From Robert Bierstedt, The Making of Society. New York:Modern Library, 1959, pp. 241-251.
Charles Darwin (1809-1882) was born in Shrewsbury, England, ofwealthy parents and was educated at Cambridge University, with theostensible intention of going into the church or medicine. As a youngman, however, he developed an unusually intense interest in naturalscience. He had an opportunity, during a long voyage around the worldon the "Beagle," to observe the natural world about him and tocollect specimens of the incredible profusion of its fauna and flora.He very early had come to accept the theory of the gradualmodifications of species and to reject the older notion of speciesthat were fixed and stable as an act of special creation. He lacked,however, an explanation of the causes of this variation, a principlethat would correspond to the changes produced by the "artificial"selection practiced by plant and animal breeders. It was in October,1838, while reading Malthus on population "for amusement" that he hitupon the answer--natural selection based upon the struggle forexistence and the survival of the fittest in a world in which thereproduction of animals was far in excess of that needed for thecontinuation of any species.
Darwin went ahead to assemble, with the utmost patience, theevidence that this hypothesis required and published his great book,The Origin of Species, in 1859. In 1871, in The Descent ofMan, he applied the same principle to the origin of man and gaveto man a place in the evolutionary process.
Although Darwin was not, of course, a sociologist, his theory gavea tremendous impetus to the evolutionary interpretation of humansocieties and social institutions.
Natural Selection--its power compared with marksselection--its power on characters of trifling importance--its powerat all ages and on both sexes--Sexual Selection.
How will the struggle for existence act in regard to variation?Can the principle of selection, which we have seen is so potent inthe hands of man, apply under nature? I think we shall see that itcan act most efficiently. Let the endless number of slight variationsand individual differences occurring in our domestic productions,and, in a lesser decree, in those under nature, be borne in mind; aswell as the strength of the hereditary tendency. Under domestication,it may be truly said that the whole organisation becomes in somedegree plastic. But the variability, which we almost universally meetwith in our domestic productions, is not directly produced, as Hookerand Asa Gray have well remarked, by man; he can neither originatevarieties, nor prevent their occurrence; he can only preserve andaccumulate such as do occur. Unintentionally he exposes organicbeings to new and changing conditions of life, and variabilityensues; but similar changes of conditions might and do occur undernature. Let it also be borne in mind how infinitely complex andclose-fitting are the mutual relations of all organic beings to eachother and to their physical conditions of life; and consequently whatinfinitely varied diversities of structure might be of use to eachbeing under changing conditions of life. Can it, then, be thoughtimprobable, seeing that variations useful to man have undoubtedlyoccurred, that other variations useful in some way to each being inthe great and complex battle of life should occur in the course ofmany successive generations? If such do occur, can we doubt(remembering that many more individuals are born than can possiblysurvive) that individuals have any advantage, however slight, overothers, would have the best chance of surviving and of procreatingtheir kind? On the other hand, we may feel sure that any variation inthe least degree injurious would be rigidly destroyed. Thispreservation of favorable individual differences and variations, andthe destruction of those which are injurious, I have called NaturalSelection, or the Survival of the Fittest. Variations neither usefulnor injurious would not be affected by natural selection, and wouldbe left either a fluctuating element, as perhaps we see in certainpolymorphic species, or would ultimately become fixed, owing to thenature of the organism and the nature of the conditions.
Several writers have misapprehended or objected to the termNatural Selection. Some have even imagined that natural selectioninduces variability, whereas it implies only the preservation of suchvariations as arise and are beneficial to the being under itsconditions of life. No one objects to agriculturists speaking of thepotent effects of man's selection; and in this case the individualdifferences given by nature, which man for some object selects, mustof necessity first occur. Others have objected that the termselection implies conscious choice in the animals which becomemodified; and it has even been urged that, as plants have novolition, natural selection is not applicable to them! In the literalsense of the word, no doubt, natural selection is a false term; butwho ever objected to chemists speaking of the elective affinities ofthe various elements?--and yet an acid cannot strictly be said toelect the base with which it in preference combines. It has been saidthat I speak of natural selection as an active power or Deity; butwho objects to an author speaking of the attraction of gravity asruling the movements of the planets? Everyone knows what is meant andis implied by such metaphorical expressions; and they are almostnecessary for brevity. So again it is difficult to avoid personifyingthe word Nature; but I mean by Nature, only the aggregate action andproduct of many natural laws, and by laws the sequence of events asascertained by us. With a little familiarity such superficialobjections will be forgotten.
We shall best understand the probable course of natural selectionby taking the case of a country undergoing some slight physicalchange, for instance, of climate. The proportional numbers of itsinhabitants will almost immediately undergo a change, and somespecies will probably become extinct. We may conclude, from what wehave seen of the intimate and complex manner in which the inhabitantsof each country are bound together, that any change in the numericalproportions of the inhabitants, independently of the change ofclimate itself, would seriously affect the others. If the countrywere open on its borders, new forms would certainly immigrate, andthis would likewise seriously disturb the relations of some of theformer inhabitants. Let it be remembered how powerful the influenceof a single introduced tree or mammal has been shown to be. But inthe case of an island, or of a country partly surrounded by barriers,into which new and better adapted forms could not freely enter, weshould then have places in the economy of nature which wouldassuredly be better filled up, if some of the original inhabitantswere in some manner modified; for, had the area been open toimmigration, these same places would have been seized on byintruders. In such cases slight modifications, which in any wayfavored the individuals of any species, by better adapting them totheir altered conditions would tend to be preserved; and naturalselection would have free scope for the work of improvement.
