h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I really disagree with the evolutionary analysis in this entry. If it were the case that the overriding factor in genetic survival of primitive humans was 'genetic variety', i.e. having as many mates as possible, then the family system would never have developed. Much more likely is that monogamy was taken up due overwhelming benefits of the close social bonds the nuclear family allows.

The idea that evolution has always favoured those who have the most children is a myth. What it actually does is favour those whose children are able to survive to childbearing age. Therefore, mothers, then as now had a big incentive to keep their men loyal, and sleeping will all his mates has never been a logical way to go about that (outside the world of porn, which did not exist back then).

At the same time, in a society without locked doors, it would have been very easy to kill someone in their sleep, or when they are out hunting, so if men really annoyed each other (by sleeping with each others partners), they could quite easily get away with murder. Social taboos in a society without economic security may well have dealt with infidelity much more harshly than has been the case since the development of agriculture, and the welfare it brought with it.

Therefore, in such a society, those of both sexes who behaved themselves and treated their partners with love and respect, and avoided pissing other people of, probably had the best chance of having the maximum number of their own offspring survive to childbearing age.