Biological adaptation

“ And, indeed, here if anywhere we have the biological phenomenon of adaptation in its clearest form. There are very abnormal changes of the functional state of the organism, and the organism is able to compensate these changes in their minutest detail in almost any case. The problem of the specification of the reactions leading to immunity seems to me, as far as I can judge as an outsider, to stand at present in the very forefront of the science. ”

“ Thus, the species which are the latest in acquiring a stable form are the highest up in the biological scale, because the privilege of carrying forward the process of evolution belongs to those species which have not yet become fixed. An apparent weakness, instability, an active capacity for adaptation, are consequently so many signs of superiority, as regards a potential power of evolution—just as the nudity and sensibility of animal cells, for example, are signs of superiority, as compared with vegetable cells—and of man, as compared with the lower animals. ”

“ The word 'adaptation' is itself the cause of much fallacious reasoning and confusion of ideas, inasmuch as it suggests a process rather than a condition, and by biological writers is often used at one time to mean the former and at others the latter. We may take the mammary glands of mammals or organs adapted for the secretion of milk, whose only function is obviously the nourishment of the offspring. Here the function is certain whatever view we take of the origin of the organs, whether we believe they were created or evolved. ”

“ Lamarck explained the gradual formation of organic species by the interaction of two physiological functions—adaptation and heredity. Adaptation consists in the improvement of organs by use, and degeneration by disuse; heredity acts by transmitting the features thus acquired to posterity. New species arise by physiological transformation from older species. ”

“ 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. ”

“ 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? ”

“ 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."... ”

“ 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. ”

“ 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 ”

“ 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. ”

“ 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. ”

“ Taking for granted the existence of the original organism or group of organisms, the fact of reproduction, and the tendency of such reproduction to beget increase in a geometrical ratio, he deduced from these elementary given factors the necessary corollary of survival of the fittest, with all its marvellous and far-reaching implications of adaptation to the environment and specific distinctions. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ In other words, adaptability is a fundamental character of life. Hence the fact that multicellular organisms which cannot, as a whole, fuse with others, adapt themselves to these conditions by the allotment of special cells for that purpose; while, again, the production of multicellular organisms is itself an adaptation to Nature’s need for the higher organization of life. ”

“ 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. ”

“ That certain organs of nutrition and respiration and locomotion are repeated in each segment of a dorsibranchiate annelid, may be regarded as functionally advantageous for a creature following its mode of life. But why should there be a hundred or even two hundred pairs of ovaries? This is an arrangement at variance with that physiological division of labour which every organism profits by—is a less advantageous arrangement than might have been adopted. That is to say, the hypothesis of a designed adaptation fails to explain the facts. ”

“ 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 ”

“ 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. ”

“ Now, since these organs are found, in a rudimentary state, in the lower animals, and since nature offers us many intermediaries between the pigment-spot of the simplest organisms and the infinitely complex eye of the vertebrates, it may just as well be alleged that the result has been brought about by natural selection perfecting the organ automatically. In short, if there is a case in which it seems justifiable to invoke adaptation, it is this particular one. ”

“ As these simple organisms lived through the ages and became more and more complex by modifications and adaptations to an ever-changing environment, they still evolved their kind in reproduction. Every new adaptation gained by the parent was transmitted by heredity, in the course of time, to the offspring; every form and structure modified in the parent was modified by heredity in the offspring ”

“ But the pectoral fin of a fish is equally 'adapted' for aquatic locomotion, but it is certainly not the fore-leg of a terrestrial mammal adapted for that purpose. The original meaning of adaptation in animals and plants, of organic adaptation to use another term, is the relation of a mechanism to its action or of a tool to its work. ”

“ All of the organs are thus fitted or adjusted to a particular place in the body where they may most efficiently perform their duties. Each organ therefore occupies a particular place in an organic environment, so to speak. Thus the principle of adaptation holds true for the organs which constitute an organism, as well as for organisms themselves in their relations to their surroundings.
The various organs of living things are grouped so as to form the several organic systems. There are eight of these, and each performs a group of related tasks which are necessary for complete life. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”