These wolf-like creatures have a high pitch howel and are slim in size, because it is cold where they live most of them have thick fur but because of genetic variation some are hairless but most hairless animals die young
there is a severe flood that separates the population  half the population goes to a warmer environment and half goes to a colder environment
the population that stayed in the colder environment traits stayed pretty much the same because the population had already evolved through natural selection to do well in that environment 
over time the local population that was separated and went to the warm environment began to evolve through selective breeding to lose their fur and they also started to get larger because the prey in their new environment are bigger and being bigger will help the animals hunt the prey easier additionally over time do to pure chance a lower tone mating call took over and now this population has a lower mating call then the other population
after a long time the river that was formed by the flood dried up and the population that was separated and went to the warmer environment went back to the cold area
when the two populations find each other again they do not realize they can breed because there mating calls are different and they look so different which causes  them to not recognise each other
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