Birth Order
Recent studies found an increased chance of homosexuality in men whose mothers previously carried to term many male children. This effect is nullified if the man is left-handed.
Known as the ‘‘fraternal birth order’’ (FBO) effect, this theory has been backed up by strong evidence of its prenatal origin, although no evidence thus far has linked it to an exact prenatal mechanism. However, research suggests that this may be of immunological origin, caused by a maternal immune reaction against a substance crucial to male fetal development during pregnancy, which becomes increasingly likely after every male gestation. As a result of this immune effect, alterations in later-born males' prenatal development have been thought to occur. This process, known as the maternal immunization hypothesis (MIH), would begin when cells from a male fetus enter the mother's circulation during pregnancy or while giving birth. These Y-linked proteins would not be recognized in the mother's immune system due to the fact that she is female, causing her to develop antibodies which would travel through the placental barrier into the fetal compartment. From here, the anti-male bodies would then cross the blood/brain barrier (BBB) of the developing fetal brain, altering sex-dimorphic brain structures relative to sexual orientation, causing the exposed son to be more attracted to men over women.
Read more about this topic: Sexual Orientation, Measuring Sexual Orientation
Famous quotes containing the words birth and/or order:
“A small boy puts his hand on the wall, and looks down intently as he wriggles his toes. The birth of thought?”
—Mason Cooley (b. 1927)
“Women do not have to sacrifice personhood if they are mothers. They do not have to sacrifice motherhood in order to be persons. Liberation was meant to expand women’s opportunities, not to limit them. The self-esteem that has been found in new pursuits can also be found in mothering.”
—Elaine Heffner (20th century)