The following article was posted to soc.motss in September 1991. The +quot;I+quot; in the
The following article was posted to soc.motss in September 1991.
The "I" in the article is the original poster, not me (though I do agree
with her statements).
Newsgroups: soc.motss
Subject: original "gay brains" article
Date: 20 Sep 91 01:21:33 GMT
Here's the original Science article on differences in the hypothalmus
between gay and straight men. There are probably a large number of
typos; I typed it by hand. I omitted some of the references, but the
footnotes with information or discussion other than references remain.
I omitted the figures, of course.
Before the start of the original article, I'd like to take this
opportunity to rebut 3 claims I've heard about this research that
I don't believe to be true.
1. Claim: the sample size is too small for it to mean
anything.
Rebuttal: One of the things statistical analysis is for is to
account for sample size. At a number of points in the article,
LeVay gives a conclusion, then a value called "P". P is the
probability that the observed situation could have occured by
chance; the calculation of P takes sample size into account.
A lower P means a better chance that you've observed a real
phenomenon. LeVay's values for P are all acceptably low.
2. Claim: the fact that the study doesn't include lesbians
stems from ignorance and sexism, i.e. the usual causes of
lesbian invisibility.
Rebuttal: The only time that sexual orientation makes it into
hospital records is when a patient has AIDS, and even then may
not be included for female patients. And even if it is often
recorded for female AIDS patients, relatively few lesbians have
AIDS. It's very difficult, barring interviews with patients or
their next-of-kin, to *get* female brains where you know the
orientation of the person they come from, especially lesbian
brains. LeVay acknowledges in the article that this is a
flaw.
3. Claim: all the gay men in the study died of AIDS, which
affects the brain; this invalidates the conclusions.
Rebuttal: Because of this concern, LeVay did a comparison
between the gay men and just the straight men who had died of
AIDS. The difference was still there. P was slightly higher,
(which you would expect from a smaller sample size, see above),
but still acceptably low.
I don't think the research is perfect. In particular, it demonstrates
only correlation, not any particular cause-effect relationship. Also,
chances are that some of the patients presumed to be straight were in
fact gay. It's unlikely that there were enough of these to seriously
corrupt the data, though. Overall, it strikes me as a sound piece of
work.
And here it is -- judge for yourself.
Copied without permission from Science, 30 August 1991.
----------------------------- begin included text ----------------
A Difference in Hypothalmic Structure Between Heterosexual and
Homosexual Men
Simon LeVay
abstract:
The anterior hypothalmus of the brain participates in the regulation of
male-typical sexual behavior. The volumes of four cell groups in this
region [interstitial nuclei of the anterior hypothalmus (INAH) 1, 2, 3,
and 4] were measured in postmortem tissue from three subject groups:
women, men who were presumed to be heterosexual, and homosexual men. No
differences were found between the groups in the volumes of INAH 1, 2,
or 4. As has been reported previously, INAH 3 was more than twice as
large in the heterosexual men as in the women. It was also, however,
more than twice as large in the heterosexual men as in the homosexual
men. This finding indicates that INAH is dimorphic with sexual
orientation, at least in men, and suggests that sexual orientation has a
biological substrate.
body of article:
Sexual orientation -- specifically, the direction of sexual feelings or
behavior towards members of one's own or the opposite sex -- has
traditionally been studied at the level of psychology, anthropology, or
ethics (1). Although efforts have been made to establish the biological
basis of sexual orientation, for example, by the application of
cytogenetic, endocrinological, or neuroanatomical methods, these efforts
have largely failed to establish differences between homosexual and
heterosexual individuals (2, 3).
A likely biological substrate for sexual orientation is the brain region
involved in the regulation of sexual behavior. In nonhuman primates,
the medial zone pf the anterior hypothalmus has been implicated in the
generation of male-typical sexual behavior (4). Lesions in this region
in male monkeys impair heterosexual behavior without eliminating sexual
drive (5). In a morphometric study of the comparable region of the
human hypothalmus (from men and women of unknown sexual orientation),
two small groups of neurons (INAH 2 and 3) were reported to be
significantly larger in men than women (6). Thus, these two nuclei
could be involved in the generation of male-typical sexual behavior.
