Subspecies

“ But, besides such differences, all naturalists admit that natural varieties exist, which are considered sufficiently distinct to be worthy of record in systematic works. No one has drawn any clear distinction between individual differences and slight varieties; or between more plainly marked varieties and subspecies and species. ”

“ The difficulty lies in the fact that there are no fixed and definite criteria, by which a given series of individuals can be surely distinguished as a variety, a species or a genus; it is a matter for the judgment and experience of the systematist himself. The individuals of a species may differ quite widely among [53] themselves, provided that they are all connected by intergradations, and the more or less constant varieties or subspecies are to be distinguished from the individual variants, which are inconstant and fluctuating. ”

“ Morphological or comparative studies need a material standard, by which it may be readily decided whether certain groups of animals and plants are to be described or de-nominated as species, as subspecies or as varieties. To get at the inner nature of the differences is in most cases impossible, but a decision must be made. The physiological line of inquiry has more time at its disposal; it calls for no haste. Its experiments ordinarily cover years, and a conclusion is only to be reached after long and often weary trials. ”

“ When these characters are easily observable and definable their possessors are usually referred to different species, which are supposed to “represent” one another in their respective areas, and are hence often called “representative species.” When the distinguishing characters are slight and less easily recognizable it has recently become the practice, especially among American naturalists, to designate their possessors as “subspecies,” and, in order to indicate this, to add a third “subspecific” name to the ordinary generic and specific terms. ”

“ Generic areas differ in character according as the genus is large, that is, comprising many species, or small and having but few species, or, it may be, a single one. The species, as a rule, occupy each its own area, and the areas may be entirely distinct, or they may be contiguous and more or less extensively overlapping, though it seldom happens that two or more species of the same genus inhabit exactly the same area. Often some physical feature, such as a range of high mountains, a great river, the edge of a forest, plain or desert, exactly defines the limits of species of the same genus. ”

“ Among 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. How many of the birds and insects in North America and Europe, which differ very slightly from each other, have been ranked by one eminent naturalist as undoubted species, and by another as varieties, or, as they are often called, geographical races! ”

“ To what extent these hints for the discrimination of species will be found to avail in practice, it is difficult to say, but it seems desirable that they should speedily be brought to the test of experience, since there is no genus, of the same extent, in which it is so difficult to determine the species. ”

“ As allied or representative species, when inhabiting a continuous area, are generally distributed in such a manner that each has a wide range, with a comparatively narrow neutral territory between them, in which they become rather suddenly rarer and rarer; then, as varieties do not essentially differ from species, the same rule will probably apply to both; and if we take a varying species inhabiting a very large area, we shall have to adapt two varieties to two large areas, and a third variety to a narrow intermediate zone. ”

“ When two groups of species differ from each other constantly in one or more of these latter particulars they are said to belong to different genera. We have already seen that species vary in these more important as well as in the more superficial characters. If, then, in any part of the area occupied by a species some change of habits becomes useful to it, all such structural variations as facilitate the change will be accumulated by natural selection, and when they have become fixed in the proportions most beneficial to the animal, we shall have the first species of a new genus. ”

“ In the preceding list, when all the specimens I have seen from a particular habitat have a similar and peculiar character, I have considered them as species; on the contrary when the specimens from the same locality offer variations among themselves, as in those of the genus Hepoona, where the extent of the whiteness on the tail, and the variation in the colour of the body appear to differ in the specimens from the same place, I have regarded them as belonging to the same species, believing it to be a variable species which has an extensive range. ”

“ And this certainly is the case, if varieties be looked at as incipient species; for my tables clearly show as a general rule that, wherever many species of a genus have been formed, the species of that genus present a number of varieties, that is of incipient species, beyond the average. It is not that all large genera are now varying much, and are thus increasing in the number of their species, or that no small genera are now varying and increasing ”

“ In accordance with our present conception there is selection of species and selection within the species. The struggle for life determines which of a group of elementary species shall survive and which shall disappear. In agricultural practice the corresponding process is usually designated by the name of variety-testing. Within the species, or within the variety, the sieve of natural selection is constantly eliminating poor specimens and preserving those that are best adapted to live under the given conditions. ”

“ If the variety is found not to breed with the regular species, but to keep apart and breed only with other individuals like itself, then we say, "This is no mere variety! It is a distinct species!" Unfortunately we have vast series of animals, insects, and others, from all parts of the world, collected and preserved in our museums, of which we know only the dead preserved specimens. So that we cannot be sure in doubtful cases whether a series of forms differing a little from the ordinary members of a species indicate distinct species, as defined and tested by breeding. ”

“ But sometimes a species has a wide range into countries which differ in physical conditions, and then it often happens that one or other of the extremes will predominate in a portion of its range. These form local varieties, but as they occur mixed with the other forms, they are not considered to be distinct species, although they may differ from the other extreme form quite as much as species often do from each other. ”

