Claim CB403:
Evolution does not explain homosexuality. Traits evolve as a result of
greater reproductive success, and homosexuals are less likely to
reproduce..
Source:
Response:
- There are several possible explanations for this:
- Although homosexuality probably has a genetic component, much of its
cause, perhaps most of it, appears to be nongenetic (Haynes 1995;
Kendler et al. 2000; Kirk et al. 2000). To the extent it is not
genetic, selection would not affect it.
- Homosexuals still have children. Sexual orientation is not an
either-or trait but exists as a continuum (Haynes 1995). Those
with some heterosexual orientation can still contribute homosexual
genes (to the extent it is genetic; see above). And even the most
extreme homosexuals sometimes have children.
The most manifest heterosexuals may have homosexual tendencies, too.
Homophobic male heterosexuals showed more arousal to homosexual
images than did nonhomophobic heterosexuals (Adams et al. 1996).
Societal condemnation of homosexuality may contribute to its genes
being propagated by causing latent homosexuals to behave
heterosexually.
- Genes for homosexuality could be beneficial on the whole.
In bonobo chimpanzees, homosexual interactions are a form of social
cement. It is possible that homosexuality evolved to serve social
functions in humans, too (Kirkpatrick 2000). After all,
social cohesion is still a main function of sex in humans.
The genetic etiology of homosexuality may come from a collection of
traits that, when expressed strongly and in concert, result in
homosexuality; expressed less strongly or without supporting traits,
these traits contribute to the robust nature of our species. The
genes for these traits persist because they usually combine to
make us better at survival and reproduction.
Genetic factors linked to homosexuality in men apparently boost
fertility in women. Female relatives of gay men, on their mother's
side of the family, had more children than female relatives of
heterosexual men. (Corna et al. 2004)
It should be noted that the question of explaining homosexuality is not
limited to humans. Homosexuality exists in hundreds of animal species
(Bagemihl 1998).
References:
- Adams, H. E., L. W. Wright Jr. and B. A. Lohr, 1996. Is homophobia
associated with homosexual arousal? Journal of Abnormal Psychology
105(3): 440-445.
- Bagemihl, Bruce, 1998. Biological Exuberance: Animal Homosexuality
and Natural Diversity. New York: St. Martin Press.
- Corna, F., A. Camperio-Ciani and C. Capiluppi, 2004. Evidence for
maternally inherited factors favouring male homosexuality and promoting
female fecundity. Proceedings: Biological Sciences 271: 2217-2221.
- Haynes, J. D., 1995. A critique of the possibility of genetic
inheritance of homosexual orientation. Journal of Homosexuality
28(1-2): 91-113.
- Kendler, K. S., L. M. Thornton, S. E. Gilman and R. C. Kessler, 2000.
Sexual orientation in a U.S. national sample of twin and nontwin
sibling pairs. American Journal of Psychiatry 157(11): 1843-1846.
- Kirk, K. M., J. M. Bailey, M. P. Dunne and N. G. Martin, 2000.
Measurement models for sexual orientation in a community twin sample.
Behavior Genetics 30(4): 345-356.
- Kirkpatrick, R. C., 2000. (see below)
Further Reading:
Kirkpatrick R. C., 2000. The evolution of human homosexual behavior.
Current Anthropololgy 39(1): 385-413. (technical)
Wright, Robert, 1994. The Moral Animal: The new science of evolutionary
psychology. New York: Pantheon, pp. 384-386.
created 2003-5-2, modified 2004-10-14