The Doctrine of Evolution: Its Basis and Its Scope

by Henry Edward Crampton

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Without leaving the group of one-celled animals typified by Amoeba, we find colonies of the most elementary biological nature, where other natural obligations are added to the two of greatest importance. Some species of the bell-animalcule, Vorticella, provide characteristic examples of these primitive compound protozoa. Here the assemblage is made up of one-celled individuals essentially similar to one another in structure and in physiological activities; in the latter respect each one of them is like Amoeba as well. They may remain together for a longer or shorter period, or during their whole existence until the time of reproduction. Like the solitary protozoön, each member leads a complete life in and by itself, equivalent to that of every biological unit. It obeys the two great laws already laid down, but in addition it seems to be required to remain with the others for some mutual good. The biological value of the association which imposes this additional obligation may be found perhaps in the fact that a large group is not so readily eaten by an enemy as an individual cell; but it is clearer that the process of reproduction, which consists of the fusion of small "gametes," or nucleated fragments produced by diverse or similar parents, must be greatly facilitated by the occurrence of gamete-forming individuals in one and the same colony. "To remain together" is the new duty imposed by nature for the good of all and for the welfare of each member of the group. Some biological advantage accrues to the several components, just as the banding of wolves enables the pack to accomplish something which the single wolf is unable to do, although in the latter case it is not so much a reproductive alliance that is formed as an offensive and defensive union.

One step higher in the scale stands the plant-form called Volvox, near the border-line between the one-celled and the many-celled organisms. This aquatic type, about the size of the head of an ordinary pin, is a hollow spherical colony, with a wall composed of closely set cellular components. These elements are not all alike, as in the case of colonial protozoa like Vorticella, for they fall into two classes which are distinguished by certain structural and functional characteristics. Most of them are simple feeding individuals which absorb nourishment for themselves primarily, but they pass on their surplus supplies to less favored neighbors if occasion demands. The other members begin life like the first-named, but later they become specialized to serve as reproductive individuals solely. Every member of the colony must obey the first precept of nature, otherwise it would be unable to play its part in the life of the whole community. But the discharge of the second natural obligation, namely to preserve the race, is here assigned to some, and to some only, of the whole group of cell individuals. It follows therefore that the division of the tasks necessary for the maintenance of a complete biological individual, and the differentiation of the members of the group into two kinds, leads to the establishment of an individuality of a higher order than the cell. Neither the purely nutritive nor the reproducing member is complete in itself; the two kinds must be combined to make a perfect organism. The life of any member can be selfish no longer, for if it is to exist itself, it must help others for the mutual advantage of all. A clear social relation is thus established; and the reflex conduct of the units of a Volvox colony can be justly denoted altruistic, even though in this case, as before, there can be no conscious recognition of the reasons why mutual interests are best served by what is actually done.

One of the most interesting and significant aspects of the life-history of Volvox is the appearance for the first time of biological death. More elementary organisms are immortal potentially even if not actually, for every portion of the body is capable of passing over into an animal of a succeeding generation. But in Volvox a division of labor has been effected of such a nature that most of the components discharge the tasks of individual value, and with the performance of these they die. Only the reproductive members are immortal in the sense that Amoeba is, for they only have a place in the chain of consecutive generations of Volvox colonies. From the standpoint of the nutritive individual it is better to be relieved of the reproductive task in order that there may be no interruption of its specialized activities for the good of all, but the entailed mortality is certainly disadvantageous to it. It is the higher interest of the colony as a whole that supersedes the welfare of the parts taken singly, and this larger welfare is safeguarded by a differentiation worked out by natural evolution which results in the assignment of personal and racial duties to different individuals, at the cost ultimately of the lives of the former.

We now reach the realm of the true many-celled animals, or Metazoa, where the biological units are combined to form an organic association displaying many more resemblances to a human society. The freshwater polyp Hydra, like the foregoing illustrations, is one whose structure has already been discussed in the earlier chapters, but now we may use it for an analysis of another series of biological phenomena. Its sac-like body consists of two cell-layers; the outer one is concerned primarily with offense and defense, while the inner layer is made up of digesting or nutritive elements. The essential cells concerned solely with reproduction lie below the outer sheet. Comparing this animal with an association like Volvox, we discover the same differentiation into immortal germ-elements and mortal cells, concerned respectively with the Hydra's racial existence and with its individual life; but far-reaching changes have come about in the biological relationships of the second class of cells. In describing the new phenomena it is absolutely necessary to employ the terms of human social organization, because the Hydra's body is a true colony of diverse cells in exactly the same sense that a nation is a body of human beings with more or less dissimilar social functions.

