Even if the pregnancy was unplanned, the two people chose to have sex for a complex set of factors, only one of which was attractiveness or prettiness, which by itself is very subjective and relative.
If two people just got drunk and had sex, they would probably be more likely to pursue contraceptive options like Plan B and abortion than a couple that had consciously decided and planned to have a child. There are exceptions to everything but I maintain that for the most part in the modern world what has replaced "natural selection" is not "sexual selection" but a "conscious selection" that incorporates sexual desire as well as other factors.
