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What, let me ask, are the principal phenomena of heredity? There must be physical continuity between parent, or parents, and offspring, so that the offspring is, as Erasmus Darwin well said, a kind of elongation of the life of the parent.

Erasmus Darwin put the matter so well that I may as well give his words in full; he wrote:–

“Owing to the imperfection of language the offspring is termed a new animal, but is in truth a branch or elongation of the parent, since a part of the embryon animal is, or was, a part of the parent, and therefore, in strict language, cannot be said to be entirely new at the time of its production; and therefore it may retain some of the habits of the parent system.

“At the earliest period of its existence the embryon would seem to consist of a living filament with certain capabilities of irritation, sensation, volition, and association, and also with some acquired habits or propensities peculiar to the parent; the former of these are in common with other animals; the latter seem to distinguish or produce the kind of animal, whether man or quadruped, with the similarity of feature or form to the parent.” {39}

Those who accept evolution insist on unbroken physical continuity between the earliest known life and ourselves, so that we both are and are not personally identical with the unicellular organism from which we have descended in the course of many millions of years, exactly in the same way as an octogenarian both is and is not personally identical with the microscopic impregnate ovum from which he grew up. Everything both is and is not. There is no such thing as strict identity between any two things in any two consecutive seconds. In strictness they are identical and yet not identical, so that in strictness they violate a fundamental rule of strictness–namely, that a thing shall never be itself and not itself at one and the same time; we must choose between logic and dealing in a practical spirit with time and space; it is not surprising, therefore, that logic, in spite of the show of respect outwardly paid to her, is told to stand aside when people come to practice. In practice identity is generally held to exist where continuity is only broken slowly and piecemeal, nevertheless, that occasional periods of even rapid change are not held to bar identity, appears from the fact that no one denies this to hold between the microscopically small impregnate ovum and the born child that springs from it, nor yet, therefore, between the impregnate ovum and the octogenarian into which the child grows; for both ovum and octogenarian are held personally identical with the newborn baby, and things that are identical with the same are identical with one another.

The first, then, and most important element of heredity is that there should be unbroken continuity, and hence sameness of personality, between parents and offspring, in neither more nor less than the same sense as that in which any other two personalities are said to be the same. The repetition, therefore, of its developmental stages by any offspring must be regarded as something which the embryo repeating them has already done once, in the person of one or other parent; and if once, then, as many times as there have been generations between any given embryo now repeating it, and the point in life from which we started–say, for example, the amoeba. In the case of asexually and sexually produced organisms alike, the offspring must be held to continue the personality of the parent or parents, and hence on the occasion of every fresh development, to be repeating something which in the person of its parent or parents it has done once, and if once, then any number of times, already.

It is obvious, therefore, that the germ-plasm (or whatever the fancy word for it may be) of any one generation is as physically identical with the germ-plasm of its predecessor as any two things can be. The difference between Professor Weismann and, we will say, Heringians consists in the fact that the first maintains the new germ-plasm when on the point of repeating its developmental processes to take practically no cognisance of anything that has happened to it since the last occasion on which it developed itself; while the latter maintain that offspring takes much the same kind of account of what has happened to it in the persons of its parents since the last occasion on which it developed itself, as people in ordinary life take of things that happen to them. In daily life people let fairly normal circumstances come and go without much heed as matters of course. If they have been lucky they make a note of it and try to repeat their success. If they have been unfortunate but have recovered rapidly they soon forget it; if they have suffered long and deeply they grizzle over it and are scared and scarred by it for a long time. The question is one of cognisance or non-cognisance on the part of the new germs, of the more profound impressions made on them while they were one with their parents, between the occasion of their last preceding development, and the new course on which they are about to enter. Those who accept the theory put forward independently by Professor Hering of Prague (whose work on this subject is translated in my book, “Unconscious Memory”) {40} and by myself in “Life and Habit,” {41} believe in cognizance, as do Lamarckians generally. Weismannites, and with them the orthodoxy of English science, find non-cognisance more acceptable.