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

by T. W. Rolleston

“If,” wrote Darwin, “it could be proved that any part of the structure of any one species had been formed for the exclusive good of another species, it would annihilate my theory, for such could not have been produced through natural selection.”[107]

Certainly it could not, but neither could other adaptations. Natural selection, as Darwin knew well enough, does not “produce” anything—all it can do is to depress the less favourable variations presented to it in favour of the more favourable ones. As Darwin never professed to have sounded the depths of the problem of variation, it is not clear why variations favourable to another species than the one in which they occur should be presumed to be impossible. It is true that they would not illustrate or come under the operation of natural selection, but neither would they contradict it—they would simply be outside it. Individuals unquestionably exhibit modifications intended not for their own personal benefit, but for that of the species—for instance, the maternal instincts. The modification of a part in the interest of the whole to which it belongs may, perhaps, turn out to have the same essential significance whether the part is an organ or instinct belonging to the synthesis called an individual, or an individual belonging to the synthesis called a species, or a species belonging to some fauna or flora of the globe. In any case, the question where synthesis is arrested, and where the fight for one’s own hand begins, is one of great interest and must be here briefly discussed. Cases such as those of which Darwin rejected the possibility certainly appear to be rare, if they exist at all. The naturalists of the older school, of course, saw them everywhere—the rattlesnake’s rattle was to warn its victims, the colouring of flowers was to give pleasure to man, and so forth. Most of these cases have been exploded by modern research. The modern naturalists, however, may not be right in refusing to see them anywhere. The question demands much special study and observation. Reverting to the case of flowers and their secretion of honey, one is struck by the fact that in the Viola family there exist flowers more or less conspicuous, and endowed with scent and with honey-filled nectaries, which usually do not play any part at all in fertilization. The process of fertilization in Viola is carried on by small flowers hidden under the leaves which never open, and which fertilize themselves. Again, at the base of the laurel leaf, on each side of the midrib, there are two small glands filled with honey, and bees may be observed biting into these in the early part of the year before flower-honey is plentiful. Nägeli has an ingenious argument to show the existence, not exactly of disinterested aid among species, but of something which would make such aid look more possible than it does, of a mutual responsiveness, namely, between the form of the honey-receptacles of certain flowers and the probosces of the insects which frequent them. Taking a short honey-tube as the normal and original condition among plants, and a short proboscis among insects, he argues that the honey-tube could not have lengthened without depriving the species in which it did so of the chances of insect-fertilization unless the insect-proboscis in certain species lengthened simultaneously.[108] Cases also have been noticed of sea-anemones, which attach themselves to the shells of hermit crabs and by their poisonous tentacles repel attacks on the crab.[109] The crab is no doubt useful to its guest by providing it with the means of locomotion. Still, the case of mutual help between two such different orders of beings is remarkable. A very peculiar case is that of the waterfern, Azolla, which has certain roomy cavities on the underside of its leaves. These are always found to be occupied by a small unicellular organism of the Alga order (Anabæna). It is of no apparent use to the Azolla, which provides it a home. The arrangement must have been of immensely long standing, for it occurs in all the four species of Azolla, one of which is found in America, two distributed over Australia, Asia, and Africa, and one only in the Nile. It must, therefore, have arisen before the original species split into four.[110]

It would be rash to conclude from these and some similar curiosities that we are really in the presence of the phenomenon of disinterested aid given by one species to another. The question needs more investigation. But an important general consideration arises in this connexion. It is clear that there could be no advance in evolution if nature consisted solely of a multitude of independent units of life, fiercely competing against or warring with each other. It is equally clear that no advance could take place if every organism found an environment so perfectly adapted to it as to call for the very minimum of effort and strain in the maintenance of life. Between the chaos of the first supposition and the lubberland of the second there must be a condition of nature in which synthetic organization is carried just to the point at which life will have the maximum power to perfect and to realize itself. Looking at the conditions of nature as we know them, and at the majestic expression of material and spiritual life which those conditions have permitted, we may well be content to believe that both the synthetic process, as far as it goes, and its apparent suspension at a certain point in the ascending scale, are the outcome of one and the same motive and have one and the same significance—they both alike mean and make for the conservation, the development, the enrichment of life.

Against this view there is an argument which has hitherto only been glanced at, but which must now be discussed in more detail. It is represented in a recent work by Prof. Conrad Günther, one of the latest champions of the theory of chance variations and natural selection as the sole explanation of evolution, who has assembled a number of instances to show that the “purposive force” which biologists are now coming to believe in “often fails in living beings.” Such are, for example, the fact that an Amœba seeking nourishment will take in a particle of stone or anything that comes in its way;[111] that the mutual relations of flowers and insects are often unsuitable; that a bee will sting a human being just as it will another insect, although the sting, only meant for the latter kind of use, cannot be withdrawn from the human skin; that embryos often go astray during development; that a cricket which tries to escape in the open by burying itself in the earth will act similarly if you set it on a glass plate; and so forth. Nature, of course, teems with such cases—one might add the singular degeneration of the slave-making ants already described in some detail.[112] “If,” he concludes, “the purposive reaction in the vital force of animals were independent of the external world, they would be armed against all contingencies, and that is not the case.”[113]

Thus, too, Prof. Eimer, who in dealing with cases where the alleged X factor in Nature has gone wrong, writes:—

“The zoologist can hardly accept the existence of such a dominant inner factor ever pushing toward advance, when he recalls the host of regressive structures which he has to see.”[114]

Now when the cause of physico-chemical versus vital agencies comes to be tried, not in the laboratory but in the study, not by science but by philosophy, the first question that will be asked is, What, then, is your distinction between ‘vital’ and ‘physico-chemical’ energies? How are we to recognize when we are in presence of the one or of the other? The usual answer to this searching question is that in vital agency we find a directive, a purposeful, a psychic element, whereas physico-chemical energies seem to be nothing but the play of a blind, indifferent mechanism. But, it will be rejoined, how can any one affirm that physico-chemical energies are not also vital, directive, psychic? Is there not, in fact, something psychic in the very conception of energy? To these questions there seems to me no conceivable reply. When a ‘vital’ energy has been reduced to a ‘physico-chemical,’ we have evidently explained nothing—we have only exchanged one mystery for another.

Yet if there is no difference in essential nature between one kind of energy and another, there does appear a marked difference when we come to consider them in relation to particular results of their operation. Let us take an example. We explain that classic instance of gravitation, the fall of an apple, by reference to the law formulated by Newton which extends to every particle of matter in the visible universe. But we also find that the fall of the apple is, for apples, a necessity of life; if the seed did not fall to the ground when ripe there would be no more apple trees. Yet gravitation acts quite indifferently to the life of the apple. Whether the branches overhang a river, or a street, or a plot of fertile ground, the apple will fall straight towards the centre of the earth. The fulfilment, therefore, of the vital needs of the apple is plainly a by-product of the force of gravitation. In this relation, gravity has no directive or psychic element. Yet in larger relations, we have to take note of the fact that if there were no such thing as gravity, there would be no apples and no earth. Thus the law of gravitation is a condition of life as we now know it. The fact that it acts mechanically, without selection or purpose, in relation to particular occurrences is quite consistent with the view that it, or the conditions of the ether from which it possibly arises, may be directive and psychic in relation to life as a whole, or rather to what we recognize as the manifestation of life in the material universe.