to the origin of single species, expose itself to the fate of being a priori rejected by science as unjustified, and of being a posteriori confuted by facts-a fate which it has richly and clearly experienced in the first half of our century. But the discussion of the metaphysical way does not belong to the present purely scientific part of our investigation; it will, however, be shortly taken up again in Book II. The other way, the scientificempirical, will have to be looked upon as correct when it can show the impelling forces of development in such powers and laws as are either still active to-day or at least have their points of connection in powers and laws active to-day. Such an attempt is the selection theory. We have already in Chap. II, § 1 and 2, given an outline of this theory, and have only yet to discuss its present state of tenability.

§ 3. The Theory of Selection.

The selection theory also is not entirely without support in the realm of observed facts. How simply it explains the fixedness of the differences of closely related species arising from their geographical and climatical home! how simply the similarity of the color of many animals from the color of their abode, through which they have protection against persecution! how simply the so-called mimicry-i.e., the similarity of certain species in form and color with form and color of entirely different species in the midst of which they live, a similarity which often gives them protection against persecution! The best known examples of this, in our regions, are the spinning caterpillars, which in a state of rest look strikingly like a twig of a tree or a shrub on which

they live. In other regions there is a multitude of the most striking freaks of nature of this kind-for instance, butterflies and other insects, which at rest look like the leaves of plants under which they live; butterflies living among other butterflies which, by an offensive odor, are protected against persecution, and although they are themselves a favorite food for birds, carrying the form and color of that badly-smelling family of butterflies. We can also add the orchideæ, and their resemblance to bees, flies, butterflies, spiders, etc. A. R. Wallace and Darwin themselves recur often to these striking appear

ances.

But herewith we have mentioned nearly every support which the selection theory has on the ground of observed facts. More numerous and more weighty are the objections to it. First of all, we have to state that the selection theory no longer enjoys that protection which the descent and evolution theories can justly claim, against the main objection, mentioned in Chap. III, §1, to all the ideas of descent, development and selection. That main objection is the permanence of species, observed through thousands of years; and the defense with which the descent and evolution theories successfully weaken it, is the statement of the fact that, since man appeared, no new species has originated, and that therefore the principle of the generation of species seems to have come to a stand-still. Now this fact is no longer in favor of the selection theory, but directly repugnant to it. For the selection theory expressly declares the origin of species through agencies that are all active still, and, therefore, if they really suffice to explain the origin of species, would not only have to generate new species,

but also to develop all the existing species. All those circumstances which, according to the selection theory, have led to change of species, are just as active to-day as they are supposed to have been from the beginning of organic life; and the effect which we observe is not change but permanence of species. The individuals still have individual qualities; they still have the tendency to inherit, in addition to the qualities of the species, those of the individual; the individuals still change their abode, and therewith also their conditions of life; a natural selection still takes place in the struggle for existence; and what is the result? From an observation stretching over thousands of years, we find nowhere an effect of natural selection going farther than alterations in growth and color and purely external changes in form. All the dispositions of organisms and their reciprocal action aim not at increasing the individual differences, but at reducing them to the average character of the species. When the species change their abode or their conditions of life, they either perish or remain constant; at least, with the exception of the slight modifications before mentioned. Even those alterations which artificial breeding produces, have a tendency to return to the original species: as soon as cultivated plants and domestic animals are left to themselves, they run wild, i. e., they reassume their original qualities. Even the bastard-formations either cease to be fertile, or, remaining fertile, finally return to one or the other stem-form of the originally crossed species. Nor can we oppose to these facts the consideration that the period of time during which mankind has observed the organisms is too short. For the permanence of very many

species can be traced through thousands of years, and the shortness of the period of our observations is amply counterbalanced on the one hand by the multitude of species from all parts of the organic systems which come under our notice, on the other by the immense alterations in the conditions of existence to which man submits plants and animals. How great, for instance, are the alterations in the conditions of existence which tropical plants undergo in our hot-houses and gardens! And the only alteration they show is that they are stunted and only bear blossoms with difficulty and fruits with still greater difficulty.* Now, if the ever-active selection principle does not produce in thousands of years even minimum alterations which can be observed, science certainly is justified in doubting for the present the asserted effect of that principle.

Thus not only are the facts directly opposed to the autocracy of the selection principle; but logic is also none the less so. For, under the most favorable circumstances, selection would only explain the preservation and perhaps also the increase of useful qualities and organs, if the same are already in existence and have shown themselves useful to the individual; but would not explain their origination. This would rather most emphatically be left to chance. According to the strict selection theory, it would be pure chance that among the thousands and thousands of individual qualities of the individuals of a species, such qualities are always existing as offer advantages to the individual in his struggle for existence. And it would be a second series of chances, which from generation to generation would * Compare v. Baer, "Studies, etc,” p. 294 ff.

have to coincide with the first, that among the individual qualities advantageous to the individual and making it victorious in the struggle for existence, there should be found always just those qualities which develop the species and raise it to a higher rank and order in the zoölogical and botanical systems. But the total of improbabilities which would have to be overcome continually in this theatre of chance, would in the course of generations necessarily amount to infinity. Thus, in the very beginning, insuperable doubts arise as to how we can explain from two causes the world of organisms which is so richly, beautifully, and systematically arranged. The first of these causes is the inclination to individual alteration, inherited indeed in the organisms, but in itself absolutely indifferent for the systematical idea in the framework of the organic systems and for the progressive element in the development. The other is the struggle for existence and natural selection, which approaches the organisms purely from without like individual variability, must as a whole appear a necessity, but in each single case in the concrete mixture of coinciding circumstances, would seem a work of chance for the individual which is to be changed.

Moreover, it is a demonstrable impossibility to explain the origin of just those organs and members in the structure of organisms which are systematically the most significant and functionally the most important, by means of natural selection. It is true that many of these organs and members, in their perfected state, offer to the organism an immense advantage over lower organisms; but if they had been originated through gradual development, they would have been in their first