It isn't just biology, cultural taboos are huge. Take monogomy for example, many people have killed because it was breached in fairly minor ways. Where as in other places polygamy is an accepted part of society...
Well, yeah, culture has a large impact on what exactly is considered moral or immoral - but the same basic emotions are the cause of it, and there's a large degree of commonality in what morality focuses on throughout every society on the planet, from stone age foragers to modern America.
With the polygamy/monogamy example, it would appear that the level of equality or inequality in a society strongly affects how mating goes. If things are fairly economically equal, it's usually monogamy that predominates, with some exceptions, like in the West - most people are monogamous (including serial monogamy) but a few very successful alpha males have a number of lovers, or a wife and a mistress, and so on. Whereas in a society with much inequality, it's more advantageous for women to be second or third wives of the men who have the resources, instead of first wives of broke peasants, hence you see polygamy. Things get more complicated when one system or the other gets codified into religion, of course, or declared evil - but that's what basically goes on, even if it's outside the law or social norms.