Various sorts of morally reprehensible behaviour exist in humans because they confer biological advantages on the agents. Similar sorts of behaviour exist in animals.
For example, male lions tend to kill cubs that they did not sire. In doing so, they “make room” for their own cubs – “room” that consists of scarce resources such as the mother’s care, and shared food and protection of the rest of the pride. By killing the offspring of others, they give life to their own offspring – which carry genes for infanticidal behaviour and thus ensure that it continues.
Or again, mallard ducks are notorious rapists. This behaviour continues from one generation to the next, again for obvious evolutionary reasons.
Like male ducks, men are potential rapists, and for the same evolutionary reasons. Rapists who are accused of rape generally do not admit to rape – so they’re liars as well as rapists. And again, they’re liars for evolutionary reasons. Rapists who don’t admit to rape are more likely to rape again and pass their genes on so that the raping and lying continues from one generation to the next. Their behaviour is morally reprehensible, but its biological causes are well-understood.
Women’s behaviour can also be morally reprehensible, as well as being well-understood biologically. For example, women sometimes commit infanticide – not just by killing other women’s children to make more room for their own children, as men do, but also by sometimes killing their own children. The second sort of behaviour makes more room for later children of their own at a more opportune time, such as when they can hope for better provisioning.
Like men, women are prone to mendacity in circumstances where it is biologically advantageous to tell lies. These circumstances need not be as dramatic as rape, although lack of consent of one party or another (such as a cuckolded husband) is always involved. “Ordinary” extra-marital “cheating” can be biologically advantageous to those who can get away with it by lying successfully. Although the respective advantages can differ slightly, cheating can enable both sexes to produce a larger number of offspring and/or offspring with a wider variety. But secrecy is essential – mendacity evolved with the cheating behaviour. Through cuckoldry, both men and women can raise offspring provisioned by victims of mendacity – those who have been duped into thinking they are provisioning their own offspring. This is common among monogamous animals, and humans are no exception.
Intelligent and just law-making must take account of the biological roots of these sorts of mendacity. For example, if a woman accuses a man of rape, no decent, just law would simply “take the man’s word for it” if he denies it. (Nor would it simply take the word of the woman who asserts it.) Similarly, if a woman claims a man is the father of her child, we shouldn’t simply take her word for it, as it might be an attempt to dupe him into provisioning someone else’s offspring. To overlook this possibility is to court injustice.
In principle I welcome the suggestion that a child’s birth certificate should carry the names of both mother and father. But the law must ensure that the name of the father is decided by more than the mother’s say-so.