I tested the idea that one or both of these nuclei exhibit a size
dimorphism, not with sex, but with sexual orientation. Specifically, I
hypothesized that INAH 2 or INAH 3 is large in individuals sexually
oriented toward women (heterosexual men and homosexual women) and small
in individuals sexually oriented toward men (heterosexual women and
homosexual men). Because tissue from homosexual women could not be
obtained, however, only that part of the hypothesis relating to sexual
orientation in men could be tested.
Brain tissue was obtained from 41 subjects at routine autopsies of
persons who died at seven metropolitan hospitals in New York and
California. Nineteen subjects were homosexual men who died of
complications of acquired immune deficiency syndrome (AIDS) (one bisexual
man was included in this group). Sixteen subjects were presumed (7)
heterosexual men: size of these subjects died of AIDS and ten of other
causes (8). Six subjects were presumed heterosexual women. One of
these women had died of AIDS and five of other causes (8). The mean age
of the homosexual men was 38.2 years (range, 26 to 53 years), that of
the heterosexual men was 42.8 years (range, 33 to 59 years), and that of
the women was 41.2 years (range, 29 to 59 years). The subjects were
younger and closer in age than those studied in previous investigations:
tissue was not taken from elderly heterosexual men or women so that an
approximate age-match would be preserved with the homosexual men, who
were predominantly young or middle-aged adults (9).
The brains were fixed by immersion for 1 to 2 weeks in 10 or 20%
buffered formalin. Tissue blocks containing the anterior hypothalmus
were dissected from these slices and stored for 1 to 8 weeks in 10%
buffered formalin. These blocks were then given code numbers; all
subsequent processing and morphometric analysis was done without
knowledge of the subject group to which each block belonged. The blocks
were infiltrated with 30% sucrose and frozen-sectioned at a thickness of
52 micrometers in planes parallel to the original slices. The sections
were mounted serially on slides, dried, defatted in xylene, stained with
1% thionin in acetate buffer (15 to 30 min), and differentiated with 5%
rosin in 95% alcohol (4 to 10 min). With the aid of a compound
microscope equipped with a camera lucida attachment, the outlines of the
four nuclei (INAH 1, 2, 3, and 4) were traced in every section at a
linear magnification of x83. These four nuclei included the two nuclei
reported by Allen et al. (6) to be sexually dimorphic and two other
nuclei (INAH 1 and 4) for which no sex differences were found (6). The
criteria described in (6) were followed in identifying and delineating
the nuclei (Fig. 1). The outline of each nucleus was drawn as the
shortest line that included every cell of the type characteristic for
that nucleus, regardless of cell density. In 15 cases the nuclei in
both left and right hypothalmus were traced. In 12 cases only the left
hypothalmus was studied, and in 14 cases only the right. The areas of
the traced outlines were determined with a digitizing tablet, and the
volume of each nucleus was calculated as the summed area of the serial
outlines multiplied by the section thickness.
In the 15 cases where both left and right sides were studied, no
significant interhemispheric differences were found for any of the four
nuclei. Therefore, in furthur analysis, the mean of the two sides was
used, and the cases where only one side was available were analysed
without regard to the side of origin.
One-way analysis of variance (ANOVA) was used to look for significant
differences between subject groups (Fig. 2). No differences were found
for INAH 1, 2, or 4. The results from INAH 1 and 4 are consistent with
those of Allen et al. (6, 10). However, INAH 2 was reported to be about
twofold larger in men than women (6). The failure to replicate that
finding may have to do with the relatively young age of the subjects in
the present study; as noted in (6), no sex difference was apparent
when women of repropductive age were compared with men of similar ages.
Thus INAH 2 is not dimorphic with either sex or with sexual orientation,
at least within the age range studied.
