Stop me if you've heard this before. I had this thought that the reason people divorce is evolutionary. We share half of our Gene's with our siblings and children and with each of our parents. But we have a more distant relation to our spouse. Very often people go to great lengths to maintain custody of their kids after a messy divorce. They often don't care as much about their spouse than their kids. I think lifetime monogamy is very difficult. A philosopher said that with science it is often appropriate to try many different research strategies rather than putting all your eggs in one basket. Similarly, having many kids with different spouses might increase your chances of propagating your Gene's. This also explains domestic spouse violence. I think this might predict marriages with kids last longer. This is why families are at the core of civilization. The relationships you choose require more support than the relationships of blood. It is harder to be monogamous and raise your kids intensively rather than being profligate in reproduction. This also speaks in favor of abortion. If you have an insecure attachment then it makes sense to have lots of kids. If secure it's better to concentrate on a few.