Читать книгу: «The Atlantic Monthly, Volume 09, No. 54, April, 1862», страница 8

IX

The well-known meaning of the words generic and specific may serve, in the absence of a more precise definition, to express the relative importance of those groups of animals called Genera and Species in our scientific systems. The Genus is the more comprehensive of the two kinds of groups, while the Species is the most precisely defined, or at least the most easily recognized, of all the divisions of the Animal Kingdom. But neither the term Genus nor Species has always been taken in the same sense. Genus especially has varied in its acceptation, from the time when Aristotle applied it indiscriminately to any kind of comprehensive group, from the Classes down to what we commonly call Genera, till the present day. But we have already seen, that, instead of calling all the various kinds of more comprehensive divisions by the name of Genera, modern science has applied special names to each of them, and we have now Families, Orders, Classes, and Branches above Genera proper. If the foregoing discussion upon the nature of these groups is based upon trustworthy principles, we must admit that they are all founded upon distinct categories of characters,—the primary divisions, or the Branches, on plan of structure, the Classes upon the manner of its execution, the Orders upon the greater or less complication of a given mode of execution, the Families upon form; and it now remains to be ascertained whether Genera also exist in Nature, and by what kind of characteristics they may be distinguished. Taking the practice of the ablest naturalists in discriminating Genera as a guide in our estimation of their true nature, we must, nevertheless, remember that even now, while their classifications of the more comprehensive groups usually agree, they differ greatly in their limitation of Genera, so that the Genera of some authors correspond to the Families of others, and vice versa. This undoubtedly arises from the absence of a definite standard for the estimation of these divisions. But the different categories of structure which form the distinctive criteria of the more comprehensive divisions once established, the question is narrowed down to an inquiry into the special category upon which Genera may be determined; and if this can be accurately defined, no difference of opinion need interfere hereafter with their uniform limitation. Considering all these divisions of the Animal Kingdom from this point of view, it is evident that the more comprehensive ones must be those which are based on the broadest characters,—Branches, as united upon plan of structure, standing of course at the head; next to these the Classes, since the general mode of executing the plan presents a wider category of characters than the complication of structure on which Orders rest; after Orders come Families, or the patterns of form in which these greater or less complications of structure are clothed; and proceeding in the same way from more general to more special considerations, we can have no other category of structure as characteristic of Genera than the details of structure by which members of the same Family may differ from each other, and this I consider as the only true basis on which to limit Genera, while it is at the same time in perfect accordance with the practice of the most eminent modern zoologists. It is in this way that Cuvier has distinguished the large number of Genera he has characterized in his great Natural History of the Fishes, in connection with Valenciennes. Latreille has done the same for the Crustacea and Insects; and Milne Edwards, with the coöperation of Haime, has recently proceeded upon the same principle in characterizing a great number of Genera among the Corals. Many others have followed this example, but few have kept in view the necessity of a uniform mode of proceeding, or, if they have done their researches have covered too limited a ground, to be taken into consideration in a discussion of principles. It is, in fact, only when extending over a whole Class that the study of Genera acquires a truly scientific importance, as it then shows in a connected manner, in what way, by what features, and to what extent a large number of animals are closely linked together in Nature. Considering the Animal Kingdom as a single complete work of one Creative Intellect, consistent throughout, such keen analysis and close criticism of all its parts have the same kind of interest, in a higher degree, as that which attaches to other studies undertaken in the spirit of careful comparative research. These different categories of characters are, as it were, different peculiarities of style in the author, different modes of treating the same material, new combinations of evidence bearing on the same general principles. The study of Genera is a department of Natural History which thus far has received too little attention even at the hands of our best zoologists, and has been treated in the most arbitrary manner; it should henceforth be made a philosophical investigation into the closer affinities which naturally bind in minor groups all the representatives of a natural Family.