INAH 3 did exhibit dimorphism. One-way ANOVA showed that the three
sample groups (from women, heterosexual men, and homosexual men) were
unlikely to have come from the same population (P = 0.0014). Consistent
with the hypothesis outlined above, the volume of this nucleus was more
than twice as large in the heterosexual men (0.12 +/- 0.01 mm^3, mean
+/- SEM) as in the homosexual men (0.051 +/- 0.01 mm^3). Because of
uncertainty about the nature of the underlying distribution, the
dignificance of this difference was evaluated by a Monte Carlo
procedure (11); this showed the difference to be highly significant (P
= 0.001). The differenc e was still significant when the homosexual men
were compared with only the six heterosexual men who died of
complications of AIDS (P = 0.028). There was a similar difference
between the heterosexual men and the women (mean 0.056 +/- 0.02 mm^3;
P = 0.019), replicating the observations in (6). There was no
significant difference in the volume of INAH 3 between the heterosexual
men who died of AIDS and those who died of other causes or between the
homosexual men and the women. These data support the hypothesis that
INAH 3 is dimorphic not with sex but with sexual orientation, at least
in men (12).
INAH 3 is situated about 1 mm lateral to the wall of the third
ventricle, and about 1 to 2 mm dorsal to the anterior tip of the
paraventricular nucleus. It is spherical or ellipsoidal and contains
relatively large, densely staining, polygonal neurons (Fig. 1B). The
borders of the nucleus are not well demarcated; hence a blind procedure
was used to reduce bias effects. In most of the homosexual men (and
most of the women) the nucleus was represented by only scattered cells
(Fig. 1C). Because of the difficulty in precisely defining the neurons
belonging to INAH 3, however, no attempt was made to measure cell number
or density.
Brain tissue from individuals known to be homosexual has only become
available as a result of the AIDS epidemic. Nevertheless, the use of
this tissue source raises several problems. First, it does not provide
tissue from homosexual women because this group has not been affected
by the epidemic to any great extent. Thus, the prediction that INAH 3
is larger in homosexual than in heterosexual women remains untested.
Second, there is the possibility that the small size of INAH 3 in the
homosexual men is the result of AIDS or its complications and is not
related to the men's sexual orientation. This does not seem to be the
case because (i) the size difference in INAH 3 was apparent even when
comparing the homosexual men with heterosexual AIDS patients, (ii)
there was no effect of AIDS on the volumes of the three other nuclei
examined (INAH 1, 2, and 4), and (iii) in the entire sample of AIDS
patients there was no correlation between the volume of INAH 3 and the
length of survival from the time of diagnosis. Nevertheless, until
tissue from homosexual men dying of other causes becomes available, the
possibility that the small size of INAH 3 in these men reflects a
disease effect that is peculiar to homosexual AIDS patients cannot be
rigorously excluded.
A third problem is that possibility that AIDS patients constitute an
unrepresentative subset of gay men, characterized, for example, by a
tendency to engage in sexual relations with large numbers of different
partners or by a strong preference for the receptive role in anal
intercourse [both of which are major risk factors for acquiring human
immunodeficiency virus (HIV) infection (13)]. Sexual activity with
large numbers of partners is (or was until recently) common among gay
men, however, and therefore does not define an unrepresentative
minority (14). In addition, the majority of homosexual men who acquired
HIV infection during the Multicenter AIDS Cohort Study (15) reported
that they took both the insertive and the receptive role in anal
intercourse, and the same is likely to be true of the homosexual
subjects in my study. Nevertheless, the use of postmortem material,
with the consequent impossibility of obtaining detailed information
about the sexuality of the subjects, limits the ability to make
correlations between brain structure and the diversity of sexual
behavior that undoubtedly exists within the homosexual and the
heterosexual populations.
The existence of "exceptions" in the present sample (that is, presumed
heterosexual men with small INAH 3 nuclei, and homosexual men with
large ones) hints at the possibility that sexual orientation, although
an important variable, may not be the sole determinant of INAH 3 size.
It is also possible, however, that these exceptions are due to
technical shortcomings or to misassignment of subjects to their subject
groups.
