[14] Carpenter's Physiology, new edition, page 783.
CHAPTER IV.[ToC]
Atavism, or Ancestral Influence.
It may not be easy to say whether this phenomenon is more connected with the law of similarity, or with that of variation. Youatt, in his work on cattle published by the Society for the Diffusion of Useful Knowledge, inclines to the former. He speaks of it as showing the universality of the application of the axiom that "like produces like"—that when this "may not seem to hold good, it is often because the lost resemblance to generations gone by is strongly revived." The phenomenon, or law, as it is sometimes called, of atavism,[15] or ancestral influence, is one of considerable practical importance, and well deserves careful attention by the breeder of farm stock.
Every one is aware that it is nothing unusual for a child to resemble its grandfather or grandmother or some ancestor still farther back, more than it does either its own father or mother. The fact is too familiar to require the citing of examples. We find the same occurrence among our domestic animals, and oftener in proportion as the breeds are crossed or mixed up. Among our common stock of neat cattle, (natives, as they are often called,) originating as they have done from animals brought from England, Scotland, Denmark, France and Spain, each possessing different characteristics of form, color and use; and bred, as our common stock has usually been, indiscriminately together, with no special point in view, no attempt to obtain any particular type or form, or to secure adaptation for any particular purpose, we have very frequent opportunities of witnessing the results of the operation of this law of hereditary transmission. So common indeed is its occurrence, that the remark is often made, that however good a cow may be, there is no telling beforehand what sort of a calf she may have.
The fact is sufficiently obvious that certain peculiarities often lie dormant for a generation or two and then reappear in subsequent progeny. Stockmen often speak of it as "breeding back," or "crying back." The cause of this phenomenon we may not fully understand. A late writer says, "it is to be explained on the supposition that the qualities were transmitted by the grandfather to the father in whom they were masked by the presence of some antagonistic or controlling influence, and were thence transmitted to the son in whom the antagonistic influence being withdrawn they manifest themselves." A French writer on Physiology says, if there is not inheritance of paternal characteristics, there is at least an aptitude to inherit them, a disposition to reproduce them; and there is always a transmission of this aptitude to some new descendants, among whom these traits will manifest themselves sooner or later.[16] Mr. Singer, let us say, has a remarkable aptitude for music; but the influence of Mrs. Singer is such that their children inheriting her imperfect ear, manifest no musical talent whatever. These children however have inherited the disposition of the father in spite of its non-manifestation; and if, when they transmit what in them is latent, the influence of their wives is favorable, the grand-children may turn out musically gifted.
The lesson taught by the law of atavism is very plain. It shows the importance of seeking "thorough-bred" or "well-bred" animals; and by these terms are simply meant such as are descended from a line of ancestors in which for many generations the desirable forms, qualities and characteristics have been uniformly shown. In such a case, even if ancestral influence does come in play, no material difference appears in the offspring, the ancestors being all essentially alike. From this stand point we best perceive in what consists the money value of a good "pedigree." It is in the evidence which it brings that the animal is descended from a line all the individuals of which were alike, and excellent of their kind, and so is almost sure to transmit like excellencies to its progeny in turn;—not that every animal with a long pedigree full of high-sounding names is necessarily of great value as a breeder, for in every race or breed, as we have seen while speaking of the law of variation, there will be here and there some which are less perfect and symmetrical of their kind than others; and if such be bred from, they may likely enough transmit undesirable points; and if they be mated with others possessing similar failings, they are almost sure to deteriorate very considerably.