Is homosexuality due to genetics or social influence? This has been one of the hotest debates in science and medicine over the last two decades. The fraternal birth order theory was developed after numerous studies supported evidence that the more older male siblings a boy has the more likely he is to be gay or a homosexual.
There are many who object to this theory. So to test the theory researchers in Canada enrolled more than 1,000 men into a study and analyzed birth order, number of male siblings, social influence, and whether or not they were homosexual. They also accounted for biological and non-biological siblings. They wanted to determine if the fraternal birth order effect was genetic or psychosocial in nature.
The results supported a genetic fraternal birth order effect. They found that men who had the most older biological male siblings were most likely to be be homosexual. This effect was positive for males who did not have any relationship with biological siblings, did not live in the same home, and was regardless of time spent with siblings or father.
As well men who lived with many older brothers that were not biologically related did not have an increased likelihood of being homosexual. Proving that the effect is not psychosocial in nature.
The study suggests a prenatal or genetic origin for male homosexuality. The authors suggest that there may be an immunological response to the male fetus in the mother that builds strength with each subsequent male pregnancy. The greater the immune response, the more effect on the developing male, which may cause changes to genes or brain centers responsible for sexual orientation.
Posted by Dr. Christina Gutierrez on June 30, 2006 07:44 PM
