Animal Breeding the Law of Correlation
Animal Breeding the Law of Correlation Three principal laws have been given in previous chapters which govern the breeding of domestic animals. These are the law that like produces like, the law of variation, and the law of atavism. In ad dition to these there is another law, viz. : the law of correlation.
This law, however, is more of what may be termed an inherent feature of the organization than of modification in the same and yet it would not be correct to say that it is not susceptible of modification. The relation of the different parts of the organization in virtue of this law may be much modified but this relation can never be entirely obliterated.
Definition of Correlation. —Correlation in its relation to animal life means that correspondence or relation which exists as to form and function between the different organs of the body. In virtue of this relation certain peculiarities of structure will obtain between those organs which belong inherently to the species. It may be said to form a dividing line between the species.
In fact, without it the classification of animal life would be impossible. Because of this law there must be a certain relation in kind be- tween the teeth of the cat and the claws of the cat and between form in an animal and the breeding qualities of the same animal. As intimated previously, these relations may be modified but never entirely suppressed.
The Law of Correlation Defined. —The law of correlation means that interdependent principle of development and suppression that seems to obtain between the different organs of the body and the various functions of the same. By the operation of this law a change in one organ or set of organs is followed by a corresponding change in another organ or set of organs, in some part of the body.
For instance, in wild cattle there is a certain relation between the parts of the individual animal in virtue of the species to which it belongs because the form and action of the jaw are of such a kind, the form of the digestive organs and the nature of the digestion are of such a kind.
This relation always obtains without great modification. There will also be a certain relation between development in the fore and hind parts of the animal respectively. When they need to graze on rugged pastures and among enemies, development will be large and strong in the muscles of the front limbs.
They have both to climb and run. Subject the same class of animals for generations to level pastures and domestic or semi-domestic conditions, and these relations will change. The muscles that help to control locomotion in the front part of the body will grow less relatively, and those still at govern locomotion in the hind parts of the same will increase. And the modification of the parts is always or always of an opposite character.
If there is an increase in one part of the animal there will be a decrease in some other part of the same, and the change is usually proportionate in degree to the change made in the co-related organ or set of organs. In some instances the corresponding change is dependent on a change in structure, in others on a change in function, and is of like kind, that is to say, a change in structure is dependent on a change in structure, and a change in function on a change in function, and in vet other instances the change, whether of structure or function, may, to some extent, be dependent on changes in both structure and function.
The Anatomist and Correlated Structure. —Correlated structure in an animal enables the anatomist to determine from a single bone:
1, The class and order to which it belongs;
2, its habits and modes of life; and
3, the food required for its support. For instance, the jawbone of the skeleton of an ox with the teeth in it, tells the anatomist that the living animal chewed the cud and that, therefore, it belonged to the order of cloven-hoofed mammals. Since it chewed the cud, its natural food was coarse herbage.
Because its natural food was coarse herbage it had the grazing or browsing habit or both, and since it was a mammal, it suckled its young. These are only a few of the conclusions that could be reached regarding the animal and its kind from the jawbone mentioned and its bony belongings. How easily then could the skilled anatomist construct a perfect skeleton of an animal that no man had ever seen alive, from a con- fused mass of skeleton materials which contained in it all the parts of the bony framework of such an animal.
Correlation with Reference to Structure. Structure. —Illustrations of the law of correlation with reference to structure are numerous.
1. They may be found in the highly organized carnivora, in whom, as Cuvier has said, the form of the teeth has an intimate correspondence to that of the condyle, blade bone, femur, and claws.
In the lion, for instance, there are teeth to lacerate and hold. There are also teeth to cut> which play upon each other like scissor blades. This calls for great strength of jaw and a cutting motion up and down. Both are made possible by the form of the condyle, of the teeth and jaws and of the strong muscles attached to the jaws. The blade bone is powerful and so muscled as to give great strength. The femur is so formed with the muscles attached to it as to admit of crouching when lying in wait for prey, and the claws are of a character to enable the animal to grasp its prey and to lacerate it almost at will.
- In the structure of ruminants, there is an intimate relation between hoof and horn development, and also between the form of the teeth, the articulation of the jaw and the complex character of the digestive organs.
Ruminant animals all have cloven hoofs, and they all have horns that grow out from the frontal bone. Moreover, the number of the horns corresponds to the number of the divisions in the hoof.
