The evolution of British cattle and the fashioning of breeds/The Melting-Pot
VIII
THE MELTING-POT
Having now identified the races of cattle that at one time or another have arrived in Britain and partaken[1] in the production of the breeds we now possess, we have next to inquire how each race modified or was modified by the races that arrived before or behind it. It has already been stated, that the great agricultural awakening commenced in the seventeenth century. From that time forward the desire for improvement grew keener and keener, and although, even at the present day, that desire is happily still strong, it might be said quite fairly, considering all the circumstances, that it reached its height about the junction of the eighteenth and nineteenth centuries. One of its many forms was to improve the livestock of the country. Men travelled long distances in order to procure cattle which they thought better than those of their own district, and as the cattle imported from the Low Countries were larger and, in the opinion of eighteenth-century stock-breeders, better than those that were in Britain before them, it was to their descendants that men turned for stock with which to improve their own. The Longhorns, which were a combination of the Dutch and several of the races in Britain before them, were the great "improvers" till the end of the eighteenth century, when they were ousted from that position by the Shorthorns, and to some extent, the Herefords, two breeds also of composite character. But we shall better understand the process by which some of our modern breeds have been produced—the jumbling together, as it were, of different races and the emergence of new types of stock—after a short consideration of Mendel's theories, just as we should better understand how certain salts may be mixed together and new ones produced, by some knowledge of chemistry.
It is one of the greatest tragedies in science that Mendel's "Experiments with Plant Hybrids" ("Versuche über Pflanzen Hybriden"), which was published by the Natural History Society of Brünn in 1865, remained unknown till the present century. It is impossible to imagine where we should have been to-day in our knowledge of heredity had Darwin only known of Mendel's work. But Darwin's own discovery so entranced the world that Mendel's was condemned to oblivion till years after both discoverers were dead. As it is, we must now go back, and partially, at least, revise some of Darwin's conclusions.
One of Darwin's main contentions was that races of animals vary, but, as he thought, slowly and constantly; that, to take a homely case, the neck of a giraffe is slightly longer than his father's, that his father's is slightly longer than his grandfather's, and so on backwards: thus, that the differences between a set of animals and their descendants a hundred generations younger are really the sum of all the small accretions added on (or taken off, for that matter) by each successive generation.
But De Vries has shown that sudden and observable changes take place among plants, and that these changes may be inherited: " Varieties have often been observed to appear at once, and quite unexpectedly in horticulture and agriculture."[2] Let us view De Vries 's discovery as described by Professor Arthur Thomson[3]: —
"In 1886 De Vries began hunting about around Amsterdam for a plant which would show hints of being in what we may call a changeful mood. He tried over a hundred species, bringing them under cultivation, but almost all were disappointingly conservative. It seemed as if most of the species around Amsterdam were in a non-mutable state. It is possible, as Weismann suggested in one of his first evolutionary essays (1872), that in the life of species, periods of constancy alternate with periods of changefulness. The human historian has often made a similar remark.
"In the course of his wanderings around Amsterdam, De Vries came across a deserted potato-field at Hilversum—a field of treasure for him. For there he found his long-looked-for mutable plant, an evening primrose (Œnothera lamarkiana). Like its nearest relatives, Œnothera biennis and Œnothera muricata, which it excels in size and beauty of flowers, it probably came from America, where it is a native. It had probably 'escaped' at Hilversum about 1875, and in the following ten years it had spread in hundreds over the field. It had been extremely prolific in its freedom; but that was not its chief interest.
"Its chief interest was its changefulness. It had, so to speak, frolicked in its freedom. Almost all its organisms were varying—as if swayed by a restless tide of life. It showed minute fluctuations from generation to generation; it showed extraordinary freaks like fasciation and pitcher-forming; it showed hesitancy as to how long it meant to live, for while the majority were biennial, many were annual, and a few were triennial; best of all, it showed what can hardly be otherwise described than as new species in the making.
"It is possible that the prolific;multiplication in a new environment may have had something to do with the awakening of the impulsive mutability.
"In 1887, a year after his discovery of the potato-field, De Vries found two well-defined new forms—a short-styled O. brevistylis and a beautiful smooth-leaved O. lævifolia—distinguishable from the parent in many details. He hailed these as two new ' elementary species,' and he applied one of the crucial tests of specific or sub-specific rank: Did they breed true? He found that it was so; from their self-fertilised seeds similar forms arose. Neither of the two new forms was represented in the herbaria at Leyden, Paris, or Kew; neither had been described in the literature of Onagraceæ, They seemed to be distinctly new. It is interesting to note that in 1887 there were few examples of these two new elementary species, and that each occurred on a single plot on the field. The impression conveyed was that each had arisen—by a sudden mutation—from the seed of an individual parent.
