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Study 17 (continued) into the cause(s) of
sexual orientation: Nature vs. Nurture.

Part 2 of three parts

A small-scale study appears to
show that epigenetics working
before birth is a (or perhaps the
only) cause of homosexuality:

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This topic is continued from an earlier essay

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Lady Gaga's 2011 hit song "Baby, I was born this way" may have turned out to be accurate!

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2012-DEC: A new possible explanation for the cause of homosexuality is unveiled (Cont'd):

The National Institute for Mathematical and Biological Synthesis (NIMBioS) at the University of Tennessee defines "homosexuality" to include same-sex sexual attraction, and thus include the full range of homosexual and bisexual orientations.

Some researchers suspected that same-sex attraction may be caused or influenced by epigenetic markers. These are:

"... chemical changes to DNA that affect how genes are expressed, but not the information they contain." 5

At that time, their concept of the influence of epi-marks as the cause of homosexuality was untested. However, the idea neatly fits with many observations and studies of sexual orientation including:

  • The perseverance of homosexuality in spite of evolutionary forces which might normally have been expected to have either eradicated it over time, or have increased its prevalence significantly,

  • The 16 or so other studies of homosexuality described in this section that all apparently show that sexual orientation is set up before birth and discovered by the individual later in life, and

  • The inability of other researchers to definitively find a gay gene or group of genes that cause a person to have a homosexual orientation, in spite of massive efforts by multiple research groups spread over decades. The largest study examined 409 pairs of gay brothers. It found that gay males shared similarities in their X chromosome and chromosome 83. But they are still searching within these chromosomes for the specific genes or other components that contribute to sexual orientation.

William Rice, the study’s lead author, said:

"We've found a story that looks really good.This can be tested and proven within six months. It's easy to test. If it's a bad idea, we can throw it away in short order." 1

This time interval appears to have been slightly over-optimistic.

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According to Nathan Bailey, an evolutionary biologist at the University of St Andrews in Scotland, who was not involved in the research:

"The study provides a very interesting, but as yet untested, genetic mechanism for the evolutionary maintenance of human homosexuality. We are going to have to wait until more evidence is in, but I do think it would be exciting to know whether epi-marks contribute to the expression of sexual orientation in humans." 2

Reaction to this new concept was mixed:

  • Some religious conservatives are unhappy because the tentative results from the epigenetics study conflict with their belief that homosexual orientation is caused by family dysfunction and/or childhood sexual molestation. If the epi-mark concept is confirmed, it would prove a pre-natal cause for homosexuality with a hereditary component. It would also let parents "off the hook" for causing homosexuality in their child.

  • Some in the lesbian, gay and bisexual community are unhappy because they feel that a scientific investigation is not needed to justify who they are. Some are alarmed because the study might lead to a test for homosexuality, perhaps even one that could be performed on a fetus. That might motivate some parents to choose to terminate the pregnancy. It might also be developed into a homosexual and bisexual screening test for children and adults.

  • Some in the scientific community have expressed strong interest in conducting experiments that will test the concept and show whether it is valid. 3

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2015-OCT-08: An epigenetic test has been developed that predicts homosexual orientation in most cases:

Virginia Hughes, Science Editor for BuzzFeed News wrote:

"By analyzing five 'epigenetic' tags -- chemicals that latch onto DNA and help turn genes on or off -- the algorithm can reportedly predict a man’s sexual orientation with 67% accuracy, according to Tuck Ngun, who led the work as a postdoctoral fellow at UCLA."

T.C. Ngun is himself gay and was motivated by his own sexual orientation to undertake the study. He said:

"I was kind of curious about myself — why I turned out like I did." 4

He sensed that he was gay at a young age -- when he was 5 years old. He said:

"I didn’t necessarily have a word for it at the time, but I knew --- that I was not quite the same as my other guy friends."

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This study involved sampling the saliva of 37 pairs of male twins in which one was gay and the other straight, as well as ten pairs of male twins who were both gay. Their DNA was extracted from the saliva and analyzed. The team looked at 400,000 methylation marks on the samples and found five that were different between the gay and straight twins.

Ngun said:

"Those five seem to be the most informative. They seem to be able to best tell you whether someone is likely to be gay or straight."

Their test predicted a straight man's orientation with about 50% accuracy, and a gay man's orientation with an accuracy of about 83%.

Adding other epi-marks in addition to the five methylated ones used in this stud would probably increase the test's accuracy.

Peng Jin, a professor of human genetics at Emory University, said:

"The sample size is very small." 4

J. Michael Bailey, a professor of psychology at Northwestern University, said:

"All predictive models need replication with larger samples, and this one certainly does."

Alan Sanders, a psychiatric geneticist at the NorthShore Research Institute in Evanston, IL said:

"I think it certainly has the potential to add some knowledge."5

Ngun commented that the findings of the study that he led:

"... became a little bit troubling to me, what I was actually doing. Having done this now, I could sort of foresee a not-so-happy outcome."

A report on the study has been published. The abstract states in part:

"To our knowledge, this is the first example of a biomarker-based predictive model for sexual orientation." 6

He has left this field of research and is planning to do future unrelated research in industry. He may be concerned that further research might lead to a reliable test of homosexuality orientation that might be useable on fetuses as well as newborns, children, and adults. Some readers of the article in BuzzFeed News posted comments suggesting that a screening test might be developed that could be used to detect homosexuality in adults. Some countries -- primarily in Africa and the Middle East -- still consider same-gender sexual behavior to be a criminal act. This test could then be used to detect persons with a homosexual orientation detect, who could be monitored and charged if they are sexually active.

There are 76 countries worldwide where same-gender sexual behavior is a crime. Amnesty International reports that homosexuality is illegal in 37 countries in Africa alone; in four of these, it carries the death penalty. 7 The death penalty is also a possibility in some predominately Muslim countries in the Middle East and Asia.

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This topic is continued in the next essay.

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References used:

The following information sources were used to prepare and update the above essay. The hyperlinks are not necessarily still active today.

  1. Christine Roberts, "Scientists uncover possible source of homosexuality," New York Daily News, 2012-DEC-12, at:
  2. Randy Astaiza, "NEW THEORY: The Gay Trait Is Passed Down From Parent To Child," Business Insider, 2012-DEC-14, at:
  3. Laura Blue, "New Insight into the (Epi)Genetic Roots of Homosexuality, Time, 2012-DEC-13, at:
  4. Virginia Hughes, "Epigenetic Test Can Predict Homosexuality, Controversial Study Claims," BuzzFeed News, 2015-OCT-08, at:
  5. Sara Reardon, "Epigenetic 'tags' linked to homosexuality in men," Nature magazine, 2015-OCT-08, at:
  6. T.C. Ngun et al., "PgmNr 95: A novel predictive model of sexual orientation using epigenetic markers," Event Pilot, undated, at:
  7. "Mapping anti-gay laws in Africa," Amnesty International UK, 2015-JUL-22, at:

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Copyright © 2016 and 2017 by Ontario Consultants on Religious Tolerance
Latest update: 2017-JUN-19
Author: B.A. Robinson

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