If you control for income, though, out-of-wedlock birth rates for black and white mothers are now very similar, though. “Our Kids” by Robert Putnam is a good summary.
Is this cause or effect? Unmarried motherhood has a very high correlation with poverty but I always assumed that poverty was the effect, not the cause.
I suspect it's a both/and situation, depending on the situation.
Tax and benefits wise it is usually a mistake to get married and if you are already near the survival minimum it can be a horrible mistake.