Journal of medical ethics, I980, 6, 133-138
Biological aspects of homosexuality
Malcolm MacCulloch Park Lane Hospital, Maghull, Liverpool
Editor's note Table i The association between homosexual type (primary and
secondary) and success at latestfollow up in response to avoidance
This paper is another of those prepared for a London learning. Series and trial patients are combined
Medical Group symposium on homosexuality held in
October 1979. Dr MacCulloch describes a clinical trial Primary Secondary Total
conducted on 73 patients, 30 ofwhom were selected. Early Success 5 36 41
calculations at the end of the trial confirmed an impression Failure I2 10 22
that there were two categories of homosexuals primary Total 17 46 63
and secondary the former being those who reported that
they had never shown any heterosexual interest. A case X2 = 12.2I
history of identical twins is highlighted in the control trial p = <O.OOI
between two kinds of aversion therapy and psychotherapy. because he was finding the strain of maintaining a
Dr MacCulloch offers evidence of a biochemical heterosexual 'front' intolerable.
aetiology ofprimary homosexuality and suggests that ifthis
is upheld it will lead to markedly less hostility in the Sexual history
attitudes of the puMlic and professions to homosexuals and The patient's first sexual experience at the age of 13
to a different view of society by the homosexuals was that of having another boy's naked body held
themselves. against his at a swimming baths. He was excited by
this; on other similar occasions he later came to admire
the physique of other boys. He began auto-
Introduction masturbation and phantasised males of his own age at
The origin of my argument that some homosexual the age of 17. He also bought physical culture books.
behaviour has a biological cause is clinical. In the At the age of i8 he was picked up by a male in a public
course of treating 43 unselected patients presenting convenience but declined to go with him for the pur-
complaining of homosexual behaviour and of treating a pose of mutual masturbation. Later he regretted this
further 30 selected patients in a clinical trial, it was decision and at the age of 23 he met a 35 year old man
noticed that patients who never had a history of under similar circumstances and practised intracrural
heterosexual interest throughout their lives appeared sexual intercourse with pleasure mixed with some
to do rather less well than those patients who did give a anxiety and nervousness. Within weeks he began to
positive heterosexual history. Preliminary calculations make regular homosexual pick-ups and then began to
at the end of the trial confirmed this impression and the go to another city specifically to make homosexual
patients are divided into two categories, primary and pick-ups. He did so in order to avoid recognition in his
secondary homosexuals, the former being those cases own town. He practised sodomy once at the age of 23
who, by their own report, had never at any time shown following a heavy intake of alcohol. At the time of the
any heterosexual interest. Because the importance of interview he was making homosexual pick-ups once
this primary secondary dichotomy was not appreci-
- per week and practised intracrural sexual intercourse,
ated at the beginning of the trial, the random assigna- kissing and petting. His auto-masturbatory phantasy
tion of patients to treatment was made without was of well-built males and various homosexual acts.
reference to this factor. Within that trial the small He played with girls a good deal as a younger child,
group and sub-group numbers made statistical evalua- preferring their company to that of boys and he did not
tion difficult but, however, it was possible to combine play games. He was never attracted to females but
the total cohort of 30 trial patients and 36 of the series commenced heterosexual dating at the age of I 5
patients for analysis and the association between 'because it was the thing to do'. He disliked holding
primary homosexuality and successful outcome at lat- hands. Six months prior to presentation he tried kis-
est follow up was significant (p = <o.ooi). sing and petting but he said, 'I just can't bring myself
to put on a normal act. I dislike girls'. (His sister-in-law
During the course of our control trial between two did not attract him in any sense).
kinds of aversion therapy and psychotherapy we saw a
24 year old man who was one of a pair of identical Personal history
twins. His twin was exclusively heterosexual. The The twin birth was uncomplicated and his upbringing
patient referred himself via his general practitioner unexceptional. He was described by the heterosexual
134 Malcolm MacCulloch
twin as doing 'girlish type things' as a child. There is a during the early years tended to smother the patient.
clear difference in their temperaments, the heterosex- On presentation he was tending to go out in the even-
ual twin being more outgoing and aggressive; the latter ings in order to avoid listening to his mother's health
felt that the patient was more close to their mother and complaints. She was, no doubt, the dominant parent.
was shown more physical affection.
PERSONALITY The patient received 24 sessions of anticipatory avoid-
There was evidence of life long self insecure personal- ance" followed by 24 sessions of classical condition-
ity abnormality showing sensitive features and at times ing and showed no shift either clinically or by the
ideas of reference. The homosexuality was beginning sexual orientation method.'
to have a developmental effect. He showed obsessional
features also. There was no hint of previous illness and FOLLOW UP
on examination his mental state was normal. His twin No change in sexual orientation had occurred at final
was interviewed using the same initial questionnaire follow up at 66 weeks post-treatment. His final Kinsey
and the common parental history was confirmed. The rating was 6.
twin was entirely heterosexual and had always been so.
