If half of the human population lives on the surface and the other half lives below the surface?

Question

for a couple of hundreds of thousand of years, would the same branch of humans be split into two different types of species due to the course of evolution?

Answer 1

More than likely though they may not be different species (i.e. they would still be able to reproduce) as 100,000s of years isn't that long.

I would suspect that the differences - if they were both technological societies - however would be less due to environment and more to cultural preferences and random mutations. In other words, if you split the same population by putting them on different continents and not allowing interaction, the same would happen

Answer 2

When subsets of any population are separated and kept from intermingling, they begin to diverge genetically. Random mutations and adaptations present in one of the subsets will not be present in the other, and vice versa.

While this may result in many remarkable physical differences in the two subsets (dark skin vs albinism, 'normal' eyes vs enlarged or no eyes), I doubt that a new species would be the result in such a 'short' period of time. The two subsets would probably still be able to mate and create fertile offspring, which is the accepted definition of a species.

If they were separated for a longer time, say millions of years, then yes, I think you would have two different species.

Answer 3

could be possible

environment does contribute in evolution

Answer 4

I swear I've seen this on some old sci-fi film.

But yeah, it might happen that they would be different - the ones under the surface may develop different eyesight because there was no light but that time scale probably wouldn't be enough to mutate into two different species - unless one of the two human populations came into contact with a large source of mutagens that change the genes more quickly e.g. radioactivity and smoking.