When one theory is simpler than its competitor, this fact is relevant to saying what the world is like.
Elliott SoberDarwin repeatedly used the hypothesis of common ancestry as a platform on which to build his various ideas about testing hypotheses concerning natural selection. He also argued that adaptive similarities provide little or no evidence for common ancestry. Although this second claim needs to be fine-tuned, Darwin was right that ample evidence for common ancestry can exist even if none of the characteristics we observe were caused to evolve by natural selection.
Elliott SoberCreationists have long held that evolutionary theory is atheistic; defenders of the theory do the theory no favor when they agree.
Elliott SoberThis 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.
Elliott SoberAnother 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.
Elliott Sober