Moral philosophy is a huge topic and it's discourse is not dominated by looking at DNA.
Everyone can choose their preferred state then, at least to the extent it is not indoctrinated or biologically determined. It is rational to invest energy into maintaining or achieving this state (because the state presumably provides you with a steady source of reward), which might involve convincing others of your preferred state or prevent them from threating it (e.g. by putting them into jail). There is likely an absolute truth (to the extent physics is consistent from our point of view), but no absolute morale (because it's all memes in an undirected process). Terrorists do nothing wrong from their point of view, but from mine it threatens my preferred state, so I will try to prevent terrorism. We may seem lucky that many preferred states converge to the same goals which are even fairly sustainable, but that is just an evolutionary necessity and perhaps mostly a result of empathy and the will to survive (otherwise our species wouldn't have survived in paleolithic groups of hunters and gatherers).
Basically your argument is: "I can't think of a way to justify morality besides saying that it's my own prefered state, therefore nobody can come up with an argument to justify morality."
The most recent post in December's Stupid Questions article is from the 11th.
I suppose as the article's been pushed further down the list of new articles, it's had less exposure, so here's another one for the rest of December.
Plus I have a few questions, so I'll get it kicked off.
It was said in the last one, and it's good advice, I think:
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.