"The next chapter in the famous investigation began with a transference of samples of the new forms and the parent stock—partly as plants and partly as seeds—from the potato-field at Hilversum to the botanic garden at Amsterdam.
"The three stocks gave rise under cultivation to many thousands of individuals, which bred true along certain lines, and yet gave rise to other new forms. In short, De Vries had found a plant in the process of evolution.
"The predisposition to mutability—which remains a mystery—was present. De Vries gave it scope, and like the primeval gardener he had the pleasure of giving names to a crop of new creations which emerged before him. From each of these three samples there arose distinctive groups—which, if they had been found in nature, would have been reckoned as distinct species of evening primrose. But the most interesting feature was the apparent abruptness in the origin of the new forms. They seemed to rise by leaps and bounds, by organic jerks; they illustrated what De Vries has called 'mutation.'"
It does not concern us here whether De Vries 's mutations were the result of a new environment or of some other cause. The point for us is that while there may be variation in the Darwinian sense, there are also sudden changes when animals of different characters are bred together, and under certain circumstances these changes are inherited. Mendel's theory explains both the changes and their inheritance. Mendel's original experiments were made with plants, but, as similar results have been obtained again and again with animals, we may substitute animals for plants. When white cattle are mated with red, their progeny (first crosses) are roan; but when these roans are mated together, a quarter of their progeny return in colour to the white parent race and a quarter to the red parent race, while the remainder are roans again, like their parents. Mendel's theory explains such phenomena. He conceived the idea that an animal carries, from its very beginning, determinants which are going to decide, one its eventual colour, another its size, another its length of limb, and so on; and that a half of each determinant is inherited from each parent Each determinant is therefore, as it were, bicellular, bouble-barrelled.
A roan animal's red parent carries a double-barrelled determinant for redness, which we may represent thus: , while its white parent carries another for whiteness, which we may represent thus: .
When a red animal is mated with a white, their determinants meet, and the young, taking a half of that offered by each parent, starts off with a determinant, one half of which is for redness, the other half for whiteness, thus: , and its coat is a mixture of red hairs and white—that is, roan. The proportions of the two kinds of hair vary greatly: the white hairs being sometimes so few that the roan is almost a red, and the red sometimes so few that it is almost a white.[4]
When roan crosses are bred together their progeny select their colour determinant one half from each parent, and the chances are one that both halves will be red; two that one will be white and one red; and one that both will be white. It may be a union of these these
↘ , or these
↗ , or these Consequently, from a sufficient number of matings, a quarter of the calves must be red, a half roan, and a quarter white.
Again, when red cattle are mated with roan ones, one half their calves are red, the other half roan. Combining the four little diagrams as above, →
⤨→ gives two reds , and two roans .
Further, when white cattle are mated with roans, one half their progeny are white, the other half roan. →
⤨→ gives two whites and two roans .
The following table shows the average numbers of calves of each of these colours that may be produced by all the possible matings:—
| Red % |
Roan % |
White % | |
| Red × Red | 100 | 0 | 0 |
| White × White | 0 | 0 | 100 |
| Red × White | 0 | 100 | 0 |
| Red × Roan | 50 | 50 | 0 |
| White × Roan | 0 | 50 | 50 |
| Roan × Roan | 25 | 50 | 25 |
Thus it will be seen that, although by crossing white cattle and red a new colour, roan, is produced, that new colour itself is unstable and throws back constantly to one or other parent race. A similar result follows when white cattle are crossed with black: the intermediate hybrid, as it is called in Mendelian phraseology, being in this case a blue roan.
But, although these intermediate hybrids are unstable, they may be the means of transferring the colour of one kind of cattle from that kind to another kind. The transference of the white colour of the Roman cattle to the black Welsh cattle is a simple case. A white Roman bull breeds with black Welsh cows and produces blue-roan calves. These again breed together, and 25 per cent, of their calves are white. In other respects some of these white calves are Romans, some Welsh, and thus, in two generations only, some black Welsh cattle may be turned white.
Perhaps, for exposition's sake, a more striking case could be imagined. If one or more white Shorthorn bulls were put to a herd of red North Devon cows, their progeny would all be roans. At the same time, they would be intermediate between their parents in size, as well, perhaps, as in some other things which we may neglect for the present. If those roan crosses were bred together, 25 per cent, of their progeny would be white, 50 per cent, roan, and 25 per cent. red. At the same time, 25 per cent, of the whole would be Shorthorns in size, 25 per cent. Devons, and 50 per cent, intermediates. But, as the chances are absolutely against both colour and size varying together, there are reds, whites, and roans among the cattle of Shorthorn size, and reds, whites, and roans among those of Devon size. The white-coloured cattle of Devon size are white Devons, from which any number of white Devons might be produced, and by the use of such cattle the whole red Devon breed could be made white in not so very many generations.