The discovery that the nucleus differs in size between heterosexual and
homosexual men illustrates that sexual orientation in humans is
amenable to study at the biological level, and this discovery opens the
door to studies of neurotransmitters or receptors that might be
involved in regulating this aspect of personality. Further
interpretation of the results of this study must be considered
speculative. In particular, the results do not allow one to decide if
the size of INAH 3 in an individual is the cause or consequence of that
individual's sexual orientation, or if the size of INAH 3 and sexual
orientation covary under the influence of some third, unidentified
variable. In rats, however, that sexual dimorphism of the apparently
comparable hypothalmic nucleus, the sexually dimorphic nucleus of the
preoptic area, (SDN-POA) (16), arises as a consequence of the
dependence of its constituent neurons on circulating androgen during a
perinatal sensitive period (17). After this period, even extreme
interventions, such as castration, have little effect on the size of
the nucleus. Furthermore, even among normal male rats there is a
variablity in the size of SDN-POA that is strongly correlated with the
amount of male-typical sexual behavior shown by the animals (18).
Although the validity of the comparison between species is uncertain,
it seems more likely that in humans, too, the size of INAH 3 is
established early in life and later influences sexual behavior than
that the reverse is true. In this connection it would be of interest
to establish when the neurons composing INAH 3 are generated and when
they differentiate into a dimorphic nucleus.
REFERENCES AND NOTES:
1. For examples of the variety of approaches to the topic, see S.
Freud [_Three Essays on the Theory of Sexuality_, in _Collected Works of
Freud_, J. Strachey, Ed. and Transl. (Hogarth, London, 1959), pp.
125-243], C. S. Ford and F. A. Beach [_Patterns of Sexual Behavior_
(Ace, New York, 1951)], Vatican Council II [_Declaration on Certain
Problems of Sexual Ethics_, in _Vatican Collection_, A. Flannery, Ed.
and Transl. (Eerdmans, Grand Rapids, MI, 1982), vol. 2, pp. 486-499],
M. Ruse, _J. Homosex._ 6, 5 (1981)], and R. C. Friedman [_Male
Homosexuality: A Contemporary Psychoanalytic Perspective_ (Yale Univ.
Press, New Haven, CT, 1988)].
2. [I'm going to omit detailed references -- if you're going to go to
a science library to get the referenced journal, you can get Science as
well. I'll just include notes. -- Chris]
3. The suprachiasmatic nucleus (SCN) of the hypothalmus has been
reported to be larger in homosexual than in heterosexual men. [ref
omitted]. There is little evidence, however, to suggest that SCN is
involved in regulation of sexual behavior aside from its circadian
rhythmicity [ref omitted].
4, 5, 6 [refs omitted]
7. Two of these subjects (both AIDS patients) had denied homosexual
activity. The records of the remaining 14 patients contained no
information about their sexual orientation; they are assumed to be
heterosexual on the basis of the numerical preponderance of
heterosexual men in the population [ref to Kinsey omitted].
8. The causes of death for the ten male subjects who did not die of
AIDS were lung carcinoma (two cases), renal failure (two cases),
coronary thrombosis, acute lymphocyte leukemia, amytropic lateral
sclerosis, pancreatic carcinoma, pulmonary embolism, and aspiration
pneumonia. For the five female subjects who did not die of AIDS, the
causes of death were systemic lupus erythematosus, pancreatic
carcinoma, liver failure (two cases), and abdominal sepsis secondary to
renal transplantation. All six of the heterosexual male AIDS patients
and three of the homosexual men had history of intravenous drug abuse.
Three of the women, two heterosexual men who did not have AIDS, and one
homosexual man had histories of chronic alcohol abuse.
9. Criteria for inclusion of subjects in the study were as follows:
(i) age 18 to 60, (ii) availability of medical records, (iii) in AIDS
patients, statement in the records of at least one AIDS risk group to
which the patient belonged (homosexual, intravenous drug abuser, or
recipient of blood transfusions), (iv) no evidence of pathalogical
changes in the hypothalmus, and (v) no damage to the INAH nuclei during
removal of the brain or transection of these nuclei in the initial
slicing of the brain. Fourteen specimens (over and above the 41 used
in the study) were rejected for one of these reasons; in all cases the
decision to reject was made before decoding.
10. INAH 1 is the same as the nucleus named the "sexually dimorphic
nucleus" and reported to be larger in men than women [ref omitted]. My
results support the contention by Allen et al. (6) that this nucleus is
not dimorphic.
