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On Homosexuality

Rachel Townsend's picture
In reading Darwin's On the Origin of Species and discussing the book in class, I have found myself thinking a lot about the evolutionary significance of homosexuality.  I have been struggling not with the existence of homosexuality but instead with its' long history and continuation within our species, for if evolutionary theory is to be accepted, homosexuality, which is not a selective reproductive trait, should not continue to appear in the species.  According to Darwin's theory of evolution, the appearance of homosexuality is not surprising because the basic principle of the theory is based on the randomness of mutation within a species.  Given this, the existence of homosexuality is not surprising at all but, as mentioned before, the fact that it has continued within the population is a quandary which has interested me throughout our conversations.   
In preparing to write this paper I was reading various pieces on the internet and came across a book called Straight Science: Homosexuality, Evolution, and Adaptation.  I began reading the portions of this book available online, seeing as it seemed directly applicable to my topic.  The author, Jim McKnight, began his project due to very similar concerns about the seeming discontinuity of the continuation of homosexuality and evolutionary theory.   Of course this was my main concern here so I continued on from McKnight's Preface to read his first chapter.  This is when the problem arose.  The first sentence of McKnight's Chapter 1: Is Male Homosexuality Adaptive? reads "Male homosexuality is a major puzzle for evolutionary theory, for if evolution has a purpose it is reproductive fitness, the passing of our genes to our children." (1)  My problem is less with the overall idea of this statement than with the word choice.  After all of our class discussion of the randomness of evolution, I was really taken aback by McKnight's use of the word "purpose" in reference to evolution, even with the qualifying "if."  To even suggest that the theory of evolution can be distilled down to something with a purpose seems to completely go against the main components of the theory.  The random characteristic of the theory of evolution is what makes the current state of the world truly amazing.  
For some time now there has been a common scientific understanding that genes do indeed contribute to a person's sexual orientation.  Specifically, in 1993 Science News published a short article discussing the genetics of male homosexuality. (2)  The piece, entitled "Genetic Clue to Male Homosexuality Emerges," relates that male homosexuality has been linked to a certain gene on the X chromosome. (2)  So if homosexuality is in a person's genes and it has continued to persist in humans, then there must be some reason beyond mutation for its' appearance among the human population. And this evidence is precisely what makes homosexuality such a conundrum for evolutionary theorists and biologists.  
To complicate matters, the correlation of genes and female homosexuality has not been as straightforward as that between genes and male homosexuality.  Some scientists maintain that exclusive homosexuality is less prevalent among females than males. (3)  Possibly this difference in prevalence means that female homosexuality is genetically different than male homosexuality or this says something profound about the difference of sexuality in males and females in general.  
Since the scientific community has been bumping up against this problem of the persistence of homosexuality, many have begun doing research to further our understanding of the seeming contradiction that is persisting homosexuality.  Currently scientists from the Queensland Institute of Medical Research, University of Colorado, Boulder, and Northwestern University are suggesting that genetic factors which predispose people to homosexuality, while not readily being passed along by homosexuals, may actually increase reproductive success in heterosexuals carrying the genes. (4)  If such is the case we would no longer need to struggle with the question of how homosexuality persists or why it persists.  The fact that genes predisposing individuals to homosexuality increase reproductive success among heterosexuals means that there is a genetic reason for the existence for homosexuality or at least a gene which contributes to it.  
Clearly we have come to a point where we can recognize that the reason persisting homosexuality challenges the theory of evolution is because we do not yet understand how it has contributed to reproductive success.  If we have accepted that homosexuality is in a person's genes and that homosexuality has been present in human populations since antiquity, then we must see that the only way for us to reconcile this with evolutionary theory is to accept that homosexuality must have some part to play in the overall reproductive success of our species.  

1. McKnight, Jim. Straight Science: Homosexuality, Evolution, and Adaptation. New York: Routledge, 1997.
2. Bower, B. "Genetic Clue to Male Homosexuality Emerges." Science News. Vol. 144, No. 3 (July 17, 1993), p. 37.
3. Rahman, Qazi and Glenn D. Wilson. "Born gay? The psychobiology of human sexual orientation." Personality and Individual Differences. Vol. 34, No. 8 (June 2003), pp. 1337-1382.  
4. Zietsch, Brendan P. et al. "Genetic factors predisposing to homosexuality may increase mating success in heterosexuals." Evolution and Human Behavior. Vol. 29, No. 6 (Nov 2008), pp. 424-433.   


Serendip Visitor's picture

There is nothing wrong with

There is nothing wrong with encouraging the acceptance homosexuality and bisexuality in society. It certainly won't hurt anyone. It should be seen as normal and equal to heterosexuality, because it is! A huge benefit to society is that same-sex couples can adopt babies to give them a loving home and family.

chris gomes's picture

Homosexuality's Origin

Hi Rachel,

If you'd like to read a provocative and compelling theory of human sexuality that gives explanations for heterosexuality, homosexuality, and also accounts for animal sexual behavior, then go to . Based on your blog entry above you are very interested in getting answers to your questions on human sexuality.

In order to get an understanding of human sexuality you have to look at the relationship between instinct and intelligence, the roles they play in animals, and the contraints evolution places on both. In reading my paper you will learn that in the course of human evolution as our intelligence level rose, our instincts declined - until we reached a point of becoming so intelligent that evolution favoured the human line losing all our instincts, including the sexual instinct.

So, both our heterosexuality and homosexuality do not have a genetic basis - both are a function of experience. I propose that indeed humans are born without any sexual inclination at all, but during childhood we would develop a greater tendency to develop a homosexual orientation (due to inevitable sexual exploration behaviors with our own bodies) than a heterosexual one - if not conditioned by our societies to be heterosexual.

Society has always had to contend with this dominant homosexual bias in human beings, and has had to encourage a heterosexual orientation in order for it to survive. We human beings are therefore a sexually unstable species, something unique in all of nature.

Just let me know what your comments are - I have a forum and blog for your responses, or you may also post them here on this website.


Paul Grobstein's picture

evolution and homosexuality

"the only way for us to reconcile this with evolutionary theory is to accept that homosexuality must have some part to play in the overall reproductive success of our species."

Makes sense to me.  And certainly one way to do it is to suggest that "genes predisposing individuals to homosexuality increase reproductive success among heterosexuals."  But there are certainly other ways as well.  Is homosexuality a special case, or does one have exactly the same issue with many other features of humans?  Of other organisms?