The appellation "variety" being very commonly misapplied to individuals of a species, which are merely undergoing a regular natural change, either progressing from youth to maturity, or gradually shifting, according to fixed laws, their colours with the seasons, I conceive that it will be useful to some, to point out a few of the less generally known changes which naturally take place in various British animals; some few of which appear to have been hitherto overlooked, and others to have been described incorrectly.
The term "variety" is understood to signify a departure from the acknowledged type of a species, either in structure, in size, or in colour; but is vague in the degree of being alike used to denote the slightest individual variation, and the most dissimilar breeds which have originated from one common stock. The term is, however, quite inapplicable to an animal in any state of periodical change natural to the species to which it belongs.
Varieties require some classification; and though I feel myself hardly adequate to the task, I shall here propose to arrange them under four principal heads; in the hope that this endeavour will induce some naturalists, more competent than myself, to follow out this intricate and complicated subject, into all its details.
I would distinguish, then, what are called varieties, into simple variations, acquired variations, breeds, and true varieties. These appear, in general, sufficiently distinct, although the exact limits of each are sometimes very difficult to be assigned. Indeed, in many cases they only differ in degree, and in others they may be all combined in one individual. Moreover, the , varieties of either class have a much greater tendency to produce varieties of another class, than the typical animals of a species have to produce any sort of variety.
I. Simple Variations. The first class, which I propose to style simple or slight individual variations, differs only in degree from the last, or true varieties; and consists of mere differences of colour or of stature, unaccompanied by any remarkable structural deviation; also of slight individual peculiarities of any kind, which are more or less observable in all animals, whether wild or tame, and which, having a tendency to perpetuate themselves by generation, may, under particular circumstances, become the origin of true breeds (which constitute my third class of varieties), but which, in a state of nature, are generally lost in the course of two or three generations. Albinos belong to this first division, and also the other numerous anomalies mentioned in VII, 589-591, 593-598.1 These simple variations occur both in wild and in domestic animals, but are much more frequent in the latter, and are commonly observed in all breeds and true varieties.
Among the Mammalia, total or partial absence of colour is always, I believe, continued through life; excepting, of course, the cases of mere seasonal change; and, in this class of animals generally, perfect albinos are much more numerous than among birds. Perfect albinos are peculiar to warm-blooded animals, and in them there is a total deficiency of colouring matter in the rete mucosum, and, consequently, in the fur, and even the pigmentum nigrum of the eye is entirely wanting. In birds, these prefect albinos are extremely rare, although several instances have been recorded in VII, 593-598. There are three sorts, however of true permanent albinos, which may be thus designated:
Albinos, when paired together, as is well known, produce chiefly albino offspring, and a breed of them may thus be perpetuated; but, even in a domestic state, they not unfrequently produce young of the usual colour; and, if paired with an ordinary individual, they sometimes produce partial albinos, or semi-albinoes [1, 178], and occasionally, if the original colour be brown (as in the case of mice or rabbits), a black, sandy, or slate-coloured offspring, or an individual with one of these colours more or less varied with white, is produced; but, in the majority of instances, the young wholly resemble one of their parents, and the preponderance is decidedly in favour of the natural hue.2
The coloured offspring of an albino, however, even if matched with another coloured individual, has still a tendency to produce albinos, and this fact has been noticed in the human species; but, as Mr. Lawrence observes on the subject (in his Lectures on the Physiology, Zoology, and the Natural History of Man), "the disposition to change is 'generally' exhausted in one individual, and the characters of the original stock return, unless the variety is kept up by the precaution above mentioned, of excluding from the breed all which have not the new characters.3
Thus, when African albinos intermix with the common race, the offspring generally is black," etc. These observations apply alike to all simple or individual variations, and to most other varieties, and afford one of many reasons why marked breeds are in a state of nature so rarely perpetuated.
There is yet, however, before quitting this subject, another sort of albino to be considered, which, I believe, is peculiar to the feathered race, and which is not, like the others, permanent; these, therefore, I shall denominate temporary albinoes. Most of the pale, white, and pied varieties of birds, which are produced in a state of nature, are of this kind. A friend informs me that a perfectly white lark in his possession moulted, and became of the ordinary hue. I lately shot a sparrow which was all over of a very pale brown, or cream color; it was molting, and some of the new feathers that were coming were of the usual color, and others were of a pure white: on the next molt, probably, no more white feathers would have appeared.
