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In search of
Part fourteen In a series of articles
Yes, No and Maybe:
the genetic basis of
homosexuality
by Dr. Donald W. Smith, PhD.
Although it has been thought by many that
homosexual behavior was determined at least in
part by genes, evidence for this theory is highly
contradictory. The idea that “breeding” or genetics
resulted in homosexuality is based in part on the
keen observations of common people.
In folklore, there is the notion of the “late-life”
baby, the child bom to a mother who was soon to
go into menopause. Late-life babies were supposed
to suffer from all sorts of problems including over
sensitivity, emotional instability and often non-
conforming sexuality. The idea of the higher sus
ceptibility of late-life babies to physical, tempera
mental and intellectual problems was in part sup
ported by fact. Unlike males, whose sperm cells are
being constantly renewed, a female is bom with all
of the egg cells she will ever produce. Through out
her life, she will be exposed to radiation and toxic,
chemicals which can damage the egg cells. Conse
quently, children bom to older women are more
likely to have chromosomal changes resulting in
birth defects and mental retardation. For example,
women over thirty-five have a much greater chance
of giving birth to a child with Down’s syndrome.
Down’s syndrome is the result of an egg developing
with an extra twenty-third chromosome. In addi
tion, the “late-life” child was often either the last
child in a string of siblings or the long awaited only
child. The “baby” or only child is often treated
differently by the parents and other family mem
bers. Such different treatment is likely to influence
the later behavior or temperament of child.
In response to the idea of the late-life baby,
scientists undertook two lines of research seeking
biological causes of homosexual behavior.
The first line of research that grew out of the
idea of the late-life baby, were studies of the
relationship between birth order and sexual orien
tation. Birth order simply means the ranking indi
vidual by the date of their birth relative to the dates
of birth of their siblings, i.e., first, second, third, etc.
In 1962, E. Slater reported the finding of a study of
the birth order of 401 homosexual men. He found
that homosexual men tended to be bom later in a
set of siblings than would be expected by chance.
The tendency for homosexual men to be bom later
in sibling groups has been found to hold up in
subsequent studies as late as 1992. In addition,
homosexual males tend to have more brothers than
would be expected by chance alone. Homosexual
females however have shown no marked tendency
to bomlater in a series of siblings. The meaning of
these findings is unclear at best. On explanation
was the “aging egg/damaged chromosome” which
was quickly put to the test.
The second line of research involved examin
ing the chromosomes of known homosexuals and
comparing then) with the chromosomes of hetero
sexuals. These studies revealed that there were no
consistent differences in the grqss structure and
number of the chromosomes of heterosexuals and
homosexuals. Indeed, the idea that homosexual
male children were bom to older mothers has not
been supported in actual research. One might
think that this would be the end of the story on
chromosomes and sexual orientation. It,would be
if it were not for existence of people who are
biologically hermaphrodites.
Most people whether they are heterosexual,
homosexual or bisexual have a
chromosomal makeup of 46 chromosomes. The X
chromosome is called the female chromosome and
contains the genes for producing a biological fe
male or a biological male. However, the X chromo
some does not contain the genes that trigger the
activation of the testes to produce male hormones.
In normal females, the 46 chromosomes contain
two X chromosomes and no Y chromosomes
(46 XX). The Y chromosome contains the genes for
triggering the activation of testicular tissues to
produce male hormones. In normal males, the 46
chromosomes include X chromosome and one Y
chromosome (46,XY). There are however indi
viduals who have different numbers of sex chro
me sc mes and these individual seem to have differ
ing propensities for homosexual behavior or
transsexualism.
A very small number of individuals are born
with only 45 chromosomes, due to the presence of
only one X chromosome (45,X). This condition is
cal^fl Turner’s syndrome. Individual with Turner’s
syndrome have external female genitalia. How
ever, internally they do not have ovaries. Conse
quently, they must be treated with female hor
mones to go through puberty. No women with
Turner’s Syndrome have been reported to also be
lesbian. Why the presence of Turner’s syndrome
seems to be incompatible with lesbianism is not
known. One hypothesis is that the failure to form
ovaries results in the failure of the body to produce
sufficient female hormones but also the failure to
produce any of the small amounts of male hor
mones found in normal females. As the result of the
total absence of male hormones while the child’s
brain is developing, the brain is totally feminized.
Consequently, the (45,X) individual, while not
having a high sex drive, is only attracted to men.
There are no male counterparts to female with
Turner’s syndrome. The chromosomal makeup of
(45,Y) appears to be universally fatal. The reason
for this is apparently that the X chromosome
contain necessary genetic information for the for
mation of a healthy body either male or female,
whereas the Y chromosome appears to only con
tain the genetic trigger to turn on the testes (and in
a few cases a gene for hairy ears!).
Adding extra sex chromosomes does not to
appear to have much effect on female genetic
females (all X chromosomes and no Y chromo
somes). Females with (47,XXX) and (47, XXXX)
have been identified. The sexual behavior differs
not at all from females with (46,XX) chromosomal
patterns. However adding one or more extra X or
Y chromosomes to genetic males (any individual
with a Ychromosome) has profound consequences
physically and may have some impact psychologi
cally.
About one male out of 500 is bom with an
extra X chromosome (47.XXY). This condition is
called Kleinfelder’s syndrome. (47,XXY) male have
normal appearing external male genitalia, however
their testes are small and may produce low levels of
male hormones. Even when the (47,XXY) indi
vidual has normal level of male hormones in his
blood stream, the presence of the extra X chromo
some interferes with the ability various organs to
respond to the presence of the hormones. Conse
quently, (47,XXY) men are usually sterile. At the
present time, there is insufficient data to generalize
about the impact of the extra X chromosome on
sexual orientation, except to note that (47.XXY)
men tend to have low sex drives. However, one
interesting piece of anecdote evidence indicates
that (47.XXY) men are over represented among
transsexuals. If this observation is true, the ten
dency to transsexuality may not be purely a bio
logical one. Males with Kleinfelder’s syndrome