Phenotype

“ If then, the results of all the tests that have been made on all mental traits be studied, it will be found that human mental ability as shown in at least 95% of all the traits that have been measured, is distributed throughout the race in various degrees, in accordance with the law of chance, and that if one could measure all the members of the species and plot a curve for these measurements, in any trait, he would get this smooth, continuous curve. ”

“ Each organism transmits to its descendants a part of the morphological and physiological qualities that it has received from its parents and ancestors. On the other hand, progressive heredity brings new characters to the species—characters that were not found in preceding generations. Each organism may transmit to its offspring a part of the morphological and physiological features that it has itself acquired, by adaptation, in the course of its individual career, through the use or disuse of particular organs, the influence of environment, climate, nutrition, etc. ”

“ Change in one part entails, by reaction on the organism, changes, in other parts, the functions of which are necessarily changed. 2. Such changes worked in the individual, affect, in some way, the reproductive elements: these being found to evolve unusual structures when the constitutional balance has been continuously disturbed. 3. But the changes in the reproductive elements thus caused, are not such as represent these functionally-produced changes: the modifications conveyed to offspring are irrelevant to these various modifications functionally produced in the organs of the parents. ”

“ A third characteristic of undisturbed physiological evolution is this: the developed organs, when their evolution is complete, and indeed during their development, present a typical uniformity of structure; that is to say, organisms whose development has been perfectly natural, provided they are of the same age, sex, species, etc., are alike; and the several organs of different individuals present a uniform standard of size, shape, and functional power, any slight existing differences being so inappreciable as to evade ordinary methods of observation. ”

“ It is probable that naturalists would have avoided much confusion of ideas if they had more frequently borne these necessary limitations of our knowledge in mind. But while it may safely be admitted that we are acquainted with only the morphological characters of the vast majority of species—the functional, or physiological, peculiarities of a few have been carefully investigated, and the result of that study forms a large and most interesting portion of the physiology of reproduction. ”

“ Biology uses experiment and hence begins with germ cells: social science is based on observation and hence its data are the visible differences which the study of men affords. Both call their data characters, but as a loose terminology creates confusion, I shall call the germinal variations the biologist finds through experiment characters, while the visible differences in men open to observation I shall call traits. The problem then is what is the relation of biologic characters to visible traits? Is there a character for each trait, or do independent laws govern traits? ”

“ 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. ”

“ Those belonging to one group are the results of external [ 42 ] influences in each ontogeny and are not inherited; they represent nutrition varieties, are experimentally demonstrable, and constitute the subject matter of experimental physiology. (2) The others are inherited and again transmitted; they belong to the physiology of the idioplasm. This subject is mainly occupied with the origin of the determinants, hence with the formation of varieties and species. It is not the subject of experiment, and constitutes the phylogeny or the physiology of the formation of determinants. ”

“ Thus the multitude of small individual variations, which probably occur in every species, but which strike us most in Man—the differences in the development of mouth, nose, and eyes, in the hair, in the colour of skin, &c., as far as they are without significance in the struggle for existence—depend upon processes of germinal selection, which permitted the greater development of one group of determinants, or of one kind of biophor in one case, of another in another. ”

“ A direct connection is assumed between the visible trait to be favored or eliminated and the characters of the germ cell that are passed on from generation to generation. If the character make the visible trait, rigid selection based on the elimination of traits is the only way of ridding the race of undesirable traits. Improving the condition of individuals would help them, but if traits do not influence characters, such betterments would have no effect on coming generations. ”

“ But when the struggle for existence becomes severe, that variety which is best adapted to the conditions of existence always supplants that which is imperfectly adapted; therefore by Natural Selection the sterile varieties of the two forms will become established as the only ones.
10. Now let a fresh series of variations in the amount of sterility and in the disinclination to crossed unions occur,—also in certain parts of the area: exactly the same result must recur, and the progeny of this new physiological variety again in time occupy the whole area. ”

“ It is indeed an expression of opinion concerning the metaphysics of instinct. Leaving the question of ultimate origin precisely where it stood in the times of Addison and of Spence, modern science seeks to trace the natural antecedents of all natural phenomena, and regards structure and behaviour alike as the products of evolution, endeavouring to explain the manner of their genetic origin in terms of progressive heredity. ”

“ 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. ”

“ More specifically, the genetic aspect differentiates the outlines of the stages of growth; in its terms are described the orbit of the psychological cycle. It yields the psychology of infancy, of adolescence, of maturity, of senescence, and presents the course of the included qualities in mutual illumination. The genetic argument emphasizes a progressive environment and a progressive purpose; it enlarges the scope of adaptation, and it interprets the impetus and goal of varying interests and endeavors. ”

