Fixity of species

“ It is in fact conceded by many eminent zoologists and botanists, as before explained, that whatever may be the nature of the species-making power or law, its effects are of such a character as to imitate the results which variation, guided by natural selection, would produce, if only we could assume with certainty that there are no limits to the variability of species. ”

“ By 'Natural Selection' is meant the result of all the destructive agencies of Nature, destructive to individuals and to races by destroying their lives or their powers of propagation. Evidently, the cause of the distinction of species (supposing such distinction to be brought about in natural generation) must be that which causes variation, and variation in one determinate direction in at least several individuals simultaneously. ”

“ And the dilemma then presents itself to us anew:—either we must accept the doctrine of the transmutation of species, and must suppose that the organized species of one geological epoch were transmuted into those of another by some long-continued agency of natural causes; or else, we must believe in many successive acts of creation and extinction of species, out of the common course of nature ”

“ May not the fifty thousand species of beings now discoverable, be all the species whose existences have continued to be fit, compatible, and harmonious? May not the known extinction of many species be received as evidence, therefore, of the gradual decay of the powers which sustain organized being on our planet? May not the extinction of one species render the existence of others more unfit, by diminishing the number of final causes? ”

“ But it is the object of the present paper to show that this assumption is altogether false, that there is a general principle in nature which will cause many varieties to survive the parent species, and to give rise to successive variations departing further and further from the original type, and which also produces, in domesticated animals, the tendency of varieties to return to the parent form.
The life of wild animals is a struggle for existence. ”

“ 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. ”

“ Since species are continually undergoing modifications giving them some superiority over other species or enabling them to occupy fresh places in nature, it may be asked—Why do any low forms continue to exist? ”

“ We must be cautious in attempting to correlate as strictly contemporaneous two formations, which include few identical species, by the general succession of their forms of life. As species are produced and exterminated by slowly acting and still existing causes, and not by miraculous acts of creation and by catastrophes ”

“ Should it be urged that the present tendency toward reducing species be taken as an evidence that species had not before been properly defined, then it offers a stronger argument still in favor of the fact that species are even more variable than had before been supposed, leaving the greater possibility of larger numbers of these ultimately surviving. Again, the assumption that the limitation of specific variation had not been properly indicated, shows how reprehensible has been the work of some of those who have burdened our literature with their bad species. ”

“ Nevertheless, such a conclusion, even if well founded, would be unsatisfactory, until it could be shown how the innumerable species, inhabiting this world have been modified, so as to acquire that perfection of structure and coadaptation which justly excites our admiration. Naturalists continually refer to external conditions, such as climate, food, etc., as the only possible cause of variation. ”

“ Besides, it is an established fact, confirmed by all our observations stretching over thousands of years, that the characteristics of species are preserved in spite of all individual modifications, and that this preservation of the characteristics of species has its cause essentially in the free crossing of individuals. ”

“ Between these extremes the species will present various degrees of capacity for ensuring the means of preserving life; and it is thus we account for the abundance or rarity of species. Our ignorance will generally prevent us from accurately tracing the effects to their causes ”

“ The answer in each case is, that all such causes of modification in the animal kingdom are limited; that when once a distinct species is in existence, we have no evidence that it loses its distinct type or merges itself in another, although the earth may be full of evidence that types which formerly existed are no longer among the living organisms. ”

“ Why, in making a brand-new species, shouldn't Nature have all the latest improvements from the start, just as man does in building a brand-new home? If each species was separately created it is hard to understand why these useless or harmful organs should be kept ”

“ And it is this period of increase, of abundance, not a period of struggle, which has developed the variations we now have before our eyes. In the same manner one must conclude, with regard to the rarer species, that the formerly existing numerous varieties were destroyed during the period of decline, that is, of overpowering pressure. We have abundant proof of this in the fact that domesticated species, which are carefully tended and fed, and so wholly withdrawn from the struggle for existence, vary enormously, and produce the most wonderful monstrosities. ”

“ But I vehemently protest against you or any one making such cases especial marvels, without you are prepared to say why each species in any flora is twice or thrice, etc., rarer than each other species which grows in the same soil. The more I think, the more evident is it to me how utterly ignorant we are of the thousand contingencies on which range, frequency, and extinction of each species depend. ”

“ Finally, we have seen that natural selection, which results from the struggle for existence, and which almost inevitably induces extinction and divergence of character in the many descendants from one dominant parent-species, explains that great and universal feature in the affinities of all organic beings, namely, their subordination in group under group. ”

“ And the apparent existence of such a radical distinction between the varieties produced under domestication and true physiological species was an objection, not only against natural selection, but also against evolution itself; for it meant that we do not see now, nor within the limits of human observation, organisms actually getting transformed, through the accumulation of variations, into new species differing from their progenitors by the final test of specificity of character. ”

“ Do species under stress, and feeding on strange food or living in unaccustomed climates, betray any exceptional tendency to produce abnormality? Have there been, so to speak, storms and riots of variation in some cases? Can differences establish themselves while outer necessity remains neutral? Can variations amounting to specific differences in colour and form arise as a sort of play of the germ plasm and be tolerated rather than selected by nature? ”

