Explain why evolution is a unifying theme

Unify means to make or become united uniform, or whole.

(I personally don't agree that evolution is true; but here is my answer)

Evolution is a way Scientists like to theorize the world was made/ created. They try to explain why everything can about in a uniform way. Everything has a reason or theory. Even though scientists haven't been able to prove that Evolution actually exists, many people like the idea of it- just for the reason that it gives a more believable whole approach to how the Earth and Universe came about. For some people, it is more uniform than a religion.

I hope this helped you!