Cohabitation and Divorce
"Paradoxically, though, the choice of marriage preceded by cohabitation apparently attracts some couples who are less committed than others to lifelong relationships, since these marriages end in divorce at a far higher rate than those not preceded by cohabitation."
It is a possible explanation, but I am not sure it is the correct one, and she offers no evidence for it. I have some data of my own, although the sample size is a bit small. My first marriage was preceded by cohabitation and lasted about four years. The second was not, and has been going for more than twenty.
On the basis of that experience, I offer two alternative explanations:
1. Humans, like some species of birds, pair mate--not exclusively, but as an important element in our reproductive strategy. Part of what makes that workable is a link between sexual activity and our emotions, hardwired by evolution. Sleeping with someone, especially on a regular basis, creates emotional bonds. Breaking them can be hard. Those bonds, once created, may result in your marrying someone who, absent those bonds, you would have recognized as insufficiently well suited to you for a permanent relation.
2. Humans have a tendency to heavily discount future benefits in their decisions. This makes evolutionary sense, since we evolved in a very risky environment. Giving up benefits today in order to get larger benefits ten years from now is a bad bet--unless the benefits are a lot larger--if you are quite likely to starve to death in a famine or get eaten by a predator before the benefits arrive. We deal with the conflict between hardwired inclination and rational calculation by a variety of devices, such as Christmas clubs to precommit us to save and awarding status to wealth as well as to consumption.
For many people, cohabitation is much pleasanter than search. Not only does it result in a lot more sex, it also provides a range of emotional and practical support. If you are cohabiting with someone sufficiently well suited to you to make cohabitation workable but not to justify marriage, abandoning cohabitation in favor of continued search means giving up a current benefit in exchange for a distant and uncertain future benefit. So you may continue to cohabit, which means you are not searching--or at least searching much less. Lack of search means you don't find a better partner, so you eventually marry the one you have.
This is, of course, a drastically incomplete account of human mating behavior. Most obviously, humans, especially males, have an alternative strategy--promiscuity. A classic article by Brinig, "Rings or Promises," argued that the custom of giving engagement rings developed as a female defense against that strategy--a performance bond on the promise to marry in a world where intercourse conditioned on that promise was common, but loss of virginity sharply reduced marital opportunities--when courts stopped permitting damage suits for breach of promise. For a more expert account than mine of the relation between evolution and human sexual behavior, I recommend the work of David Buss.
But I think mine is a sufficiently accurate account to explain why cohabitation may sometimes be a mistake.