Parallel Paths: A Study in Biology, Ethics, and Art

by T. W. Rolleston

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.

However, we have to see now what Weismann, protagonist among contemporary biologists of the mechanical theory of the world, has to answer to the crucial question which he has allowed Osborn to set him.

The problem is to discover how innate, germinal variations can come about, of such a nature as to adapt an organism with striking accuracy to its surroundings and way of life, without our assuming either (1) that the exercise of function had any influence in causing heritable variations, or (2) that they were caused by any non-mechanical power, which, so to speak, had in view the objects which they fulfil. For the variations are to be regarded, on Weismann’s theory of life, as completely fortuitous in respect of the objects they serve. How, then, do they come to serve them, in most cases, so admirably well?

The general nature of Weismann’s explanation may be summed up in a curious illustration given by him in The Evolution Theory.[68] Let us suppose, he says, a snow-field surrounded by precipices on all sides, but with a narrow track leading away from it at one point. Scattered about on the snow-field are a number of persons. A sleigh is now projected among them from some outside point. Each person, when the sleigh comes near him, gives it a push, but he has no object in pushing it anywhere in particular, and simply sends it flying off in whatever direction he chances to be looking. What will happen under these circumstances? After more or less bandying about, the sleigh will, in the vast majority of cases, fall into one of the abysses round the snow-field and be lost But another is then launched on to the snow-field, and then another and another without end; and so, at last, it may happen that a series of pushes will take place which will send the sleigh over the narrow track to its goal.

The goal is supposed to represent some condition to which the organism (the sleigh) has to adapt itself. The random pushes which it receives are the multitude of variations constantly occurring in the reproductive cells. Most of these variations have no decisive tendency, favourable or unfavourable. If a series of unfavourable ones should occur, leading to some development which markedly impairs the chances of the organism for success in life, it, or its line of succession, dies out, and the unfavourable variation is, therefore, not perpetuated. This is illustrated by the sleigh going into the abyss. But if a favourable variation occurs, and is increased till it reaches ‘selection value,’ i.e. till it gives the organisms possessing it a distinct advantage over others in the battle of life, then this favoured type will ultimately, by the action of natural selection, drive out the less favoured, and will establish itself as the sole representative of the species. Having reached this level, of course the same process will go on further indefinitely.

Before criticizing this conception of evolutionary processes, we must inquire into the vital point of how the variations, the random pushes given to the sleighs, ever rise to such intensity as to have selection-value, and to make head against the influence of intercrossing. The explanation is certainly ingenious, but is so purely hypothetical and has an air so fantastic that it has commended itself to very few students of biology. Weismann would have us suppose that the determinants of which the hereditary substance in the reproductive cells is made up are carrying on with each other an incessant struggle for nutriment. If one of them succeeds in getting a little more than its neighbours it thereby grows stronger, and is able to attract still more nutriment to itself, and to impoverish those around it. It is thus launched, as it were, on an ascending scale, and will go on automatically if the variation caused by it proves favourable to the species. If it proves unfavourable (which ex hypothesi it is just as likely to do) its career will be put a stop to by the extinction of the line of descent which inherits this variation. Weismann’s theory of “Germinal Selection” is therefore simply an application to the reproductive cell and its contents of the Darwinian principle of Natural Selection.

The theory is one which plainly makes immense demands upon our faith. As regards the existence of a continual competition among the determinants, there may be reason to accept it, but hardly in the Weismann sense. Suppose two parents to unite, one healthy, well-nourished, full-blooded, the other starved and weakly, it is very likely that, in the resulting offspring, other things being equal, the determinants coming from the well-nourished frame will be seen to have surpassed in potency those from the weakly one. For the determinants are living protoplasm—they depend on nourishment derived from the blood of the organism in which they are lodged, and they are capable, no doubt, of being well-nourished or ill-nourished or possibly over-nourished, according to the constitution and history of that organism. But this is a very different thing from supposing that one determinant can begin to grow in the same cell at the expense of another, when both are absolutely embedded in an ocean of the same nutritive matter. There is not—of course in the nature of things there cannot be—a particle of evidence for the supposition. It is a pure imaginative hypothesis, and on the face of it a most improbable one. It is difficult to believe that it could ever have been adopted save as a desperate attempt to break through the ever-narrowing ring of evidence which is forcing investigation more and more towards a non-mechanical explanation of the processes of life. But even if it were true, what is gained by it? “Appropriate variational tendencies,” writes Weismann, “not only may present themselves, they must do so, if the germ-plasm contains determinants at all by whose fluctuations in a plus or minus direction the appropriate variation is attainable.”[69] But why must they? There is no ‘must’ about Chance, unless one extends its operations to infinity. Why is it so certain that the inequalities of nutriment, on which hereditary variability is supposed to depend, must necessarily run the gamut of all possible variations? There is no ‘must’ in this theory, except that it is the last ditch of the “mechanical conception of the economy of life.” It ‘must’ be true—or that conception must quit the field.