Originally Posted by Elfwreck
There's a substantial legal difference as well. Father and child cannot marry, no matter what happens to them later in life; a step-parent who gets divorced can later marry the step-child.
Don't think that's true. I'm pretty sure there are some states in the US (Massachusetts and Michigan, I think) that don't allow it. It's only allowed in the UK if both are over 21 and they didn't live in the same household before the child was 18.