Dr. James O’Keefe gave a recent TED talk at TEDxTallaght in Dublin about homosexuality—and how it's not about sex, but survival.

O'Keefe's son Jimmy is gay, and when Jimmy came out to him and his wife 12 years ago, O'Keefe confessed that he was worried for his safety and his son's happiness, but the more he thought about it the more he realized that homosexuality wasn't abnormal, but a way for a species to survive.

“Viewed in the light of evolution, homosexuality seems to be a real self-defeating non-productive strategy," O'Keefe told the audience at his TED talk. "Gays have 80 percent fewer kids than heterosexuals. This is a trait that ought to go extinct in a few generations, yet down through recorded history in every culture and many animal species as well, homosexuality has been a small but distinct subgroup. If this were a genetic error, natural selection should have long ago culled this from the gene pool.”

O'Keefe suggests circumstances like the mother giving birth to a high number of male offspring or severe prenatal stress can increase the chances of giving birth to a gay son.

He also brings up the theory of epigenetics, genes that "express themselves in different ways based on external circumstances."

“If the [human]family is flush with plenty of kids and/or it’s a stressful place in time, nature occasionally flips these epigenetic switches to turn on the gay genes. This alters brain development that changes sexual orientation.”

“You probably have gay genes in your DNA,” he told the audience, “but unless they were activated in your mother’s womb, they remained coiled up and silent.”

Watch his fascinating talk below.

h/t: Unicorn Booty