The evolutionary roots of the morals of 1001 Nights

Went to see 1001 Nights at the Festival last week. Excellent. The main theme though seems to be sexual jealousy from husband towards apparently adulterous wives. The moral message from some of the stories is that it's OK to brutally murder such a wife, but make sure you have your facts correct first!

With honour killings, Sharia law, and, maybe to a lesser extent, everyday attitudes, this moral code clearly persists. Why? A simple model of investment costs towards the next generation might explain this:

Suppose both parents invest the same (in terms of effort, resources etc) in the children that they bring up within the family unit that they live in. Clearly, pre-birth, men and women both have an incentive to seek the highest quality genes in their partner, but the costs of infidelity at this point are perhaps assymmetric.

The evolutionary cost to women of male infidelity is that the man chooses to live with someone else and make this investment elsewhere. The infidelity may change the ex-ante probability of the man choosing another partner, but despite the infidelity there is still some probabilty that there will be zero cost to to woman (i.e. the man stays).

The evolutionary cost to men of female infidelity is that the child is not theirs. Their investment will therefore be, from the point of view of their own genes, wasted. There is no probability one way or the other (there may be uncertainty that looks like a probability distribution, but the die has already been cast). Women never have a reason to doubt where to make their investment since they always have proof that the child is theirs.

It may be (game theory's not my game so I'm not going to attempt to construct a full model of this strategic interaction) that the evolutionary costs of female infidelity to men are higher than the evolutionary costs of male infidelity to women, and if so then maybe there's a biological basis for the moral code expressed in 1001 Nights.

This could be sorted in these modern times by genetic testing and putting the biological father on the birth certificate. This is perhaps not the best social policy from a child-centred point of view and maybe feels wrong from some sense of fundamental morals. But morals are not fundamental: they have a biological basis that is embedded in a cultural framework. Choosing social policy on a child-centred basis is not playing evolution's game: if we want to change morality so that sexual jealousy and sexual violence are less of a problem then we need to change the evolutionary biological incentives.