The point is one of first-class importance, for it illustrates at once the fixity and the weakness of that anti-Catholic—and irrational—spirit which will support any thesis however blown upon, so it be still of some service against the Christian Faith.
Let me give as briefly as possible the story of this old-fashioned theory of Natural Selection—which seemed so convenient for getting rid of God—and of its breakdown. I will first note the motives under which it arose during the mid-nineteenth century; next describe the theory itself; after that, give the arguments by which it was more and more shown to be untenable. Those arguments have long been familiar to all educated Europe.
Organic Genetic Evolution, i.e. the theory that one kind of living being arises from another kind, is as old as human observation and human thought. Common experience suggests it to everyone, because we know of no way in which living beings can appear upon earth save as the product of other living beings.
When, therefore, men first took notice of, say, donkeys and horses, or tigers and cats, they naturally said to themselves, “These things look as though they had a common ancestor.” The next step is to suppose that there would be a common ancestor to more widely different types. It is even admissible, though not probable, that all life on this earth sprang from one very simple origin. Our old Pagan forefathers—those of them who were civilized—discussed all this centuries ago, and the Fathers of the Christian Church spoke in the same terms.
Though criticism, and instruction in physical science as well, declined in the Dark Ages, and though popular imagination had then, as ever, a simple imagery, the idea was not so much contradicted or denied as neglected.
In the Middle Ages it reappears, very vaguely, under the conception of Mediate Creation. God is the Creator of every living thing. Yet every living thing has a parent or parents. That is an example of Mediate Creation; and it at once suggests the idea that groups as well as individuals might originate in the same way. Indeed, St. Thomas, the great teacher of the Middle Ages, by concluding exceptionally that the creation of Man was not mediate, but direct, implies the possibility or probability of Mediate Creation for organisms other than Man.
With the growth of Modern Science in the eighteenth century full discussion of the Idea was revived, and from a hundred and fifty years ago Evolution was discussed throughout educated Europe. During the nineteenth century a great mass of evidence was accumulated in its favour, and to-day it is almost (but not quite) universally held by specialists who have authority to speak upon such matters.
It is true that the process Organic Evolution may have taken becomes more and more doubtful as modern research and debate advance.
Have the various species of Plants and Animals branched out from one original living cell or from many? It is uncertain.
Have the new origins of life appeared in succession and separately at long intervals of time? It is possible or probable.