Variability

“ So it is with selection, whether applied by man or by nature; for though variability is indispensably necessary, yet, when we look at some highly complex and excellently adapted organism, variability sinks to a quite subordinate position in importance in comparison with selection, in the same manner as the shape of each fragment used by our supposed architect is unimportant in comparison with his skill. ”

“ I do not believe that variability is an inherent and necessary contingency, under all circumstances, with all organic beings, as some authors have thought. The effects of variability are modified by various degrees of inheritance and of reversion. Variability is governed by many unknown laws, more especially by that of correlation of growth. Something may be attributed to the direct action of the conditions of life. Something must be attributed to use and disuse. ”

“ We may therefore conclude that for large classes of characters, both animal and vegetable, the variability of an individual, as measured by the standard deviation of its undifferentiated but repeated organs, is a constant fraction of the variability of its race, as measured by the standard deviation of the corresponding series of organs produced by all the individuals of its race. ”

“ As an example of my meaning, I will quote a passage to which I called attention in 'Life and Habit.' It runs:—
"In the earlier editions of this work I underrated, as now seems probable, the frequency and importance of modifications due to spontaneous variability. But it is impossible to attribute to this cause" (i. e. spontaneous [Pg 359] variability, which is itself only an expression for unknown causes) "the innumerable structures which are so well adapted to the habits of life of each species. ”

“ If we take not merely the variability of stature or weight at a given age, but the variability of the actual successive increments in each yearly period, we see that this latter coefficient of variability tends to increase steadily, and more and more rapidly, within the limits of age for which we have information; and this phenomenon is, in the main, easy of explanation. ”

“ Universal variability—small in amount but in every direction, ever fluctuating about a mean condition until made to advance in a given direction by “election,” natural or artificial,—is the simple basis for the indefinite modification of the forms of life;—partial, unbalanced, and consequently unstable modifications being produced by man, while those developed under the unrestrained action of natural laws, are at every step self-adjusted to external conditions by the dying out of all unadjusted forms, and are therefore stable and comparatively permanent. ”

“ Every new adaptation necessarily implies variability, and so the stage which is in process of transformation must have its period of variability, which gradually returns again to greater constancy, and this the more completely the longer the series of generations through which the weeding out of the less well-adapted has endured. ”

“ Thus in Darwin’s theoretical world of natural selection a certain assumption is made, the assumption of indefinite variability—slight variability it is true, over any appreciable lapse of time, but indefinite in the postulated epochs of transformation—and a whole chain of results is shown to follow. ”

“ 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. ”

“ Hence, in studying the degrees of mental variability shown us in the daily lives of the different races, we must ask how far variability characterizes the whole mind, and how far it holds only of parts of the mind. ”

“ We have now shown in some detail, at the risk of being tedious, that individual variability is a general character of all common and widespread species of animals or plants; and, further, that this variability extends, so far as we know, to every part and organ, whether external or internal, as well as to every mental faculty. Yet more important is the fact that each part or organ varies to a considerable extent independently of other parts. ”

“ Just as the tendency to variability is of necessity a steadily increasing factor in the evolution of animals, so it is in man, and proportionately more so as he is raised above the level of the brute. Increase of complexity leads to that instability which is the mother of variability. ”

“ Not that, as I believe, any extreme amount of variability is necessary; as man can certainly produce great results by adding up in any given direction mere individual differences, so could Nature, but far more easily, from having incomparably longer time at her disposal. ”

“ The proof of such constant indefinite variability has been much increased of late years, and if you consider that instead of tens or hundreds of individuals, Nature has as many thousands or millions to be selected from, every year or two, it will be clear that the materials for adaptation are ample. ”

“ In the one case, as in the other, selection does nothing without variability, and this depends in some manner on the action of the surrounding circumstances on the organism. I have, also, often personified the word Nature ”

“ That the different stages of development of a species may actually be partly variable and partly constant, and that the variable or constant character of one stage has no influence on the other stages, is shown by the following cases, which are, at the same time, well adapted to throw light on the causes of variability, and are thus calculated to contribute towards the solution of the main problem with which this investigation is concerned. ”

“ The facts of variability, of the struggle for existence, of adaptation to conditions, were notorious enough; but none of us had suspected that the road to the heart of the species problem lay through them, until Darwin and Wallace dispelled the darkness, and the beacon-fire of the 'Origin' guided the benighted. ”

“ In this way, it is not variability itself which is called upon to explain beautiful adaptations, but it is quite sufficient to suppose that natural selection has operated during long periods in the same way. ”

“ The fact of individual variability can in this way be well understood; the living organism contains in itself no principle of variability—it is the statical682 element in the developmental processes of the organic world, and would always reproduce exact copies of itself if the inequality of the external influences did not affect the developmental course of each new individual ”

