Animal species

“ In a former discussion, I have asked for facts which show, aside from the theory, that any one species of animal, distinctly marked as a continuing type, is connected by intermediate types or forms with any pre-existing race of another character. ”

“ But there is no recorded or known instance in which there has been produced under domestication an animal which can be said to be of a different species from its immediate known progenitors, or one that differed from its remote known progenitors in any but minor and adventitious peculiarities of structure. ”

“ CROSSING OF RACES AND SPECIES IN THE ANIMAL AND VEGETABLE KINGDOMS.—MONGRELS AND HYBRIDS. I. Sexual unions in plants, as in animals, can take place between individuals of the same species and the same race; further, between different races of the same species, and, finally, between different species. ”

“ Considerations of this character should be encouraging to those who may be intimidated by the idea of large numbers of species. Then, of course, it should be remembered that there are many aspects of ecological work which do not meet with this variety of animals. ”

“ Referring the reader to the articles Histology and Physiology for evidence of the similarity of minute or ganisation both in structure and function, through the range of animal life upward to man, and to the article Animal Kingdom for the general classification of the series of invertebrate and vertebrate animals, we have here to show in outline the relations between man and the species most closely approaching him. ”

“ They may be said to be the dominant race of mammals in the present day, for whilst over a thousand species are known to science, and these mostly of very wide geographical range, there are vast and increasing numbers of individuals representing many of the species. ”

“ Every one who has tried to make extensive local lists of species knows that it requires many years of collecting to secure a large number of species. These rare species are generally of quite minor importance ecologically. ”

“ yet, they can show that any existing species—animal or vegetable—when placed under conditions different from its previous ones, immediately begins to undergo certain changes fitting it for the new conditions. They can show that in successive generations these changes continue; until, ultimately, the new conditions become the natural ones. They can show that in cultivated plants, in domesticated animals, and in the several races of men, such alterations have taken place. ”

“ There is another and allied difficulty, which is much more serious. I allude to the manner in which species belonging to several of the main divisions of the animal kingdom suddenly appear in the lowest known fossiliferous rocks. ”

“ This historical method of investigation applied to the organic world has brought new and unexpected views regarding the antiquity of life.
The Diversity of Living Forms.—Sooner or later the question of the derivation of the animals and plants is bound to come to the mind of the observer of nature. There exist at present more than a million different kinds of animals. The waters, the earth, the air teem with life. The fishes of the sea are almost innumerable, and in a single order of the insect-world, the beetles, more than 50,000 species are known and described. ”

“ Let us see how far above principles of variation apply to wild animals. Wild animals vary exceedingly little—yet they are known as individuals{47}. British Plants, in many genera number quite uncertain of varieties and species: in shells chiefly external conditions{48}. ”

“ 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. ”

“ One is that the plants and animals now existing mostly differ from the plants and animals which have existed. Though there are species common to our present Fauna and to past Faunas, yet the facies of our present Fauna differs, more or less, from the facies of each past Fauna. ”

“ We have a practical illustration of the difficulty in the never-ending doubts whether many closely-allied mammals, birds, insects, and plants, which represent each other respectively in North America and Europe, should be ranked as species or geographical races ”

“ Amongst animals which unite for each birth, and which are highly locomotive, doubtful forms, ranked by one zoologist as a species and by another as a variety, can rarely be found within the same country, but are common in separated areas. ”

“ But the best illustrations are yielded by animals—those animals at least in which we have, besides an increased supply of nutriment, a diminished expenditure. Two classes of comparisons, alike in their implications, may be made—comparisons between tame and wild animals of the same species or genus, and comparisons between tame animals of the same species differently treated. ”

“ The Creator has bountifully stored the earth and the ocean with animals and vegetables. Our attention is here circumscribed to the most exalted class, the Human Species; leaving to the naturalist a description of quadrupeds, birds, fishes, insects, and vegetables. By far the largest proportion of the human species are stationed to the north side of the equator, and even to the north of the tropick of cancer. ”

“ Under these circumstances, as it is admitted on all sides that races occur in Nature, how are we to know whether any apparently distinct animals are really of different physiological species, or not, seeing that the amount of morphological difference is no safe guide? ”

“ He told me how varieties in animals gradually develop into species; how certain causes, which in brief periods produce varieties, in long periods give rise to types; how the colors of animals are useful for concealment from their prey ”

“ Hence it is the most flourishing, or, as they may be called, the dominant species,— those which range widely, are the most diffused in their own country, and are the most numerous in individuals,— which oftenest produce well-marked varieties, or, as I consider them, incipient species. ”

“ Having now obtained some notion of how animals are dispersed over the earth's surface, whether as single species or as collected in those groups termed genera, families, and orders, it will be well, before proceeding further, to understand something of the classification of the facts we have been considering, and some of the simpler conclusions these facts lead to. ”

