper look at the results reveals no basis for such a conclusion, and in fact, to the contrary, opposite conclusions are easily justified. Assuming there are no major flaws in the study, it can lead to three very exciting implications. 

First, the study seems to rule out the possibility that homosexuality is caused entirely by genetic causes. Identical twins are genetically exactly the same, so the correlation would have to be 100%, not 52%, if the homosexuality were entirely a genetic condition. 

Second, the high correlation of homosexuality among fraternal twins makes a powerful case for environmental causes. Fraternal twins are no more alike genetically than any two brothers who are born several years apart, and yet there is a much higher homosexual correlation among fraternal twins than among other sets of brothers. If fraternal twins don't share a common genetic make-up, then what is it they do share that makes this correlation so much higher? What they share is a nearly identical environment. They are almost the same in birth order; they arrive at the same time in their parents' lives; they grow up in the exact same circumstances as regards their family's life situation. Their parents are at the same stage in their own lives with respect to economics, marital stability, spiritual growth, divorce, lifestyle, etc. The fraternal twins are growing up in the same home, as similar an environment as is possible for two boys to experience. 

When compared to non-twins, what else could account for the high correlation of homosexuality? There are a couple of possibilities, but both are developmental, not genetic. Conceivably, one homosexual boy could influence the other to become homosexual. This seems highly unlikely, and besides, the same could happen with non-twins. Also, there is the possibility that events occur while the boys are in the womb that would influence both boys to become homosexual. Researchers have come up with no evidence of this, however, and such influences, again, are developmental, not genetic. 

The third implication from the twin study is more theological and philosophical, but is perhaps the most exciting. Going back to the identical twins, if they share an identical genetic make-up and an almost identical environmental experience, why isn't the correlation much higher than 52%? Why isn't it closer to 90 or 100%? The answer, I believe, is one that the world will not accept, but one which should immediately apparent to Christians -- free will. Given what we come into the world with, and given our life experiences, we still have the freedom to make choices. 

We live in a world so imbued with the philosophy of determinism, that even Christians have a difficulty thinking about man as truly free. We are so influenced by the teaching that we are totally a product of our genes and our past experiences that we struggle even with the story of Adam and the fall. God made Adam a certain way, and God totally determined the environment in which Adam would live. Wasn't it God's fault, then, that Adam chose to eat of the forbidden tree? Hadn't God set him up for it? Wasn't his decision inevitable? If we answer yes to each of these questions, then we serve a cruel and capricious God. No, by some means, Adam had to be truly free to eat or to not eat of the forbidden fruit; to chose God's way or his own. 

Free will is indeed a mystery. No doubt it is one of those factors that makes us "in the image of God." It is an awesome thing. It is a terrifying thing to bear a great responsibility for one's own fate. But it is what sets us apart from every other part of creation; from the trees and the animals and the birds. Free will sets us apart from machines, and makes us a little less than the angels. 

As Christians we must believe we can make choices. Identical twin brothers, growing up with the same parents, in the same time and place, at the same point in history, can make separate choices. We need to stress here as we do so often, that we don't choose to be homosexual. One twin doesn't choose to be homosexual and the other not, but all of our choices have consequences that go far beyond what we can anticipate. We can choose how we will respond to our life situation. I chose to respond to my father's mental illness and my family's dysfunction by separating from my parents emotionally and by retreating into a fantasy world. I did not choose to be homosexual, but I can see now that certain choices I made set me on the course towards homosexuality. 

We cannot be adamant about the causes of homosexuality; we don't have enough information yet. Maybe we never will. But for now, the evidence still points to developmental causes, and for those of us who believe that man is more than a programmed machine, we see an element of choice in what we become. 

This is indeed good news, because we can make new choices, and we can have new experiences of growth and healing that offer for the homosexual the promise of very significant change. 

Copyright 1992 Alan P. Medinger and Regeneration. All rights reserved. Used with permission.