11. The ratio of the mean INAH 3 volumes for the heterosexual and
homosexual male groups was calculated. The INAH 3 volume values were
then randomly reassigned to the subjects, and the ratio of means was
recalculated. The procedure was repeated 1000 times, and the ordinal
position of the actual ratio in the set of shuffled ratios was used as
a measure of the probability that the actual difference between groups
arose by chance. Only one of the shuffled ratios was larger than the
actual ratio, giving a probability of 0.001.
12. Application of ANOVA or correlation measures failed to identify
any confounding effects of age, race, brain weight, hospital of origin,
length of time between death and autopsy, nature of fixative (10 or 20%
formalin), duration of fixation, or, in the AIDS patients, duration of
survival after diagnosis, occurrence of particular complications, or
the nature of the complication or complications that caused death.
There were no significant positive or negative correlations between the
volumes of the four individual nuclei across the entire sample,
suggesting that there were no unidentified common-mode effects such as
might be caused by variations in tissue shrinkage. The mean brain
weight for the women (1256 +/- 41 g) was smaller than for either the
heterosexual (1364 +/- 46 g) or the homosexual (1392 +/- 32 g), but
normalizing the data for brain weight had no effect on the results.
There was no correlation between subject age and the volume of any of
the four nuclei, whether for the whole sample or for any subject
groups; this finding does not necessarily conflict with the report in
(6) of age effects in INAH 1, and possibly INAH 2, because in (6) a
much wider range of ages was examined than was used in the present
study.
13. [ref omitted]
14. In the largest relevant study [ref omitted, 1978], nearly half the
homosexual male respondents reported having had over 500 sexual
partners.
15, 16, 17, 18 [refs omitted]
19. I thank the pathologists who made this study possible by providing
access to autopsy tissue; [various other acknowledgements omitted]
29 January 1991; accepted 24 June 1991.
End of article 47013 (of 47027)
From: geoffp@cup.portal.com (Geoffrey Scott Puterbaugh)
Newsgroups: soc.motss
Subject: Re: original "gay brains" article
Message-ID: <47580@cup.portal.com>
Date: 23 Sep 91 02:46:37 GMT
References: <15232@sybase.sybase.com>
Organization: The Portal System (TM)
Lines: 101
Brain Studies Starter Kit
----------------------------
"Is Homosexuality Biological?" Marcia Barinaga, Science,
vol. 253, Aug. 30th, 1991, p. 253. Good overview of Simon
LeVay and his work, establishing its findings in context.
The two following articles ("The Brain as 'Sexual Organ'"
and "Is 'Gender Gap' Narrowing?") are also OK.
------------------------------------
"An enlarged suprachiasmatic nucleus in homosexual men" D.F.
Swaab and M.A. Hofman, Brain Research, v. 537, p. 141, 1990.
This article reports an enlarged SCN in gay men, and also
reports on a sexually dimorphic nucleus (SDN). Both of
these areas are in the region of the anterior hypothalamus.
Swaab and Fliers reported earlier on the "SDN" in 1985.
-------------------------------------
"Two sexually dimorphic cell groups in the human brain"
Laura S. Allen et. al., The Journal of Neuroscience, Feb.
1989, vol 9(2), p. 497.
This article, by the Roger Gorski group at UCLA, proposes a
re-mapping of the area reported on by Swaab and Hofman.
They find four cell groups in the "pre-optic-anterior
hypothalamic area." They propose naming them Interstitial
Nuclei of the Anterior Hypothalamus or INAH for short. The
area they call INAH-1 appears to be the same area as Swaab's
"SDN" and they cannot replicate his findings. Several possible
reasons for this failure are examined, including different
sample sizes and the fact that Swaab did not control for age.
However, they do find that INAH-3 is sexually dimorphic, being twice as
large in males as in females.
INAH-2 also is reported as sexually dimorphic, but
related to circulating hormone levels in women.
-------------------------------------
"A difference in hypothalamic structure between heterosexual
and homosexual men" Simon LeVay, Science (same issue as
first article) p. 1034.
