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From: john@anasaz.UUCP (John Moore)
Newsgroups: sci.med,sci.bio,sci.psychology
Subject: Re: The persistance of homosexuality in a gene pool
Message-ID: <2801@anasaz.UUCP>
Date: 30 Jul 90 03:36:05 GMT
References: <1990Jul23.022511.28161@mtcchi.uucp> <11095@netcom.UUCP> <10615@cs.utexas.edu> <1990Jul29.050038.24791@wolves.uucp> <32214@cup.portal.com>
Reply-To: john@anasaz.UUCP (John Moore)
Followup-To: sci.med
Organization: Anasazi, Inc.
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In article <32214@cup.portal.com> geoffp@cup.portal.com (Geoffrey Scott Puterbaugh) writes:
]     The true concordance rate is not yet known.  If it
]should prove to be as high as 80 or 90 per cent, then it
]would probably be enough to settle the nature/nurture
]debate.  This conclusion may seem startling, since many
]people believe that even one discordant MZ pair must
]disprove the entire genetic case.  Identical twins have
]identical genes: if they are discordant in regard to
]homosexuality, then clearly something else is at work.
]
]     The error in such reasoning lies in a faulty
]assumption, which is pointed out by two authors, Money and
]Klintworth: we already know that MZ twins are not
]necessarily identical in their gene complements.  This has
]appeared in cases of MZ twins discordant for Down's syndrome
]and Turner's syndrome.  Slight differences in the genotype
]can and do occur in ways which we are trying to determine
](even Gregor Mendel has been rightly faulted for doctoring
]his pea studies to obtain exact ratios, where nature was not
]quite so exact).  And this very slight difference may well
]be the mechanism which makes the concordance rate for male
]homosexuality less than 100%.

Thank you for the excellent, factual posting.  Another possibility 
for the discordance is that there are different
kinds of homosexual personalities, with different causes.
There might be a genetic homosexual persuasion, and there might also
be an environmental one. Is there any research that seeks to
separate these two groups, and possibly differentiate them
on grounds other than sexual preference (such as aesthetic
ability, handedness, etc)?

Another, more general question about twin studies: is the
tendency to have twins hereditary? If so, does this mean that
some twin studies might be biased due to traits linked to
the twinning trait?
-- 
John Moore HAM:NJ7E/CAP:T-Bird 381 {ames!ncar!noao!asuvax,mcdphx}!anasaz!john 
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