It’s entirely natural, but I don’t like reducing behaviours to “human nature”, since we can’t fully separate our thoughts, feelings, and behaviours from the social context we live in, there’s definitely going to be some interaction going on since we live in a complex society. Especially since the discussion at hand isn’t necessarily a human urge to reproduce, which would more be accidental, it’s actual family planning. You figure in family planning the discussion is a little bit more different, and the reason one might opt to have a family rather than adopt would be more due to social pressures than instinct.