Herbert Spencer

“ As authority for this conclusion, we have not simply the universal truth that change of every order is towards equilibrium; but we have also the truth that life itself is a moving equilibrium between inner and outer actions—a continuous adjustment of internal relations to external relations; or the maintenance of a balance between the forces to which an organism is subject and the forces which it evolves. Hence all changes which enable a species to live under altered conditions, are changes towards equilibrium with the altered conditions ”

“ Unless the change in the environment is so violent as to be universally fatal to the species, it must affect more or less differently the slightly-different moving equilibria which the members of the species present. Inevitably some will be more stable than others when exposed to this new or altered factor. That is to say, those individuals whose functions are most out of equilibrium with the modified aggregate of external forces, will be those to die; and those will survive whose functions happen to be most nearly in equilibrium with the modified aggregate of external forces. ”

“ Besides the multiplicity of directly-coöperative organs, the multiplicity of organs which do not coöperate, save in the degree implied by their combination in the same organism, seems to me a further hindrance to the development of special structures by natural selection alone. Where the life is simple, or where circumstances render some one function supremely important, survival of the fittest may readily bring about the appropriate structural change, without aid from the transmission of functionally-caused modifications. ”

“ That organisms which live, thereby prove themselves fit for living, in so far as they have been tried, while organisms which die, thereby prove themselves in some respects unfitted for living, are facts no less manifest than is the fact that this self-purification of a species must tend ever to insure adaptation between it and its environment. ”

“ While, in the aggregate of influences amid which a species exists, there are some which tend to overthrow the moving equilibria of its members, there are others which facilitate the maintenance of their moving equilibria, and some which are capable of giving their moving equilibria increased stability: instance the spread into their habitat of some new kind of prey, which is abundant at seasons when other prey is scarce. Now what is the process by which the moving equilibrium in any species becomes adapted to some additional external factor furthering its maintenance? ”

“ Though evidence may be required to show that natural selection accounts for everything ascribed to it, yet no evidence is required to show that natural selection has always been going on, is going on now, and must ever continue to go on. ”

“ The probability seems rather to be that, by gamogenesis, this extra endowment will, on the average, be diminished in posterity—just serving in the long run to make up for the deficient endowments of those whose special powers lie in other directions; and so to keep up the normal structure of the species. As fast as the number of bodily and mental faculties increases, and as fast as maintenance of life comes to depend less on the amount of any one and more on the combined actions of all; so fast does the production of specialities of character by natural selection alone, become difficult. ”

“ Had they lived and left offspring, the next generation would have had the same average powers as preceding generations: there would have been a like proportion of individuals less endowed with the needful power, and individuals more endowed with it. But the more-endowed individuals being alone left to continue the race, there must result a new generation characterized by a larger average endowment of this power. That is to say, on the moving equilibrium of a species, an action producing change in a given direction is followed, in the next generation, by a reaction producing an opposite change. ”

“ That they must be extremely slight, is, as before said, a deduction from the hypothesis of natural selection. Mr. Darwin himself argues "that natural selection is continually trying to economise in every part of the organization. If under changed conditions of life a structure before useful becomes less useful, any diminution, however slight, in its development, will be seized on by natural selection, for it will profit the individual not to have its nutriment wasted in building up an useless structure." ”

“ Just as each plant bears a multitude of seeds, out of which some two or three happen to fulfil all the conditions required for reaching maturity and continuing the race; so each species is ever producing numerous slightly-modified forms, deviating in all directions from the average, out of which most fit the surrounding conditions no better than their parents, or not so well, but some few of which fit the conditions better; and, doing so, are enabled the better to preserve themselves, and to produce offspring similarly capable of preserving themselves. ”

“ Now if the individuals of a species are thus necessarily made unlike in countless ways and degrees—if in one individual the amount of energy in a particular direction is greater than in any other individual, or if here a peculiar combination gives a resulting action which is not found elsewhere; then, among all the individuals, some will be less liable than others to have their equilibria overthrown by a particular incident force previously unexperienced. ”

“ On previous occasions we have contemplated the assemblage of individuals composing a species, as an aggregate in a state of moving equilibrium. We have seen that its powers of multiplication give it an expansive energy which is antagonized by other energies ”

“ Rejecting metaphor we see that the process called Natural Selection is literally a survival of the fittest; and the outcome of the above argument is that survival of the fittest is a maintenance of the moving equilibrium of the functions in presence of outer actions: implying the possession of an equilibrium which is relatively stable in contrast with the unstable equilibria of those which do not survive. ”

