Which studies are they? Surely if homosexuality were genetic then both twins would be gay, after all they have identical genes. Is this the study you were referring to?
"Briefly, a Northwestern University study by J. Michael Bailey and Richard Pillard of 56 sets of identical twins in which at least one twin was a homosexual, discovered that in 52% of the cases, the other twin was homosexual also. Among 54 sets of fraternal twins in which one was homosexual, the other was homosexual 22% of the time. They also studied adoptive brothers and there found an 11 percent correlation.
The press, in reporting the study, immediately announced that it "implies a genetic basis for sexual orientation." A deeper look at the results reveals no basis for such a conclusion, and in fact, to the contrary, opposite conclusions are easily justified. Assuming there are no major flaws in the study, it can lead to three very exciting implications.
First, the study seems to rule out the possibility that homosexuality is caused entirely by genetic causes. Identical twins are genetically exactly the same, so the correlation would have to be 100%, not 52%, if the homosexuality were entirely a genetic condition.
Second, the high correlation of homosexuality among fraternal twins makes a powerful case for environmental causes. Fraternal twins are no more alike genetically than any two brothers who are born several years apart, and yet there is a much higher homosexual correlation among fraternal twins than among other sets of brothers. If fraternal twins don't share a common genetic make-up, then what is it they do share that makes this correlation so much higher? What they share is a nearly identical environment. They are almost the same in birth order; they arrive at the same time in their parents' lives; they grow up in the exact same circumstances as regards their family's life situation. Their parents are at the same stage in their own lives with respect to economics, marital stability, spiritual growth, divorce, lifestyle, etc. The fraternal twins are growing up in the same home, as similar an environment as is possible for two boys to experience. More at the link. "
