Gay AND Straight Identical Twins: National Geographic Discusses Possible Bases For Orientation

Timothy Kincaid:

Sexual orientation is genetic… but not fully genetic.

Each person has about a 4-6% chance of being same-sex attracted. If, however, one has a twin brother that’s gay, the odds increase to about 12%. Make it an identical twin and you have a 50/50 chance that you too will be gay.

Anti-gay activists irrationally declare that this proves that “there is no gay gene.” In a sense they are correct, if orientation were entirely determined by purely genetic composition, then identical twins (who have the same genes) would always have the same orientation.

But the increase in odd with the increase in genetic similarity does show that genes play a part, and a big part. Which leaves the question, how does one twin end up gay and the other straight? The answer may be in how epigenetics triggers genes and can cause identical genes to respond differently.

In the following National Geographic video, the narrator discusses what might cause identical twins to have non-identical orientation.