Our confidence that evolution occurred centers upon three general arguments. First, we have abundant, direct observational evidence of evolution in action, from both field and laboratory. This evidence ranges from countless experiments on change in nearly everything from fruit flies subjected to artificial selection in the laboratory to the famous populations of British moths that became black when industrial soot darkened the trees upon which the moths rest. (Moths gain protection from sharp-sighted bird predators by blending into the background.) Creationists do not deny these observations: how could they? Creationists have tightened their act. They now argue that God only created “basic kinds,” and allowed for limited evolutionary meandering within them. Thus toy poodles and Great Danes come from the dog kind and moths can change color, but nature cannot convert a dog t a cat or a monkey to a man.
The second and third argumentsfor evolution – the case for major changes – do not involve direct observation of evolution in action. They rest upon inference, but are no less secure for that reason. Major evolutionary change requires too much time for direct observation on the scale of recorded human history. All historical sciences rest upon inference, and evolution is no different than geology, or human history in this respect. In principle, we cannot observe processes that operated in the past.
The second argument – that the imperfection of nature reveals evolution reveals evolution – strikes many people as ironic, for they feel that evolution should be most elegantly displayed in the nearly perfect adaptation expressed by some organisms – the camber of a gull’s wing , or butterflies that cannot be seen in ground because they mimic leaves so precisely. But perfection could be imposed by a wise creator or evolved by natural seelection. Perfection covers the track of past history. And past history – the evidence of descent – is the mark of evolution.
Evolution lies exposed in the imperfections that record a history of descent. Why should a rat run, a bat fly, a porpoise swim, and I type this essay with structures built of the same bones unless we all inherited them from a common ancestor? An engineer, starting from scratch, could design better limbs in each case. Why should all the large native mammals of Australia be marsupials, unless they descended from a common ancestor isolated on this island continent? Marsupials are not “better,” or ideally suited to Australia; many have been wiped out by placenta mammals imported by man from other continents. This principle of imperfection extends to all historical sciences. When we recognize the etymology of September, October, November and December (seventh, eight, ninth, and tenth), we know that the year once started in March, or that two additional months must have been added to an original calendar of ten months.
The third Argument is more direct: transitions are often found in the fossil record. Preserved transitions are not common – and should not be, according to our understanding of evolution (see next section) – but they are not entirely wanting, as creationists often claim.