D.F. Swaab

When a mother is fearful during pregnancy, she can permanently activate her baby’s stress axis, thus increasing the risk of phobia, impulsiveness, ADHD, and depression later in life.

Brain cells are created with incredible rapidity in the womb and shortly after birth, and this process continues, somewhat more slowly, until around the fourth year of life. Brain maturation goes on much longer; in the case of the prefrontal cortex, it continues right up to the age of twenty-five.

Alfred Kinsey didn’t attract any notice when he published his doctoral thesis on gall wasps. But in 1948, when he produced the report Sexual Behavior in the Human Male and then, five years later, Sexual Behavior in the Human Female, he became a celebrity. He devised the “Kinsey scale,” which went from 0 to 6, 0 signifying exclusively heterosexual and 6 exclusively homosexual. Being bisexual, he himself would have been classified as a “Kinsey 3.”
A person’s position on the scale is determined in the womb by his or her genetic background and the effects of hormones and other substances on the developing brain. Studies of twins and families show that sexual orientation is 50 percent genetically determined, but the genes in question haven’t yet been identified.