CHAPTER XA.
THE INTEGRATION OF THE ORGANIC WORLD.
§ 314a. That from the beginning of life there has been an ever-increasing heterogeneity in the Earth’s Flora and Fauna, is a truth recognized by all biologists who accept the doctrine of evolution. In discussing the origin of species Mr. Darwin and others have been mainly occupied in explaining the genesis of now this and now that form of organism, considered as a member of one or other series, and regarded as becoming differentiated from its allies. But by implication, if not avowedly, there has been simultaneously accepted the belief that the forms continually produced by divergences and re-divergences, have constituted an assemblage increasingly multiform in its included kinds. And this, which we are shown by the process of organic evolution as followed out in its details, is a corollary from the doctrine of evolution at large, as was pointed out in § 159 of First Principles.
Meanwhile there has been little if any recognition of an accompanying change, no less fundamental. In the general transformation which constitutes Evolution, differentiation and integration advance hand in hand; so that along with the production of unlike parts there progresses the union of these unlike parts into a whole. Examples of various kinds before given will recur to the reader, and an addition to them has just been set forth in the chapter on “Physiological Integration.” One more example, world-wide in its reach, has still to be named.
For here it remains to point out that along with the increasing multiplication of types of organisms covering the Earth’s surface, there has been ever going on an increasing mutual dependence of them—an increasing integration of the entire aggregate of living things.
Many facts which are obvious and many which are quite familiar will be named as evidence. But I must be excused for reminding the reader of things that he knows and things that he may easily observe, since, unless the evidence, trite as it may be, is gathered together and properly marshalled, the generalization enunciated will not be thought valid.
§ 314b. Respecting the physiological characters of the earliest forms there is an assumption from which no escape seems possible—the assumption that they united animal and vegetal characters. Even among existing microscopic types of the lowest classes, there is such community of plant-traits and animal-traits that doubts respecting their proper places in one or the other kingdom are continually raised—doubts, too, whether, if regarded as vegetal, they are to be grouped as algoid or fungoid.
Here, however, without entering on moot questions, we may draw the à priori conclusion that these earliest living things were double-natured, in so far that they must have had the ability to assimilate from the inorganic world all the materials of which protoplasm consists—must therefore, along with the power of appropriating carbon from its gaseous compound, also have had the power of appropriating nitrogen, either from one of its combined oxides or directly from the air with which water is more or less charged. For before organic substances existed there could have been none but inorganic sources from which nitrogen could be obtained.
This conclusion concerns us only because it implies homogeneity of nature in these primordial forms of life. There could not at first have existed among these minutest of Protozoa even such vague distinctions as are now presented in a shadowy way by their modern representatives. And the implication is that during the period throughout which these smallest, lowest, and simplest living things alone existed, there could have been, in the absence of kinds, no mutual dependence.
Since, among various of the lowest types now known to us, the same individual exhibits a life which is now predominantly vegetal and now predominantly animal, we cannot err in assuming that there eventually took place differentiations of this original plant-animal type into types permanently unlike: some in which the traits were more markedly vegetal and others in which they were more markedly animal. As fast as this differentiation arose, there came the beginnings of co-operation between the predominantly vegetal types which by the aid of light formed organic matter from the inorganic world, and the predominantly animal types which, in chief measure, utilized the matter so formed. Evidently with the rise of such a differentiation came an incipient mutual dependence. If to the implied algoid type and the animal type there be added the fungoid type, somewhat intermediate in character, which in a large proportion of cases lives on the decaying remnants of the other two, we are furnished with a rude conception of the primary differentiations and the accompanying vague mutual dependences.
Speculation aside, it suffices to say that early in the history of life there must have arisen the distinction between Protozoa and Protophyta, and that this distinction foreshadowed that widest contrast which the higher organic world presents—the contrast between plants and animals. It is needless to do more than name the mutual dependence between these two great divisions. That, as being respectively decomposers of carbon dioxide and exhalers of carbon dioxide, they act reciprocally, as also in some measure by interchange of nitrogenous matters; and that the implied general co-operation serves in an indirect way to unite their lives, and in that sense to integrate the two kingdoms; needs not to be insisted upon. Further complications of the mutual dependence will be mentioned by and by. For the present it suffices to recognize this division of organic functions as the first which arose and as continuing to be that fundamental one which more than all others binds organisms at large together.