Yeah, I noticed that, but let's think about it a minute. Who is more likely to stay together; a couple that invests heavily in the raising of their offspring, or two people just fucking like bunnies to have as many babies as possible.

And a quick side note, I realize that most women (and men) today aren't having sex to have kids, but the offspring thing still applies, as our instincts/DNA don't exactly understand things like birth control, lol.