TimD
I chose dogs as an example because mine happen to be here right beside me. And during the years I've owned them, their similarities and differences have become obvious to me.
Yes, man has been instrumental in many breed's development...but that's only been in the past 10,000 years or so. Prior to that, Pugs developed separately from Greyhounds naturally, in separate environments, over hundreds of thousands or millions of years.
As did man. The Australian aboriginees evolved separately from the tribes of the British Isles over the same time period. It's only been within the past few centuries that human races have intermingled to any degree.
As far as mating goes, until recent times, humans never travelled far from their own village. They generally lived and died in a few mile radius of where they were born. They also wound up interbreeding to the point that most "tribe members" were all related. At best, they would marry someone from the next tribe over. They weren't overly picky either. And who knows what humans were like prior to written history? Like animals I imagine.
Let's forget about dogs or domesticated animals and think about all the other animals ( and plants ) in the world. Man didn't meddle in the developement of Lions, Tigers, Lynx, Cheetahs, Panthers, etc. But again, despite being members of the same species, each has developed it's own evolutionary characteristics. Some are bigger, some are faster, some live longer, etc. etc.
The people of Nepal have developed superior lung capacity to most people because of their environment. Why is it so hard to believe that different races may have developed different hearing responses for the same sort of reasons.
Survival is in fact the main catalyst for evolution. If one tribe's survival depended on being able to hear a Lion sneaking up on them and another's depended on hearing a snake...perhaps their hearing would evolve differently.