Trait X is fitter than trait Y in a population of organisms if those organisms have other biological traits T and live in an environment that has properties E. The theory of natural selection is filled with statements of this form.

I have spent a lot of time arguing that the theory of group selection is not the stupid, pernicious doctrine that many biologists once claimed it to be. The theory is not just conceptually coherent; there are adaptations out there in nature (like reduced virulence in some viruses) that evolved because there was group selection.

This is not to deny that there are versions of theism that do conflict with evolutionary biology. Young Earth Creationism is an example; it claims that God created life on earth within the past 10,000 to 50,000 years. But other types of theism are different.

Some philosophical arguments (e.g., in connection with the mind/body problem) look pretty good, while others (e.g., those that criticize moral realism) do not.

I don't endorse deism or interventionist theism. My point is just that evolutionary biology is logically compatible with the former and with some versions of the latter.

In many contexts, simplicity is not an aesthetic frill.

Another way to test hypotheses about adaptation is to consider trait variation across a group of species instead of focusing on the trait of a single species. Rather than seeking to explain why polar bears have fur of a certain thickness, one tries to explain why bears in colder climates have thicker fur than bears in warmer climates. The former problem is hard to solve, since it is hard to say exactly what fur thickness polar bears should have if natural selection guided the evolution of that trait.