Of course it's possible. Routes to that could be social.( people of one type or region selecting only that type or region for mates. Even the "untouchable effect. Those deemed inferior mates by most mating with others also deemed inferior)regional if we were to colonize other planets. I am sure there are other ways that haven't occured to me.
I have noticed that the immigrants I meet seem far more skilled and capable than my contemporaries and counyrypeople. I have frequently wondered if natural selection still acting so strongly in third world countries has made their surviving population more "fit".

Yeah republicans into nasty species

If class system becomes too deep, with one class not mixing with another one, with one class using selective breeding for example.
Or a space expansion that don't go to well and we loose contact with one or more of the colonies.

Yes. But it won't be driven by random mutations and natural selection. It will be because of physical and cognitive performance enhancing chemicals and genetic manipulation made possible by scientific research and military funding.

Of course. Other species have evolved into different lines.

[britannica.com]

Homeo sapiens will kill itself off before that could occur.

Oh you know it has already happened, one species is called a Democrat, and the other is called a Republican, but in all seriousness read this.

"Mr. Chau, an American thought to be in his 20s, was floating in a kayak off a remote island in the Andaman Sea. He was about to set foot on one of the most sealed-off parts of India, an island inhabited by a small, enigmatic and highly isolated tribe whose members have killed outsiders for simply stepping on their shore.

Fishermen warned him not to go. Few outsiders had ever been there. And Indian government regulations clearly prohibited any interaction with people on the island, called North Sentinel."

[nytimes.com]

You are seeing it right now on a scale of intellectual evolution. Welcome to Agnostic.com.

H.G. Wells thought it likely, Morlochs as a subterrianian superior species and the Eloi as an unthinking eugenically bred cattle like race as their food source.

Of course. Other species have evolved along different lines. This is how diversity happens. I think it's more likely that we'll go extinct instead.

At the moment I don't see any evolutionary impetus for that to happen. Extinction of the species is a more likely outcome.

One of the things that is needed for the divergence of a species is geographic isolation whereby a gene pool can evolve separately from the original population. This could only happen on this planet if we left the planet and colonized another planet and had no contact with the home world.

The other aspect needed is a driving environmental stressor that necessitates some type of evolutionary adaptation for survival. We are all in general, under the same stressors and their is no population I know of that is experiencing unique stressors to cause them to adapt differently from the rest of the world's population.

Hmmm interesting question! My mind immediately went to the political divide.
Practically, I think you are right that geographical separation would be needed.

In zero g, space faring - it is possible.