Fundamentalists and other Evangelical Christians generally attribute the
cause of homosexuality to some element in the person's upbringing. They expected this for at least two reasons:
Most believe that God is intimately involved in every event in one's
life. This naturally includes each conception. If homosexuality were
genetic, then God must intentionally create about one in twenty pre-embryos as gay or lesbian. However, since
religious conservatives generally believe that God hates homosexual behavior, it makes no sense that he would intentionally create homosexuals.
If homosexuality is genetic, then it would probably be impossible to
change. But many interpret 1 Corinthians 6 as showing that change is
possible. Thus, they reason that homosexuality cannot be genetic.
Conservative Christian writers seem to have copied their beliefs on the identical twin study from
fellow Christians rather than researching scientific literature. Some
examples of their writing are listed below.
Comments from Focus on the Family publications:
We start with three quotations from Focus on the Family -- a fundamentalist Christian advocacy group that has taken a particularly leading role -- particularly in the past -- to oppose equal rights for lesbians, gays, bisexuals, transgender persons and transsexuals:
In a Focus on the Family publication. author Mike Haley wrote:
"So, if the study showed that homosexuality in [identical] twins was purely genetic, then both
of the twins would have been homosexual 100% of the time." 1
James Dobson, founder of Focus on the Family, wrote in a 2002-JUN family
newsletter that if homosexuality is genetically determined:
"...since identical twins share the same chromosomal pattern, or DNA, the genetic contributions are exactly the same
within each of the pairs. therefore, if one twin is 'born' homosexual then the other should inevitably have that characteristic too." 2
James Dobson also wrote in his Family
Reference Guide:
"...if it were specifically a genetic influence,
then all identical twins would either have it or not have it. Their
genes are exact duplicates, so anything deriving specifically from
their DNA would express itself identically in the two individuals."3
These statements are particularly unexpected because James Dobson -- the founder of Focus on the Family and its leader at the time these statements were published -- has a degree in child psychology. Thus, one would expect that he is very familiar with the workings of genes. Genetics would have formed a major part of his academic courses. In particular, one would expect that he would know that alleles (variations) of various genes have a penetrance (effectiveness) factor that is often much less than 100%.
Still, there is no evidence that he is aware of his error or that he is intentionally trying to deceive his audience. His academic training occurred many decades in the past; he may have simply forgotten how genes work.
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Comments from other conservative Christian groups about identical twin studies:
Kerby Anderson wrote an article for Probe Ministries. He
wrote:
"...why aren't nearly all identical twin brothers
of homosexuals also homosexual? In other words, if biology is
determinative, why are nearly half the identical twins not
homosexual?" 4
Daniel R. Heimbach wrote:
"Identical twins have identical
constitutions, but one may become homosexual while the other is firmly
heterosexual." 5
Sue Bohlin wrote:
"Others ask, What about the identical twins where only one is
gay? If sexual orientation is genetic, how do you explain the twins
with such divergent orientations?" 6
N. E. Whitehead wrote an article for the National Association
for Research and Therapy of Homosexuality (NARTH). They teach
that homosexuality is a disordered state that is abnormal, unnatural,
and changeable via reparative therapy. He
wrote:
"If homosexuality was a biological condition produced
inescapably by the genes (e.g. eye color), then if one identical twin
was homosexual, in 100% of the cases his brother would be too." 7
Rich Nathan has authored a fascinating book in which he discusses
individuals who are (in his opinion) rejected by evangelicals :
postmodernists, feminists, gays, lesbians, New Agers and religious
liberals. He writes:
"If biology (and not family structure or other
environmental causes) really determined a person's sexual orientation,
then identical twins ought to have a 100 percent concordance rate,
since they are genetically identical. The 52 percent concordance rate
actually argues against the notion of biological determinism and
suggests other factors have influenced sexual orientation." 8
Dallin H. Oaks, a member of the Quorum of the Twelve Apostles of
the LDS (Mormon) church wrote
a definitive article in the magazine Ensign, titled "Same Gender Attraction." He wrote:
"A study of fifty-six pairs of identical male twins in which one twin
classified himself as "gay" reported that 52 percent of the co-twins
also classified themselves as gay. 9 A similar study of female identical twins yielded approximately the same
proportion of co-twins who classified themselves as gay (thirty-four of
seventy one pairs 48 percent).10 If these studies show some inherited influence on whatever causes a man
or woman to classify himself or herself as homosexual or lesbian, it is
clear that this influence is not determinative. As a prominent scientist
observed, "Even the identical twin of a gay man has a 50 percent or more
chance of being heterosexual -- even though he has the exact same genes
and is reared by the same parents." 11
Joe Dallas is an evangelical author who has written extensively about homosexuality. In the book titled "The Complete Christian Guide to Understanding Homosexuality" that he wrote with Nancy Heche, they discuss an identical twin study, writing:
"Pillard and Bailey' suggested that the higher incidence of shared homosexuality among identical twins meant that homosexuality was genetic in origin. But this suggestion, like LeVay's, had its problems.
Pillard and Bailey's findings actually indicate that something besides genes must account for homosexuality. If 48 percent of identical twins who are closely linked genetically, do not share the same sexual orientation, then genetics alone cannot account for homosexuality." 12
Daniel R. Heimbach, "Notes for The Bible in the Moral War
over the Rejection of Homosexuality by the Military Services: A View from Inside
the Pentagon," PREMISE, Volume II, Number 7, 1995-AUG-27, Page 10.
Online at: http://capo.org/premise/95/august/
J. M. Bailey & R. C. Pillard, "A Genetic Study of Male Sexual Orientation,"
Archives of General Psychiatry 48 (1991): Pages 1089 to 1096.
J. M. Bailey & R. C. Pillard, et al., "Heritable Factors Influence Sexual
Orientation in Women," Archives of General Psychiatry 50 (1993), Page 217 to
223.
Dallin H. Oaks, "Same-gender attraction," Ensign, 1995-OCT, Pages 7 to 14.
Joe Dallas & Nancy Heche, "The Complete Christian Guide to Understanding Homosexuality: A biblical and compassionate response to same-sex attraction," Harvest House Publishers, (2010), Page 183. 
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