Endemic

“ As a rule, however, formations most frequently show endemic habitat forms and species, more rarely endemic genera; regions and provinces commonly exhibit endemic species and genera, rarely endemic families; while zones and hemispheres contain endemic orders as well as families. This correspondence is readily seen to depend primarily upon the fact that increased differentiation in the taxonomic sense is a concomitant of the increased invasion of endemic species, measured in terms of distance and difference in habitat. ”

“ As Drude has shown, endemic plants may be either indigenous, as in the case of those species that have never moved out of the original habitat, or exotic, as in the much rarer instances where a polydemic species has disappeared from its original home and from all regions into which it has migrated except one. It is understood that not all indigenous or exotic species are endemic. The proportion of endemic to polydemic species is a variable and somewhat artificial one, depending upon the size of the divisions employed. ”

“ If we turn to nature to test the truth of these remarks, and look at any small isolated area, such as an oceanic island, although the total number of the species inhabiting it, will be found to be small, as we shall see in our chapter on geographical distribution; yet of these species a very large proportion are endemic,—that is, have been produced there, and nowhere else. ”

“ Although in oceanic islands the number of kinds of inhabitants is scanty, the proportion of endemic species (i.e. those found nowhere else in the world) is often extremely large. If we compare, for instance, the number of the endemic land-shells in Madeira, or of the endemic birds in the Galapagos Archipelago, with the number found on any continent, and then compare the area of the islands with that of the continent, we shall see that this is true. ”

“ Darwin and Dr. Hooker reply that when animals or plants migrate into new countries, whether assisted by man or without his aid, the most successful colonisers appertain by no means to those types which are most allied to the old indigenous species. On the contrary it more frequently happens that members of genera, orders, or even classes, distinct and foreign to the invaded country, make their way most rapidly and become dominant at the expense of the endemic species. ”

“ The endemic productions of New Zealand, for instance, are perfect one compared with another; but they are now rapidly yielding before the advancing legions of plants and animals introduced from Europe. ”

“ It is equally impossible at present to distinguish different types of endemics, such as relictae, etc., as any such classification must await the elaboration of a method for determining the phylogeny of a natural group of species by an investigation of their comparative differentiation in connection with their migration in all directions from the vegetation center into new habitats. In short, it will not be possible to make a thorough study of endemism and to postulate its laws until modern methods of research have been extended to a much larger portion of the vegetation of the globe. ”

“ Plague and leprosy are typical examples, of that large group of acute and chronic germ diseases whose spread depends on social and hygienic rather than on climatic conditions, and more especially on the verminous accompaniments of filth and overcrowding: conditions which nowadays are found, to an extent and an intensity sufficient to ensure the endemic prevalence or epidemic extension of these diseases, for the most part only in warm countries. ”

“ If it can be shown to be almost invariably the case, that a region, of which most of its inhabitants are closely related to, or belong to the same genera with the species of a second region, has probably received at some former period immigrants from this other region, my theory will be strengthened; for we can clearly understand, on the principle of modification, why the inhabitants of a region should be related to those of another region, whence it has been stocked. ”

“ The study of the mixture of human races in this region has also occupied me much, and I have procured numerous photographs of all the types which I have been able to observe. The principal result at which I have arrived is, that the races bear themselves towards each other as do distinct species; that is to say, that the hybrids, which spring from the crossing of men of different races, are always a mixture of the two primitive types, and never the simple reproduction of the characters of one or the other progenitor, as is the case among the races of domestic animals. ”

“ As showing how diversified are the means of occasional transport, I have discussed at some little length the means of dispersal of fresh-water productions.
If the difficulties be not insuperable in admitting that in the long course of time all the individuals of the same species, and likewise of the several species belonging to the same genus, have proceeded from some one source; then all the grand leading facts of geographical distribution are explicable on the theory of migration, together with subsequent modification and the multiplication of new forms. ”

“ On the other hand, the work of modern systematists shows an extraordinarily exact relation between their species and geographical locality, and the fact of divergent evolution can be almost demonstrated in museum collections when localities have been recorded exactly. The decision as to whether it is the course of variation or the course of selection that has been different in different localities can be made only by the field naturalist and the experimental breeder. ”

“ What follows applies to Ethnology. The first result we get from our observations is a classification, i. e. groups of individuals, families, tribes, nations, sub-varieties, varieties, and (according to some) of species connected by some common link, and united on some common principle. There is no want of groups of this kind; and many of them [71] are so natural as to be unsusceptible of improvement. Yet the nomenclature for their different divisions is undetermined, the values of many of them uncertain, and, above all, the principle upon which they are formed is by no means uniform. ”

“ Now, before we venture upon the attempt hypothetically to explain the phyletic divergence of mankind, and the genealogical connection of its different species, we will premise a short description of the twelve named species and of their distribution. In order clearly to survey their geographical distribution, we must go back some three or four centuries, to the time when the Indian Islands and America were first discovered, and when the present great mingling of species, and more especially the influx of the Indo-Germanic race, had as yet not made great progress. ”

