Regression (biology)

“ Life may be regarded as an adaptation of inner and outer relations. Adaptation and fitness are important criteria with biological processes. What is the fitness, or utility of organs and their functions to the particular organism, and how have they come to this given state of fitness? These problems cannot be ignored by biology as a science. The whole of the Darwinian theory aims to give the key to the way the different forms of adaptations have come about. ”

“ Darwin and Lamarck assign as accounting for some of the phenomena; it is manifest, from our present stand-point, that this, so far as it is a cause of evolution, is a proximate cause and not an ultimate cause. To say that functionally-produced adaptation to conditions originates either evolution in general, or the irregularities of evolution, is to raise the further question—why is there a functionally-produced adaptation to conditions?—why do use and disuse generate appropriate changes of structure? ”

“ 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 ”

“ But why should the growth of every organism be finally arrested? Though the rate of increase may, in each case, be necessarily restricted within a narrow range of variation—though the increment that is possible in a given time, cannot exceed a certain amount ”

“ If, as any rational theory of evolution implies, the progressive differentiations of types from one another during past times, have resulted from the direct and indirect effects of external conditions—if races of organisms have become different, either by immediate adaptations to unlike habits of life, or by the mediate adaptations resulting from preservation of the individuals most fitted for such habits of life, or by both ”

“ 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? ”

“ Thus, for those progressive modifications upon modifications which organic evolution implies, we find a sufficient cause. The increasing inner changes for which we thus find a cause in the perpetual outer changes, conform, so far as we can trace them, to the universal law of the instability of the {550}homogeneous. In organisms, as in all other things, the exposure of different parts to different kinds and amounts of incident forces, has necessitated their differentiation; and, for the like reason, aggregates of individuals have been lapsing into varieties, and species, and genera, and orders. ”

“ I make no apologies for the length of this preliminary analysis, since it is precisely by the neglect of preliminary analysis that most attempts to correlate biology and sociology have failed. The salient fact emerges that with man there has been a radical change in evolutionary method. ”

“ 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. ”

“ But where the external changes are either such as are fatal when experienced by the individuals, or such as act on the individuals in ways that do not affect the equilibrium of their functions; then the re-adjustment results through the effects produced on the species as a whole—there is indirect equilibration. ”

“ As to the nature and frequency of inborn variations, Biology has recently begun to accumulate precise observations, and has renounced the bad habit of simply postulating variability without statistically or otherwise defining it. ”

“ The fact of regression is of considerable importance for the theory of evolution as well as for the subject of Eugenics when describing the phenomena of heredity in this statistical manner in whole groups without paying attention to particular individuals. ”

“ 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. ”

“ As thus understood, the phenomena of adaptation fall into harmony with first principles. The inference that organic types are fixed, because the deviations from them which can be produced within assignable periods are relatively small, and because, when a force producing deviation ceases, there is a return to something like the original state ”

“ And it will follow a priori, as we found it to do a posteriori, that the organisms exhibiting Evolution in the highest degree, exhibit the longest or the most rapid successions of changes, or both. Again, it was shown that vital change is distinguished from non-vital change by being made up of many simultaneous changes; and also that creatures possessing high vitality are marked off from those possessing low vitality, by the far greater number of their simultaneous changes. ”

“ The Newton of biology, who will discover the laws of variation and heredity, has not, it is safe [Pg 63] to say, yet appeared. Variation in a definite direction in virtue of an internal tendency in the organism (Nägeli) ; variation in response to the specific stimulus of the environment (Eimer) ; variation due, at least in animals, to the conscious effort of the individual (Lamarck) ”

“ The empirical generalization that guides the farmer in his rotation of crops, serves to bring his actions into concord with certain of the actions going on in plants and soil. The rational deductions of the educated navigator who calculates his position at sea, form a series of mental acts by which his proceedings are conformed to surrounding circumstances. Alike in the simplest inferences of the child and the most complex ones of the man of science, we find a correspondence between simultaneous and successive changes in the organism, and co-existences and sequences in its environment. ”

