Ontogeny

“ Ontogeny is the short and rapid recapitulation of phylogeny, conditioned by the physiological functions of heredity (reproduction) and adaptation (nutrition) . The organic individual (as a morphological individual of the first to the sixth order) repeats during the rapid and short course of its individual development the most important of the form-changes which its ancestors traversed during the long and slow course of their palæontological evolution according to the laws of heredity and adaptation. ”

“ A positive character has a real ontogeny. But, as we have seen, the development of any character may be interrupted at any stage. Most aberrations among organisms are due to a retardation or failure of normal development. In human affairs we recognize this tendency in the terms "degenerates" and "defectives" (constituting from 2 to 4 per cent of the population) . Indeed, there are few persons who are not defective in some physical or psychical character. ”

“ In the consideration of the development of germs into adult individuals, the accomplishment of the process is ontogeny. In the consideration of the development of individuals in generations by which the race is evolved, we may consider the result reached as phylogeny. ”

“ Comparative anatomy and ontogeny further teach us that the countless modifying processes which have led to the appearance of the various species have acted by adaptation to different environments, habits, and customs, and give us, in conjunction with heredity, a physiological explanation of this morphological transformation. ”

“ This progressive development of the individual—the ontogeny—gives us a clue to the ancestral development of the whole race—the phylogeny; and we are enabled to picture to ourselves the very slow and gradual steps by which the existing perfect adaptation has been brought about. ”

“ If ontogeny, the history of the individual, gives us no answer, we fall back upon phylogeny, the history of the race. Organs, which on the old theory of special creations were useless and meaningless, are now seen to have their explanation in the past or in the future, according as they are rudimentary or nascent. ”

“ But there is another essential element in ontogenic evolution. It is that the forces or causes of evolution are natural; that they reside in the thing developing and in the reacting environment. This we know is true of embryonic development; is it true also of the geologic succession of organic forms? It is true of ontogeny; is it true also of phylogeny? If not, then only by a metaphor can we call the process of change in the organic kingdom throughout geological history an evolution. ”

“ Parts which, in the complete animal, have disappeared without leaving a trace, appear again in each embryonic primordium, and disappear in the course of the ontogeny. Speaking metaphorically, we might express this on the basis of the determinant theory, by saying that the determinants, as they become weaker, can only control an increasingly short period of the whole ontogeny of the organ, so that ultimately nothing more than its first beginning comes into existence. ”

“ It is impossible that any part or organ should be removed suddenly from the ontogeny without bringing the whole into disorder, and the least serious disturbance of the course of development will undoubtedly be caused if the final stage of the part in question become rudimentary first. ”

“ There is, in fact, in the long ontogeny of members of high groups, a sort of rough-and-ready repetition of the characteristic features of many lower groups. This fact has so impressed some biologists that they have embodied it into a law, the so-called biogenetic law: that ontogeny recapitulates phylogeny. ”

“ As a matter of fact, it was especially for their sake that we studied the ontogeny of a special form in such detail; one always sees generalities better if one knows the specific features of at least one case. What then are the features of most general and far-reaching importance, which may be abstracted from the individual history of our sea-urchin, checked always by the teachings of other ontogenies, including those of plants? ”

“ The individual development, or the ontogenesis of every single organism, from the egg to the complete form is nothing but a growth attended by a series of diverging and progressive changes. This applies equally to animals, plants, and protista. If, for example, we consider the ontogeny of any mammal, of man, of an ape, or of a pouched animal, or if we follow the individual development of any other vertebrate animal of another class, we everywhere find essentially the same phenomena. ”

“ Now there is a well-known biological principle that "ontogeny recapitulates phylogeny"—that the child in his development passes through the same series of physical and mental stages that the adults did in the successive generations of the race's development. ”

“ The vertebratist, therefore, in his study of ontogeny, for comparison with racial history must needs follow either the entire growth of one animal, a thing manifestly impossible when the embryonic stages are considered, or study a long series of individuals in various stages of development, the securing of which in the great majority of cases is largely the result of a number of happy accidents. ”

“ But so firmly is the belief in the correspondence of ontogeny and phylogeny fixed in the minds of modern biologists that, in determining the classification and affinities of any particular animal, more reliance is placed on the facts of embryology than on those of adult structure. ”

“ In ontogeny we see exactly the same thing. There are no two daughter-cells of a mother-cell which are exactly alike, and the differences between them, if they increase in the same direction, may lead in later descendants to entire differences of structure. ”

“ That all life on the earth has been derived from one, or at most from a few original forms, is said7 to be proved by ontogeny, or the history of the germ, which in its development passes through a number of the forms which mark the ascending scale of life. ”

“ The problems of heredity and variation are included in a true physiological conception of the individual development; but some biological conceptions that have more or less status and reputation are inconsistent with it. Such are the inheritance of acquired characters, atavism, and the theory of unit characters. The first is a familiar problem that I shall not argue anew; the second logically implies the presence of ancestral representative particles in the germ, which is inconsistent with a physiological theory of development. ”

“ As the ontogenic evolution receives fresh impulse at the moment of fertilization, so the evolution of the organic kingdom receives fresh impulse at the moment of introduction of sex. As in ontogenic evolution the individual at birth enters upon a new and higher plane, in which it co-operates in its own physical growth, so the organic kingdom, with the introduction of man, enters upon a new and higher plane, in which man co-operates in the physical and spiritual growth of the race. ”

