Natural Selection

Back to our Cheetahs, if a mutation occurs that is good for the cheetah's survival,
there would evolve a slightly better Cheetah.

This new species is likely, and in most cases will,
compete more successfully with the older type Cheetahs in the territory,
on the resources the territory provides.

In time the lesser qualified cheetahs will diminish
in number and slowly disappear, leaving the territory with
just this one new species instead.

We will call this new species a Cheetah,
and say the cheetah has evolved by some small fine quality of survival. Since the lesser cheetah is now extinct,
there should be no reason why we would change its name
in the classification of the animals of Nature.

But if all the while, in another territory, some other cheetahs
linger, and if this territory is sufficiently separate so that
the better cheetahs can not reach it,
then the older species did not become extinct,
and we would need to name the new species,
once we discover that
now there are two of them.

We might call it the long-nailed-cheetah.

This process by which Nature selects
the better replications Darwin calls
Natural Selection.