Question: If most of our behaviours stem from instincs that used to keep us alive, how come homosexuality developed if we were designed to re-produce? Also can you explain why homosexuality is believed to be genetic?

Joanne Sharpe answered on 25 Jun 2018:

Such an excellent question! You would think that the genes for homosexuality would never be passed on right? But it isn’t just humans that display homosexual behaviour, it is seen in a variety of animals too.There are a few theories about this.
One theory is that the allele (variant of a gene) that might make someone more likely to behave homosexually, might also confer a survival advantage! When the individual has only one copy, or it’s not very “strong”, they might not be homosexual, but get this advantage from the low “dose” of the gene. So the allele for homosexuality stays in the population, and occasionally an individual might get two copies or a higher “dose” and be homosexual as a result.
Another theory is that gay siblings might help look after nieces and nephews, which would therefore have a greater chance of survival and pass on their genes, approx 25% of which would be shared with the homosexual individual.
Alternatively, the homosexual allele may just be an allele that makes the person more attracted to a certain sex.. so if you are a woman, a trait to be more attracted to men would be reproductively advantageous, and if you have this trait and you’re a man, you would be gay.
Those are the explanations that I’m aware of, but scientists aren’t really sure!