In an earlier post I entitled An Unexpected Artificial Intelligence Revolution- I speculated on the possibility of advanced artificial intelligences keeping human beings around essentially as house pets.
Well, if we're going to speculate along those lines, what if the same artificial intelligences deliberately bred human beings to produce specific traits that especially distinguish them, much like human beings have bred the first wolf-like dogs into creatures as small as teacup chihuahuas to as large as Saint Bernards, in the act of breeding adding spots or stripes or rings, hair of different length and colors, breeding completely different face and body shapes and wildly differing behaviors.
Presume for the sake of this idea that the same thing could be done with human beings--an argument could be made that humans already self-select for certain traits, which is perhaps why "natural" human diversity is quite large. Thinking we've already bred ourselves into a wide set of human varieties would argue against anyone being able to breed us much further, but let's put aside that line of reasoning for the sake of this story idea.
Imagine humans could be bred to be over twice as tall as the current human average and also much smaller, literal hobbit-sized. That patterns of stripes and different tones of hair could be bred into humans. E.g. one breed could have one eye that's blue and another eye that's brown, each individual member of the "breed." Imagine humans bred to have enhanced hearing or sense of scent, or specialized intelligence or other unique skills.
All of these would still be human, of course, but it would be interesting to create a story in which AIs--or aliens perhaps--deliberately pushed the limits of what it meant to be human, creating a future world in which the diversity of sizes and shapes would be so great that races and diversity as we know it would be tiny in comparison, to the extent that all humans of our age would seem basically alike. Larry Niven's Ringworld series does something like this by having his artificial world inhabited by an original progenitor race to humanity, who settled on the ringworld long ago and evolved for ages afterward, adapting to various environments over time. But humans deliberately bred could easily have a much greater diversity than Niven imagined. In a much shorter time--especially if genetic engineering were to be part of the process.
Imagine if this future world of humans bred as pets, with all the vast variety of hairiness and size and shape and color, underwent some sort of collapse. The AIs (or aliens) for some reason self-destruct. Then all these different breeds would have to face one another and build their own place in the world, crafting alliances or perhaps naturally drawn towards war, in a future science fiction story unlike any I have ever known...