“ 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 ”

“ The determination of the indigenous and derived species of a formation or larger division is of the utmost importance, as it enables us to retrace the steps by which the formation has reached its present structure, and to reconstruct formations long since disappeared. To render it less difficult, it is necessary to scrutinize the derived elements closely, first, because it is easiest to recognize the indigenous species by eliminating the derived, and second, because this analysis will show that not all derived species have entered the formation at the same time and from the same sources. ”

“ Whole tribes of plants, which at first sight seem familiar to his acquaintance, as occupying links in Nature's chain, on which he has been accustomed to depend, prove, on a nearer examination, total strangers, with other configurations, other œconomy, and other qualities; not only all the species that present themselves are new, but most of the genera, and even natural orders. ”

“ For instance, Britain is separated by a shallow channel from Europe, and the mammals are the same on both sides, and so it is with all the islands near the shores of America. The West Indian islands, on the other hand, stand on a deeply submerged bank nearly 1,000 fathoms in depth, and here we find American forms, but the species, and even the genera, are distinct. ”

“ 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. ”

“ On the contrary, as their distribution is so persistent in their respective formations throughout the globe,—the same genera and species being common to the four quarters of the world,—the presumption is, that specimens of nearly all the tribes that ever dwelt on the earth or swarmed in its waters have been handed down to us ”

“ The principle which determines the general character of the fauna and flora of oceanic islands, namely, that the inhabitants, when not identically the same, yet are plainly related to the inhabitants of that region whence colonists could most readily have been derived,—the colonists having been subsequently modified and better fitted to their new homes,—is of the widest application throughout nature. ”

“ Just as many species, like egeria, have varieties which can be regarded as adapted to northern and southern regions, so there are also several which have lowland and Alpine forms quite distinct from each other. ”

“ Applying the same principles to man that are used in the study of the geographical distribution of the lower animals, the only legitimate conclusion the naturalist can deduce from the evidence just referred to is that the branch of the human family indigenous to North America has been isolated for a sufficient length of time to develop into a new variety. ”

“ In earlier times there was a strong tendency, due to old Biblical notions, to imagine all nations as immigrants to the regions where they are now found. But when a zoologist finds a particular species or variety of animal distributed over a limited area, he makes the most natural assumption, that it has arisen through a local differentiation in that region. ”

“ But by taking these characters as absolute, and considering every slight modification of them as of generic importance, many of the most natural groups in those orders have been broken up, and split down almost to single species, classed into purely artificial tribes and sub-tribes. So, also, a character generally important may, in some instances, separate a single species from a large order with which it may agree in every other respect. ”

“ In the human species it is probable that the crossing of those varieties called national varieties, even strong national varieties, produces good results; but the crossing of varieties so divergent as those called primary races is probably bad—these approaching too nearly the nature of different species. ”

“ The more advantageous the changes experienced by the individual organs are to the variety, the more readily will it be able to adapt itself to the surrounding conditions; and the longer the undisturbed 370 breeding of a commencing variety of colonists in a new territory continues without its mingling with subsequent immigrants of the same species, the oftener a new species will arise out of the variety. ”

“ Though each species, and consequently genus, must be adapted to its country, surely adaptation is manifestly not the governing law in geographical distribution. Is this not so? and if I understand you rightly, you lessen your own means of comparison—attributing the presence of the same genera to similarity of conditions. ”

“ Besides, every one’s experience and observation will instruct him, that in populous kingdoms{xxii} those classes branch out into innumerable intermixtures, orders, and genera; and that the species and varieties are as numerous as the individuals of the human race. Amongst the ab-origines, and stationary inhabitants of most kingdoms, there are indeed some prominent features peculiar to each community ”

“ If the inhabitants of one continent formerly differed greatly from those of another continent, so will their modified descendants still differ in nearly the same manner and degree. But after very long intervals of time, and after great geographical changes, permitting much intermigration, the feebler will yield to the more dominant forms, and there will be nothing immutable in the distribution of organic beings. ”

“ Local forms may be sharply differentiated from the corresponding populations of other localities or they may be connected with them by numbers of intermediates. Not rarely also we find a fact which has always seemed to me of special significance, that the peculiarity of the local population or colony may show itself in a special liability to variation, and this variability may show itself in one of many degrees, either in the constant possession of a definite aberration, in a dimorphism, or in an extreme polymorphism. ”

“ Of course the number of individuals which form a colony may vary greatly in the different species, and the same is true of the number of parthenogenetic generations which precede the bi-sexual generation. ”

“ These races, however, generally breed readily with the typical forms of the species, and, although permanent and distinct in some localities, will generally, in some part of the area of the species, or under certain circumstances, be found to break out occasionally into a return to the typical form, or to be connected with it by numerous intermediates. ”