If we apply Maupertuis' argument to a few cases of psychological heredity, for instance mental disorder, or some special talent (for painting, or music) persisting through three or four generations, it is easy to see what becomes of Buckle's objection.

III.

The greater part of these objections would never have been raised, were it not for the serious error of reasoning only from the exceptions. To treat the question fairly, it ought first of all to have been properly stated, that is to say, the fact of heredity should have been considered, not partially, but in its whole extent in the entire domain of life, as we here propose to do.

In order to proceed logically, we should in the first place have to determine what is meant by species. We will not enter into this very difficult question. It will be enough for us to lay down a few very simple, unquestionable and elementary facts, which will be admitted by all.

When we compare together two living beings-that is to say, two sums of attributes-and find that these two beings possess in common a very large number of essential attributes, differing only in those which are secondary, so that the two beings may be regarded as very much alike, we say that they are of the same species. The many essential characteristics possessed by them in common we call specific; the few accidental characters which differentiate them we call individual. Thus, for instance, two individuals of the human species possess in common very many essential characters, being organic, vertebrate mammals, with all that is thereby implied, having senses, physiological or psychological functions, such as sensation, memory, imagination, reason. But they differ from one another in accidental or individual characteristics, as that the muscular system common to both is in the one very well developed, very slightly in the other; that the faculty of memory common to both is weak in the one, and very strong in the other; that the faculty of reason common to both does not in the one go beyond the simplest acts, while in the other it includes the highest

abstractions.

Now, by the act of generation, in which heredity has its origin, every creature produces beings like itself. In the lower forms of

generation, such as gemmation and fission, this fact is evident. In the higher forms, where the connection of the two sexes is requisite, two contrary forces are brought together, and consequently are antagonistic. The result is, that the product will (though not without exceptions) resemble one or other of the parents, or both at once. This general truth, that the organisms of a given type descend from organisms of the same type, is so well established by countless instances that it has the character of an axiom. The tendency of a living being to repeat itself in its progeny,' says a certain naturalist, 'seems to be a sort of necessity. It were difficult to imagine a creature which should not resemble its parents. In fact, so universal is this tendency that it is recognized as one of those fundamental facts which underlie all the natural sciences, and which, with regard to them, take the place held by axioms in the mathematical sciences.'

This being understood, heredity appears in its true light, and the objections brought against it can be appreciated at their value; for the question already stated, 'Are cases of psychical heredity fortuitous, or are they the result of a law?' may plainly be resolved into several parts, each of which easily admits of answer.

1. Are specific characteristics, physical or moral, transmitted by heredity? They are always transmitted, both in the animal and in man.

2. Are those less general characteristics, which constitute races and varieties, hereditary?—They also are hereditary; a spaniel was never produced by a bull-dog, nor a white man by a negro. And this holds good also of psychical qualities: a given animal possesses not only the general instincts of the species, but also the peculiar instincts of the race. The negro inherits not only the psychological faculties which are common to all men, but also a certain peculiar form of mental constitution, namely, an excess of sensibility and imagination, sensual tendencies, incapacity for abstract thought, etc.

3. Are purely individual characteristics hereditary?-Facts have demonstrated that they are often so, both in physics and in morals. In conclusion, heredity always governs those broadly general characteristics which determine the species, always those less general characteristics which constitute the variety, and often

individual characteristics. Hence the evident conclusion that heredity is the law, non-heredity the exception. Suppose a father and mother-both large, strong, healthy, active and intelligentproduce a son and a daughter possessing the opposite qualities. In this instance, wherein heredity seems completely set aside, it still holds good that the differences between parents and children are but slight, as compared with the resemblances.

Let it not be said that we have dwelt too long on points that are self-evident. They are so clear that we forget them, and argue only from isolated cases, thus changing the state of the question by the way in which it is stated. But when, on the contrary, we consider the facts as a whole, heredity appears universal, and we are less surprised at finding characteristics that are hereditary, than in finding those which are not.

CHAPTER II.

THE LAWS OF HEREDITY.

