Exotic species

“ It is also natural that the dominant, varying, and far-spreading species, which already have invaded to a certain extent the territories of other species, should be those which would have the best chance of spreading still further, and of giving rise in new countries to new varieties and species. ”

“ If we reckon 200 species of animals in the known world we shall find that more than 130 of them belonged to the old continent, and less than 70 to the new; and if we except the species common to both continents, that is, such as by their natures are capable of enduring the rigours of the north, and might have passed from one to the other, there will not remain above forty species peculiar to, and natives of, America. ”

“ At a later period, when great collections were brought together so that one observer was able to make a careful survey of specimens from all parts of the continent, it was found that many of these species merged into each other through intergrading forms from regions between the localities of the original species. So it has come about that in the case of a large number of our birds [Pg 216] and mammals we have geographical races distinctly recognized instead of separate species. ”

“ When we compare the individuals of the same variety or sub-variety of our older cultivated plants and animals, one of the first points which strikes us is, that they generally differ more from each other than do the individuals of any one species or variety in a state of nature. And if we reflect on the vast diversity of the plants and animals which have been cultivated, and which have varied during all ages under the most different climates and treatment, we are driven to conclude that this great variability is due to our domestic productions having been raised under conditions of life not so uniform as, and somewhat different from, those to which the parent species had been exposed under nature. ”

“ If, for example, all the species of a genus occur in North America, some, or even all, of them, migrating into the Neotropical region in winter, while there are no peculiar Neotropical species, then we must class that genus as strictly Nearctic ”

“ More than that--and it is in this respect above all that the inexhaustible variety of nature shines forth--however imperfect each of these animals may be, each has received its own distinct features. It is to certain localities that they are fixed; it is there that they are found to be most numerous, largest in size and most beautiful; and to the extent that they are found most distant from the appropriate place, the individuals degenerate and the species becomes gradually extinguished. ”

“ That positive and well-defined varieties, or races, should be confined to certain species, is not remarkable; but that every individual insect should differ, however slightly, from its nearest relation and ally, may perhaps require some few words of explanation, even to a naturalist. ”

“ Although many peculiar Neotropical types are absent, it yet possesses an ample supply of generic and specific forms; and, as far as concerns birds and insects, is not perhaps inferior to the richest portions of South America in the number of species to be found in equal areas. ”

“ On these same principles, we can understand, as I have endeavoured to show, why oceanic islands should have few inhabitants, but of these a great number should be endemic or peculiar; and why, in relation to the means of migration, one group of beings, even within the same class, should have all its species endemic, and another group should have all its species common to other quarters of the world. ”

“ It is in this way that horticultural and agricultural experience contribute to the problem of the conversion of varieties into species, and to the explanation of the admirable adaptations of each organism to its complex conditions of life. In the long run new forms, distinguished from their allies by quite a number of new characters, would, by the extermination of the older intermediates, become distinct species. ”

“ These groups of different species, some belonging to palatable and some to unpalatable groups, all exhibiting a close resemblance in colour and pattern, are far more strikingly developed in S. America than in either Asia or Africa, and it is not uncommon for eight or ten species to enter into such an association. ”

“ They then become what are termed dominant species, maintaining themselves in vigour and abundance over very wide areas, displacing other species with which they come into competition, and, under still further changes of conditions, becoming the parents of a new set of diverging species. ”

“ But the differences between them are such as obtain between allied species generally. Large genera are composed, in great part, of such species; and it is interesting to show how the great and beautiful diversity within a large genus is brought about by the working of laws within our comprehension.
A few remarks on the way races are produced will be here in place. Naturalists have been generally inclined to attribute the formation of local varieties or races of a species to the direct action of physical conditions on individuals belonging to it which have migrated into new localities. ”

“ Not only have many fresh-water species, belonging to quite different classes, an enormous range, but allied species prevail in a remarkable manner throughout the world. I well remember, when first collecting in the fresh waters of Brazil, feeling much surprise at the similarity of the fresh-water insects, shells, &c., and at the dissimilarity of the surrounding terrestrial beings, compared with those of Britain. ”

“ Let us take a simple case: in travelling from north to south over a continent, we generally meet at successive intervals with closely allied or representative species, evidently filling nearly the same place in the natural economy of the land. These representative species often meet and interlock; and as the one becomes rarer and rarer, the other becomes more and more frequent, till the one replaces the other. ”

“ If it would not be too troublesome, do you not think it would be very interesting, and give a very good idea of your Flora, to divide the species into three groups, viz., (a) species common to the old world, stating numbers common to Europe and Asia; (b) indigenous species, but belonging to genera found in the old world; and (c) species belonging to genera confined to America or the New World. To make (according to my ideas) perfection perfect, one ought to be told whether there are other cases, like Erica, of genera common in Europe or in Old World not found in your area. ”

“ These facts show that though only one species which is absolutely and exclusively an inhabitant of fresh water is as yet known to be found in distant continents, yet that in several other instances the same species is found in the fresh water of distant continents, and that very often the same genus is so distributed. ”