There are, however, hybrids which are not obvious intermediates, but which masquerade in the guise of one of their parents. The progeny of black and red cattle are black, yet they are hybrids nevertheless. When these masquerading hybrids are bred together, a quarter of their progeny are red, like one of their grandparents, and three quarters are black, like the other, but of the black ones only a third are genuinely black; the others are masqueraders—hybrids, like the roans, although they pretend to be otherwise.
The explanation is that, while one half of the colour determinant of these crosses is for blackness—derived from the black parent—and the other half for redness—derived from the red parent—the relationship between blackness and redness is such that blackness holds the mastery -and obscures or hides redness. Redness is all the time latent, however. In Mendelian phraseology, blackness is dominant to redness, and redness is recessive to blackness.
These phenomena may be made clear diagrammatically. We shall use letters instead of circles, and, for convenience, we shall use capitals to denote the dominant characters and small letters to denote the recessive.
Black cattle mated with red produce masquerading black hybrids, thus—
→
⤨→ gives only .
When masquerading black hybrids are bred together, their progeny receive their colour determinant, one half from each parent, and the chances are: one that both halves will be black, two that one half will be black and the other red, and one that both will be red. It may be a union of these,
these, ; or these,
↗ ; or these, →. Consequently, from a sufficient number of matings a quarter of the calves are pure black, ; a half are masquerading blacks, ; and a quarter are pure red, .
Again, when black masqueraders are bred back to pure black cattle, one half their progeny are pure black, the other half masqueraders. Thus →
⤨→ gives two pure blacks, ; and two masqueraders, .
Further, when black masqueraders are bred back to red, one half their progeny are masqueraders, the other half are red. →
⤨→ gives two masqueraders, , and two reds, .
These black masqueraders cause confusion, since they cannot be separated from the pure black ones by the naked eye; but, like the intermediate roans, they may also be the means of transmitting a colour from one set of cattle to another. For instance, red cattle of North Devon type were taken to the south of Ireland a century ago, or more, and crossed with the native black Kerry cattle. The result of the crossing and recrossing was that some calves were pure black, others were masquerading blacks, and others were pure red. The red colour is not admired by Kerry breeders, and no attempt has been made to keep it; but, because of the difficulty of identifying and, so, eliminating them, when masquerading blacks are mated together, red calves are occasionally born. If these red calves were kept and bred from, the Kerry black breed could eventually be converted into a red breed. By doing this, the Highland breed of cattle has been changed from one that once was largely black to one that is now largely red.
But the Kerry breed is of further interest because, while the Devons transmitted to it their red colour in potentia, they also transmitted their shortness of leg. In this case shortness was dominant to length. The result of the crossing was that some calves were pure short-legged, others were masquerading as short-legged, and others were long-legged. Thus among each of the three different colours of Kerry cattle—pure blacks, masquerading blacks, and reds—there are pure short-legged animals, masquerading short-legged animals, and long-legged animals. That is to say, among Kerry cattle now, as compared with Kerry cattle long ago, there are some possessing characters, redness and short-leggedness, which have been transmitted to them by another breed. Such short-legged cattle are distinguished from ordinary Kerries by being called "Dexters."
Still another case might be quoted. At one time the cattle of Suffolk were hornless and light dun, while their neighbours were horned and red. Breeders preferred the hornlessness of the one breed and the redness of the other. The hornless character is dominant to the horned; consequently, as a result of crossing horned and hornless cattle, there were produced pure hornless cattle, masquerading hornless cattle, and horned cattle; but, by continually selecting hornless ones to breed from, the masqueraders and the horned ones were worked out. When the light dun Suffolks were crossed by red cattle, there resulted yellow intermediate hybrids; but when these were crossed by red cattle, half their progeny were red. By the persistent selection of red-coloured cattle, the original light dun colour and its derivative yellow were eventually worked out. Thus the old Suffolks and their neighbours became one breed: the Suffolks giving up their colour and their neighbours their horns.
It is not necessary for us to consider cases in which three or more characters have been transferred from one breed to another.
- ↑ A few black-and-white cattle and some other cattle—the Channel Islanders, for instance—have come in, but they have taken no part in producing our present breeds.
- ↑ De Vries's "Species and Varieties," 1905, p. 16.
- ↑ "Heredity," 1908, p. 91.
- ↑ White cattle with the black or brown "points" of the "wild" park cattle behave as pure whites, and red and white flecked cattle behave as pure reds.