“ Biology, which not long ago was purely descriptive and speculative, has begun to adopt the methods of the exact sciences, recognizing that for permanent progress not only experiments are required but quantitative experiments. ”

“ In biological evolution, some organisms degenerate, some remain stationary, but the average of certain properties, and more especially their upper level, increases; and this tendency for certain properties to become more marked, this and nothing else, is what we sum up and generalize, again with perfect justification, as the law of biological progress.
The mechanism of biological progress demands a word: for it is noticeable that a mere fact, however well attested, makes a very different kind of impression from a fact explained and brought into relation with the rest of our knowledge. ”

“ This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called "natural selection, or the preservation of favoured races in the struggle for life." ”

“ And here we seem forced to conclude that the larger functional variations produced by greater external changes, are the initiators of those structural variations which, when once commenced in a species, lead by their combinations and antagonisms to multiform results. ”

“ While for all the other unlikenesses, we have, as an adequate cause, the indirect effects wrought by the survival, generation after generation, of the individuals in which favourable variations have occurred—variations such as those of which human anatomy furnishes endless instances. Thus accounting for so much, we may not unreasonably presume that these co-operative processes of direct and indirect equilibration will account for what remains. ”

“ This regression, in every generation, takes place even when both parents have been selected for their high development of the organ in question; but when there is no such selection, and crosses are allowed among individuals of every grade of development, the deterioration will be very rapid; and after a time not only will the average size of the part be greatly reduced, but the instances of full development will become very rare. ”

“ In most cells and in most lower organisms dedifferentiation and despecialization of structure and function, which we may term in general regressive tendencies, are always less pronounced than progressive impulsions, while the latter predominate still more in the higher forms of life. ”

“ It is, curiously enough, among the professional biologists that objectors to the notion of biological progress and to its corollary, the distinction of higher and lower forms of life, have chiefly been found. ”

“ 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 ”

“ By the preservation in successive generations of those whose moving equilibria are least at variance with the requirements, there is produced a changed equilibrium completely in harmony with the requirements.
§ 174. Even were this the whole of the evidence assignable for the belief that organisms have been gradually evolved, it would have a warrant higher than that of many beliefs which are regarded as established. But the evidence is far from exhausted. ”

“ Moreover, the essentials are found to be the same in the animal kingdom also, and the bearing of all these discoveries on the phenomena of reproduction, variation, and heredity in living organisms has been and is of the highest importance, for they support, control, explain and correct so many of the splendid results of Knight, Kölreuter, Sprengel, Hildebrand and Hermann Müller, and in every direction throw side-lights into the crevices of that magnificent structure, the theory of Natural Selection, erected for all time by our countryman, Charles Darwin. ”

“ This increase has not been universal; many organisms have remained stationary or have even [Pg 31] regressed; many have shown increase in one particular but not in others. But the upper level of these properties of living matter has been continually raised, their average has continually increased. It is to this increase, continuous during evolutionary time, in the average and especially in the upper level of these properties that, I venture to think, the term biological progress can be properly applied. ”

“ 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. ”

“ But, as we have seen in Chapter III, the fortuitous variation of every part or organ usually amounts to one-tenth, and often to one-sixth of the average dimensions—that is, the fortuitous variation in one generation among a limited number of the individuals of a species is as great as the cumulative effects of disuse in a thousand generations! ”

“ The effects of the struggle to survive, which here prompts a simpler life with resulting degeneracy and there a different life with resulting new developments, are far from being the only causes of morphological obscurations. Fulfilment of certain highly general requirements gives certain common traits to plants of widely divergent classes; and fulfilment of certain other highly general requirements gives certain common traits to animals of widely divergent classes. ”

“ That Darwin errs, and that full physiological perfection cannot exist except where there is full general growth, and full growth of all parts or organs, we shall clearly demonstrate when, in a future article, we treat of the laws of compensation or balancement of growth, of correlation, of crossing, and of close interbreeding. But whether there exists harmony between the organism or not, there is none the less deterioration. And when reversion to the type from which the organism has degenerated takes place under domestication, it is termed evolution. ”