New Theory...

Everybody has the first truly emotional memory. For me that was when I was eight and told quite plainly that I will have to leave the safety and comfort of my grandparents' home (because my mother missed me). I went from cosseted (seriously, you could not have found a more spoiled eight-year-old than I was) to what seemed like full independence, having to do things autonomously in a strange world with a strange language.

I think that experience probably defines the moment when I decided I can only be happy with someone else over seeing my happiness for me.

So my theory is this: That if your first truly emotional memory was that independence brought you happiness, then you would be a dominant. Otherwise, you'd be a submissive. If you were equally happy, then you'd probably be a switch (or vanilla).

Try it on for size. But of course there would be exceptions.