First: If one twin is gay, what's the likelihood of the other being gay?
Well, the most widely used numbers are cited from a 1991 study by Northwestern University psychologist Michael Bailey and psychiatrist Richard Pillard of Boston University School of Medicine in which identical and fraternal twins were studied. At least one twin in each pair was gay. The study found that 52 percent of the identical twins were both gay as opposed to only 22 percent for fraternal twins. In other words, there is a 52 percent chance that if one identical twin is gay, both are; and a 22 percent chance both fraternal twins are gay if one is gay.
Second: Does this prove that homosexuality is genetic and people are born gay?
The data collected about the identical twins provides the most insight since their genetic makeup is more closely linked. Interestingly enough, the "50/50 chance" findings have been used to support both sides of the nature vs. nurture debate. Some argue that since 52 percent of near genetically identical twins are both gay if one is gay, then homosexuality must be genetic. Opponents to the "born gay" theory cite the remaining 48 percent as support for their claim that genetics alone don't account for homosexuality. The answer will continue to be elusive as the ongoing "born or made" gay debate continues.
Other Suggested Readings:
- More on the Nature vs. Nurture Debate