The scary thing is that it really seems to be the case that having a kid changes your brain, at least for most people. People who weren't sure they wanted kids become completely different people who are absolutely obsessed with their kids.

That's probably a good thing from an evolutionary point of view, but it's freakish to see it happen. It's also sometimes a tragedy when it doesn't happen and someone who was ambivalent about having kids is not thrilled with having a kid when it happens.