Imágenes de páginas



be offered than any of these—an explanation which I think renders it possible to admit the seeming contradictions which the detailed facts present, and yet to hold by the theory.

All the civilized races, and probably also the uncivilized ones, are of mixed origin; and, as a consequence, have physical and mental constitutions in which are mingled several aboriginal oonstitutions more or less differing from each other. This heterogeneity of constitution seems to me the chief cause of the incongruities between aspect and nature which we daily meet with. Given a pure race, subject to constant conditions of climate, food, and habits of life, and there is every reason to believe that between external appearance and internal structure there will be a constant connection. Unite this race with another equally pure, but adapted to different conditions and having a correspondingly different physique, face, and morale, and there will occur in the descendants, not a homogeneous mean between the two constitutions, but a seemingly irregular combination of characteristics of the one with characteristics of the other-one feature traceable to this race, a second to that, and a third uniting the attributes of both; while in disposition and intellect there will be found a like medley of the two originals.

The fact that the forms and qualities of any offspring are not a mean between the forms and qualities of its parents, but a mixture of them, is illustrated in every family. The features and peculiarities of a child are separately referred by observers to father and mother respectively-nose and mouth to this side; colour of the hair and eyes to that—this moral peculiarity to the first; this intellectual one to the second-and so with contour and idiosyncrasies of body. Manifestly if each organ or faculty in a child was an average of the two developments of such organ or faculty in the parents, it would follow

that all brothers and sisters should be alike; or should, at any rate, differ no more than their parents differed from year to year. So far, however, from finding that this is the case, we find not only that great irregularities are produced by intermixture of traits, but that there is no constancy in the mode of intermixture, or the extent of variation produced by it.

This imperfect union of parental constitutions in the constitution of offspring, is yet more clearly illustrated by the reappearance of peculiarities traceable to bygone generations. Forms, dispositions, and diseases, possessed by distant progenitors, habitually come out from time to time in descendants. Some single feature, or some solitary tendency, will again and again show itself, after being apparently lost. It is notoriously thus with gout, scrofula, and insanity. On some of the monumental brasses in our old churches are engraved heads having traits still persistent in the same families. Wherever, as in portrait galleries, a register of ancestral faces has been kept, the same fact is more or less apparent. The pertinacity with which particular characteristics reproduce themselves is well exemplified in America, where traces of negro blood can be detected in the finger nails, when no longer visible in the complexion. Among breeders of animals it is well known that, after several generations in which no visible modifications were traceable, the effects of a cross will suddenly make their appearance. In all which facts we see the general law that an organism produced from two organisms constitutionally different, is not a homogeneous mean; but is made up of separate elements, taken in variable manner and proportion from the originals.

In a recent number of the Quarterly Journal of the Agricultural Society were published some facts respecting the mixture of French and English races of sheep, bearing collaterally on this point. Sundry attempts had been



made to improve the poor French breeds by our fine English: ones. For a long time these attempts failed. The hybrids bore no trace of their English ancestry; but were as dwarfed and poverty-stricken as their French dams. Eventually the cause of failure was found to lie in the relative heterogeneity and homogeneity of the two constitutions. The superior English sheep were of mixed race; the French sheep, though inferior, were of pure race; and the compound, imperfectly coördinated constitution of the one could not maintain itself against the simple and completely-balanced constitution of the other. This, at first an hypothesis, was presently demonstrated. French sheep of mixed constitution having been obtained by uniting two of the pure French breeds, it was found that these hybrid French sheep, when united with the English ones, produced a cross in which the English characteristics were duly displayed. Now, this inability of a mixed constitution to stand its ground against an unmixed one, quite accords with the above induction. An unmixed constitution is one in which all the organs are exactly fitted to each other—are perfectly balanced; the system, as a whole, is in stable equilibrium. A mixed constitution, on the contrary, being made up of organs belonging to two separate sets, cannot have them in exact fitness-cannot have them perfectly balanced ; and a system in comparatively unstable equilibrium results. But in proportion to the stability of the equilibrium will be the power to resist disturbing forces. Hence, when two constitutions, in stable and unstable equilibrium respectively, become disturbing forces to each other, the unstable one will be overthrown, and the stable one will assert itself unchanged.

This imperfect coördination of parts in a mixed constitution, and this consequent instability of its equilibrium, are intimately connected with the vexed question of genera, species, and varieties; and, with a view partly to the intrinsic interest of this question, and partly to the further elucidation of the topic in hand, I must again digress.

The current physiological test of distinct species is the production of a non-prolific hybrid. The ability of the offspring to reproduce itself is held to indicate that its parents are of the same species, however widely they may differ in appearance; and its inability to do this is taken as proof that, nearly allied as its parents may seem, they are distinct in kind. Of late, however, facts have been accumulating that tend more and more to throw doubt on this generalization. Cattle breeders have established it as a general fact, that the offspring of two different breeds of sheep or oxen dwindle away in a few generations if allied with themselves; and that a good result can be obtained only by mixing them with one or other of the original breeds—a fact implying that what is true of so-called species, is, under a modified form, true of varieties also. The same phenomena are observable in the mixtures of different races of men. They, too, it is alleged, cannot maintain themselves as separate varieties; but die out unless there is intermarriage with the originals. In brief, it seems that the hybrids produced from two distinct races of organisms may die out in the first, second, third, fourth, fifth, &c., generation, according as the constitutional difference of the races is greater or less.

Now, the experience of the French sheep-breeders, above quoted, suggests a rationale of these various results. For if it be true that an organism produced by two unlike organisms is not a mean between them, but a mixture of parts of the one with parts of the other-if it be true that these parts belonging to two different sets are of necessity imperfectly coördinated; then it becomes manifest that in proportion as the difference between the parent organisms is greater or less, the defects of coördination in the



offspring will be greater or less. Whence it follows, that according to the degree of organic incongruity between the parents, we may have every gradation in the offspring, from a combination of parts so incongruous that it will not work at all, up to a combination complete enough to subsist permanently as a race.

And this is just what we find in fact. Between organjsms widely differing in character, no intermediate organism is possible. When the difference is less, a non-prolific hybrid is produced-an organism so badly coördinated as to be capable only of incomplete life. When the difference is still less, there results an organism capable of reproducing itself; but not of bequeathing to its offspring complete constitutions. And as the degrees of difference are further diminished, the incompleteness of constitution is longer and longer in making its appearance; until we come to those varieties of the same species which differ so slightly that their offspring are as permanent as themselves. Even in these, however, the organic equilibrium seems less perfect; as illustrated in the case I have quoted. And in connection with this inference, it would be interesting to inquire whether pure constitutions are not superior to mixed ones, in their power of maintaining the balance of vital functions under disturbing conditions. Is it not a fact that the pure breeds are hardier than the mixed ones ? Are not the mixed ones, though superior in size, less capable of resisting unfavourable influences-extremes of temperature, bad food, &c. ? And is not the like true of mankind ?

Returning to the topic in hand, it is manifest that these facts and reasonings serve further to enforce the general truth, that the offspring of two organisms not identical in constitution is a heterogeneous mixture of the two, and not a homogeneous mean between them.

If, then, bearing in mind this truth, we remember the

« AnteriorContinuar »