We owe to Charles Darwin and Alfred Russel Wallace not the discovery of evolution but the creation of a powerful causal explanation for the small and large facts about nature that fascinate us as children and as adults. The principle of natural selection provides at least part of an explanation for a myriad of traits ranging from the shape of an orchid blossom to the visual acuity of a hawk’s eye. Darwin’s 1859 presentation of the principle in On the Origin of Species is a synthesis of observation and explanation that should amaze any curious reader. Wallace’s (1870a) discovery of natural selection is no less amazing, especially given the more difficult circumstances that surrounded his work (see Berry 2002). Their discovery is a human achievement of the first order, which should transcend political and social divisions. But it is best to understand the world as an “is” and not as a “should.” Most people believe some sort of divine explanation for the kind of facts about nature that I just mentioned; if they are aware of Darwin’s and Wallace’s discovery, they dismiss it as false. Few, if any, of these people will read this essay. You, the reader, are likely aware of the truth and importance of Darwin’s and Wallace’s discovery or are open to their discovery being correct. Even so, in order to understand how the testing of evolution has evolved, it is useful to examine the nature of Darwin’s and Wallace’s achievement, especially because it is often misunderstood even by those who recognize that it is correct.

In this context, it is worth comparing the “before” and the “after” of their discovery. To understand the “before,” it is most meaningful to consider claims about nature that at least appear to be based on substantial assemblages of facts (as opposed to claims as to the “fact” of, say, divine creation that were simply appeals to faith and referenced few, if any, facts). With this restriction, all claims we consider are arguably science, inasmuch as there is marshaling of evidence (as opposed to just an appeal to belief). Given this restriction, one finds a wide variety of claims that range from the claim that the facts are explained by divine creation (Paley 1802) to those that invoke natural causes.