From: Anders Sandberg (asa@nada.kth.se)
Date: Mon Jul 13 1998 - 11:26:25 MDT
"Jim Barnebee" <mutabletao@hotmail.com> writes:
> There is no such thing as a "gay gene". Homosexuality is not
> genetic, but environmental.
Sorry, but it isn't that simple. Practically nothing in psychology is
100% genetic or environmental, usually it is a complex mixture. Often
people misreport the discovery of a gene linked to a trait as if the
gene was the sole cause.
> Homosexuality is caused by the
> underproduction or overproduction of a certain hormone in the mother
> during the gestation of the fetus (I believe in the third trimester).
(Based on chapter 11 in _Biological Psychology_ by James W. Kalat,
which I happen to have handy. References at the end)
There is some data that levels of testosterone during the middle of
the second month to the fifth month might influence sexual
orientation; decreased levels increase the number of homosexual males
(Ellis & Ames 1987) in animal models (Adkins-Regan 1988), and
increased levels the number of homosexual females. However, these
studies also caused anatomical changes, which are not observed among
humans. Stress during the last part of the pregnancy might also
increase the number of homosexual offspring, perhaps due to
endorphines from the mother acting as anti-testosterone in the fetus'
hypthalamus (Ward, Monaghan & Ward 1986).
However, the evidence among humans for a link between maternal stress
and homosexuality is relatively weak: one study (Ellis, Ames, Peckham
& Burke 1988) found an increased number of stressful events during the
second trimester of pregnancy, but another study failed to observe it
(Bailey, Willerman & Parks 1991).
The consensus seems to be that prenatal hormones play a role, but are
not that strong influence.
The evidence for a genetic link is fairly clear, but does not explain
all homosexuality. Bailey & Pillard 1991 and Bailey, Pillard, Neale &
Agyei 1993 produced the following picture in a twin/family study of
homosexuals:
Probability of
homosexual orientation
Male Female
Monozygotic twin 52% 48%
Dizygotic twin 22% 16%
Sister 14%
Adopted brother/sister 11% 6%
The percentage of homosexuals in the population in general is around
5-10%, with fewer reported females. These results suggest that there
is a genetic correlation, but even in monozygotic twins it is not
strong enough to account for more than 50%.
In a study of more remote relatives, it was observed that for
homosexual males there was an increase in probability of homosexuality
on the mother's side, suggesting an X-chromosome linkage (Hamer, Hu,
Magnussoon, Hu & Pattuccio 1993).
So, to sum up, there is evidence for a genetic link, but it doesn't
account for all the variation, and the evidence for hormonal effects
isn't that strong. These results, together with the observed
biological changes in homosexual's brains (mostly in the diencephalon)
suggest that purely psychological explanations do not work to explain
it.
ObTranshuman: An interesting question is what would happen if it was
possible to relatively simply adjust one's brain to change sexual
preferences at will. How many people would try it? My guess is that
relatively few adults would do it, since their preferences had already
become a part of their self-image and they would not want to change
that. Among adolescents experimentation might reasonably be expected
to be higher. It would be interesting to study more what traits people
regard as too central to be changed and what traits they could accept
changing. For example, practically everybody seems to accept a better
memory or sharper perception, many people would likely want to
'polish' their personalities but not change them outright, and very
few if any people want to change their basic value systems. Is this
because the things we might accept changing are not as rooted in our
values as the 'sacred' parts?
Adkins-Regan, E 1988 Sex hormones and sexual orientation in animals,
Psychobiology 16 335-347
Bailly, Willerman & Parks 1991 A test of the maternal stress theory of
human male homosexuality. Archives of sexual behavior, 20 277-293
Bailley, Pillard 1991 A genetic study of male sexual orientation,
Archives of General Psychiatry 48 1089-1096
Bailley, Pillard, Neale & Agyei 1993 Heritable factors influence
sexual orientation in women, Archives of General Psychiatry 50 217-223
Ellis, L & Ames, MA 1987 Neurohormonal functioning and sexual
orientation: a theory of homosexuality-heterosexuality. Psychological
Bulletin 101 233-258
Ellis L, Ames M, Peckham W & Burke D 1988 Sexual orientation of human
offspring may be altered by severe maternal stress during pregnancy,
Journal of Sex Research 25 152-157
Hamer, Hu S., Magnuson, Hu N., Pattatucci 1993 A linkage between DNA
markers on the X chromosome and male sexual orientation. Science 261
321-327
Ward, OB, Monaghan EP, Ward IL 1986 Naltrexone blocks the effects of
prenatal stress on sexual behavior in male rats. Pharmacology
Biochemistry & Behavior 25 573-576
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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