Dick Gregory

If you take 12 waters from the coconut - not the ones you buy in the store, although that's good - but the fresh coconuts, the little brown ones with the three eyes, if you take 12 of those within 24 hours, your blood will go back to the way it was when you were born.

The historical novelist has to consider what has actually happened, while the SF writer is dealing in possibilities, but they are both in the business of imagining a world unlike our own and yet connected to it.