It is genetically normal. In fact, it is genetically superior. Game theorist Robert Axelrod demonstrated this over a decade ago in his landmark book, The Evolution of Cooperation. In communal species, the golden rule prevails over more predatory approaches. Simple, basic rules of cooperation and reciprocity yield more collective prosperity, and therefore more viable offspring all around.
Cooperation remains vulnerable, however.
Defectors and cheats can always prosper at the fringes, by pretending to cooperate while secretly breaking all the rules. So rules, and a willingness to enforce them, have to be maintained. Nowhere more so than in matters of sex. Sexual norms don't exist to protect one sex from the other. They protect women from other women, and men from other men.