Nicholas Kristof

We all stand on the shoulders of our ancestors. We're in a relay race, relying on the financial and human capital of our parents and grandparents. Blacks were shackled for the early part of that relay race, and although many of the fetters have come off, whites have developed a huge lead.

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.