Darwinism is not itself subject to the scientific method any more than anything in history is. The past is over; you cannot revisit it, observe it, test it, or experiment on it. All you can do is look at the surviving evidence and try to make sense of it. Darwin knew, of course, that he had no access to the past, but he reasoned that if his theory were true, then natural selection would still be operating today, and thus it should be possible to make specific predictions and test them.