To begin with the differentiation into ectoderm and endoderm, the organism is comparable to a human community made up of military and agricultural classes. The cells of the former group protect themselves and the feeding elements also, while the units of the second defenseless type devote themselves to the task of provisioning the whole community, giving supplies of food to the defenders in exchange for the protection they afford; each kind needs the other, and each performs some distinctive task for the other as well as for itself. But the parallel thus drawn need not stop here. In the case of the outer layer, the cells are mostly flat covering elements that are the first to be torn off and injured when the animal is attacked. Scattered about among them are sense-cells standing like sentinels with delicate upright processes which receive stimuli from without the sense-cells transmit impulses to the network of nerve-cells below, which is a counterpart of the signal corps of an army, keeping all parts of the whole organization in communication with one another. Most wonderful of all are the stinging-cells of the outer layer; these produce a flask-shaped, poisoned bomb which is discharged by the convulsive contraction of the cell itself so as to stun and injure the enemy or prey. The bomb-throwing cells die immediately after they have ejected their missiles; like soldiers participating in a forlorn hope, they sacrifice their lives in one supreme effort of service to the cell-community of which they are members.

These and similar facts prove conclusively that Hydra is a true community even in the human sense, and that the laws of biological association are established at a point far below the level of the insects. The individuality of the unit is still maintained, and each cell must guard its own interests to a certain degree, but the original independence of the unit has become so altered by differentiation and division of labor that a close interdependent relation has come about. The complete individual is now the whole aggregate; it is the entire Hydra itself which must obey the primary commands of nature to live efficiently and to perpetuate its kind. True it is that the life of the higher individual is the sum total of the activities performed by its constituent cells, but no one of the varied specialized elements is biologically perfect by itself or equivalent to the whole. And, as we have seen, the welfare of the complete animal takes precedence over that of any one of its parts, just as the existence of a nation may be preserved only by the death of soldiers warring for its honor and life.

If, now, we should pass on to the more complex organisms like worms and insects and vertebrates, and should disregard the communal relations of some of these animals, each individual proves to be like Hydra as regards the principles underlying its make-up and workings. A single bee, like a man, is a definitely constituted aggregate of cells, differing as a whole from Hydra only in the degree of differentiation exhibited by its constituent elements. Instead of a loose network of nerve-cells there is the far more complex nervous system whose evolution has been outlined in the sixth chapter. The blood-vascular and respiratory and excretory systems have become well organized, in response, so to speak, to the demands on the part of the nervous and alimentary organs that they may be relieved of the tasks of circulation and respiration and the discharge of ash-wastes. Therefore the cells which make up an insect and a man are more diverse, they have more varied interrelationships, and they are far more interdependent then in the case of the components of Hydra. Yet all the many-celled organisms that we are so accustomed to regard as individuals are really communities, demonstrating the existence and partial antithesis of the great laws of egoism and altruism, which are traceable even down to Amoeba and its like.

So much has been made of the lower kinds of cell-associations because the mind of the layman is unconsciously imbued with the idea that human society is a new thing,—an idea which we now see it is necessary to discard at the outset. Indeed, the cell-association of the Hydra and insect type is a more compact and a more stable kind of community than any group of human individuals worked out by nature toward the present end of the whole scheme of evolution. That is to say, the subordination of cell-interest to cell-group welfare, while it must not go so far as to render the unit incapable of doing its work, is sufficiently advanced to make uncontrolled individualism impossible. Let any class of Hydra's cells, such as the nerve or muscle network, assume to exercise a selfish preeminence or to conduct a "strike," the other classes, like the feeding cells, would not be properly served and they would be unable in consequence to work efficiently for the strikers. The immediate result would be suicidal, for the selfish nerve-class would inevitably suffer through the downfall of the whole social fabric. It is a nicely adjusted equilibrium that is established, where the "equal rights" of all the diverse cells consist in freedom to play a special part in the life of the group, serving other individuals in return for their service. The Golden Rule is a natural law as old as nature; for even in Hydra's life, unconscious discharge of duties to the race, and hence to others, is obligatory. And all these low types of organic associations evolved ages before the rules of human social order were vaguely recognized by the reflective self-consciousness of man, to be formulated as the science of ethics.

The evolution of the wonderfully varied societies found among insects begins with the solitary insect itself, just as this, viewed as a cell-community, originates from one-celled beginnings like Amoeba through progressive evolution in time. The similarity between social insects and human associations is clearer than in the case of a comparison between an example from either group and a cell-community, because the higher forms lack the organic contact of the components which is so prominent a feature in the lower instance. The social bonds are looser and they allow a freer play of the constituents; but nevertheless the same laws that control the activities of the cells making up what we now take as the individual element, command obedience on the part of the interrelated members of an insect community with equal strictness.