Natural selection

“ A propos to this point, I do not believe that anyone yet has half done justice to natural selection in respect of its action subsequent to the formation of species—at least, not expressly. But I must shut up. ”

“ We shall best understand the probable course of natural selection by taking the case of a country undergoing some slight physical change, for instance, of climate. The proportional numbers of its inhabitants will almost immediately undergo a change, and some species will probably become extinct. We may conclude, from what we have seen of the intimate and complex manner in which the inhabitants of each country are bound together, that any change in the numerical proportions of the inhabitants, independently of the change of climate itself, would seriously affect the others. ”

“ We have already seen that, when there is no change in the physical or organic conditions of a country, the effect of natural selection is to keep all the species inhabiting it in a state of perfect health and full development, and to preserve the balance that already exists between the different groups of organisms. ”

“ The expression of conditions of existence, so often insisted on by the illustrious Cuvier, is fully embraced by the principle of natural selection. For natural selection acts by either now adapting the varying parts of each being to its organic and inorganic conditions of life; or by having adapted them during past periods of time: the adaptations being aided in many cases by the increased use or disuse of parts, being affected by the direct action of external conditions of life, and subjected in all cases to the several laws of growth and variation. ”

“ Millions of years of genial climate and rich vegetation have filled the earth with a prolific and enormously varied population. Over this population the hand of natural selection is outstretched, as it were, and we are about to witness another gigantic removal of older types of life and promotion of those which contain the germs of further advance. As we have already explained, natural selection is by no means inactive during these intervening periods of warmth. ”

“ What if the orbit of Darwinism should be a little too circular? What if species should offer residual phænomena, here and there, not explicable by natural selection? Twenty years hence naturalists may be in a position to say whether this is, or is not, the case; but in either event they will owe the author of "The Origin of Species" an immense debt of gratitude. ”

“ This process of extinction Mr. Darwin has called "natural selection." Natural selection is not a force, but a process, resulting from the combined action of [279] the forces of environment. It is not a cause in any proper sense of the word, but a result of a myriad of interacting forces. The combination of these forces in a process of natural selection leading directly to a moral and spiritual goal demands an explanation in some ultimate cause. ”

“ Further, since the environment (i.e. the sum total of the external conditions of life) is continually changing, it follows that natural selection may slowly alter a type in adaptation to the slowly changing environment, and if in any case the alterations effected are sufficient in amount to lead naturalists to name the result a distinct species, then natural selection has transmuted one specific type into another. ”

“ Natural selection acts only by the preservation and accumulation of small inherited modifications, each profitable to the preserved being; and as modern geology has almost banished such views as the excavation of a great valley by a single diluvial wave, so will natural selection banish the belief of the continued creation of new organic beings, or of any great and sudden modification in their structure. ”

“ Here we see natural selection, with its iron and implacable rule, a real factor in the lives and development of these creatures, connected and increasing with an advancing animal evolution, but still only a term to express the modifying influences incidental to a struggle for existence. [33] In fact, natural selection is more an effect than a cause. ”

“ But the origination, and even the variation, still remains unexplained either by the action of insects or by any of the processes which collectively are personified by the term natural selection. We really believe that these exquisite adaptations have come to pass in the course of Nature, and under natural selection, but not that natural selection alone explains or in a just sense originates them. ”

“ Starting from the known experiences of breeders of domestic animals and cultivated plants, and duly considering the remarkable and sometimes astonishing changes that are wrought by simple selection, the problem was to detect among the multifarious phenomena of organic nature any agency capable of accomplishing what man thus accomplishes by selection. In detecting the agency of natural selection, working perpetually through the preservation of favoured individuals and races in the struggle for existence, Darwin found the true cause for which men were waiting. ”

“ To sum up the circumstances favourable and unfavourable to natural selection, as far as the extreme intricacy of the subject permits. I conclude, looking to the future, that for terrestrial productions a large continental area, which will probably undergo many oscillations of level, and which consequently will exist for long periods in a broken condition, will be the most favourable for the production of many new forms of life, likely to endure long and to spread widely. ”