“ It is a mistake to attempt to explain all the results of evolution by a principle. There are two kinds of congenital, constitutional or hereditary characters in all organisms, namely, the adaptive and the non-adaptive, and every distinct type in classification exhibits a combination of the two. ”

“ I am convinced that the theory of physiological selection is the only one that can explain the facts of inter-specific sterility on the one hand, and, on the other hand, the contrast which these facts display to the unimpaired fertility of our domesticated varieties. ”

“ In the disentanglement of the properties and interactions of these elementary factors, the science we must call to our aid is Physiological Chemistry. The relations of Genetics with the other branches of biology are close. Such work can only be conducted by those who have the good fortune to be able to count upon continual help and advice from specialists in the various branches of Zoology, Physiology, and Botany. ”

“ The factors of evolution fall under two heads—origin and guidance. The origin of variations lies in mechanical stresses, and chemical or physical influences. Whether these act on the body (and are transmitted by inheritance) or only on the germ, is a question which divides biologists into two schools. In the latter case all variations are fortuitous; in the former the development of tissue-variations has been in direct response to the physical or chemical influences. ”

“ The problem is first to be defined.
It is evident that all characters which make up a man or woman, or any other organism, must be either germinal or acquired. It is impossible to conceive of any other category. ”

“ But it is not sufficient to give the explanation of the cause which has brought about the condition of the organs of different animals—a condition which we see to be always the same in those of the same species; we must besides observe the changes of condition produced in the organs of one and the same individual during its life, by the single result of a great change in the special habits in the individuals of its species. ”

“ We have said that the following out of the properties exhibited by physiological species would lead us into difficulties, and at this point they begin to be obvious; for, if, as a result of spontaneous variation and of selective breeding, the progeny of a common stock may become separated into groups distinguished from one another by constant, not sexual, morphological characters, it is clear that the physiological definition of species is likely to clash with the morphological definition. ”

“ The development of organisms is a physiological process, depending on mechanical causes, or physico-chemical movements. 40. Ontogenesis, or the development of the organic individual, is directly determined by phylogenesis, or the evolution of the organic stem (phylon) to which it belongs. 41. Ontogenesis is a brief and rapid recapitulation of phylogenesis, determined by the physiological functions of heredity and adaptation. ”

“ While such experiments must not be stretched too far, in application to the human species, they certainly offer striking evidence of the fact that the characters of any individual are mainly due to something in the germ-plasm, and that this germ-plasm is to a surprising degree independent of any outside influence, even such an intimate influence as that of the body of the mother in which it reaches maturity. ”

“ 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. ”

“ It may be said that {333}admitting functional change to be the initiator of variation—granting that the physiological units of an organism long subject to new conditions, will tend to become modified in such way as to cause change of structure in offspring; yet there will still be no cause of the supposed heterogeneity among the physiological units of different individuals. ”

“ Since these external signs are but manifestations of the inner chemical reactions, of which the internal secretions are the determining reagents, or factors, with permutations and combinations possible in all directions, the diversity and variability of each individual and his traits stands explained and understandable. The normal, as the perfect or nearly perfect balance of forces in the organism, at any given moment, emerges as a more definite and real concept than that which would abstract it from a curve of variations. ”

“ We may thus lay down in a general sort of way a conception which I like to call the theory of psychophysical progression, fixation and regression along evolutionary and developmental lines. In the case of tics the regressive or devolutionary aspect comes in for special consideration. We may react mainly physically, or mainly psychically. But as a rule we react by both physical and psychic means, the manner and degree of our conduct being determined, as above mentioned, by our stage in evolution and development. ”

“ We can understand why a classification founded on any single character or organ—even an organ so wonderfully complex and important as the brain—or on the high development of the mental faculties, is almost sure to prove unsatisfactory. This principle has indeed been tried with hymenopterous insects; but when thus classed by their habits or instincts, the arrangement proved thoroughly artificial.257 Classifications may, of course, be based on any character whatever, as on size, colour, or the element inhabited; but naturalists have long felt a profound conviction that there is a natural system. ”

“ If we refer adaptation to selection, we have also to trace back to this source the origin of the organic combinations which make up the various tissues of the body and which go by the collective name of muscular, nervous, glandular substance, etc. ”

“ The evolutionary process has been active not only in morphological differentiation, that is, in the development of new forms, but also in physiological differentiation, that is, in the development of specialised mechanisms for the performance of the various vital functions. ”

“ Hastings Gilford147 regards the development of the human body as a whole, or of any portion of the body, as describing a curve that ascends from the time of the union of the two genetic elements to a maximum at which there is the greatest development of specialization in function and the least in the general characters, such as those of multiplication. The curve then begins to descend, with a gradual and progressive loss of differentiation in form and function and an increasing tendency of certain cells to multiply. ”