However, I think that there are certain actions that we take that are clearly defined by our genetics, like the fact that we eat, or that we have sex. And having affairs is one of those.
Which actually makes sense given your premises. A good evolutionary "strategy" would be to evolve brains that can make choices far more complex (literally, inelligently) than what can be pre-encoded by genes that change slowly and mutate randomly.
In summary, you are implying that when you have an affair, it's not a choice, but it's determined by your genes. Thus, it's not a moral issue; you have no choice. Thus, you can justify having any particular affair by claiming "genes," and you should just forgive any particular affair your wife has for the same reason. And I'm saying, no, it's a choice.
Just because we can show that cheating has evolutionary benefits and thus people are likely prediposed to cheat in certain situations does not eliminate any moral considerations. Morality is precisely the idea of overriding any base instincts with what we "know" to be proper behavior. Claiming your genes made you do it is no more a loophole for morality now than "the devil made me do it" was before the discovery of DNA.
In other words, this study suggests at least to some degree we don't even choose who we have sex with. Haha.
Are you arguing that because we have brains we can 'override' what our genes would otherwise have us do?
I didn't mean to make myself sound like that I was saying it was. I was just suggesting something and I agree with you: it is plausible, but it is still a theory at the end of the day.
We're on the same page. :)