“ Thus, as I believe, natural selection will tend in the long run to reduce any part of the organisation, as soon as it becomes, through changed habits, superfluous, without by any means causing some other part to be largely developed in a corresponding degree. And conversely, that natural selection may perfectly well succeed in largely developing an organ without requiring as a necessary compensation the reduction of some adjoining part. ”

“ Now, as I am credited by all my scientific friends with having discovered the theory of natural selection more than fifty years ago, and as the whole reading public have had this hammered into them with needless repetition during the whole of that period, it is rather amusing to be told now that I do not know what natural selection is, nor what it implies. ”

“ Whether natural selection has really thus acted in nature, in modifying and adapting the various forms of life to their several conditions and stations, must be judged of by the general tenour and balance of evidence given in the following chapters. But we already see how it entails extinction; and how largely extinction has acted in the world's history, geology plainly declares. ”

“ "I am convinced that natural selection has been the main but not the exclusive means of modification." ”

“ It is clear that a species sensitive to every shock of the environment on the organism would be unstable, and hence at a disadvantage. But, on the other hand, the ability to answer by adaptation to long-continued and persistent environmental influence or to oft-repeated and consistent performance of function would be so distinct an advantage to the species which possessed it, that, if it lay within the possibilities of organic nature, natural selection, always, as [175] we are told, on the look out for every possible advantage, would assuredly seize upon it and develop it. ”

“ To quote Darwin, "In one sense the conditions of life may be said, not only to cause variability, either directly or indirectly, but likewise to include natural selection, for the conditions determine whether this or that variety shall survive."34 The variability of man does not mean that every external influence leaves its mark upon him, but that man as an organism, by the preservation of beneficent variations and the elimination of deleterious ones, is gradually adapted to his environment, so that he can utilize most completely that which it contributes to his needs. ”

“ It is, of course, true that the significance of the argument is affected by the circumstance that organisms by the influence of natural selection can preserve a continuous adaptation to an environment which is gradually becoming modified. ”

“ Let us now look to the action of natural selection on special characters. Although nature is difficult to resist, yet man often strives against her power, and sometimes, as we shall see, with success. From the facts to be given, it will also be seen that natural selection would powerfully affect many of our domestic productions if left unprotected. ”

“ The same difficulty of distinguishing between selection and the definite effects of the conditions of life, is encountered in a still higher degree when we compare closely allied natural forms, inhabiting two countries, such as North America and Europe, which do not differ greatly in climate, nature of soil, &c., for in this case natural selection will inevitably and rigorously have acted during a long succession of ages. ”

“ Hence we see that this, incomparably the greatest work which the biological sciences have seen, begins with an explanation and defence and definition of the sphere of natural selection—then passes to consider difficulties which are partly those of natural selection, and partly of organic evolution—while it finally treats of the evidences of the latter process and the difficulties which a belief in it encounters. ”

“ One can readily see how natural selection would be evoked in order to explain this condition of affairs. Those forms that varied in the direction of looking like a leaf would be the most perfectly protected, and this feature being fostered by natural selection, would, in the course of time, produce a race of butterflies the resemblance of whose folded wings to a leaf would serve as a protection from enemies. ”

“ We have seen in the preceding chapter how every form of organic life during all the vast extent of geological time has been subject to the law of natural selection, which has incessantly moulded their bodily form and structure, external and internal, in strict adaptation to the successive changes of the world around them ”

“ Always there must have been, and always there must continue to be, a survival of the fittest; natural selection must have been in operation at the outset, and can never cease to operate. While yet organisms had small abilities to coordinate their actions, and adjust them to environing actions, natural selection worked almost alone in moulding and remoulding organisms into fitness for their changing environments; and natural selection has remained almost the sole agency by which plants and inferior orders of animals have been modified and developed. ”

“ The wide range over which the theory of natural selection applies is due to the fact that the environment is never uniform and never constant, so that modifications on the part of the organism have a chance of suiting its varied and changing character. ”