CHAPTER I. THE THEORY DEFINED AND TESTS PROPOSED. "Old things need not be therefore true, O brother men! nor yet the new. By what process have all the different kinds of animal and vegetable organisms become what we now see them to be? This is the problem which has from time to time excited the interest of solitary thinkers, and which, within the last thirty or forty years, has profoundly agitated the scientific world. Two answers have been given to this question. On the one hand, it used to be asserted (it is still asserted by some) that the different kinds of animals and plants are the lineal descendants of organisms similar to themselves, and that those remote ancestors suddenly appeared upon the earth, some six thousand years ago, endowed with the power of reproducing their like from generation to generation. On the other hand, it is contended that all existing kinds of organisms, however complex, have been produced by successive changes from the simplest and least complex forms of life. The latter is the opinion of the majority of scientific men at the present day. This process is designated by the term Organic Evolution and evolution is defined by Mr. Herbert Spencer as the result of the joint action of growth or increase in size, and of development or increase in [the complexity of] structure.* As there have been only two theories in the field, to disprove the one was to establish at least the strong probability for the other. There is, however, another kind of argument which has been brought to bear:-Looking upon the organic world as a product of the past, studying as best we can the history of the changes on the earth's surface, we arrive at the conclusion that the organic world is just what we should expect it to be, if it were the result of the principle of evolution. So far as the first line of argument is concerned, we may venture to say that the strong reasons which men supposed they had for believing in the fixity of species have been overcome by the still stronger evidence in favour of the transmutation of species. But that is not all. It is the opinion of the overwhelming majority of scientific men that the main, if not sole, agent in this transmutation is the principle of Natural Selection. We have now to consider how far this assertion can be sustained. At the outset, it is of the greatest importance that we should clearly understand what we mean by Natural Selection, and realise that the phrase implies a very complex idea. But in order to understand what Natural Selection is we must first get a clear idea of what we mean by "Selection." Why is this principle invoked, and what is it able to accomplish? The answer is, that, in order that a race should undergo a permanent change equivalent to the transmutation of one species into another, it is necessary that variations should arise, that these variations should be inherited by the offspring, and that they should be continuously inherited until they become fixed in the race. Now the nature of this process will very much depend upon the nature of the variations acted The principle of selection is indispensable only in on. connection with those variations which are necessarily and inevitably associated with sexual reproduction. These provide materials for a considerable amount of modification, and it is easy to see why this should of necessity be the case. At the outset it is safe to say of all things animate and inanimate that "No compound of this earthly ball Is like another, all in all." Hence the two parents are not alike to begin with. And it seldom happens that the offspring resemble father and mother in exactly equal degree: one "favours" the father, another the mother. In these circumstances we need not be surprised to find that the strongest family likeness does not prevent the occurrence of individual differences. "Facies non omnibus una Nec diversa tamen; qualem decet esse sororum.” Between those who most closely resemble one another there is at least, as Mr. Wallace points out, an "absence of identity." Nor is this all. The offspring are not only compounds in ever-varying proportions of father and mother: they also tend to resemble, more or less, the grandfather or the grandmother, or some more remote ancestor, by the principle known as atavism or reversion to an ancestral type. As Oliver Wendell Holmes says, in his witty fashion: "At one moment we detect the look, at another the tone of voice, at another some characteristic movement of this or that ancestor, in our relations or others. There are times when our friends do not act like themselves, but apparently in obedience to some other law than that of their own proper nature. We all do things both awake and asleep which surprise us. Perhaps we have co-tenants in this house we live in. No less than eight distinct personalities are said to have co existed in a single female mentioned by an ancient physician of unimpeachable authority. In this light we may perhaps see the meaning of a sentence from a work which will be repeatedly referred to in this narrative, viz. :-'This body in which we journey across the isthmus between the two oceans is not a private carriage, but an omnibus.'”—(The Guardian Angel.) This union of different elements is well expressed by Matthew Arnold in the following lines: "Born into life!-man grows Forth from his parents' stem, And blends their bloods, as those Of theirs are blent in them So each new man strikes root into a far fore time." -Empedocles on Etna.) In the second place, it should be observed that this "individuality of the individual" may co-exist with the most absolute fixity of the type. "Nature," says Milne Edwards, "is prodigal in variety but niggard in innovation." There is only one way of dealing with this particular kind of variation in order to produce a transmutation of species, namely, that those variations which are similar to one another should be "selected," ie., that they should be isolated for breeding purposes from the other variants which have not their peculiar characteristics. "Man," says Mr. Belt, "isolates varieties and breeds from them; and continuing to separate those that vary in the direction he wishes to follow, a very great difference is in a comparatively short time produced."* But in order that this process should be successful, the isolation must be strictly and persistently carried out for many generations until the variation is fixed in the race. Mr. Darwin assures us that 66 A species may be highly variable; but distinct races will not be formed, if, from any cause, selection be not applied. The carp is highly variable: but it would be extremely difficult to select slight variations in fishes, whilst living in their natural state, and distinct races have not been formed; on the other hand, a closely allied species the gold-fish-from being reared in glass or open vessels, and from having been carefully attended to by the Chinese, has yielded many races.”—(The Variation of Animals and Plants under Domestication. vol. ii., p. 236.) Without selection individual differences will be swallowed up in the average of the race, through the principle which Mr. Francis Galton calls the regression to mediocrity. This principle differs from the ordinary action of atavism: which, as I have pointed out, will sometimes cause an individual to resemble a remote ancestor, and which produces an influence not to be easily calculated. The regression to mediocrity, on the other hand, represents the effect of the ancestry as a whole; and Mr. Galton seems to have succeeded in ascertaining the exact amount of this influence. This principle, I venture to believe, only applies to those variations which are inevitably and necessarily associated with sexual reproduction. Thus understood, it involves the absolute necessity for the strictest isolation of similar variants, but at the same time, it cannot be understood to mean that this regression to mediocrity will take place when similar variants are isolated for breeding purposes, for such an assertion would be diametrically opposed to the experiences of the cattle breeder and the pigeon fancier. "It will be seen" (says Mr. Galton) "from the large values of the ratios of regression, how speedily all peculiarities that are possessed by any single individual to an exceptional extent, and which blend freely together with those of his or her spouse, tend to disappear. A breed of exceptional animals, rigorously selected and carefully isolated from admixture with others of the same race, would become shattered by even a brief period of opportunity to marry freely.”— (Nature. vol. xxxiii., p. 297.) But Mr. Galton emphatically states that the law of regression does not invalidate the principle of selection: |