from "Born that way" theory
By Neil Whitehead, Ph.D.
A recent study found that lesbians are slightly more likely
than are heterosexual women to have male-type finger length patterns.
Although the correlation was only slight, and although
the researchers could not explain why some heterosexual women also
had the same finger pattern, the study was quickly hailed as
further evidence that homosexually-oriented people are "born that way."
Neil Whitehead, author of the recent book, My Genes Made Me Do
It! responds to the evidence.
Neil Whitehead, author of the recent book, My Genes Made Me Do It! responds to the evidence.
In a recent article in Science, Williams et al.1 report on their study, which seems to show a biological basis for lesbianism.
They measured finger lengths in heterosexuals, homosexuals and lesbians, and found that certain finger-length ratios in lesbians are significantly less than in female heterosexuals. This suggested a biological basis to lesbianism, with the further implication that sexual-reorientation therapy for lesbians would be difficult or impossible.
However, this claim is significantly misleading. I report on this study because it is already in the popular press, and has been misinterpreted.
Williams et al. reported that the mean finger-length ratio for lesbians was significantly less than that for heterosexual women, and did this by comparing the two ratios by a statistical test. They used a large number of interviewees. In such circumstances, although the mean finger lengths may be statistically different, they are often so close that it is not practically useful to say they are different. That is what has happened in the present case.
The original normal distributions can be reconstructed from the researchers' data, and the results are shown in Figure 1. (With its two large overlapping curves, Figure 1 assumes that we are comparing an equal number of heterosexual women and lesbians).
There is obviously a very large overlap in the two populations, and although the two means may be statistically different, the difference is only 1% -- which is a small effect, and not diagnostically useful in any sense.
Within Figure 1 is also given the expected distribution of finger lengths for lesbians, assuming a United States nation-wide prevalence of 1.7% (which includes bisexual lesbians2 ). For any finger-length ratio chosen, the lesbians in the population at large are outnumbered by their heterosexual counterparts by approximately 60:1.
Figure 1 shows that there are large numbers of heterosexual women who have much more "masculine" finger-length ratios than most lesbians, but this is not considered by the researchers to be related to their sexual orientation.
Prenatal Androgen Exposure and Masculinity
Williams et al. invoke the idea of very high prenatal androgen levels (for which there is very scant evidence) to explain the difference in mean finger lengths which they find. But if this is indeed an explanation, it must rarely affect sexual orientation. An explanation which involved considerably less biological extrapolation would be preferable. For example, does a slightly more masculine pattern for a hand, influence the self-image of a developing girl?
This study is rather similar to many other reported links between homosexuality and some biologically based phenomena. Although statistical connections may be shown, only a small percentage of subjects with that biological feature actually end up homosexual.
1. Williams, T.J., Pepitone, M.E., Christensen, S.E., Cooke, B.M., Huberman, A.D., Breedlove, N.J., Breedlove, T. J., Jordan, C.L. & Breedlove, S.M. (2000): Nature 404, 455-456.
2. Whitehead, N.E. & Whitehead, B.K. (1999). My Genes Made Me Do It! Huntington House, Lafayette, Louisiana.