“ But whether it be species belonging to the same or to a distinct class, which have yielded their places to other modified and improved species, a few of the sufferers may often be preserved for a long time, from being fitted to some peculiar line of life, or from inhabiting some distant and isolated station, where they will have escaped severe competition. ”

“ The chief evidences of the theory of descent are to be found in homologies, in the correspondences of organs and functions, as revealed by comparative anatomy and physiology, in the recapitulation revealed by embryology, in the structure of parasites, in rudimentary organs and reversions to earlier stages, in the distribution of animals and plants, and in the possibility of still transforming, at least to a slight extent, one species into another, by experimental breeding.
Transformation and differentiation go on in nature as a vast, ceaseless, but blind process of selection. ”

“ But animals or plants which thus differ in a state of nature are always classed as distinct species, and thus we see how, by the continuous survival of the fittest or the preservation of favoured races in the struggle for life, new species may be originated. ”

“ To be aware that these barriers exist, and yet to feel surprised, especially in a country where the species are principally wingless, that we do not discover indications of a general uniformity in its fauna, involves an absurdity,—unless the doctrine of specific centres of creation be a mere coinage of the brain. ”

“ Thus extinction and natural selection will, as we have seen, go hand in hand. Hence, if we look at each species as descended from some other unknown form, both the parent and all the transitional varieties will generally have been exterminated by the very process of formation and perfection of the new form. ”

“ In laying hands upon the sacred ark of absolute permanency, in treating the forms that had been regarded as types of fixity and perfection as originating and passing away, the "Origin of Species" introduced a mode of thinking that in the end was bound to transform the logic of knowledge, and hence the treatment of morals, politics and religion. ”

“ We see in many cases in the more recent tertiary formations that rarity precedes extinction; and we know that this has been the progress of events with those animals which have been exterminated, either locally or wholly, through man’s agency. ”

“ Natural conditions do not permit of the existence of too many species or sub-species. But it is clear that there are types, call them genera, species, or what you will, that have, by virtue of some inherent fitness and flexibility of adaptation, survived and mastered other types. ”

“ Whenever we can precisely say why this species is more abundant in individuals than that; why this species and not another can be naturalised in a given country; then, and not until then, we may justly feel surprise why we cannot account for the extinction of any particular species or group of species. ”

“ The facts of variability, of the struggle for existence, of adaptation to conditions, were notorious enough; but none of us had suspected that the road to the heart of the species problem lay through them, until Darwin and Wallace dispelled the darkness, and the beacon-fire of the 'Origin' guided the benighted. ”

“ It might be the natural supposition, if we had only one set of species to account for, or if the successive inhabitants of the earth had no other connections or resemblances than those which adaptation to similar conditions, which final causes in the narrower sense, might explain. ”

“ The mimicked species are, he suggested, abundant because they possess some special means of protection, such as an unpleasant taste or smell, and they have an unpleasant reputation which greatly aids them in the struggle for life; while the mimicking species, by their superficial resemblance, are enabled to live upon that reputation without possessing the special means of defence. ”

“ From these several considerations I think it inevitably follows, that as new species in the course of time are formed through natural selection, others will become rarer and rarer, and finally extinct. ”

“ Thus we should have to believe that man not only formerly succeeded in thoroughly domesticating several highly abnormal species, but that these same species have since all become extinct, or are at least now unknown. ”

“ If species have died out slowly and naturally in the history of the earth, and new species have made their appearance at the same time, may not these new species have arisen slowly and naturally? Suppose these simple and purely natural causes, that had brought about the extinction of certain species, had been for others the very starting-point of development? ”

“ We have seen that it is the common, the widely-diffused, and widely-ranging species, belonging to the larger genera, which vary most; and these will tend to transmit to their modified offspring that superiority which now makes them dominant in their own countries. Natural selection, as has just been remarked, leads to divergence of character and to much extinction of the less improved and intermediate forms of life. ”

“ If you ask why, if species have descended from other species by fine gradations, do we not everywhere see innumerable transitional forms? Why is not all nature in confusion, instead of the species being, as we see them, well defined? The answer is that the intermediate species have become extinct, that we must look upon each existing species as having descended from some unknown forms; that natural selection acts slowly by preserving profitable modifications. ”

“ We are further of opinion that every species, as well as every individual, has certain periods of growth, of bloom, and of decay, but that the decay of a species is degeneration, not dissolution, as in the case of the individual. ”

“ But this is a false view; we forget that each species, even where it most abounds, is constantly suffering enormous destruction at some period of its life, from enemies or from competitors for the same place and food; and if these enemies or competitors be in the least degree favoured by any slight change of climate, they will increase in numbers; and as each area is already fully stocked with inhabitants, the other species must decrease. ”

“ When we reflect on the astonishing fecundity of each particular species, on the quick and prodigious multiplication of certain animals [88] which come into existence, as it were, to desolate the fields and ravage the earth, we are astonished they do not oppress Nature with their numbers, and after having devoured her productions become themselves victims to the destruction they have made. ”