Does not find INAH-2 dimorphic, for reasons suggested by the
group at UCLA. ("no sex difference was apparent when women
of reproductive age were compared with men of similar ages")
Replicates the finding of sexual dimorphism for INAH-3.
Twice as large in men as in women.
The new finding in this report is that INAH-3 is also
twice as large in straight men as in gay men.
---------------------------------------
Summary: so far we have two independent and unreplicated
findings of brain differences between gay men and straight
men. Swaab found an SCN which was twice as big, and LeVay
found INAH-3 the same size in gay men as in women (half the
size of straight men).
Interesting sidelight: "Brain Research" is a fairly hefty little
book, and I noticed with some surprise that it is a WEEKLY.
Whew! There is a lot of stuff going on here.
Now I will try to reproduce one of the charts from LeVay's
article:
^
* 0.20 ---|
|
^^ |
^* |
^ ^ * 0.15 ---|
^ o |
^ |
^ ** |
*^* 0.10 ---|
* |
|
* |
*** * 0.05 ---|
^ ^ * *** |
^ **** |
^* ^ * |
* * 0.00 ---|
F M HM
INAH-3
Volumes of the hypothalamic nuclei studies (INAH-3) for
the three subject groups: females (F), presumed hetero-
sexual males (M), and homosexual males (HM). Individuals
who died of complications of AIDS, *, individuals who died
of causes other than AIDS, ^; and an individual who was a
bisexual male and died of AIDS, o. For statistical
purposes this bisexual individual was included with the
homosexual men.
I'll conclude by sharing the thoughts of LeVay and many others:
wait for replication before jumping to any conclusions.
End of article 47053 (of 47074)
----------------------------------------------------------------------
Here is an excerpt from an old copy of the soc.motss FAQ, answering some
questions about Levay's study:
Biology of sexual orientation
=============================
221. What's all this about brain differences in gay men?
A brief article in the 30 Aug 1991 issue of {Science} magazine
(published in U.S.) reported research by Dr Simon LeVay. Levay
autopsied the brains of 41 persons:
- homosexual men: 19 (including 1 bisexual) who had died of AIDS;
- heterosexual men: 16, assumed to be heterosexual, including
- 6 died of AIDS (including 2 who "denied homosexual activity"
and 4 who had no sexual orientation recorded)
- 10 died of other causes and had no sexual orientation recorded
- women: 6, also assumed to be heterosexual.
LeVay found that a tiny cell group called INAH 3, part of the
anterior hypothalamus, was more than twice as large in the presumed
heterosexual men (0.12 +/- 0.01 mm^3) as in either the homosexual men
(0.051 +/- 0.01) or the presumed heterosexual women (0.056 +/- 0.02).
(INAH = interstitial nuclei of the anterior hypothalmus.) He found no
differences in INAH 1, 2, or 4.
222. Wasn't that an awfully small sample?
Statistical analysis takes into account the sample size and the
differences between results for the two groups.
The probability that this result reflects a true difference in the
general population was 99.9% as between homo and presumed hetero men,
99.1% as between presumed hetero men and presumed hetero women. When
the 19 homosexual men were compared against only the presumed hetero men
who had died of AIDS, the same difference was found, with a probability
of 97.2% that this reflects a true difference in the general population.
There was no statistically significant difference between the size
of INAH 3 between the homosexual men and the women, nor between the
presumed heterosexual men who died of AIDS and those who died of other
causes.
223. Weren't there some exceptions?
The results were not uniform: some presumed heterosexual men had
small INAH 3 nuclei, and some homosexual men had large nuclei. LeVay
says this could mean that sexual orientation, though important, "may
not be the sole determinant of INAH 3 size" or that some subjects were
assigned to the wrong groups.
Note that the statistical results in the preceding Q take these
exceptions into account.
224. What exactly does this study prove?
LeVay (who is himself gay) said that the study shows that sexual
orientation in men "is amenable to study at the biological level". It
does not show whether the size differences cause or result from differ-
ences in sexual orientation, or both are caused by some third factor as
yet unidentified. The article did not mention genetic influences.
E-Mail Fredric L. Rice / The Skeptic Tank