system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are there countless numbers of animal subspecies, but no human subspecies?
gpt
Well subspecies is a rather nebulous term. See when a two population of the same species become separated geographically, they won't exchange genetic material through breeding. If they are separated for long enough of put under enough pressure, they will genetically change enough that they will eventually become different species. But it's a long process so you have some population are that in between. Meaning they become different enough that they are clearly not the same species, but didn't change enough to be clearly two different species. But you probably don't talk about that, because there isn't that many subspecies. You probably talk about species that look similar, like how there is like 8 different species of bears.

Now it depend on what you consider human. Are human only homo sapiens or all Homo are humans? Because there was something like 16 different Homo Species. Some went extinct by their own, but other were assimilated or killed off by home sapiens. The difference between other animal and us is our intelligence. The intelligence that allowed us to spread to the whole globe very quickly. See usually animal don't spread as much and if they do, it take them a LOT of time. So by the time they reached another continent, they already became a new species. We spread so quickly, that by the time we covered all of the planet we were still the same species and competed with all the other Homo species for resources and we won all over the world.