THE MECHANICAL THEORY OF EVOLUTION: THE DARWIN-WEISMANN EXPLANATION
“Chance guides all things: mind and forethought must call it God alone!”—Menander.
“In the end,” writes M. Edmond Perrier, “every imaginable theory of evolution must lead up to one or other of two absolute doctrines, essentially antagonistic to each other. Either the inheritance of acquired characteristics must be admitted in its full scope (_dans toute sa généralité_), or else we must believe in the predestination of protoplasm, developing by virtue of its own internal forces. But in the latter case we pass from the domain of pure science to enter that of metaphysics.”[66]
We have now to consider the most conspicuous attempt made in recent times to escape from this tragic dilemma.
If the acquired and inherited variations of the Lamarckian theory drop out as a contribution to the explanation of evolution, we are reduced to two forces only—_innate_, or germinal, variability of offspring, and natural selection. Indeed it might be said that we are reduced to variability alone, since natural selection can do nothing until suitable variations are presented to it. The suitable variations do, however, turn up, and the question is, what causes them? The real difficulty for the school of biologists who, like Weismann, “assume the mechanical theory of the world to be correct,” is how to reconcile the aptness and apparent purposefulness of these variations with any mechanical theory.
“We are justified in inquiring,” writes Weismann, “whether the assumption of ‘chance’ germinal variations, which we have hitherto made with Darwin and Wallace, affords a sufficient basis for selection. Osborn says very neatly in this connection, ‘We see with Weismann and Galton the element of chance; but the dice appear to be loaded, and in the long run turn “sixes” up. Here arises the question, What loads the dice?’”[67]
What loads the dice? There is the great question in which the realms of biology and of philosophy meet each other! Through that borderland no definite frontier has ever been traced, for in thought as in matter the saying is true that natural groupings have nuclei, but no boundaries. It is all the more essential that men of science should understand philosophy and its methods, and that philosophers should understand science. It is to be feared that at present the second of these desiderata is much more fully realized than the first.