Biological transformation

“ The chief evidences of the theory of descent are to be found in homologies, in the correspondences of organs and functions, as revealed by comparative anatomy and physiology, in the recapitulation revealed by embryology, in the structure of parasites, in rudimentary organs and reversions to earlier stages, in the distribution of animals and plants, and in the possibility of still transforming, at least to a slight extent, one species into another, by experimental breeding.
Transformation and differentiation go on in nature as a vast, ceaseless, but blind process of selection. ”

“ The variations in the size of this fraction are the cause of all change in the life-expression of every organism. When the biotone increases, and the metabolism quotient becomes more than one, we have growth; when, on the other hand, it falls below one, and the biotone decreases, we have atrophy, and finally death. New biogens are constructed in regeneration. In generation or reproduction groups of biogens (as germ-plasm) are released from the parent in consequence of redundant growth, and form the foundation of new individuals. ”

“ Any change in structure and function, which can be effected by small stages, is within the power of natural selection; so that an organ rendered, through changed habits of life, useless or injurious for one purpose, might be modified and used for another purpose. An organ might, also, be retained for one alone of its former functions. ”

“ In his opinion, a change in the structure of any part of an organism was chiefly brought about when the species in question met with new conditions of life and was thus forced to assume new habits. Such habits caused an increased or diminished activity, and therefore a stronger or weaker development, of certain parts, and the modified parts were then transmitted to the offspring. ”

“ These different elements must be held together by forces of attraction, and the direction of these forces must have some common centre represented by some differentiation of the protoplasm, whether as clearer spot, or as nucleus. This spontaneously generated organism, neither animal nor plant, is nourished, as we have seen, by diffusion, by the transformation of inorganic into organic substance. The lowest organisms possess no definite organs for taking food ”

“ Pathology, therefore, is really nothing else than modified physiology. Physiological development is the evolution of organs and the growth of organisms under the impression of natural external conditions; pathological development is the evolution of organs and the growth of organisms under the impression of unnatural external conditions. Adaptation of structure to function—of organisms to surrounding media—is the designed conservative purpose of both kinds of growth. ”

“ The complete disappearance of a rudimentary organ can only take place by the operation of natural selection; this principle will lead to its elimination, inasmuch as the disappearing structure takes the place and the nutriment of other useful and important organs. ”

“ Their whole body, in the fully-developed and reproductive condition, consists of nothing but a little mass of structureless protoplasm, whose changing, variable processes all at once discharge the various life functions—movement, sensation, transmutation of matter, nutrition, growth, and reproduction. ”

“ Thus, a simple variation and adaptation has been produced, and if the same organism continues in this position, its bottom cells will estrange themselves from their original function, while those on the top will convey the food into the interior, where a cavity will be formed, ultimately with a permanent opening, the primitive gut and mouth, both very different from the 'foot.'
Thus, by adaptation and variation the organism acquires new functions, organs, features, and it gives up and eventually loses others. Its offspring is like it. Like produces like. This is the principle of heredity. ”

“ The opposing views of to-day were in existence centuries ago, and they are known in the history of science as the theory of preformation or evolution, and the theory of epigenesis. That most of the great biologists of the seventeenth and eighteenth centuries were decided upholders of evolution was the natural result of the contemporary knowledge of facts. For they knew only the external signs of the process of development. [Pg 2] All they saw was the embryo becoming adult, the bud growing out into a blossom, as the result of a process in which nutrition transformed smaller to greater parts. ”

“ It may be said that 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 ”

“ Indeed, when treating of Adaptation, we saw that an organ modified by increase or decrease of function can but slowly so react on the system at large as to bring about those correlative changes required to produce a new equilibrium; and yet only when such new equilibrium has been established, can we expect it to be fully expressed in the modified physiological units of which the organism is built—only then can we count on a complete transfer of the modification to descendants."... ”

“ In these normal cases the regeneration depends on the existence of special formative layers or groups of cells, and must be regarded in each case as a special adaptation, with individual limitations and peculiarities, rather than as a mere exhibition of the fundamental power of growth and reproduction displayed by living substance. Many tissues, even in the highest animals, are capable of replacing an abnormal loss of substance. ”

“ If the average amount of food which an animal can assimilate every day remains constant for a considerable time, it follows that a strong influx towards one organ must be accompanied by a drain upon others, and this tendency will increase, from generation to generation, in proportion to the development of the growing organ, which is favoured by natural selection in its increased blood-supply, etc.; while the operation of natural selection has also determined the organ which can bear a corresponding loss without detriment to the organism as a whole. ”

“ If we consider the introduction of natural death in connection with the foregoing statements, we may imagine the process as taking place in such a way that,—with the differentiation of Heteroplastids from Homoplastids, and the appearance of division of labour among the homogeneous cell-colonies,—natural selection not only operated upon the physiological peculiarities of feeding, moving, feeling, or reproduction, but also upon the duration of the life of single cells. ”

“ It is here suggested that persistent modification through many generations, though not transmitted to the germ, nevertheless affords the opportunity for the occurrence of germinal variation of like nature. 7. Under constant conditions of life, though variations in many directions are occurring in the organisms which have reached harmonious adjustment: to these conditions, yet natural selection eliminates all those which are of such amount as to be disadvantageous, and thus acts as a check on all variations, repressing them to within narrow limits. ”