Genera, then, are groups of a more restricted character than any of those we have examined thus far. Some of them include only one Species, while others comprise hundreds; since certain definite combinations of characters may be limited to a single Species, while other combinations may be repeated in many. We have striking examples of this among Birds: the Ostrich stands alone in its Genus, while the number of Species among the Warblers is very great. Among Mammalia the Giraffe also stands alone, while Mice and Squirrels include many Species. Genera are founded, not, as we have seen, on general structural characters, but on the finish of special parts, as, for instance, on the dentition. The Cats have only four grinders in the upper jaw and three in the lower, while the Hyenas have one more above and below, and the Dogs and Wolves have two more above and two more below. In the last, some of the teeth have also flat surfaces for crushing the food, adapted especially to their habits, since they live on vegetable as well as animal substances. The formation of the claws is another generic feature. There is a curious example with reference to this in the Cheetah, which is again a Genus containing only one Species. It belongs to the Cat Family, but differs from ordinary Lions and Tigers in having its claws so constructed that it cannot draw them back under the paws, though in every other respect they are like the claws of all the Cats. But while it has the Cat-like claw, its paws are like those of the Dog, and this singular combination of features is in direct relation to its habits, for it does not lie in wait and spring upon its prey like the Cat, but hunts it like the Dog.

While Genera themselves are, like Families, easily distinguished, the characters on which they are founded, like those of Families, are difficult to trace. There are often features belonging to these groups which attract the attention and suggest their association, though they are not those which may be truly considered generic characters. It is easy to distinguish the Genus Fox, for instance, by its bushy tail, and yet that is no true generic character; the collar of feathers round the neck of the Vultures leads us at once to separate them from the Eagles, but it is not the collar that truly marks the Genus, but rather the peculiar structure of the feathers which form it. No Bird has a more striking plumage than the Peacock, but it is not the appearance merely of its crest and spreading fan that constitutes a Genus, but the peculiar structure of the feathers. Thousands of examples might be quoted to show how easily Genera may be singled out, named, and entered in our systems, without being duly characterized, and it is much to be lamented that there is no possibility of checking the loose work of this kind with which the annals of our science are daily flooded.

It would, of course, be quite inappropriate to present here any general revision of these groups; but I may present a few instances to illustrate the principle of their classification, and to show on what characters they are properly based. Among Reptiles, we find, for instance, that the Genera of our fresh-water Turtles differ from each other in the cut of their bill, in the arrangement of their scales, in the form of their claws, etc. Among Fishes, the different Genera included under the Family of Perches are distinguished by the arrangement of their teeth, by the serratures of their gill-covers, and of the arch to which the pectoral fins are attached, by the nature and combination of the rays of their fins, by the structure of their scales, etc. Among Insects, the various Genera of the Butterflies differ in the combination of the little rods which sustain their wings, in the form and structure of their antennae, of their feet, of the minute scales which cover their wings, etc. Among Crustacea, the Genera of Shrimps vary in the form of the claws, in the structure of the parts of the mouth, in the articulations of their feelers, etc. Among Worms, the different Genera of the Leech Family are combined upon the form of the disks by which they attach themselves, upon the number and arrangement of their eyes, upon the structure of the hard parts with which the mouth is armed, etc. Among Cephalopods, the Family of Squids contains several Genera distinguished by the structure of the solid shield within the skin of the back, by the form and connection of their fins, by the structure of the suckers with which their arms are provided, by the form of their beak, etc. In every Class, we find throughout the Animal Kingdom that there is no sound basis for the discrimination of Genera except the details of their structure; but in order to define them accurately an extensive comparison of them is indispensable, and in characterizing them only such features should be enumerated as are truly generic; whereas in the present superficial method of describing them, features are frequently introduced which belong not only to the whole Family, but even to the whole Class which includes them.

