Any animal, this one included, adapts to the environment it is in or dies out... it is that simple. Survival of the most adaptable is really what Darwin meant when he said, "most fit". Most fit doesn't mean strongest, it means most adaptable.
So, this animal grew a hair coat for warmth, and hard hooves for running on the steppes, and skittishness for survival, and multitudes of other things from its ancestors...eohippus, mesohippus and others coming from a 4 toed animal about the size of a fox to what you see now. And it will continue to change as stresses on it from the environment demand change. If it can't, it dies out...
When one were born that carried a gene that tended to make it survive even a little bit better than others, in 40 or so generations, those carrying that gene would be the dominant one. This is how this animal evolved, and how any animal does.
So, true of this animal, true of any. And when an environment changes too quickly, that line dies out completely, and others then can take its place and continue to evolve and become dominant. But no animal is forever.
This is what evolution and natural selection are all about... for millions and millions of years.