“ Now it needs only to consider that the many changes thus wrought by one force upon an adult organism, will be in part paralleled in an embryo organism, to understand how here also, the evolution of the homogeneous into the heterogeneous may be due to the production of many effects by one cause. The external heat and other agencies which determine the first complications of the germ, may, by acting upon these, superinduce further complications ”

“ Darwin accepted such transmission as subordinate to natural selection, and attempted to account for it by his theory of pangenesis. According to that hypothesis all the component cells of an organism throw off minute gemmules, and these and their like, collecting in the reproductive cells, are the parental germs from which all the cells of the offspring of that organism are developed. ”

“ In order the more thoroughly to investigate these matters it is necessary to consider the mode of growth, and specially the plan of evolution or development of each organ. This is the more needful owing to the common origin of things ultimately very different one from the other, and to the presence of organs which, in the adult state, are identical or nearly so in aspect, but which nevertheless are very unlike in the early stages of their existence. ”

“ But this tendency of cells to revert to the ancestral unicellular type, to multiply at a rate that is only proportionate to the supply of nutriment and the powers of assimilation, is checked by natural selection, which, by placing at a disadvantage, brings about the ultimate elimination of multicellular organisms, in which the tendency is displayed. ”

“ If we bear in mind that even the minutest variations of the biophors and determinants express nothing more or less than reactions to changed external conditions in the direction of adaptation, and that the same is true of each of the higher categories of vital units, whether they be called cell, tissue, organ, person, or corm, we see that the whole evolution of the forms of life upon the earth depends upon adaptations following each other in unbroken succession, and fitting into each other in the most complex way. ”

“ Unless we choose or invent some new term, we must define adaptations apart from all questions of evolution as any structures or characters in an organism which can be shown either by their mere presence, or by their active function, to be either useful or necessary to the animal's existence. We must be on our guard against assuming that the word 'adaptation' implies any particular theory or conclusion concerning the method and process by which adaptations have arisen in the course of evolution. ”

“ It cannot be demonstrated in all cases, but it is nevertheless certain that this applies also to all the organs of movement, digestion, and reproduction, to all animal groups and also to the differences between them, even although these may not always be obvious adaptations to the conditions of life. What part is left for mutation to play if almost everything is an adaptation? ”

“ We only, I believe, can state the fact that there are relations between morphogenetic causes and effects which are adaptations, that functional disturbances or changes are followed by single histogenetic reactions from the organism, which are compensations of its disturbed or changed functional state. ”

“ When this accumulation of slight changes continues, the effect of adaptation goes so far in time as to produce new organs by progressive modification, or to cause actual organs to become useless and rudimentary, and finally disappear, owing to regressive metamorphosis. ”

“ Heritable novelties or variations often crop up in living creatures, and these form the raw material of evolution. These variations are the outcome of expression of changes in the germ-cells that develop into organisms. But why should there be changes in the constitution of the germ-cells? Perhaps because the living material is very complex and inherently liable to change ”

“ Very recently evidence has, indeed, been adduced to prove that "Initiative in animal evolution comes by stimulation, excitation and response in new conditions, and is followed by repetition of these phenomena until they result in structural modifications, transmitted and directed by selection and the law of genetics." ”

“ We may now further follow out the analogy between physiological and pathological evolution, by observing that structures undergoing pathological development (conservative organic modification) , like those that are being developed physiologically, manifest an intrinsic tendency, when undisturbed in their progress, to pursue a fixed, typical course to their naturally-designed termination. When permitted to pursue such a typical course, the observed structural changes are exceedingly slow, and are attended with little or no physical suffering. ”

“ 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. ”

“ There seems to be some evidence that we may stunt the growth of a plant or animal by insufficient or unsuitable food, and that all the cells of the body may thereby be reduced in size, the sexual cells among the rest, and that these reduced cells give rise to small progeny in the next generation. ”

“ Finally, the power of propagation possessed by each separate cell, using the term in its largest sense, determines the reproduction, the variability, the development and renovation of each living organism. No other attempt, as far as I am aware, has been made, imperfect as this confessedly is, to connect under one point of view these several grand classes of facts. We cannot fathom the marvellous complexity of an organic being; but on the hypothesis here advanced this complexity is much increased. ”

“ Modern embryology has completely negatived any such view as that of preformation, and as completely established that the evolution is not the unfolding of a miniature germ, but the growth and differentiation of primitively similar cell-elements. In different animals, as might be expected, the manner and course of development are different. ”

“ Moreover, it is well known that long before this no other term than evolution was used to designate the growth of a single organic individual from the primordial cell and egg to its fully developed form and vital function. ”

“ Indeed, as will be seen at the proper time, the mysteries of daily occurrence, such as growth, budding, and reproduction, are as great as any which beset the passage from form to form, from species to species. No one who has thought of it sufficiently can deny that the ordinary facts of generation, as the necessity of the union of two cells of nearly-spent vitality to produce a third cell, or a brood of cells, endowed with primeval vigor, present difficulties more unsurpassable than the origin of the germs of living things from inorganic matter ”