X

There remains but one more division of the Animal Kingdom for our consideration, the most limited of all in its circumscription,—that of Species. It is with the study of this kind of group that naturalists generally begin their investigations. I believe, however, that the study of Species as the basis of a scientific education is a great mistake. It leads us to overrate the value of Species, and to believe that they exist in Nature in some different sense from other groups; as if there were something more real and tangible in Species than in Genera, Families, Orders, Classes, or Branches. The truth is, that to study a vast number of Species without tracing the principles that combine them under more comprehensive groups is only to burden the mind with disconnected facts, and more may be learned by a faithful and careful comparison of a few Species than by a more cursory examination of a greater number. When one considers the immense number of Species already known, naturalists might well despair of becoming acquainted with them all, were they not constructed on a few fundamental patterns, so that the study of one Species teaches us a great deal for all the rest. De Candolle, who was at the same time a great botanist and a great teacher, told me once that he could undertake to illustrate the fundamental principles of his science with the aid of a dozen plants judiciously selected, and that it was his unvarying practice to induce students to make a thorough study of a few minor groups of plants, in all their relations to one another, rather than to attempt to gain a superficial acquaintance with a large number of species. The powerful influence he has had upon the progress of Botany vouches for the correctness of his views. Indeed, every profound scholar knows that sound learning can be attained only by this method, and the study of Nature makes no exception to the rule. I would therefore advise every student to select a few representatives from all the Classes, and to study these not only with reference to their specific characters, but as members also of a Genus, of a Family, of an Order, of a Class, and of a Branch. He will soon convince himself that Species have no more definite and real existence in Nature than all the other divisions of the Animal Kingdom, and that every animal is the representative of its Branch, Class, Order, Family, and Genus as much as of its Species, Specific characters are only those determining size, proportion, color, habits, and relations to surrounding circumstances and external objects. How superficial, then, must be any one's knowledge of an animal who studies it only with relation to its specific characters! He will know nothing of the finish of special parts of the body,—nothing of the relations between its form and its structure,—nothing of the relative complication of its organization as compared with other allied animals,—nothing of the general mode of execution,—nothing of the plan expressed in that mode of execution. Yet, with the exception of the ordinal characters, which, since they imply relative superiority and inferiority, require, of course, a number of specimens for comparison, his one animal would tell him all this as well as the specific characters.

All the more comprehensive groups, equally with Species, have a positive, permanent, specific principle, maintained generation after generation with all its essential characteristics. Individuals are the transient representatives of all these organic principles, which certainly have an independent, immaterial existence, since they outlive the individuals that embody them, and are no less real after the generation that has represented them for a time has passed away than they were before.

From a comparison of a number of well-known Species belonging to a natural Genus, it is not difficult to ascertain what are essentially specific characters. There is hardly among Mammalia a more natural Genus than that which includes the Rabbits and Hares, or that to which the Rats and Mice are referred. Let us see how the different Species differ from one another. Though we give two names in the vernacular to the Genus Hare, both Hares and Rabbits agree in all the structural peculiarities which constitute a Genus; but the different Species are distinguished by their absolute size when full-grown,—by the nature and color of their fur,—by the size and form of the ear,—by the relative length of their legs and tail,—by the more or less slender build of their whole body,—by their habits, some living in open grounds, others among the bushes, others in swamps, others burrowing under the earth,—by the number of young they bring forth,—by their different seasons of breeding,—and by still minor differences, such as the permanent color of the hair throughout the year in some, while in others it turns white in winter. The Rats and Mice differ in a similar way: there being large and small Species,—some gray, some brown, others rust-colored,—some with soft, others with coarse hair; they differ also in the length of the tail, and in having it more or less covered with hair,—in the cut of the ears, and their size,—in the length of their limbs, which are slender and long in some, short and thick in others,—in their various ways of living,—in the different substances on which they feed,—and also in their distribution over the surface of the earth, whether circumscribed within certain limited areas or scattered over a wider range. What is now the nature of these differences by which we distinguish Species? They are totally distinct from any of the categories on which Genera, Families, Orders, Classes, or Branches are founded, and may readily be reduced to a few heads. They are differences in the proportion of the parts and in the absolute size of the whole animal, in the color and general ornamentation of the surface of the body, and in the relations of the individuals to one another and to the world around. A farther analysis of other Genera would show us that among Birds, Reptiles, Fishes, and, in fact, throughout the Animal Kingdom, Species of well-defined natural Genera differ in the same way. We are therefore justified in saying that the category of characters on which Species are based implies no structural differences, but presents the same structure combined under certain minor differences of size, proportion, and habits. All the specific characters stand in direct reference to the generic structure, the family form, the ordinal complication of structure, the mode of execution of the Class, and the plan of structure of the Branch, all of which are embodied in the frame of each individual in each Species, even though all these individuals are constantly dying away and reproducing others; so that the specific characters have no more permanency in the individuals than those which characterize the Genus, the Family, the Order, the Class, and the Branch. I believe, therefore, that naturalists have been entirely wrong in considering the more comprehensive groups to be theoretical and in a measure arbitrary, an attempt, that is, of certain men to classify the Animal Kingdom according to their individual views, while they have ascribed to Species, as contrasted with the other divisions, a more positive existence in Nature. No further argument is needed to show that it is not only the Species that lives in the individual, but that every individual, though belonging to a distinct Species, is built upon a precise and definite plan which characterizes its Branch,—that that plan is executed in each individual in a particular way which characterizes its Class,—that every individual with its kindred occupies a definite position in a series of structural complications which characterizes its Order,—that in every individual all these structural features are combined under a definite pattern of form which characterizes its Family,—that every individual exhibits structural details in the finish of its parts which characterize its Genus,—and finally that every individual presents certain peculiarities in the proportion of its parts, in its color, in its size, in its relations to its fellow-beings and surrounding things, which constitute its specific characters; and all this is repeated in the same kind of combination, generation after generation, while the individuals die. If we accept these propositions, which seem to me self-evident, it is impossible to avoid the conclusion that Species do not exist in Nature in any other sense than the more comprehensive groups of the zoological systems.

