|Sexual orientation of men predetermined
[ 2006-07-03 09:00 ]
Liberation"，installed in Christopher Park, is a life-size bronze
sculpture by George Segal that depicts two same-sex couples, female
A man's sexual
appears to be determined in the womb, a new study suggests.
Past research by Dr. Anthony F. Bogaert of Brock University in Ontario
and colleagues has shown that the more older brothers a man has, the more
likely he is to be gay. But it has not been clear if this is a prenatal
effect or a psychosocial effect, related to growing up with older male
To investigate, Bogaert studied 944 gay and straight men, including several who were
raised with adopted, half- or step-siblings or were themselves adopted. He
reasoned that if the relationship between having older male siblings and
homosexuality was due to family environment, it would be seen whether or
not a man's older brothers were biological or adopted.
Bogaert found that the link between having older brothers and
homosexuality was present only if the siblings were biologically related
-- this relationship was seen between biological brothers who were not
raised together. The amount of time that a man was reared with older
brothers had no association with sexual orientation.
"These results support a prenatal origin to sexual orientation
development in men and indicate that the fraternal birth-order effect is
probably the result of a maternal 'memory' for male gestations or births,"
Bogaert writes in his report in PNAS.
A woman's body may see a male fetus as "foreign," Bogaert explains, and
her immune response to subsequent male fetuses may grow progressively
"If this immune theory were correct, then the link between the mother's
immune reaction and the child's future sexual orientation would probably
be some effect of maternal anti-male antibodies on the sexual
differentiation of the brain," he suggests.
sexual orientation: 性取向
related by blood（有血亲关系的）；例如：the child's biological parents（孩子们的亲父母）