Lisa Belkin in the New York Times is reporting a very interesting study from Natasha Cabrera at the University of Maryland on what makes unmarried fathers stay. Cabrera and colleagues found that the more involved the father was with the pregnancy and birth of his child, the more likely he was to still be there three years later -- if he had moved in with the mom. It did not make a big difference if they also got married in this period. Cabrera concludes that what matters is the father's "personal involvement" in the mother's and child's future, not the "paperwork."
I draw a somewhat different conclusion. The data for this study comes from the "Fragile Families" study, so they have already been selected for their weak connection to marriage. These are couples who get pregnant outside of marriage, and do not marry because they are pregnant. Some marry well after the birth of the child, and many don't marry at all. This is the subculture with the weakest understanding of marriage as a social institution to begin with. They do not see how marriage can help them strengthen their relationship in the first place, before children. They see marriage as a seal, even a reward, for an already strong relationship. This is one of the reasons that marriages in this subculture are rare and weak to begin with.
Cabrera's conclusion, that marriage is just paperwork, is not fully true for the anti-marriage subculture she is studying, and is less and less true the further you get from fragile families and move toward solid middle-class marriage subcultures.