There is one question respecting Species that gives rise to very earnest discussions in our day, not only among naturalists, but among all thinking people. How far are they permanent, and how far mutable? With reference to the permanence of Species, there is much to be learned from the geological phenomena that belong to our own period, and that bear witness to the invariability of types during hundreds of thousands of years at least. I hope to present a part of this evidence in a future article upon Coral Reefs, but in the mean time I cannot leave this subject without touching upon a point of which great use has been made in recent discussions. I refer to the variability of Species as shown in domestication.

The domesticated animals with their numerous breeds are constantly adduced as evidence of the changes which animals may undergo, and as furnishing hints respecting the way in which the diversity now observed among animals has already been produced. It is my conviction that such inferences are in no way sustained by the facts of the case, and that, however striking the differences may be between the breeds of our domesticated animals, as compared with the wild Species of the same Genus, they are of a peculiar character entirely distinct from those that prevail among the latter, and are altogether incident to the circumstances under which they occur. By this I do not mean the natural action of physical conditions, but the more or less intelligent direction of the circumstances under which they live. The inference drawn from the varieties introduced among animals in a state of domestication, with reference to the origin of Species, is usually this: that what the farmer does on a small scale Nature may do on a large one. It is true that man has been able to produce certain changes in the animals under his care, and that these changes have resulted in a variety of breeds. But in doing this, he has, in my estimation, in no way altered the character of the Species, but has only developed its pliability to the will of man, that is, to a power similar in its nature and mode of action to that power to which animals owe their very existence. The influence of man upon Animals is, in other words, the action of mind upon them; and yet the ordinary mode of arguing upon this subject is, that, because the intelligence of man has been able to produce certain varieties in domesticated animals, therefore physical causes have produced all the diversities among wild ones. Surely, the sounder logic would be to infer, that, because our finite intelligence can cause the original pattern to vary by some slight shades of difference, therefore an infinite intelligence must have established all the boundless diversity of which our boasted varieties are but the faintest echo. It is the most intelligent farmer that has the greatest success in improving his breeds; and if the animals he has so fostered are left to themselves without that intelligent care, they return to their normal condition. So with plants: the shrewd, observing, thoughtful gardener will obtain many varieties from his flowers; but those varieties will fade out, if left to themselves. There is, as it were, a certain degree of pliability and docility in the organization both of animals and plants, which may be developed by the fostering care of man, and within which he can exercise a certain influence; but the variations which he thus produces are of a peculiar kind, and do not correspond to the differences of the wild Species. Let us take some examples to illustrate this assertion.

Every Species of wild Bull differs from the others in its size; but all the individuals correspond to the average standard of size characteristic of their respective Species, and show none of those extreme differences of size so remarkable among our domesticated Cattle. Every Species of wild Bull has its peculiar color, and all the individuals of one Species share in it: not so with our domesticated Cattle, among which every individual may differ in color from every other. All the individuals of the same Species of wild Bull agree in the proportion of their parts, in the mode of growth of the hair, in its quality, whether fine or soft: not so with our domesticated Cattle, among which we find in the same Species overgrown and dwarfish individuals, those with long and short legs, with slender and stout build of the body, with horns or without, as well as the greatest variety in the mode of twisting the horns,—in short, the widest extremes of development which the degree of pliability in that Species will allow.

