Identity 2: How could I have been?

How different could I have been from the way I actually am?

Which of my properties do I have essentially, and which only accidentally or contingently?

Could I, for instance, have had different parents?

Frank Sinatra and Doris Day might have had children together. Could I have been one of them?

Or could they only have had children other than me?

Could I have died in the womb before ever becoming conscious?