Of a brood of young robins which frequented my garden, two were white, one partially so, and one of the usual mottled brown; these all molted into the ordinary color. I could add other instances to the list, especially amongst domestic poultry. But it does not hence follow that among wild birds there are no permanently white or pied varieties; or, in other words, no true partial and semi-albinoes. A blackbird with a white head has now inhabited a garden in this neighborhood for three successive years; and if the cupidity of collectors did not mark out every white or pied bird for destruction, I doubt not that I should have been able to have furnished some other similar instances of permanent variation.
II. Acquired Variations. The second class of varieties which I would designate thus, comprises the various changes which, in a single individual, or in the course of generations, are gradually brought about by the operation of known causes: such as the greater or less supply of nutriment; the influence of particular sorts of food; or, either of these combined with the various privations consequent upon conflnement; which changes would as gradually and certainly disappear if these causes were removed.
Redundance or deficiency of nutriment affects chiefly the stature of animals. Those herbivorous quadrupeds which browse the scanty vegetation on mountains are invariably much smaller than their brethren which crop the luxuriant produce of the plains; and although the cattle usually kept in these different situations are of diverse breeds, yet either of the breeds gradually removed to the other's pasture would, in two or three generations, acquire many of the characters of the other, would increase or degenerate in size, according to the supply of nutritious food; though, in either case, they would most probably soon give birth to true varieties adapted to the change. In this instance, temperature appears only to exert a secondary influence.
The Iceland breed of sheep, which feeds on the nutritious lichens of that island, is of large size; and, like the other ruminant animals which subsist on similar food, is remarkable for an extraordinary development of horns. Another example of acquired variation, dependent solely on the supply of nutriment, may be observed in the deciduous horns of the deer family, which are well known to be large or small according to the quality of their food. That temperature also does exert an influence greater or less, according to the species of animal, is very evidently shown in the case of the donkey, of which there are no breeds, nor true varieties, and but very few simple variations [VII, 590]: this animal is every where found large or small, according to the climate it inhabits.4
The influence of particular sorts of food may be exemplified by the well-known property of madder (Rubia tinctorum), which colors the secretions, and tinges even the bones of the animals which feed on it of a blood-red color. and, as another familiar instance, may be cited the fact, equally well known, of bullfinches, and one or two other small birds, becoming wholly black when fed entirely on hempseed. I have known, however, this change to take place in a bird (the small aberdevatt finch, so common in the shops), which had been wholly fed on canary seed; yet this by no means invalidates the fact, so often observed, of its being very frequently brought about by the direct influence of the former diet. In several instances which have fallen under my own observation, feeding only on hempseed has invariably superinduced the change.5
The most remarkable of acquired variations are those brought about in animals in a state of confinement or domestication: in which case an animal is supplied regularly with abundance of very nutritious, though often unnatural, food, without the trouble and exertion of having to seek for it, and it becomes, in consequence, bulky and lazy, and in a few generations often very large; while the muscles of the organs of locomotion, from being but little called into action, become rigid and comparatively powerless, or are not developed to their full size. The common domestic breeds of the rabbit, ferret, guinea-pig, turkey, goose, and duck, are thus probably only acquired variations, which, from the causes above-mentioned, have in the course of generations, become much larger and heavier (excepting, however, in the case of the turkey) than their wild prototypes, and less fitted for locomotion; but which, if turned loose into their natural haunts, would most probably return, in a very few generations, to the form, size, and degree of locomotive ability proper to the species when naturally conditioned.6
The crested varieties of domestic geese and ducks, and the hookhilled variety of the latter, are, however, in all probability, true varieties; and what are called "lob-eared" rabbits may be either a true variety, or a breed. The various slight diversities, which I call simple variations, are very common in the present class if varieties; and there is also in them a great tendency to produce what I call true varieties, as well as those slighter deviations, which, by particular management, may be increased into the sort of variety I denominate breeds.
