THE BREEDING OF LIVE STOCK

Dominion, Volume 21, Issue 8, 4 October 1927, Page 12

THE BREEDING OF LIVE STOCK

By ■

J. A. C.

Special for The Dominion. All Rights Reserved. I. Tliis is now new subject, an<l so much has been said and written upon it that to say or write more until some new discovery has been made would seem to bo quite superfluous. Scientific investigators have endeavoured to probe its mysteries since the days of Mendel, and his experience in the hybridisation of peas lias Jed to the adoption of a hypothesis which the most modern writers on animal breeding have not yet ignored. Few people outside the ranks of the scientific investigators can discern any connection between a pea and an animal from the breeder’s viewpoint, yet Mendel’s experiments with peas when repeated , in the crossing of animals such as guinea pigs. etc. (black and white), produced very similar results, and supported his theory that in successive crossings there were certain well-defined proportions of what ho called “dominants” and “recessives.” The “dominants” were those hybrid animals or plants that most clearly resembled the original parent, and they were generally produced in the proportion of I to 3 in the first cross, while the “recessives” were those of the progeny that showed greater variation in size and colour. Volumes have been written upon this line of investigation; but, interesting and informative though the subject is if our sole object, is to produce a new species, the stock breeder lias a different object in view—the improvement of his flock or herd, and is therefore not much assisted by the facts revealed in regard to hybrids. The invention of the microscope has turned investigation in another direction, and the examination of the behaviour and development of the chromosomes and centrosomes lias up to tho present day occupied the attention almost entirely of those who are studiously, and intelligently too. pursuing the mysteries of breeding. They have watched the single cell through all its phases of development and aggregation grow into the multicellular foetus and the mature animal, and yet tho mystery is not solved. They can with absolute certainty describe tho process of change that takes place from tho germ plasm to the birth of an animal, but the elusive principle that directs

that growth will continue to elude them until the origin of life itself has been discovered, and that time is not yet Hence it may bo stated that those researches also are at present of little avail to the anxious breeder whose object is to produce this year better animals than those he possessed last year. Yet another line of research has engaged the attention of quite an army of clever men, who have ransacked the museums, dived into the bowels of the earth for specimens of animal structure, made comparisons, and arranged them in chronological order showing beyond dispute that our present stock have descended from primitive animals of vastly different structure. Thev have shown, too, that this process of change has been very slow and continuous over immense periods of time, controlled only by Nature, and therefore those examples (now well classified and preserved) afford most valuable lessons to the students of animal propagation. These will ho again referred to.

It is not here intended to throw any doubt, or discredit upon the work of those biologists of the Mendelian school, such as Weismann, Lubliock. de Vries, and others, for the worst, that can be said of it is that, while it contains important discoveries in regard to heredity, it is not so helpful to the modern breeder as that of Darwin, Nilsson, Rutmeyer, Cuvier, Lamarck, and a host of other paleontologists who have shown us the path of evolution along the centuries, and pointed the way to further development. Yet we find one of the latest of tho Mendelian school (Darbfshire. 1911) committing himself to the following statement .—

“Mendel's work points to the established principle that the contents of the germ cells, and not .the outward characteristics of the animals , dealt with, must be our guide in breeding. If that is so (and it may bo strictly correct) there is but a gloomy prospect IGr the farmer who is endeavouring to improve his flock or herd, for bow is be to study the germ cells of his live animals before deciding year by year how he is to mate them? Is he simply to sit down and wait for further discoveries of the microscopists? No farmer will be inclined to accept that view whether or not it may be scientifically true, but he need not worry, because other authorities’ do not support it. One, of the latter (W. L- Tower) says;

“Knowledge concerning the germ cells, which are the germ plasm or the carriers of it, is largely anatomical in character, derived from the studies in cystology, and in the main is onesided, incomplete, aud has been too much directed ’to the study of chromosomes/'

Tho curious thing about these two contradictory views of the question Is that either or both may be right. Darbishire’s statement cannot reasonably be contradicted, because it his been clearly shown that the single-celled chromosome is the starting point in the formation of the future animal. It is clearly observed under the microscope to multiply itself by a process of fission in the formation of body tissue: its details, minute as they are, do not evade our vision; but it exhibits one quality of which we know nothing, that is life. Its anatomy is clear; .its functions are learly demonstarted but what it is that gives movement to its anatomical parts and directs them to perform those functions so unerringly is tne mystery that may never be known. The potential principle of its movement cannot be explained at present, and until that can be done Mr. Darbishire’s dictum can neither be denied nor affirmed. Nor is it necessary to oppose his view except to say that the "outward characteristics of which lie speaks must surely be resultant purely and entirely on tlie innate potency of the germ cells themselves. That they conform in every way to unalterable natural laws is equally certain, hence those characteristics must be regarded as a safe and unerring guide in the matter of propagation. So Tower’s view must be accepted also. The ordinary breeder can find no use for a microscope in his business, so he has necessarily to fall back upon the study of “outward characteristics,” and, convinced of the fact that "like begets like,” lie proceeds accordingly. He leaves too much to chance, however, and is too often surprised to find in comparing his results with their immediate pedecessors that the word “like” is a very elastic term. He finds also that there is not exact equality in the “outward characteristics” of sire and son or of mother and daughter. The younger generation in either a little better or a little worse than their parents when those characteristics have been compared._ In plain language, his results are either on an ascending or a descending grade, and are never on the exact level, for there is no such thing in breeding as absolute equality, and Nature never stands still. This principle mav be illustrated by a graph showing results year by year. The horizontal lines A A and C C re- § resent the limits of improvement and eterioration. Th? perpendicular line*

I) D, E E, F F, and G G denote the successive years, and the wave line B B th* varying results of each year’s braeding. The improvement or deterioration that inevitably takes place from one generation to another is what is known lay th* term "variation.” Sometimes it is exhibited iff a very marked degree in hybrids and to a far lesser degree in purebred animals. This is an important fact to remember, and it is well described by the German philosopher Buchner in th* following sentences: — “Incessant and minute change is one of the conditions of life. Sudden change is disease, and no change at all incipient death.” Whether it is applied to the, Russian revolutions, the collapse of an organio body, the abnormal growth of body tissue, or variation in successive generations of animals that axiom is “as true as gospel.” It is clear, therefore, that the breeder who attempts to make sudden changes in bis flock or herd by intro, ducing new blood from lines dissimilar to his own animals in "outward characteristics” needs no “daylight saving legislation, because he has already put back the clock. The first lesson, then, that the practical breeder must learn is to avoid sudden changes in type and "outward characteristics” by crossing widely divergent types. If he disregards that truism ne is most assuredly on the down grade with his experiments, and lie is losing valuable time and money too, because, in the hope of correcting errors in the "outwad characteristics, he has called upon Nature to take toe wide a step—to hurrj' on, as it were, and to perform in one eneration what Nature reouires several generations to accomplish. Ho has not grasped the idea that “incessant and..minute change” is the unalterable rule in healthy development, and that Nature’s laws cannot be successfully interfered with. Far too many breeders are convinced of the notion that faulty characteristics in stud animals can be corrected in one Here we may be reminded of our statement that "oiir present stock have descended from primitive animals of vastly different structure,” and it may be pertinently asked how Nature of its own volition has produced such vastly different types if radical change is so abhor rent to it? The answer is plain and complete, snd the paleontologists hav* supplied it. , „ (To be continued.) »