These are, according to Mr. Youmans, the “demonstrated truths” on which the theory of evolution has been built, and which, according to the same writer, “demonstrate evolution as a fact.” We think, on the contrary, that the only fact demonstrated by this passage is the blindness (voluntary or not) of a certain class of scientists. A cursory examination of it will suffice to convince all unprejudiced men that such is the case.
That the stream of generations flows on “by reproduction and genetic connection in the regular order of nature” is indeed a fact accordant with all observation, and to which there never has been known a solitary exception; but all observation proves that the regular order of nature in generation is confined within the limits of the species to which parents belong. This precludes the possibility of drawing from this fact any conclusion in favor of evolution.
That living forms “are liable to variations, which accumulate through inheritance,” is _not_ a demonstrated fact. We see, on the contrary, that all such accidental variations, instead of accumulating, tend to disappear within a few generations, whenever they cease to be under the influence of the agencies to which they owe their origin. But let us admit, for the sake of argument, that all living forms are liable to variations which accumulate through inheritance; then we ask whether all such variations are confined within the limit of each species, or some of them overstep that limit. If they are confined within that limit, the fact proves nothing in favor of the evolution of species. If, on the contrary, any one says that they overstep that limit, then the fact itself needs demonstration; for it has never been observed. Therefore to argue from this fact in favor of evolution is to beg the question. We have no need of dwelling on Mr. Youmans’ statement that the ratio of multiplication in the living world is out of all proportion to the means of subsistence, so that only comparatively few germs mature, while myriads are destroyed. The statement is true; but it has nothing to do with the theory of evolution. That, in the struggles of life, the fittest to the conditions survive, is another fact which does not in the least bear out the theory. For the fittest among animals are those which enjoy the plenitude of their specific properties, and which, therefore, are best apt to transfuse them into their offspring whole, unmixed, and unimpaired.