A curious instance of the power of man, not only in developing the pliability of an animal's organization, but in adapting it to suit his own caprices, is that of the Golden Carp, so frequently seen in bowls and tanks as the ornament of drawing-rooms and gardens. Not only an infinite variety of spotted, striped, variegated colors has been produced in these Fishes, but, especially among the Chinese, so famous for their morbid love of whatever is distorted and warped from its natural shape and appearance, all sorts of changes have been brought about in this single Species. A book of Chinese paintings showing the Golden Carp in its varieties represents some as short and stout, others long and slender,—some with the ventral side swollen, others hunch-backed,—some with the mouth greatly enlarged, while in others the caudal fin, which in the normal condition of the Species is placed vertically at the end of the tail and is forked like those of other Fishes, has become crested and arched, or is double, or crooked, or has swerved in some other way from its original pattern. But in all these variations there is nothing which recalls the characteristic specific differences among the representatives of the Carp Family, which in their wild state are very monotonous in their appearance all the world over.

Were it appropriate to accumulate evidence here upon this subject, I could bring forward many more examples quite as striking as those above mentioned. The various breeds of our domesticated Horses present the same kind of irregularities, and do not differ from each other in the same way as the wild Species differ from one another. Or take the Genus Dog: the differences between its wild Species do not correspond in the least with the differences observed among the domesticated ones. Compare the differences between the various kinds of Jackals and Wolves with those that exist between the Bull-Dog and Greyhound, for instance, or between the St. Charles and the Terrier, or between the Esquimaux and the Newfoundland Dog. I need hardly add that what is true of the Horses, the Cattle, the Dogs, is true also of the Donkey, the Goat, the Sheep, the Pig, the Cat, the Rabbit, the different kinds of barn-yard fowl,—in short, of all those animals that are in domesticity the chosen companions of man.

In fact, all the variability among domesticated Species is due to the fostering care, or, in its more extravagant freaks, to the fancies of man, and it has never been observed in the wild Species, where, on the contrary, everything shows the closest adherence to the distinct, well-defined, and invariable limits of the Species. It surely does not follow, that, because the Chinese can, under abnormal conditions, produce a variety of fantastic shapes in the Golden Carp, therefore water, or the physical conditions established in the water, can create a Fish, any more than it follows, that, because they can dwarf a tree, or alter its aspect by stunting its growth in one direction and forcing it in another, therefore the earth, or the physical conditions connected with their growth, can create a Pine, an Oak, a Birch, or a Maple. I confess that in all the arguments derived from the phenomena of domestication, to prove that all animals owe their origin and diversity to the natural action of the conditions under which they live, the conclusion does not seem to me to follow logically from the premises. And the fact that the domesticated animals of all races of men, equally with the white race, vary among themselves in the same way and differ in the same way from the wild Species, makes it still more evident that domesticated varieties do not explain the origin of Species, except, as I have said, by showing that the intelligent will of man can produce effects which physical causes have never been known to produce, and that we must therefore look to some cause outside of Nature, corresponding in kind, though so different in degree, to the intelligence of man, for all the phenomena connected with the existence of animals in their wild state. So far from attributing these original differences among animals to natural influences, it would seem, that, while a certain freedom of development is left, within the limits of which man can exercise his intelligence and his ingenuity, not even this superficial influence is allowed to physical conditions unaided by some guiding power, since in their normal state the wild Species remain, so far as we have been able to discover, entirely unchanged,—maintained, it is true, in their integrity by the circumstances that were established for their support by the power that created both, but never altered by them. Nature holds inviolable the stamp that God has set upon his creatures; and if man is able to influence their organization in some slight degree, it is because the Creator has given to his relations with the animals he has intended for his companions the same plasticity which he has allowed to every other side of his life, in virtue of which he may in some sort mould and shape it to his own ends, and be held responsible also for its results.

The common sense of a civilized community has already pointed out the true distinction in applying another word to the discrimination of the different kinds of domesticated animals. They are called Breeds, and Breeds among animals are the work of man;—Species were created by God.

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