Family history Discussion
His father was a foreman concreter and was a strict Perhaps the most striking feature of this case was the
parent with sensitive personality features. The patient complete discordance for sexual object choice. The
had little or no emotional contact with his father. His avoidance latencies are extremely irregular and do not
mother tended to complain of bodily ailments and show any evidence of learning.
PATIENT 17 AVOIDANCE LATENCIES
*2 f- 2 ez ei
;* O. li
6 e x us
A;i 7. 750 Z I
Z o ',
rA . *,
1~ - 1; Z I
'Z ; ...................................
6 ^ 3 Z 2 i
5* I 2 I ;6 * a * A * v*
a - V -W I . V . . --r-9 -W . . . , . .
a is 6 12. 16 co, IZ kk ; . 1. ;3 z ;A 4 4 Z, i a ;6 ib 6 #a a m
24 TRIALS PRECEDED BY ESCAPE TRIALS
Fig. i Twenty-four sessions of aversion therapy avoidance latencies with 24 trials in each session -
Biological aspects of homosexuality 135
SEXUAL ATTITUDE SCORE
PRE TREATMENT WITHIN TREATMENT POST TREATMENT FOLLQW UP
- . - i
48 -X $k
) X x " X -It
5 4 3
4 12 24 36 48
i 2 4 53
MONTH SESSIONS MONTHS
Fig. 2 The male andfemale sexual orientation method scores for a monozygotic twin patient 4 months prior to anticipatory avoidance
averson therapy treatment.
During 72 sessions of treatment, for 3 months after theory. It therefore seemed to us that an explanation
treatment, and at latest follow up 66 weeks post- must be sought which superposes change on an embryo
treatment the scores show no deviation from the pre- before learning takes place and which does not depend
treatment levels. I have not seen another case where the directly on heritable mechanisms. We have previously
sexually orientated method figures totally fail to vary postulated' that there may be hormonally sensitive
in response to treatment. areas in the human fetal brain which 'are critically
We were able to interview both his twin who had a susceptible to circulating levels of male and female
totally discordant early history and later sexual history hormones' (p i69). We therefore turned to the animal
and his mother who confirmed the histories given by literature on sexual dimorphism which is extensive and
both twins. They had been reared together under which by the early I970s had generally concluded that
apparently normal conditions and their monozygocity for the inherent programme of sexual differentiation in
was established beyond doubt. The combined evi- both sexes, man was as female.
dence of the primaries'resistance to treatment, their The presence of androgens during the critical
markedly different histories from the secondary periods of sexual differentiation in animals has been
homosexuals and this pair of discordant monozygotic found to organise both genetic males and females to
twins led my colleagues and myself to begin to think possess masculine reproductive organs,2 masculinise
about an explanation for homosexual behaviour which hepatic steroidogenic enzymes,3 cause tonic (male pat-
would account for learned patterns of homosexual tern) hypothalamic control of gonadotrophic secre-
behaviour occurring in relatively normal people and tion4- and produce male sexual behaviour.7 At that
the existence of those in whom there has never been time it was thought that an absence of either gonad
any heterosexual interest or arousal and who appear during the critical developmental period allowed the
'different'. The monozygotic discordant twins expression of female characteristics which were
appeared to me to disallow a learning theory for the thought to be inborn.8 t
homosexual twin's condition and the heterosexual Experiments by Phoenix et al° showed how a gen-
twin's 'normality' would seem to disallow a genetic etic female could be masculinised by androgens and,
136 Malcolm MacCulloch
paradoxically, by oestrogen. They left unsolved the describe the occasional incidence of male external
problem of why fetal female brins were not mascu- genitalia in girls born to mothers treated prenatally
linised by normal levels of endogenous fetal with male hormones. These females have almost
oestrogen. This problem was resolved by the critical always been raised as boys and have themselves pre-
experiments of Shapiro et all who concluded that ferred to continue in this way even when increased
raised serum progesterone in the female rat neonate ovarian activity at puberty has begun to induce secon-
could function both to cause feminisation ofthe brain dary feminine characteristics. This syndrome is sug-
and as a hormone antagonist to protect the develop- gestive of male brain differentiation in the human
ing female brain from the masculinising effect of female following prenatal exposure to abnormally high
both androgen and oestrogen. levels of male sex hormones that are sufficient to over-
To date there is little direct evidence that the brain is come the normal protective effect of progesterone
sexually dimorphic in humans although there is one against normally occurring amounts of androgen and is
striking experiment in humans that is very closely entirely consistent with our theory of female homosex-
analogous to that of Phoenix et al. 10 Wilkins et al"2 uality.
