I am no expert on this. This is entirely out of my anus.

Primates, like humans, like all organisms are interested in passing down their genes. Both females and males, are programmed, biologically and thus psychologically, to do so.

Females have a critical advantage over males because they own the means of producing offspring. They are always sure that their kids are theirs. That their offspring carry their own genes. Both, however, are not programmed to care much about who was responsible for the other half of the genetic load carried by their child.

Fish don't care much about their offspring. A male fish will fertilize the eggs by spraying some sperm over a collection of fish eggs. A male fish will be proud of its fatherly duties for a second or so.

To ensure their survival, mammals can't produce offspring and leave them to the wilderness. Primates need to nurse their offspring for extended periods of time. This time is at its maximum in humans.

For males, providing for both the mother and the offspring -- the mother to nurse the offspring and whatever is necessary for a father to do in nurturing his child -- is a cost.

Honour, that is women's virtue and chastity, is, in my opinion (I am sure this is not a new thing), an invention by men to make sure they are not raising children that are not their own. It is of their best interest to funnel these costs to children carrying their own genes first.

The social invention of honour is critical to men because they can never be sure if a child is theirs. So they created a social program that they think will work to minimize the number of men a woman can get in contact with. The more strict the better, the more sure they will be that their kids are really their own.