Which statement best explains why organisms of the same species that become isolated eventually become different from
each other over time?
Their DNA mutates.
They are exposed to different environments.
They both find ways to survive.
They do not have any of the same genes.

They are exposed to different environments.

Explanation:

The isolated organism should have the same gene pool. This gene pool should be maintained if there is no other factor that disrupts it.

But the condition of the habitat might be different and this will create a natural selection. The environment will give advantages to certain traits while giving disadvantages to other traits. But a different environment will support different traits, so this can create variation.

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.

i think it is true in my reasonment ..