Adaptation (biology)

“ 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 is adaptation as a process, rather than as a product, which perhaps interests him most, and emphasis needs to be placed upon this distinction. The problem of adaptation as a process may be a different and separate one from that of evolution, but individual [Pg 10] animals must have shown adjustive adaptation, or there could have been no perpetuation to continue the struggle of adjustment. ”

“ 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? ”

“ The new form may appear suddenly, often in a single generation, or gradually, but in either case it is the result of adaptation that is necessarily advantageous, because it is the result of adjustment to controlling physical factors. Origin by adaptation is perhaps only a special kind of origin by variation, but this might be said with equal truth of mutation. New forms resulting from adaptation are like those produced from mutation, in that they appear suddenly as a rule and without the agency of selection. ”

“ We have to consider not only the changes in an organism in the direction of more or less perfect adaptation to its environment, but also changes in the environment. These changes are in the direction of increased simplicity or of increased complexity. So [183] that we may say that the modification of life is in the direction of more or of less complete adaptation to simpler or to more complex conditions. Where the adaptation advances to more complex conditions, we speak of elaboration; where it retrogrades to less complex conditions, we speak of degeneration ”

“ But the most convincing proof of the organism's power of adaptation is to be found in the fact that the possibility of living parasitically within other animals is taken advantage of in the fullest manner, and by the most diverse groups, and that their bodies exhibit the most marvellous and far-reaching adaptations to the special conditions prevailing within the bodies of other animals. ”

“ In other words, so far as your view is critical of natural selection considered as a hypothetical cause of adaptive evolution, I can well believe you have adduced a formidable array of facts. But I fail to follow, when you pass on to the constructive part of your case—or your suggested substitute for natural selection in self-adaptation. ”

“ This is natural selection by means of the survival of the fittest in the struggle for existence. Changes in the conditions and surroundings of life, and more or less [41] perfect adaptation of the organisms to the new conditions of form, color, food and habit, are the main causes of those individual variations, the accumulation of which through many generations produces so great effects. ”

“ Many naturalists, and especially many botanists, regard adaptation as something secondary, something given to species by the way, to improve the conditions of their existence, but not affecting their nature—comparable perhaps to the clothing worn by man to protect himself from cold ”

“ 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."... ”

“ It seems to me that Darwin was not so clear on another question, that of the relation between improvement and adaptation. He wrote to Lyell: "When you contrast natural selection and 'improvement,' you seem always to overlook... that every step in the natural selection of each species implies improvement in that species IN RELATION TO ITS CONDITION OF LIFE... ”

“ The factors of fundamental importance in the study of the theory of Evolution, or the doctrine of the Transmutations of Organisms, are Cells, Heredity and Variation, Environment, Natural Selection, and Isolation.
The evolution of an organism means its descent from preceding organisms with continuous adaptation to its Environment. Its adaptation occurs chiefly, if not entirely, through the Natural Selection of its useful Variations, and the tending of these variations to be transmitted to the offspring by the forces of Heredity. ”

“ It is, of course, true that the significance of the argument is affected by the circumstance that organisms by the influence of natural selection can preserve a continuous adaptation to an environment which is gradually becoming modified. ”

“ It is here suggested that the modification as such, is not inherited, but is the condition under which congenital variations are favored and given time to get a hold on the organism, and are thus enabled by degrees to reach the fully adaptive level. When we remember that plastic modification and germinal variation have been working together all along the line of organic evolution, to reach the common goal of adaptation, it is difficult to believe that they have been all along wholly independent of each other. ”

“ The very diverse potency of the faculty of regeneration in animals belonging to the same small group, and nearly, if not quite, at the same level of organization, seems to show clearly that we have here to do with adaptation to different conditions of life, although we cannot demonstrate this in detail. ”

“ We venture to maintain that everything in the world of organisms that has permanence and significance depends upon adaptation, and has arisen through a sifting of the variations which presented themselves, that is, through selection. Everything is adaptation, from the smallest and simplest up to the largest and most complex, for if it were not it could not endure, but would perish. ”

“ Hence, the two terms, as we will use them here, may be defined as follows: morphological adaptation is a change in the structural character of the species in order that it may be better fitted to meet the needs of the new conditions of growth; while physiological adaptation is an acquired power to survive and develop under abnormal conditions, which is not accompanied by any visible change in the characteristic structure of the species. ”

