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from "Born that way" theory
The New Finger-Length Study on Lesbians
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.
Figure 1. Distribution of finger length ratios
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.
The Findings
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.
N.E.Whitehead
whiteh@paradise.net.nz
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.
Updated: 3 September 2008
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