THUS, then, heredity presents itself to us as a biological law, that is, inherent in every living thing, having no other limits than those of life itself. Life under all its forms-vegetal, animal and human, normal and morbid, physical and mental—is governed by this law. It is, in fact, concerned with the essential and inmost nature of vital activity. Among the various functions which in their united action constitute life, two are primary-the one, nutrition, which preserves the individual, the other, generation, which perpetuates the species. Some physiologists even reduce these to one, nutrition being, in their view, only a form of generation, or in the words of Claude Bernard, ‘a continuous creation of organized matter by means of the histogenic processes appertaining to the living creature.' Ultimately, therefore, the vital functions are reduced to generation; and as it is from this that heredity immediately flows, we must conclude that the law of hereditary transmission has its rise in the sources of life itself.

If we accept the foregoing views, the law of heredity would seem to be one of absolute simplicity. Like produces like: the progenitor is repeated in the descendant. Thus the primitive types would

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remain, being continually reproduced, and the world of life would present the spectacle of perfect regularity and supreme monotony. But this is true only in theory. So soon as we come to the facts, we find the law is resolved into secondary laws, or it even appears to vanish in the exceptions. Not to speak of the external causes (chance, influence of circumstances) which interfere with the action of heredity, there are interior causes, inherent in heredity itself, which hinder the law from pursuing the simple course from like to like. A moment's reflection will make this plain.

In the inferior creatures, in which generation takes place without sexual connection, hereditary transmission from the parent to the progeny occurs in a perfectly natural way. This happens in cases of fission, as in Trembley's hydra, or in the Nais, which naturally divide into two or more individuals like themselves; and also in cases of gemmation, where a bud forms on an animal and is soon itself changed into a new and complete animal.

But in the higher forms of generation sexual connection is indispensable; as a struggle necessarily arises between the sexes, each parent tends to produce its like. Here hereditary transmission can at best produce only a mixed constitution, holding from both parents. 'Clearly,' says De Quatrefages, 'the mathematical law of heredity would be for the parent creature to reproduce itself completely in its progeny. And perhaps this law, absolute though it be, is to be found underlying all natural phenomena, but in every case it is masked by accessory circumstances, by the conditions amid which heredity acts. But it does not only rest on theoretical considerations, it rests also on facts. Although subject to profound and continual disturbance, still, if we note all the phenomena which show in individuals a tendency to obey the mathematical law, heredity is found to realize in the aggregate of each species the result which it fails to realize in isolated individuals. To use a figurative expression, the true meaning of which cannot fail to be apprehended, while it cannot be verified in the whole, it may be in detail.'

The question is still more complicated when we descend to individual facts. We meet with so many oddities and exceptions, and so many contradictory opinions in explanation of them, that it seems as though, when we pass from theory to practice, all law

had vanished. Still these facts, however numerous and varied they may be, may all be brought within the compass of a few formulas, which might be called the empirical laws of heredity. These real laws, which are so many aspects or incomplete expressions of the ideal law, are the following, so far as observation reveals them.

1. Direct heredity, which consists in the transmission of paternal and maternal qualities to the children. This form of heredity offers two aspects:

(1.) The child takes after father and mother equally as regards both physical and moral characters, a case, strictly speaking, of very rare occurrence, for the very ideal of the law would then be realized.

Or (2), the child, while taking after both parents, more specially resembles one of them; and here again we must distinguish between two cases.

a. The first of these is when the heredity takes place in the same sex-from father to son, from mother to daughter.

ß. The other, which occurs more frequently, is where heredity occurs between different sexes-from father to daughter, from mother to son.

2. Reversional Heredity, or atavism, consists in the reproduction in the descendants of the moral or physical qualities of their ancestors. It occurs frequently between grandfather and grandson, grandmother and granddaughter.

3. Collateral, or indirect heredity, which is of rarer occurrence than the foregoing, subsists, as indicated by its name, between individuals and their ancestors in the indirect line-uncle, or grand-uncle and nephew, aunt and niece.

4. Finally, to complete the classification, we must mention the heredity of influence, very rare from the physiological point of view, and of which probably no single instance is proved in the moral order. It consists in the reproduction in the children by a second marriage of some peculiarity belonging to a former spouse. Such are the various formulas under which all the facts of heredity may be classed. We propose to study them in succession. When to this we have added, as the necessary complement, the study of the exceptions to these laws, we shall have passed in review every single case of heredity.