In ruminants the teeth are made to grind. The joints of the jaw bones and the muscles of the jaws provide for the lateral or grinding movement of the latter, and the digestion in its complexity provides for the grinding of the food in chewing the cud. when the animal is otherwise at- rest.
- In the development of the brain in men and reptiles respectively and of the bones which surround these. In the former the brain cavity is large and the bones encircling it are relatively light, whereas in the latter the opposite conformation exists.
And 4, They are further found in the development of the fore and hind parts respectively of the bat and kangaroo. In the bat the anterior members are widely extended and the posterior but slightly, so as to facilitate rising easily.
In the kangaroo there is much development in the posterior members and little in the anterior, to facilitate the taking of long leaps
- In the comparative unproductiveness of the male Sebright-bantams without sickle feathers and of rumpless fowls.
And 6, in the effect of castration upon other organs of the body, as witnessed in the decreased development of the muscles of the neck which it produces and the loss of fighting spirit which results from it. The two illustrations given last also bear somewhat on the relation which structure must function.
Correlation with Reference to Function. —Illustrations of the law of correlation with reference to function are found : 1. In the influence of extreme development of the beef form on milk production, and vice versa. Experience in growing beef cattle has shown -that when the beef form is pushed to an extreme, milk production is lessened, and that when the dairy form is pushed to an extreme, beef production is hindered.
An illustration is thus given of the influence of a change in structure on function. But in this instance, modification of structure is not the sole cause of modification in function. The former works hand in hand with habit in producing such modification. Nor is the fact to be overlooked that what may be termed middle ground modification is consistent with the production of a fair amount of meat and of milk in the one animal as illustrated in ‘the development of the dual-purpose cow’.
- In the influence of a marked increase or de- crease in flesh production on locomotion. The wild hog is swift as well as fierce. He is well muscled. But not loaded down with fat, hence he can run swiftly. His descendant, the domestic hog, when loaded with flesh cannot run fast. It is possible to load him with fat that he rises upon his feet with difficulty.
Here, again, is an illustration of the modifying influence of structure upon function.
- In the close relation between abundant milk production and prolificacy. It has been noticed that females which produce milk freely, breed more regularly than those which are shy milkers. They also breed more abundantly when more than -one animal is produced at birth, and, of course, the opposite of tins is true.
In this fact an illustration is furnished of the modifying influence of function on function, both in the direction of suppression and increase.
And 4, in the unusual development of one sense where another is deficient. Usually, people who are blind are possess- ed of the sense of touch to an unusual degree. This, of course, is owing chiefly to the care bestowed by the individual in educating that sense, which is to say, in developing the sense of touch. But it shows at the same time the indirect influence of function on function.
Similarly, the sense of hearing is sometimes developed in an unusual degree by persons who are blind, and also the sense of smell. The same principle is operative in plant life. When an unusual growth is produced in grain or in fruit trees, it is so produced at the expense of grain production in the one instance and of fruit production in the other.
Influences that affect Correlation. Correlation. —The chief influences that affect correlation are Environment, habit and use, food and selection. Illustrations of the influence of environment on correlation found in the lack of size in Shorthorns, confine to mountain pastures, without a corresponding decrease in the size of the bone; also, in the adverse influence of conditions too artificial on the breeding* powers, though these conditions may secure good physical development.
The influence of habit and use on correlation is shown in the increase of capacity in brain power, which is frequently obtained at, the expense of diminished muscular development, and in the increase in muscular development and staying power which may be obtained in the hard-working boy and even in the athlete, though frequently at the expense of mental development. But, as with the development of milk and beef in the same animal in equilibrium, so is it with physical and mental development. It is only when either is carried to an extreme that it becomes incompatible.
The influence exerted by food may be seen in various ways. Keep a young and growing animal on scant supplies, and the relation between the normal development of muscle and bone will be disturbed. There will be want of development in the former and overmuch development in the latter.
Again, feed a young calf an undue quantity of hay tea and adjuncts instead of new milk, and what may be termed the correlated harmony of development will be disturbed. The stomach will so distend that the animal will be always somewhat paunchy, and this, of course, at the expense of harmony of development.
That selection in breeding may be made to exercise a powerful influence on correlation may be readily shown from any one of a hundred illustrations that may be given. For instance, cross pure Southdown rams upon pure American Merinos and upon the progeny for several generations.
Eventually the progeny will have the Southdown form, which is to say, an excellent mutton form, but it will have been obtained at a sacrifice of quantity and fineness in the wool.