III Breeds are my third class of varieties; and though these may possibly be sometimes formed by accidental isolation in a state of nature, yet they are, for the most part, artificially brought about by the direct agency of man.7 It is a general law of nature for all creatures to propagate the like of themselves: and this extends even to the most trivial minutiae, to the slightest individual peculiarities; and thus, among ourselves, we see a family likeness transmitted from generation to generation.
When two animals are matched together, each remarkable for a certain given peculiarity, no matter how trivial, there is also a decided tendency in nature for that peculiarity to increase; and if the produce of these animals be set apart, and only those in which the same peculiarity is most apparent, be selected to breed from, the next generation will possess it in a still more remarkable degree; and so on, till at length the variety I designate a breed, is formed, which may be very unlike the original type.
The examples of this class of varieties must be too obvious to need specification: many of the varieties of cattle, and, in all probability, the greater number of those of domestic pigeons, have been generally brought about in this manner. It is worthy of remark, however, that the original and typical form of an animal is in great measure kept up by the same identical means by which a true breed is produced.
The original form of a species is unquestionably better adapted to its natural habits than any modification of that form; and, as the sexual passions excite to rivalry and conflict, and the stronger must always prevail over the weaker, the latter, in a state of nature, is allowed but few opportunities of continuing its race. In a large herd of cattle, the strongest bull drives from him all the younger and weaker individuals of his own sex, and remains sole master of the herd; so that all the young which are produced must have had their origin from one which possessed the maximum of power and physical strength; and which, consequently, in the struggle for existence, was the best able to maintain his ground, and defend himself from every enemy.
In like manner, among animals which procure their food by means of their agility, strength, or delicacy of sense, the one best organized must always obtain the greatest quantity; and must, therefore, become physically the strongest, and be thus enabled, by routing its opponents, to transmit its superior qualities to a greater number of offspring. The same law, therefore, which was intended by Providence to keep up the typical qualities of a species, can be easily converted by man into a means of raising different varieties; but it is also clear that, if man did not keep up these breeds by regulating the sexual intercourse, they would all naturally soon revert to the original type. Farther, it is only on this principle that we can satisfactorily account for the degenerating effects said to be produced by the muchcensured practice of "breeding in and in."8
There would almost seem, in some species, to be a tendency, in every separate family, to some particular kind of deviation; which is only counteracted by the various crossings which, in a state of nature, must take place, and by the above-mentioned law, which causes each race to be chiefly propagated by the most typical and perfect individuals.
IV True Varieties. The last of these divisions to which I more peculiarly restrict the term variety, consists of what are, in fact a kind of deformities, or monstrous births, the peculiarities of which, from reasons already mentioned, would very rarely, if ever, be perpetuated in a state of nature; but which, by man's agency, often become the origin of a new race. Such, for example, is the breed of sheep, now common in North America, and known by the name of ancons or otter sheep9. A ewe produced a male lamb of peculiar form, with a long body, and short and crooked limbs: the offspring of this animal, with ordinary females, was found sometimes to resemble the one parent, and sometimes the other; but did not usually blend the characters of each; and, in the cases of twins, the two lambs were often equally diverse with their parents. This variety was extensively propagated, in consequence of being less able to jump over fences than the ordinary breeds of sheep. The solidungular ["donkey-footed"] variety of swine, tailless cats, back-feathered, five-toed, and rumpless fowls, together with many sorts of dogs, and probably , also the race of fan-tailed pigeons, are other striking examples of true varieties.
The deviations of this kind do not appear to have any tendency to revert to the original form: this, most probably, could only be restored, in a direct manner, by the way in which the variety was first produced. To this class may be also referred, with more than probability, some of the more remarkable varieties of the human species.
With regard to color, we know that temperature exerts no permanent gradual influence whatever: white races remain unchanged at slight elevations within the tropics; and the natives of Boothia Felix are very dark; the swarthy inhabitants of Mauritania are a white race, and their sunburnt hue is merely an acquired variation, which is not transmissible by generat tion, and which does not extend to those parts which are not exposed to the sun.
The coloring principle of black races is inherent in them, and is quite independent of external agency; is even darkest in some parts which are the least exposed, and vice versa. The Ethiopian race is nowhere more black than in the vicinity of the Cape of Good Hope, where the crops are sometimes injured by the winter's frost. Strangely enough, this invariableness of color constitutes about, perhaps, the most fixed character of these races.