In my project, which portrays a modern take on the classic Asimovian "human empire among the stars", I have a society connected by stable wormholes which are as instantaneous as the portals in the game ... Portal. Energy is practically boundless because fusion has been mastered, and hydrogen is everywhere in space.
The time it takes to travel from world A to world B is only the time consumed going from A to the edge of A's solar system, and then from the edge of B's solar system to B. Fusion-powered ships could do this in weeks or possibly days by most reckonings.
[Question has been refined after this point!]
Goods and people travel between these worlds with the overall expense, regularity and ease with which early 20th century people would travel between continents. Not something one would do every week, but something almost anyone would possibly do at least once in their lifetime if they wanted to.
Genetic engineering is of course a very old (and thoroughly perfected) science at this point. However, most cultures abstain from its use beyond negative eugenics (the elimination of congenital defects). Others used it early on to shape the founders of settlements to better thrive on worlds that while habitable without terraforming, were not earthlike.
So, with all that said, my question is, would natural humans, which aren't actively engineering themselves on a genetic level, and which are no more physically isolated from other groups than continents were before jet air travel, still result in new races of human beings?
By races, I mean the fast and loose definition of a "race" - a group of people with unique physical traits that stand out and visually identify them as members of such a race. Traits that consistently are passed on to future generations.
Of course, if left isolated, any group of people would, over many generations, result in such a thing. But with the lack of isolation, would it still happen?
I hope this didn't sound ... racist or ignorant somehow due to my wording. I botched the question originally in trying to avoid that.
[Another quick edit]
When I first posited this question, I hadn't settled on an exact number for the age of this empire. I knew I wanted it to be quite old (by our standards). I've settled on 31,000 years. Which places it roughly 33,000 years into the future (this empire was not an entity immediately upon colonizing our own solar system or nearby stars reachable without the impossible concept of FTL or the wormholes later used).
A decent time frame may help with this question if anyone has anything further to add.