Value of the Knowledge of Correlated Structure. —A knowledge of the correlated structure of domestic animals is of great practical utility, as by certain indications of external form cognizant to the senses we can judge qualities hidden from view. For instance: 1. A strong horn and head and many bones in the limbs and tail indicate an undue amount of bone in the system for the highest production of meat.
Because of this an animal, large and heavy, will frequently be rejected by the skilled butcher for one less in size but with bone less coarse, for he knows the latter is likely to kill better it is likely to have less waste in the carcass and to possess a superior quality of meat. It is by external form accompanied by handling qualities as described in Chapter XVIII. that he is guided in the choice of animals for the block. From what he sees and finds without, he knows what to look for in the matter of flesh and fat within.
- A wide chest and a low set, compact form is a guaranty of a good constitution. These are not by any means all the indications of a good constitution, as shown in Chapter XXIII. But so frequently has such a form been found to indicate good constitution, that it is looked upon as a reasonably safe guide in judging of constitution, aside from the influence of the taint of inherited disease.
- A long neck, flat ribs, hollow flanks, large joints, and ungainly limbs are among the indications of a natural tendency to delicacy of form as shown in Chapter VII.
- Large capacity of body, a fine head, neck, and limbs, and good development of udder, are among the leading indications of good milking qualities.
Though they may not furnish an exact measure of milking capacity they furnish so safe a guide as to enable the dairyman to rely much upon these indications when choosing dairy animals.
5, a hard, unyielding skin and harsh coarse hair indicate poor feeding qualities.
These indications are further discussed in Chapter VII. From what has just been said, it will be evident that a knowledge of the laws of correlation lies at the basis of all selection in livestock, whether the selection has reference to the block, to the pail, or to breeding.
Correlation, and Highest Development of Individual Qua! Hies. —This Law explains the difficulty experienced by breeders whose aim has been too secure, in the highest degree, development of essentially different characteristics and qualities in the same animal, as illustrated:
1, in the apparent antagonism in the development of beef producing and milk producing qualities in bovines; :
2, in the difficulty in producing wool and flesh of the highest excellence in the one individual sheep; and
3, in the apparently impossible attainment of highest excellence in mental and physical achievement by the one person. Push beef production beyond a certain limit and it reacts against milk production. Push milk production beyond a certain limit and it reacts against beef production.
These results have been experienced so frequently as to put this question beyond the realm of doubt. The highest excellence in wool production, at least as regards fineness, has been found incompatible with a high standard of mutton production, as witnessed in the breed known as Saxon Merino. The experiments of Bakewell in perfecting the mutton form were found to be antagonistic to equally high development in wool production.
The most renowned thinkers in the world have never stood in the first rank as athletes, and those on the pinnacle of attainment in athletics have not stood in the first rank as thinkers. Carry attainment to its possible limit in any one of these directions and by the action of this law of correlation it hinders attainment in the other. It has the effect of lessening stamina even in the athlete.
Those, therefore, who seek highest development in one quality will fail unless they give due heed to the retention of stamina in the same. It must not be concluded, however, that “the development of antagonistic characters, at least in degree, is strictly incompatible. Their simultaneous development up to a certain limit is not only not in- compatible but it is mutually helpful.
The dairy animal may be bred so far away from the beef form as to weaken dairy qualities. The beef form may be bred so far away from the dairy form as to almost obliterate the milking qualities and thereby react against beef production. Comparisons similar in their results could be made between a wool and flesh production in sheep, and between mental and physical attainments in men.
Dual attainment, therefore, up to a certain limit in each of the two kinds of development thus contrasted is positively advantageous. This is strikingly apparent in the adverse influence which lack of physical vigor exercises on mental development. But it may not be possible to tell exactly where the border line runs between action that is co- operative and helpful in the development of these different characters, and action that becomes antagonistic and hurtful.
Equilibrium in the Organization and Correlation. —From what has been said it will be very evident that an equilibrium of the organization can only be attained by the arrangement of its elements in strict accordance with the laws of correlation. A modification of a single character may involve re-arrangement of the dominant characteristics, and this may result in the transposition of latent characteristics which generate atavic tendencies.
And this tendency to reversion may be much influenced by the character of the surroundings. For instance, when the attempt has been made to modify size in a breed beyond what the natural food supplies will maintain it has been noticed that the tendencies to reversion are particularly strong, and that these tendencies are further accentuated when cross breeding has been called in to aid in making the change. This accounts, in part, at least, for the many difficulties experienced by those who have attempted to improve animals by crossing them.
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