From: chromos@athena.mit.edu (Wesley Y Miyazaki)
Subject: Re: Heredity of homosexuality
Organization: Massachusetts Institute of Technology
Date: Fri, 28 Aug 1992 22:50:02 GMT

In article <78584@ut-emx.uucp> zeus@ccwf.cc.utexas.edu (Mark Gansle) writes:
>
>I think what Jeff was saying was that a gene for homosexuality must
>necessarily be evolutionarily disadvantageous.  Women and men who had no
>desire to have sex with members of the opposite sex would be unable to
>bear children and so unable to pass the gene (or genes) for
>homosexuality on to offspring.  Perhaps, one might argue, that the genes
>for sexuality are extremely touchy and the slightest mutation can change
>heterosexuality into homosexuality.  This may be possible, but I think
>it is an idea offensive to most.
>
>There is in fact little evidence to support the idea that homosexuality
>is hereditary ("nature made me this way").  The best anyone can come up
>with is a statistical *correlation* between the size of a gland in the
>brain and homosexuality.  There is no evidence for causation in any
>form.  Also, a twins study with about 50% match-up of homosexual twins
>is often cited as evidence, but of course that fifty percent is not a
>very strong indicator of heredity.  Even if we assume heredity, we're
>left with the conclusion that a large percentage were anle to *choose*
>not to be homosexual.
>
>And therein lies the difference between racism and discrimination
>against homosexuals.  One is proven to be hereditary and so cannot be
>changed and is not a subject for ridicule.  The other seems very likely
>to be a personal choice, and like all personal choices, is subject to
>judgment. 

Yuck. As a geneticist-soon-to-be, I hate it when people try to use
pseudo-genetics to 'prove' a point. 

There are many flaws with your argument, Mr. Gansle. Number one, you
cannot argue allele frequencies in a population when you are talking
about a phenotype which can be hidden or obscured. In common parlance,
this would be the "closet." It is easy to see therefore that while
homosexual men and women through the ages may have had no _desire_ for
members of the opposite sex, they could still sire or bear children
(homosexuality is not = sterility). Thus the putative gene conferring
homosexuality could easily be passed on in heterozygous fashion
through the generations (i.e., "carriers"). 

Number two, in spite of the lack of any hard data regarding a genetic
basis for homosexuality, you conclude that a sexual orientation gene
must be easily mutable to a homosexual allele, and that this idea
would be "offensive to most." I had no idea that Mother Nature
conducted public-opinion polls about how she was doing. The fact is,
there is nothing that one can say a priori about the nature about the
mutability of any putative orientation gene (save that if it exists,
it probably mutates to a recessive form). Thus such a possibility
cannot be deemed "offensive." 

Number three, the hypothalamic nucleus data of LeVay was never touted
to be a genetic argument for homosexuality but a biological
correlation. I smell a straw man. Moreover, it was noted that cause or
effect was not determinable from the data. 

Number four, the fact that there was only a 50% correlation of
homosexuality among identical twins is not sufficient evidence to
conclude that the data is "not a very strong indicator of heredity."
One must take into account the possibility of incomplete penetrance of
the phenotype, an occurrence which is not uncommon in human genetic
traits and which can confound analysis in human pedigrees. That is,
even though individuals may be genetically identical, the expression
of the phenotype (homosexuality in this case) may be variable. Without
knowing the extent of such a phenomenon, we are unable to conclude
anything about the percentage of individuals able to "choose," as you
suggest is possible. 

In summary, you are correct when you say that there is no firm data
suggesting a genetic basis for homosexuality, BUT this absence of data
is not now evidence suggesting that there is NOT a genetic basis. The
paucity of genetic data (or the uninterpretability of it) does not
make the "personal choice" model more attractive. It simply indicates
that this avenue of research is not yet exhausted (or even yet begun). You
can't have it both ways, Mr. Gansle. On the one hand, you dismiss the
data suggestive of a genetic basis as not worthy of looking at, but
then you go on to use the data to argue *your own point*. 

In the absence of any good data either way, I withold judgment. It
seems that you think differently, Mr. Gansle. In the absence of data,
you feel that your position is now "proven" and feel that is now your
God-given right to judge those who have made a "personal choice."
Judge not!! Hmmm, I wonder if it were ever written in the Bible:
"Judge not, unless you can prove it isn't hereditary"!!

wes

P.S. At what age did YOU choose to be a heterosexual?