And by the way, I wanted to point out that Kindred is not science fiction. You'll note there's no science in it. It's a kind of grim fantasy.
But my problem with fantasy, and horror, and related genres, is that sometimes the problems are illogical.
Fantasy is totally wide open; all you really have to do is follow the rules you've set. But if you're writing about science, you have to first learn what you're writing about.