“ Impressed by this, we have now to ask whether all the transformations of organisms may not be referred to adaptation to the continually changing conditions of life? We shall return to this question later, but in the meantime we are far from being able to answer it in the affirmative, for there are undoubtedly a great many characters, at least in animals, which cannot have owed their origin to natural selection in the form in which we have studied it so far. ”

“ Viewed as a whole, there can be little doubt that the general tendency of evolution is towards more complete adaptation to more diverse and complex environment. And this tendency is accompanied by a general increase of differentiation and of integration; of differentiation whereby the constituent elements of life, whether cells, tissues, organs, organisms, or groups of organisms, become progressively more specialized and more different from one another ”

“ Everything centers then about the question as to the origin of adult specific forms, which exhibit adaptation.
Realizing this, we may pass on immediately to consider how through the study of adaptation, Darwin was led to formulate his potent theories, which have been the basis for recent progress. As the other speakers upon biological sciences have already stated, the most striking feature of animals and plants is their adjustment to their vital conditions. ”

“ Since the configuration of the idioplasm, which becomes more complex from internal causes, always assumes a definite character of adaptation in consequence of the action of external causes, the adaptation determinants capable of development may become more and more weakened and at last latent when other external causes produce other adaptation determinants. But these determinants may be revived by the renewed activity of the former causes, and thus rendered capable of development. Hence the organism may show the most various reversions with respect to its adaptations. ”

“ There is another aspect of the Adaptation problem to which I can only allude very briefly. May not our present ideas of the universality and precision of Adaptation be greatly exaggerated? The fit of organism to its environment is not after all so very close—a proposition unwelcome perhaps, but one which could be illustrated by very copious evidence. Natural Selection is stern, but she has her tolerant moods. ”

“ Unless, therefore, we exclude adaptive avoidance from the category of adaptations, we cannot regard all organic adaptation in a changing environment as a phenomenon of organic imitation due to a circular process tending to the reinstatement of stimulation. ”

“ In this theory of perfect natural adaptation, whether it be left to stand upon its old teleological basis, or be placed, as some modern investigators would place it, upon a genetic one, a very important factor has been left out, viz., the influence which plants exert upon one another. Adaptation, as the term is employed, is applied to a supposed correlation between the plant and its inorganic environment ”

“ 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. ”

“ Thus we frequently observe modifications of structure induced by exceptional conditions that have been brought to act upon the body, of so trivial a character that they can hardly be called diseases, while at the same time they are in some measure anomalous deviations from the typical standard of the species; but in these, as in the higher grades of structural modification, it will be seen that the conservative purpose of adaptation is carried out. ”

“ 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. ”

“ Korschinsky and the Moderns. (7) The adaptation which the struggle for existence brings about has nothing to do with perfecting, for the organisms which are physiologically and morphologically higher are by no means always better adapted to external circumstances than those lower in the scale. Evolution cannot be explained mechanically. The origin of higher forms from lower is only possible if there is a tendency to progress innate in the organism itself. This tendency is nearly related to or identical with the tendency to variation. ”

“ To account for adaptation, for the almost perfect fitness of every plant and every animal to its position in life, for the existence (in other words) of definitely correlated parts and organs, we must call in the aid of survival of the fittest. Without that potent selective agent, our conception of the becoming of life is a mere chaos ”

“ Such a view has been advocated by some recent authors, especially by Klebs, Holmes, and Child:85 it is refuted I think by the simple fact that the first phase of every process of restitution, be it regeneration proper or be it a sort of harmonious differentiation, goes on without functioning at all, and only for future functioning.86
And there has been advocated still another view in order to amplify the sphere of adaptation: all individual morphogenesis, not only restitution, is adaptation, it has been said. ”

“ Animal and vegetable organisms have been analyzed, and 'the idea of adaptation developed into the conception that life itself, "is the definite combination of heterogeneous changes, both simultaneous and successive in correspondence with external co-existence and sequences."' Now to the masses who are pardonably curious concerning this problem of existence, is this result perfectly satisfactory? ”

“ If, on the other hand, cumulative adaptation is unjustly regarded solely in relation to its second factor, and the transforming action of the organism235 itself, its reaction against the external influences, its change by practice, habit, use, or non-use of organs, is put into the foreground, then we forget that this reaction is first called into play by the action of external conditions of existence. ”

“ Thus my first argument is the well-known one of accident being quite unable to explain the co-ordination of variations necessary to adaptation.
The point is this, that not only one accidental advantageous variation which might give an animal a better chance of survival has to be considered, but the general adaptation of all the organism to new conditions; not only that, but the marvellous adaptation of thousands upon thousands of special relations within complex organisms such as are the higher animals. ”