File this one under duh. To think that a phenotype [is a behavioral characteristic like homosexuality (in humans) a phenotype? I would suggest it is not as phenotypes are typically considered to be observable and I would argue homosexuality (in humans) is not observable, at least not in a simple, direct observational, way. In fact you could argue it is not observable at all and can only ultimately be determined through psychological i.e. direct questioning of the person, means. Even observing a given person engaged in a homosexual act is not enough as non homosexuals have and do engage in homosexual acts. That it is a phenotype in non human animals is an easier argument to make though still full of slippery questions such as how many homosexual acts does it take a given animal before it is fully, truly homosexual? Must it only ever have sexual relations with its own sex or can one or two or three, etc. deviations from this be permitted? And of course many argue that homosexuality is a human only phenomenon though this seems hard to believe given the evidence to the contrary.], as complex as homosexuality could possibly be under the control of just one gene is absolute madness and the height of ridiculousness. The fact that this was commonly believed to be true highlights the continued dominance of DNA determinism in public discourse as I have written about many times. The worst thing about the DNA determinists is that they are typically the most ignorant of the complexity of molecular biology, and the tendency to oversimplification runs rampant among them. Usually the endpoint of this is Gene X causes trait/feature/characteristic/attribute Y. Therefore if you have Gene X you will be Y. There are so many things wrong with a statement like that I don’t even know where to begin. What a waste of resources that an actual study had to be conducted to “prove” this most obvious of things.
I wrote a (slightly) expanded version of this response for a more recently published article linked below.