“ The reasons for variability are again, according to Professor Boas, largely environmental. "We have seen, when a people is descended from a small uniform group, that then its variability will decrease; while on the other hand, when a group has a much-varied origin or when the ancestors belong to entirely distinct types the variability may be considerably increased." ”

“ And a people of variable and therefore widely diversified mental capacities will, even though its average capacity is no greater than that of a more homogeneous people, be more likely to make progress in civilisation, and this for three reasons.
First, variability is the essential condition of all race progress by biological adaptation; for it is by the selection of variations, the survival and multiplication of types varying in certain directions in larger proportions than the average type, that all race progress and adaptation seems to have been achieved. ”

“ These facts, and innumerable others which could be added, indicate that a change of almost any kind in the conditions of life suffices to cause variability—different changes acting on different organisms. ”

“ In the variability of instinct, also, we find mechanical organization less domineering, and in the study of wasps, to which we have just referred, the one preeminent, unmistakable and ever-present fact is variability. ”

“ But the evidence seems to me overwhelming that a well-marked species is the product, not of a single or of a few variations, but of a long series of modifications, each modification resulting chiefly from adaptation to infinitely complex conditions (including the inhabitants of the same country) , with more or less inheritance of all the preceding modifications. Moreover, as variability depends more on the nature of the organism than on that of the environment, the variations will tend to differ at each successive stage of descent. ”

“ The second effect is produced whenever the conditions vary, when, taking advantage of the variations continually occurring in all well-adapted and therefore populous species, the same process will slowly but surely bring about complete adaptation to the new conditions. And here another fact—the normal variability of all populous or dominant species, which is seldom27 realized except by those who have largely and minutely compared the individuals of many species in a state of nature—comes into play. ”

“ This variability is indefinite, and is rendered definite by the competition and antagonism, so that every particular variation is the resultant of a composition of forces. The forces in operation are the internal and external conditions of existence—i. e. the nature of the organism, and its response to the actions of its medium. A change may take place120 in the medium without a corresponding response from the organism; or the change may find a response and the organism become modified. Every modification is a selection, determined by laws of growth ”

“ Causes of Variability — Effects of Habit and the use or disuse of Parts — Correlated Variation — Inheritance — Character of Domestic Varieties — Difficulty of distinguishing between Varieties and Species — Origin of Domestic Varieties from one or more Species — Domestic Pigeons, their Differences and Origin — Principles of Selection, anciently followed, their Effects — Methodical and Unconscious Selection — Unknown Origin of our Domestic Productions — Circumstances favourable to Man's power of Selection. ”

“ To effect a modification and new adaptation to changes in the environment the moments of the desultory type have no other mode of modification but by the slowly working factors of spontaneous variations and natural selection, a process of adaptation and useful modification prolonged throughout the course of generations. ”

“ Whether variation depends upon some intricate machinery—if I may use the phrase—of the living organism itself, or whether it arises through the influence of conditions upon that form, is not certain, and the question may, for the present, be left open. But the important point is that granting the existence of the tendency to the production of variations ”

“ Secondly, there is a variation, to a certain extent—though, in all probability, the influence of this cause has been very much exaggerated—but there is no doubt that variation is produced, to a certain extent, by what are commonly known as external conditions,—such as temperature, food, warmth, and moisture. In the long run, every variation depends, in some sense, upon external conditions, seeing that everything has a cause of its own. ”

“ Or variation may occur through the establishment of new relations between the species inhabiting some locality while inanimate nature remains uniform, or through migration into new inanimate or animate surroundings. Variations, in short, may arise under the influence of any change in the general environment which renders necessary adaptive changes in structure. But this adaptation in some cases takes place in the mind, new actions or methods of meeting the contingency being adopted which render physical changes unnecessary. ”

“ 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) ”

“ But perhaps the most discouraging circumstance of all is, that in scarcely a single actual instance in nature can we assert whether an observed variation is useful or not—a drawback that I distinctly pointed out some time ago. ”

“ It is conceivable, on the other hand, that the tendency to vary is both originated and directed by the influence of external conditions, while it is also conceivable that both variation and the direction which variation takes are partly determined by intrinsic and partly by extrinsic conditions.—The American Cyclopœdia. ”

“ But if the constant ones undergo a gradual change, or if the variable ones, instead of balancing each other suffer one or more of their number to begin to acquire a preponderating influence, so as to put a sort of bias upon their aggregate effect, the mean will at once begin, so to say, to shift its ground. And having once begun to shift, it may continue to do so, to whatever extent we recognize that Species are variable and Development is a fact. ”

“ Variation is more widespread than is generally supposed, but granting freedom of intercourse over a wide area and a stability of environment, the extreme variations are less liable to occur, and, furthermore, it is the average organism which is the most stable. ”

“ Hence, as functional deviation must ever be inducing structural deviation, each individual throughout the area occupied tends to become fitted for the particular habits which its particular conditions necessitate; and in so far, unfitted for the average habits proper to the species. But these undue specializations are continually checked by gamogenesis. ”