Pathogens are evolving.
New pathogens are being created by humans.
Also I think selective mating will over time produce distinct races if things continue as they are where people are selecting mates of similar caliber.
You may end up with a caste system like in India where people of different castes have distinctly different "ethnicity" from selective breeding.
I'm sorry but this is more inaccurate than even the original point. The opposite has been happening continuously, as class systems have gradually broken down in most countries, people are traveling more, there is less inbreeding, and interracial mating is becoming less taboo. If anything, people are gradually going to look more similar than different. More and more people are having kids outside of their race and religion, that's a fact. And yes, humans are making new pathogens that could potentially spread. We're also working on new antibodies. We also first evolved to walk, then make tools, then fire, then weapons that helped us kill more mammoths than other predators could, then we domesticated animals (which caused them to spread pathogens to new locations and spread unnatural disease there), at what point did it become an "unnatural conclusion"? I really don't mean to be testy, and you bring up interesting ideas, but religious misinterpretations of evolution is something I worry about.
Clear, it is because people have a larger selection of mates that humanity is dividing into classes.
The attractive, athletic, intelligent people choose others with good traits. This repeats over generations forming a separate genetic pool.
Likewise the unattractive, physically weak, dumb people will choose whoever they can get, and this repeats over generations forming a separate genetic pool.
Because the rules of selecting a mate that is equal or better than yourself are rarely ever broken and because there is no limiting factor on those you can choose as a mate, these differences will become more pronounced over time.
Have you ever noticed that some families are full of intelligent, attractive, and athletic members? And other families have members with weak constitutions, slow minds, and homely features?
That's because selective breeding in a globalized world has already started producing results.
As for new pathogens, just the pathogens from fossil fuels floating around in the air is considerable, not to mention the petrol derivatives being used as food colorings and preservatives. Then there is nuclear waste, antibiotic resistant bacteria, fungicide resistant fungi, cross contamination of parasites between countries, new chemical compounds, new viruses, and whatever biotech labs are cooking up.