“ The survival of the fittest must nearly always further the production of modifications which produce fitness, whether they be incidental modifications, or modifications caused by direct adaptation. Evidently, those individuals whose constitutions have facilitated the production in them of any structural change consequent on any functional change demanded by some new external condition, will be the individuals most likely to live and to leave descendants. There must be a natural selection of functionally-acquired peculiarities, as well as of spontaneously-acquired peculiarities ”

“ The disappearance of those individuals which meet the destroying forces by the smallest preserving forces, is tantamount to the yielding of the species as a whole at the places where the resistances are the least. Or if by some general influence, such as alteration of climate, the members of a species are subject to increase of external actions which are ever tending to overthrow their equilibria, and which they are ever counter-balancing by certain physiological actions, which are the first to die? ”

“ If the alteration of some external factor is so great that it leaves alive only the few individuals possessing extreme endowments of the power required to antagonize it; then, in succeeding generations, there is a rapid multiplication of individuals similarly possessing extreme endowments of this power—the force impressed calls out an equivalent conflicting force. ”

“ Darwin shows how natural selection explains peculiar relations between individuals in certain species. Such facts as the dimorphism of the primrose and other flowers, he proves to be in harmony with his hypothesis, though stumbling-blocks to all other hypotheses. The various differences which accompany difference of sex, sometimes slight, sometimes very great, are similarly accounted for. As before suggested ( § 79) , natural selection appears capable of producing and maintaining the right proportion of the sexes in each species ”

“ In other words, if any muscle has more fibres than are required, or if a bone is stronger than needful, no advantage results but rather a disadvantage—a disadvantage which will decrease the chances of survival. Hence it follows that among any organs which habitually act in concert, an increase of one can be of no service unless there is a concomitant increase of the rest. ”

“ Among animals the like process results in the like development of various structures which cannot have been affected by the performance of functions—their functions being purely passive. The thick shell of a mollusk cannot have arisen from direct reactions of the organism against the external actions to which it is exposed; but it is quite explicable as an effect of the survival, generation after generation, of individuals whose thicker coverings protected them against enemies. ”

“ Elsewhere neither muscle nor tendon is damaged, but the bone breaks. Joining with these instances the general fact that, under the same adverse conditions, different individuals show their slight differences of constitution by going wrong some in one way and some in another; and that even in the same individual, similar adverse conditions will now affect one viscus and now another; it becomes manifest that though there cannot be maintained an accurate balance among the powers of the organs composing an organism, yet their excesses and deficiencies of power are extremely slight. ”

“ A stronger muscle must have a stronger bone to resist its contractions; must have stronger correlated muscles and ligaments to secure the neighbouring articulations; must have larger blood-vessels to bring it supplies; must have a more massive nerve to transmit stimulus, and some extra development of a nervous centre to supply the extra stimulus. The question arises, then,—do variations of the appropriate kinds occur simultaneously in all these co-operative parts? Have we any reason to think that the parts spontaneously increase or decrease together? ”

“ Increase of it can result only if individuals possessing average endowments of it are more frequently killed off than individuals highly endowed with it; and this can happen only when the attribute is one of greater importance, for the time being, than most of the other attributes. If those members of the species which have but ordinary shares of it, nevertheless survive by virtue of other superiorities which they severally possess; then it is not easy to see how this particular attribute can be developed by natural selection in subsequent generations. ”

“ While one saves its life by higher speed, another does the like by clearer vision, another by keener scent, another by quicker hearing, another by greater strength, another by unusual power of enduring cold or hunger, another by special sagacity, another by special timidity, another by special courage; and others by other bodily and mental attributes. Conditions being alike, each of these life-saving attributes is likely to be transmitted to posterity. But we may not assume that it will be increased in subsequent generations by natural selection. ”

“ On another occasion ( § 96) it was shown that the aggregate of individuals constituting a species, has a kind of general life which, "like the life of an individual, is maintained by the unequal and ever-varying actions of incident forces on its different parts." We saw that "just as, in each organism, incident forces constantly produce divergences from the mean state in various directions, which are constantly balanced by opposite divergences indirectly produced by other incident forces; and just as the combination of rhythmical functions thus maintained, constitutes the life of the organism ”

“ Doubtless many who have looked at Nature with philosophic eyes, have observed that death of the worst and multiplication of the best, tends towards maintenance of a constitution in harmony with surrounding circumstances. ”

“ It may be objected that this mode of expressing the facts does not include the cases in which a species becomes modified in relation to surrounding agencies of a passive kind—cases like that of a plant which acquires hooked seed-vessels, by which it lays hold of the skins of passing animals, and makes them the distributors of its seeds—cases in which the outer agency has no direct tendency at first to affect the species, but in which the species so alters itself as to take advantage of the outer agency. ”