I think you’re looking for the concept of ‘mutational variance’. This is the amount of variation in a trait that is generated by random mutation. The variance in a trait is going to be determined by the balance of mutational variance and selective effects. Things with lots of genes effecting them will have a large ‘mutational target size’. So for instance intellectual disability has a large mutational target size because there are so many different ways to break a brain, while some kinds of haemophilia have a large mutational target size because the particular sequences of DNA involved mutate a lot.
In general mutation variance is very difficult to measure outside of single celled organisms, although good approximations have been done in e.g. fruit flies. The problem is that it’s very difficult to stop evolution from exerting it’s filtering effect on your mutations before you can measure them.
So in the absence of direct measures, It’s difficult to guess at how many genes might be involved in something like homosexuality, and what the mutational variance could be. On the surface, we can imagine it’s just a simple trait that should have few genes effecting it. Such is the case in fruit flies. But actually, we just don’t know enough about how evolution has created the human mind. Without knowing how genes produce a brain, we don’t know enough to say that homosexuality isn’t just a particularly common “failure mode” of the brain, like autism and ID. Maybe something about the way the human brain has evolved makes it turn out gay a lot.
Myself I don’t really buy the ‘gayness is selected for’ explanations. My own opinion is that exclusive homosexuality might be more due to our own present society than anything else, and it’s need to cordon off homosexual behaviour from normal, straight behaviour. If that’s the case most of the mystery disappears.
Short answer—no, this is a hard, ongoing problem.
I think you’re looking for the concept of ‘mutational variance’. This is the amount of variation in a trait that is generated by random mutation. The variance in a trait is going to be determined by the balance of mutational variance and selective effects. Things with lots of genes effecting them will have a large ‘mutational target size’. So for instance intellectual disability has a large mutational target size because there are so many different ways to break a brain, while some kinds of haemophilia have a large mutational target size because the particular sequences of DNA involved mutate a lot.
In general mutation variance is very difficult to measure outside of single celled organisms, although good approximations have been done in e.g. fruit flies. The problem is that it’s very difficult to stop evolution from exerting it’s filtering effect on your mutations before you can measure them.
So in the absence of direct measures, It’s difficult to guess at how many genes might be involved in something like homosexuality, and what the mutational variance could be. On the surface, we can imagine it’s just a simple trait that should have few genes effecting it. Such is the case in fruit flies. But actually, we just don’t know enough about how evolution has created the human mind. Without knowing how genes produce a brain, we don’t know enough to say that homosexuality isn’t just a particularly common “failure mode” of the brain, like autism and ID. Maybe something about the way the human brain has evolved makes it turn out gay a lot.
Myself I don’t really buy the ‘gayness is selected for’ explanations. My own opinion is that exclusive homosexuality might be more due to our own present society than anything else, and it’s need to cordon off homosexual behaviour from normal, straight behaviour. If that’s the case most of the mystery disappears.