Testing the Theory
Very rapidly this conception of Natural Selection was extended by naturalists until it came to be regarded as the general process of life. They came to realise that all species, all genera, all classes of life, whatever else may be happening to them, are and always have been varying through the process of Natural Selection, some rapidly, some slowly; some so slowly as hardly to change at all through vast ages. I have stated the a priori case by which, given birth and death and individuality and changing conditions and sufficient time, it appears logically inevitable that the change and differentiation of species must occur, and must be now going on. If we had no material evidence at all it would still be possible to infer the evolution of species.
That a priori case has never been answered, and it seems to me unanswerable. But scientific men, with their obstinate preference for observation and experiment over mere logical gymnastics, rarely rest their convictions on a priori cases. A sustaining scepticism is a matter of conscience with them. To them an a priori case is merely a theory—that is to say, a generalisation under trial. For nearly three-quarters of a century, therefore, biologists have been examining whatever instances they could discover that seemed to contradict this assumption that the process of specific change under Natural Selection is the general condition of life. To this day this view is still called the Theory of Natural Selection, though to a great number it has come to have the substantial quality of an embracing fact.
It would have been amusing if Mr. Belloc had told us more of his ideas of the scientific world. Apparently he knows scarcely anything of museums or laboratories or the spirit and methods of research. And manifestly he has not the faintest suspicion of the way in which the whole world of vital phenomena has been ransacked and scrutinised to test, correct, supplement, amplify, or alter this great generalisation about life. He probably shares the delusion of most other men in the street, that scientific theories are scientific finalities, that they are supposed to be as ultimate as the dogmas of some infallible religion. He imagines them put over chiefly by asseveration, just as the assertions of a polemical journalist are put over. He has still to learn that theories are trial material, testing targets, directives for research. Shooting at established theories is the normal occupation of the scientific investigator. Mr. Belloc’s figure of the scientific investigator is probably a queer, frowsty, and often, alas! atheistical individual, poking about almost aimlessly among facts in the hope of hitting upon some “discovery” or “getting rid of a God.” He does not understand the tense relevance of the vast amount of work in progress. But for three-quarters of a century the thought and work of myriads of people round and about the world have borne directly or almost directly upon the probing, sounding, testing, of the theory of Natural Selection. It stands clarified and, it would seem, impregnable to-day.