“ The problem of development is closely bound up with that of “heredity.” A developing organism follows the parental type. The acorn in its growth follows the type of the parent oak, repeating all its morphological and physiological characters down to the most intimate detail. And the animal organism adds to this also the whole psychical equipment, the instincts, the capacities of will and consciousness which distinguish its parents. The problems of the fifth and sixth order are closely inter-related, the sixth problem being in reality the same as the fifth, only in greater complexity. ”

“ These are the functions and capacities of living organisms in general, and in particular those of variation and inheritance, of development and self-differentiation. What is, and whence comes this mysterious power of the organism to build itself up from the smallest beginnings, from the germ? And the equally mysterious power of faithfully repeating the type of its ancestors? And, again, of varying and becoming different from its ancestors? Even the “mechanical” theory of selection is forced to presuppose the secret of life. ”

“ But it will be as well to reach our result in a different way, by considering certain further implications of the concept of evolution which are manifestly only present in the case of finite individuality.
In every process of development or evolution there are involved a pair of interrelated factors, the individual nature which develops, and the environment which contains the conditions under which and the stimuli in response to which it develops. The undeveloped germ is as yet a mere possibility, something which will yet exhibit qualities not as yet possessed by it. ”

“ Pathogenesis of Infantilism.—At this point it might be asked: Why do we grow? We hide the mechanism of growth under very vague expressions: biological final causes, ontogenetic evolution, heredity. But, if we stop to think, such expressions are not greatly different from those which they have replaced: the divine purpose, creation. ”

“ If the mere anxiety connected with an ill-healing wound inflicted on but one generation is sometimes found to have so impressed the germ-cells that they hand down its scars to offspring, how much more shall not anxieties that have directed action of all kinds from birth till death, not in one generation only but in a longer series of generations than the mind can realize to itself, modify, and indeed control, the organization of every species? ”

“ Individuals unquestionably exhibit modifications intended not for their own personal benefit, but for that of the species—for instance, the maternal instincts. The modification of a part in the interest of the whole to which it belongs may, perhaps, turn out to have the same essential significance whether the part is an organ or instinct belonging to the synthesis called an individual, or an individual belonging to the synthesis called a species, or a species belonging to some fauna or flora of the globe. ”

“ We know that rapidity of development is no less influenced by these two causes, and that, in general, the more subject an anatomical or physiological trait is to the influence of environment, the less definitely can we speak of a controlling influence of heredity, and the less are we justified in claiming that nature, not nurture, is the deciding element. ”

“ But it is possible, with present knowledge, to say that human traits, mental as well as physical, are inherited, in a high degree. Even before the final details as to the inheritance of all traits are worked out—a task that is never likely to be accomplished—there is ample material on which to base action for eugenics. The basal differences in the mental traits of man (and the physical as well, of course) are known to be due to heredity, and little modified by training. ”

“ Thus, by an intelligent process, new habits are established, which by heredity become part of the patrimony of instinct, modifying the latter and constituting elements essential to its evolution. Of these instincts acquired through an intelligent apprenticeship Forel was led to say that they are reasoning made automatic, and it is to them particularly that we may apply the idea of certain biologists that instincts are habits which have become hereditary and automatic. ”

“ We have to distinguish here, as in other matters, between being and becoming, and, further, to distinguish between two kinds of becoming—namely, the development of the organ in the individual and its evolution in the course of descent. ”

“ In a former work on the evolution of morality I have described the manner in which the hereditary tendencies and instincts arise from habit, induced in the nervous cellules by a sufficient repetition of the same acts. The instinct of procreation has, and can have, no other origin. The animal species, during the long phases of their evolution, have reproduced themselves unconsciously, and by very simple processes, which we may still observe in certain zoophytes. ”

“ When hereditary transmission lasts through many generations, and is strengthened by cumulative adaptation, it becomes an instinct. 5. Even in the protist cœnobia (the cell-communities of the protophyta and protozoa) social instincts are formed by association of cells. 6. The antithesis of the individual and social instinct, or of egoism and altruism, increases in the animal kingdom in proportion to the development of psychic activity and social life. ”

“ Natural development always proceeds from the simple to the complex—not inversely; progress consists in differentiation, i.e., in the evolution of originally similar parts into special organs of different structure and independent functions, and not in the retrogression of differentiated beings of rich specialization to a protoplasm without physiognomy. ”

“ It is the business of eugenics to throw the whole weight of human purpose into the scale of the good.
Evolution not necessarily progress.—No excessive space has been devoted to this distinction between the fittest and the best and to the real meaning of Spencer's famous phrase, if perchance it should avail in any degree to dispel one of the commonest of the many common delusions regarding the nature of organic evolution and its outcome. ”

“ But it may be questioned whether an innate tendency may not have favored and assisted the action of the environment in the later of these generations, whether, indeed, the continuity everywhere supposed in evolution does not compel us to assume, between the first appearance of any function, trait, or habit, and its attainment, after several generations, of sufficient strength to render its hereditary character noticeable, intermediate degrees of strength in the intermediate generations. ”