“ In a second work I shall discuss the variability of organic beings in a state of nature; namely, the individual differences presented by animals and plants, and those slightly greater and generally inherited differences which are ranked by naturalists as varieties or geographical races. We shall see how difficult, or rather how impossible it often is, to distinguish between races and sub-species, as the less well-marked forms have sometimes been denominated; and again between sub-species and true species. ”

“ Whenever the zoologist observes two forms distinguished by peculiarities of organisation, such as cannot be conceived to be the effects of an external or internal cause, disappearing with the disappearance of that cause, and which forms have been propagated and are being propagated uniformly through all the generations within the limits of our observations, and are yet most probably to be propagated during the existence of mankind, he is obliged to describe these forms as distinct, and they will commonly be called species. ”

“ Many people think of zoology as it was in the time of Linnæus, or, at best, as it was in the early part of the nineteenth century, when the spiritless activity of species-making was its prominent feature. ”

“ 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. ”

“ The exact proportions of the various species of plants, the numbers of each kind of insect or of bird, the peculiarities of more or less exposure to sunshine or to wind at certain critical epochs, and other slight differences which to us are absolutely immaterial and unrecognisable, may be of the highest significance to these humble creatures, and be quite sufficient to require some slight adjustments of size, form, or colour, which natural selection will bring about. ”

“ The diversity and specialization of the forms of these animals is, therefore, easily explained by the fact, that, once introduced they have been left to multiply under the influence of a variety of local conditions, which inevitably lead, in the course of ages, to the formation of new varieties and new species. ”

“ Individuals of the same species often present, as is known to every one, great differences of structure, independently of variation, as in the two sexes of various animals, in the two or three castes of sterile females or workers among insects, and in the immature and larval states of many of the lower animals. ”

“ After commenting on these purely imaginary causes, I pointed out in 1832, as the two great flaws in Lamarck's attempt to explain the origin of species, first, that he had failed to adduce a single instance of the initiation of a new organ in any species of animal or plant; and secondly, that variation, whether taking place in the course of nature or assisted artificially by the breeder and horticulturist, had never yet gone so far as to produce two races sufficiently remote from each other in physiological constitution as to be sterile when intermarried, or, if fertile, only capable of producing sterile hybrids, &c. ”

“ It must be granted, however, that both lines of work are essential to the sound development of zoological science, for experimental investigations in which the accurate diagnosis of species is ignored always result in confusion.
Ecology.—The marvelous modifications in structure and instincts by which the various animals are adapted to their surroundings now forms a special topic in biological research and one of the most fascinating. The adaptations in habitat, time, behavior, appearance and even in structure are found capable of a certain individual modification when studied experimentally. ”

“ That this does habitually happen, we must infer from most of the innumerable species throughout nature presenting well-marked differences; whereas varieties, the supposed prototypes and parents of future well-marked species, present slight and ill-defined differences. ”

“ If the environment be taken to be the cause of the diversification of the species, how is it that, where the scope for diversity of environment is apparently the least, the greater is the variety of species? We have before observed that there are about 120,000 species of animals ”

“ If we examine these animals in the places best adapted to their growth, we shall see their different species, the forms of which, as varied as they are elegant, become rounded into balls, spread out into fans, or ramify into trees, mingling together, blending with each other, and reflecting the varied hues of red, yellow, blue and violet. ”

“ These interesting facts entirely support the belief in the variability of all animals in all their parts and organs, to an extent amply sufficient for natural selection to work with. We may, indeed, admit that these are extreme cases, and that the majority of species do not vary half or a quarter so much as shown in the examples quoted, and we shall still have ample variation for all purposes of specific modification. ”

“ The proof that all the members of any given group of animals, or plants, had thus descended, would be ordinarily considered sufficient to entitle them to the rank of physiological species, for most physiologists consider species to be definable as "the offspring of a single primitive stock." ”

“ However bare and simple this definition of species may appear to be, we confidently appeal to all practical naturalists, whether zoologists, botanists, or palaeontologists, to say if, in the vast majority of cases, they know, or mean to affirm, anything more of the group of animals or plants they so denominate than what has just been stated. ”

“ An argument against it, however, may be drawn from the fact, that certain animals, though placed under the influence of those exceptional causes of variation to which domestic animals are subject, have yet never been known to vary, even in a degree equal to that in which certain wild kinds have been ascertained to vary. ”

“ A few examples among mammalia have been referred to in our first chapter, but it may be said that these are examples of the very common phenomenon of a species being only found in the station for which its organisation adapts it ”

“ He who believes that each being has been created as we now see it, must occasionally have felt surprise when he has met with an animal having habits and structure not at all in agreement. ”