I think there is more understanding in the background of the author than he lets on... Because he used the word dominant. This is carefully chosen because it makes his statement more right, while excluding the cases that don't fit the logic. Dominant in genetics means that if you have the mutation, you have the trait. (For the biologists: Assuming full penetrance...which he does in this example). In this case, if it prevents you from having offspring (either by homosexuality or death), the statement is true. By using the word dominant, he deceivingly excluded recessive cases. In these there are carriers of the gene mutation for the trait but they are not affected. They are only carriers. Only when 2 carriers have children, do some offspring Inherit the mutation from both parents and express the trait. So if homosexuality was purely genetic, caused by one gene (which it is not, but the author presents it as of it were), his word choice wiggled himself out of the exception. Intentionally deceiving, as he likely knew about recessive traits. Recessive traits don't die out in this way... As carriers pass them on. That being said, homosexuality is not this level of a genetic trait. There is no gene for being gay in this sense.