“ All that we have to do is to leave them both alone, and both flourish. The very existence of a preying species must show an abundance of the species preyed upon in exact proportion to its own, as is—or was—well seen in a country like Africa. ”

“ On the doctrine, therefore, that the chief races owe their differences to their descent from distinct species, we must admit that at least eight or nine, or more probably a dozen species, all having the same habit of breeding and roosting on rocks and living in society, either now exist somewhere, or formerly existed but have become extinct as wild birds. ”

“ By the collection of great series of specimens in North America and elsewhere in the world it has been proved that it is common for a single species of mammal to occupy a great area, including such diverse climatic conditions as humid forested districts near the sea-level, sections of arid desert plains in the interior, and high rugged mountain slopes. In each area of differing conditions it is ordinarily found that representatives of a species, under certain conditions, vary from those in other areas mainly in shades of color and in proportions. ”

“ 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 ”

“ This is proved to have been the case in Europe, and is supported by much evidence both as regards North and South America.
It is clear that so complete and sudden a change in the higher forms of life, does not represent the normal state of things. Species and genera have not, at all times, become so rapidly extinct. ”

“ If then it varied, natural selection would probably favour different varieties in the different islands. Some species, however, might spread and yet retain the same character throughout the group, just as we see on continents some species spreading widely and remaining the same. ”

“ The question might well be asked, Where do the native species come in? The answer would have to be that wherever man goes certain species of animals and plants follow him, and become established if the conditions are suitable; while another section he either takes with him for their utility or introduces afterwards for various reasons; and the native species gradually get pushed out. ”

“ Not only do we find this community of genera over 118 vast extents of country greater in diameter than the African continent, but there are also many species which range as widely or nearly as widely as the case may be as the genus to which they belong. ”

“ But the spots where such rich deposits occur are exceedingly few and far between when compared with the vast areas of continental land, and we have every reason to believe that in past ages, as now, numbers of curious species were rare or local, the commoner and more abundant species giving a very imperfect idea of the existing series of animal forms. ”

“ A wide distance between the homes of two doubtful forms leads many naturalists to rank both as distinct species; but what distance, it has been well asked, will suffice? if that between America and Europe is ample, will that between the Continent and the Azores, or Madeira, or the Canaries, or Ireland, be sufficient? It must be admitted that many forms, considered by highly-competent judges as varieties, have so perfectly the character of species that they are ranked by other highly-competent judges as good and true species. ”

“ Firstly.—If the eleven chief races have not arisen from the variation of some one species, together with its geographical races, they must be descended from several extremely distinct aboriginal species; for no amount of crossing between only six or seven wild forms could produce races so distinct as Pouters, Carriers, Runts, Fantails, Turbits, Short-faced Tumblers, Jacobins, and Trumpeters. ”

“ It is difficult, even in contemplation, to anticipate the time when we shall be entitled to make any other hypothesis in regard to all the marine tribes, and to by far the greater number of the terrestrial;—such as birds, which possess such unlimited powers of migration; insects, which, besides the variability of each species in number, are also so capable of being diffused to vast distances; and cryptogamous plants, to which, as to many other classes, both of the animal and vegetable kingdom, similar observations are applicable. ”

“ But on the special-creation theory we can see no reason why the 400 species should all have been deposited in America. And, as already observed, we must remember that this correlation between a geographically restricted habitat and the zoological or botanical affinities of its inhabitants, is repeated over and over and over again in the [213] faunas and floras of the world, so that merely to enumerate the instances would require a separate chapter. ”

“ Natural selection occurs not only in the wild state, but is also active in cultivated fields. Here it regulates the struggle of the selected varieties and improved races with the older types, and even with the wild species. In a previous [803] lecture I have detailed the rapid increase of the wild oats in certain years, and described the experiments of Risler and Rimpau in the running out of select varieties. The agency is always the same. ”

“ Portions of my collections of skins I sent to my friends in Europe at different times, and in this manner I parted with those of some newly discovered species before I had named them, so careless have I hitherto been respecting "priority." While forming my collection, I have often been pleased to find that many species, which, twenty-five years ago, were scarce and rarely to be met with, are now comparatively abundant;—a circumstance which I attribute to the increase of cultivated land in the United States. ”

“ In determining whether the supposed varieties of the same kind of domestic animal should be ranked as such, or as specifically distinct, that is, whether any of them are descended from distinct wild species, every naturalist would lay much stress on the fact of their external parasites being specifically distinct. ”

“ We know that insects and plants are so transported. Birds and ocean-currents carry seeds from land to land. Insects on a blade of grass or a fallen bough are carried down a river by the current to found colonies of their race far from their place of origin. And such circumstances give rise to races and varieties among species modifiable by the peculiarities of their new localities. The accidental migrations of man may be considered as belonging to the epoch of culture-migration, since they must more usually have occurred with a race advanced in the art of navigation. ”

“ Nevertheless, the fact remains indisputable that domesticated varieties of animals and of plants, which differ greatly from each other in structure, but which are certainly descended from the same aboriginal species, such as the races of the fowl, pigeon, many vegetables, and a host of other productions, are extremely fertile when crossed; and this seems to make a broad and impassable barrier between domestic varieties and natural species. ”