Orientation and older brothers
Ray Blanchard, adjunct professor in the Department of Psychiatry at the University of Toronto, is the ninth speaker in MSU’s semester-long series, “Whom You Love: the biology of sexual orientation,” which aims to demonstrate that homosexuality is a natural occurrence in humans. His speech is called “How and Why Do Older Brothers Influence Sexual Orientation in Men?” based on his scientific theory called “the fraternal birth order effect,” which links the number of older brothers a man has with an increased likelihood of his being gay.
What causes the fraternal birth order effect?
The theory that I and my colleagues have advanced is the “maternal immune hypothesis,” which proposes the progressive immunization of some mothers to male-specific antigens by each succeeding male fetus. The probability — or strength — of maternal immunization increases with each male fetus; therefore, the probability of homosexuality increases with each older brother.
I estimate that the proportion of homosexual men who owe their sexual orientation to fraternal birth order is probably around 15 to 30 percent.
How can you test this theory?
I am a co-investigator in a study currently being conducted that is testing the maternal immune hypothesis by drawing blood samples from mothers of gay men and mothers of straight men. However, antibody concentrations generally decline after exposure to an antigen is removed. Thus, a mother might have had a high concentration of anti-male antibodies when she was pregnant with her future gay son, but have no detectable level of antibodies when she agrees to testing 20 or 30 years later because her son is grown and known to her as gay. There are ways around this, using memory T-cells or memory B-calls, but these are complex and difficult procedures.
What inspired you to follow this type of research?
I was about 33 years old before it ever
crossed my mind to do sex research. My first permanent, full-time job
after my postdoctoral work was in a prison in a suburb of Toronto where I
met Kurt Freund, one of the most important researchers in human
sexuality in the latter half of the 20th century. He was a rather
As for my research on birth order and homosexuality in men, I stumbled into it.
I recognized from early on that a progressively strong or progressively probable maternal immune reaction could explain why older brothers increase the probability of homosexuality in later-born males. However, the notion that the hypothesized maternal antibodies would be directed at testosterone is extremely improbable, and I subsequently looked for other fetal substances as possible instigators and targets of a maternal immune response.
What do you think this speaker series could do for the public opinion of homosexuality?
There is some survey research to suggest that people are more accepting of homosexuality if they believe that it is both biologically determined and immutable. I think it is a good and desirable thing if this lecture series has the effect of increasing public acceptance of homosexuality.
I need to add more to that statement, however. I would be suspicious of any biological research conducted for the express purpose of increasing public acceptance of homosexuality. I think there is a danger of behavioral researchers losing their objectivity if they think they are acting in the service of some higher social good. There are researchers who, consciously or unconsciously, believe that research is the continuation of politics by other means. Fortunately, I know almost every speaker in this series personally, and I do not think that any of them is fundamentally motivated by extra-scientific considerations.
“How and Why Do Older Brothers Influence Sexual Orientation in Men?”
Wells Hall room 115B