Wednesday, May 11, 2005

What's so great about homosexuality?

With this additional evidence that homosexuality is wired-in and not learned, I started wondering why it exists. Is there some evolutionary advantage to the species in having males and females who are not sexually attracted to the opposite gender? I've come across some ideas that because gays tend to have fewer offspring, that would give societies relatively more adults. But that didn't seem specific enough to incur an actual evolutionary advantage.

After some quick googling, I found an interesting paper titled Toward an Equilibrium Reproductive Economics of Homosexuality, by Edward M. Miller, Ph.D. of the Department of Economics and Finance at the University of New Orleans. Here's the abstract:
The survival of a human predisposition for homosexuality can be explained by sexual orientation being a polygenetic trait that is influenced by a number of genes. During development these shift male brain development in the female direction. Inheritance of several such alleles produces homosexuality. Single alleles make for greater sensitivity, empathy, tendermindedness, and kindness. These traits make heterosexual carriers of the genes better fathers and more attractive mates. There is a balanced polymorphism in which the feminizing effect of these alleles in heterosexuals offsets the adverse effects (on reproductive success) of these alleles' contribution to homosexuality. A similar effect probably occurs for genes that can produce lesbianism in females. The whole system survives because it serves to provide a high degree of variability among the personalities of offspring, providing the genotype with diversification and reducing competition among offspring for the same niches. An allele with a large effect can survive in these circumstances in males, but it is less likely to survive in females. The birth order effect on homosexuality is probably a by-product of a biological mechanism that shifts personalities more in the feminine direction in the later born sons, reducing the probability of these sons engaging in unproductive competition with each other.

So basically you can consider homosexuality to be too much of a good thing :) I was intrigued that this analysis came from an economist. I shouldn't be too surprised, what is evolution but a cost/benefit analysis played out over the long term?

Here's a link that will get you to the abstract of the paper.


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