Androgen/Progesterone mixture produced
by the feto placental Unit
A>P X P>A
Androgen effect Progesterone effect
Male Brain Female Brain
Male Differentiated Brain Female Differentiated Brain
Male Identity Fej e Identity
Male Behaviour Female Behaviour
Fig. 3 Summary ofparts of the mechanism responsible for normal sexual dimorphism in man.
Biological aspects of homosexuality 137
Under production Over production Ant ibody absorpt ion
of androgen of progesterone of androgen
Abnormal A < P ratio
Normal A:P ratio
14 Target cell
Feminised hypothalamic neurone
Fig. 4 Some possible mechanisms which would lead to a female sexual differentiation in a male brain.
A biochemical theory for the aetiology of male and human, hormones control brain differentiation and the
female homosexuality direction of subsequent sexual object choice in adult
The of androgens during critical periods in
presence Co-workers have suggested that the behaviour of
utero organises masculinisation of offspring and their primary male homosexuals has as its essential cause a
absence allows the expression of female characteristics; female differentiated brain. We see this mis-
the limited available evidence in the human male is in differentiation as resulting from the absence of an
support of this concept. Additionally, in animals, brain androgen effect in the hypothalamus during the critical
feminisation itself may in fact be hormonally con- period for brain sex differentiation.
trolled by the in utero conditions. It may be that in the As regards female homosexuals the findings of
138 Malcolm MacCulloch
Shapiro et allI relating to brain feminisation and to the ety at large feels free to take a hostile view if the
protection of the brain from the masculinising effect of behaviour in question is one which has been pro-
both androgens and oestrogens by progesterone pro- scribed. In the case of homosexual behaviour there
vides a new theoretical basis for an explanation of remains much hostility and disapprobation towards
primary lesbianism. We suggest that this behaviour homosexuals even amongst the supposedly more
arises from a male differentiated brain in a genetic enlightened members of society such as doctors,
female. As with male homosexuals, we suggest that lawyers and judges. It seems clear to me that a
primary lesbians could comprise aetiologically biochemical view of the aetiology of primary homo-
heterogenous groups consisting of subjects whose sexuality, if upheld, is bound to lead to a marked
foetal hypothalami were insufficiently feminised change in the attitudes of the public and professions
and/or protected from normal amounts of oestrogen by to homosexuals and to a different view of society by
deficits in progesterone and subjects whose brains were the homosexuals themselves.
masculinised by abnormal amounts of androgen in the
presence of a normal amount of progesterone.
The nature of the in utero defect 'Feldman, M P and MacCulloch, M J (I971). Homosexual
behaviour: therapy and assessment. In: H J Eysenck
Bidlingmaier et al'3 in a very striking experiment have (Ed). Experimental psychology, vol I4. Oxford,
described how an immune reaction to testosterone in Pergamon Press. pp 20-30, 55-64, 95-I05.
the pregnant rabbit could alter the sexual development 2Jost, A (1953). Recent progress in hormone research, 8,
of male offsprings. They produced pregnant female 319-4I3.
rabbits whose serum contained antibodies capable of 3Demoor, P (I968). Endocrinology, 82, 480-492.
neutralising the biological activity of testosterone and 4Pfeiffer, C A (1936). American journal of anatomy, 58,
whose male offsprings were shown to have elevated 195-225.
serum testosterone levels and a development of their 5Wilson, J G, Hamilton, J B and Young, W C (i94i). Endoc-
rinology, 29, 784-789.
reproductive system identical to that in a normal 6Barraclough, C A and Gorski, R A (I961 ). Endocrinology, 68,
female rabbit. This experiment demonstrates that tes- 68-79.
tosterone antibodies can pass the placental barrier and 7Grady, K L, Phoenix, C H and Young, W C (i965).Journal
that developing sex organs can be deprived ofthe effect ofcomparative and physiological psychology, 59, 176-i82.
of testosterone (despite a feedback-induced increase in 8Grady, K L and Phoenix, C H (I963). American zoologist, 3,
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"Shapiro, B H, Goldman, A S, Bongiouanni, A M and
Conclusion Marino, J M (0976b). Nature, 264, 795-796.
"Wilkins, L, Jones, H W, Holman, G H and Stempeel, R S
Where an identifiable enduring pattern of behaviour is (I958). Journal of clinical endocrinology, x8, 559-585.
known to arise predominantly from environmental fac- 3Bidlingmaier, F, Knorr, D and Neumann, F (I977).
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