“ There are other relations between the species of large genera and their recorded varieties which deserve notice. We have seen that there is no infallible criterion by which to distinguish species and well-marked varieties; and in those cases in which intermediate links have not been found between doubtful forms, naturalists are compelled to come to a determination by the amount of difference between them, judging by analogy whether or not the amount suffices to raise one or both to the rank of species. ”

“ In another work I shall discuss, if time and health permit, 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. ”

“ A single specimen, perhaps, of a dried plant, or a stuffed bird or quadruped; a shell, without the soft parts of the animal; an insect in one stage of its numerous transformations;—these are the scanty and imperfect data which the naturalist possesses. Such information may enable us to separate species which stand at a considerable distance from each other; but we have no right to expect any thing but difficulty and ambiguity, if we attempt, from such imperfect opportunities, to obtain distinctive marks for defining the characters of species which are closely related. ”

“ Observation further acquaints us with the fact, that, sometimes, an individual member of a species may exhibit a more or less marked variation, which is propagated through all the offspring of that individual, and may even become intensified in them. And, in this manner, a variety, or race, is generated within the species; which variety, or race, if nothing were known respecting its origin, might have every claim to be regarded as a separate morphological species. ”

“ First in order of importance comes the fact that not only are there uniformly transmitted from an organism to its offspring, those traits of structure which distinguish the class, order, genus, and species; but also those which distinguish the variety. We have numerous cases, among both plants and animals, where, by natural or artificial conditions, there have been produced divergent modifications of the same species; and abundant proof exists that the members of any one sub-species habitually transmit their distinctive peculiarities to their descendants. ”

“ Hence, during a long-continued course of modification, the slight differences, characteristic of varieties of the same species, tend to be augmented into the greater differences characteristic of the species of the same genus. New and improved varieties will inevitably supplant and exterminate the older, less improved, and intermediate varieties; and thus species are rendered to a large extent defined and distinct objects. Dominant species belonging to the larger groups within each class tend to give birth to new and dominant forms ”

“ It is to be noted that the individuals may themselves be judged to fall into groups of minor rank, known as sub-species or local varieties, but such subordinate assemblages are elevated to specific rank, if they appear not to intergrade so as to form a linked. species, whilst on the other hand assemblages judged to be species are merged, or degraded to sub-species, if they are found to intergrade by discoveries of linking forms. ”

“ As to the alleged absence of intermediate varieties connecting one species with another, every zoologist and botanist who has engaged in the task of classification has been occasionally thrown into this dilemma—if I make more than one species in this group, I must, to be consistent, make a great many. ”

“ It is, in fact, so much the more peculiar that certain species are more or less cosmopolitan, or occur at widely distant points. It is less peculiar, of course, to find different species of the same genus at different depths or in different areas, for any slight variation in a species advantageous to new conditions would readily be fixed, and give rise to a new species. ”

“ It is by no means improbable, that, when the series of species of certain genera is very full, they may be found to differ less widely from each other than do the mere varieties or races of certain species. ”

“ When two or more species of any genus now inhabit the same waters, they are usually species whose differentiation is of long standing,—species, therefore, which can be readily distinguished from one another. ”

“ The general limitation of species to certain areas, suggests the idea that each of them, with all their varieties, have sprung from a common parent, and have spread in various directions from a common centre. The frequency also of the grouping of genera within certain geographical limits, is in favour of the same law, although the migration of species may sometimes cause apparent exceptions to the rule, and make the same types appear to have originated independently at different spots. ”

“ There is no doubt that many uncertain species, founded on few or isolated specimens, have had their true nature determined by the study of a good series of examples: they have been thereby established as species or as varieties ”

“ There are few points about which we know less than the causes of distribution and rarity, although there are certain tolerably well recognized laws which govern the occurrence of some species in certain localities. ”

“ After this glance at the variations peculiar to each species, a more important consideration presents itself, that of the change of the species themselves; that ancient and immemorial degeneration made in each family, or in every genus, under which we may comprehend the proximating species. Among all terrestrial animals there are only a few detached species, which, like the human, at once compose both species and genus. ”

“ It is immaterial for us whether a multitude of doubtful forms be called species or sub-species or varieties; what rank, for instance, the two or three hundred doubtful forms of British plants are entitled to hold, if the existence of any well-marked varieties be admitted. But the mere existence of individual variability and of some few well-marked varieties, though necessary as the foundation for the work, helps us but little in understanding how species arise in nature. ”

“ Hence it is the most flourishing, or, as they may be called, the dominant species,— those which range widely over the world, 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. ”

“ But it is a far more important consideration, that during the process of further modification, by which two varieties are supposed to be converted and perfected into two distinct species, the two which exist in larger numbers, from inhabiting larger areas, will have a great advantage over the intermediate variety, which exists in smaller numbers in a narrow and intermediate zone. ”