We have good reason to believe that changes in the conditions oflife give a tendency to increased variability, and in the foregoingcases the conditions have changed, and this would manifestly befavorable to natural selection, by affording a better chance of theoccurrence of profitable variations. Unless such occur, naturalselection can do nothing. Under the term of "variations," it mustnever be forgotten that mere individual differences are included. Asman can produce a great result with his domestic animals and plantsby adding up in any given direction individual differences, so couldnatural selection, but far more easily, from having incomparablylonger time for action. Nor do I believe that any great physicalchange, as of climate, or any unusual degree of isolation to checkimmigration, is necessary in order that new and unoccupied placesshould be left, for natural selection to fill up by improving some ofthe varying inhabitants. For as all the inhabitants of each countryare struggling together with nicely balanced forces, extremely slightmodifications in the structure or habits of one species would oftengive it an advantage over others; and still further modifications ofthe same kind would often still further increase the advantage, aslong as the species continued under the same conditions of life andprofited by similar means of subsistence and defense. No country canbe named in which all the native inhabitants are now so perfectlyadapted to each other and to the physical conditions under which theylive, that none of them could be still better adapted or improved;for in all countries the natives have been so far conquered bynaturalized productions, that they have allowed some foreigners totake firm possession of the land. And as foreigners have thus inevery country beaten some of the natives, we may safely conclude thatthe natives might have been modified with advantage, so as to havebetter resisted the intruders.
As man can produce, and certainly has produced, a great result byhis methodical and unconscious means of selection, what may notnatural selection effect? Man can act only on external and visiblecharacters: Nature, if I may be allowed to personify the naturalpreservation or survival of the fittest, cares nothing forappearances, except in so far as they are useful to any being. Shecan act on every internal organ, on every shade of constitutionaldifference, on the whole machinery of life. Man selects only for hisown good: Nature only for that of the being which she tends. Everyselected character is fully exercised by her, as is implied by thefact of their selection. Man keeps the natives of many climates inthe same country; he seldom exercises each selected character in somepeculiar and fitting manner; he feeds a long- and a short-beakedpigeon on the same food; he does not exercise a long-backed orlong-legged quadruped in any peculiar manner; he exposes sheep withlong and short wool to the same climate. He does not allow the mostvigorous males to struggle for the females. He does not rigidlydestroy all inferior animals, but protects during each varyingseason, as far as lies in his power, all his productions. He oftenbegins his selection by some half-monstrous form; or at least by somemodification prominent enough to catch the eye or to be plainlyuseful to him. Under nature, the slightest differences of structureor constitution may well turn the nicely balanced scale in thestruggle for life, and so be preserved. How fleeting are the wishesand efforts of man! how short his time! and consequently how poorwill be his results, compared with those accumulated by Nature duringwhole geological periods! Can we wonder, then, that Nature'sproductions should be far "truer" in character than man'sproductions, that they should be infinitely better adapted to themost complex conditions of life, and should plainly bear the stamp offar higher workmanship?
It may metaphorically be said that natural selection is daily andhourly scrutinizing throughout the world, the slightest variations;rejecting those that are bad, preserving and adding up all that aregood; silently and insensibly working, whenever and whereveropportunity offers, at the improvement of each organic being inrelation to its organic and inorganic conditions of life. We seenothing of these slow changes in progress, until the hand of time hasmarked the lapse of ages, and then so imperfect is our view intolong-past geological ages, that we see only that the forms of lifeare now different from what they formerly were.
In order that any great amount of modification should be effectedin a species, a variety when once formed must again, perhaps after along interval of time, vary or present individual differences of thesame favorable nature as before; and these I must be again preserved,and so onwards step by step. Seeing that individual differences ofthe same kind perpetually recur, this can hardly be considered as anunwarrantable assumption. But whether it is true, we can judge onlyby seeing how far the hypothesis accords with and explains thegeneral phenomena of nature. On the other hand, the ordinary beliefthat the amount of possible variation is a strictly limited quantityis likewise a simple assumption.
Although natural selection can act only through and for the goodof each being, yet characters and structures, which we are apt toconsider as of very trifling importance, may thus be acted on. Whenwe see leaf-eating insects green, and bark feeders mottled grey; thealpine ptarmigan white in winter, the red grouse the colour ofheather, we must believe that these tints are of service to thesebirds and insects in preserving them from danger. Grouse, if notdestroyed at some period of their lives, would increase in countlessnumbers; they are known to suffer largely from birds of prey; andhawks are guided by eyesight to their prey--so much so, that on partsof the Continent persons art warned not to keep white pigeons, asbeing the most liable to destruction. Hence natural selection mightbe effective in giving the proper color to each kind of grouse, andin keeping that color, when once acquired, true and constant. Norought we to think that the occasional destruction of an animal of anyparticular color would produce little effect: we should remember howessential it is in a flock of white sheep to destroy a lamb with thefaintest trace of black. We have seen how the color of the hogs,which feed on the "paint root" in Virginia, determines whether theyshall live or die. In plants, the down on the fruit and the color ofthe flesh are considered by botanists as characters of the mosttrifling importance: yet we hear from an excellent horticulturist,Downing, that in the United States smooth-skinned fruits suffer farmore from a beetle, a Curculio, than those with down; thatpurple plums suffer far more from a certain disease than yellowplums; whereas another disease attacks yellow-fleshed peaches farmore than those with other colored flesh. If, with all the aids ofart, these slight differences make a great difference in cultivatingthe several varieties, assuredly, in a state of nature, where thetrees would have to struggle with other trees and with a host ofenemies, such differences would effectually settle which variety,whether a smooth or downy, a yellow or purple-fleshed fruit, shouldsucceed.
In looking at many small points of difference between species,which, as far as our ignorance permits us to judge, seem quiteunimportant, we must not forget that climate, food, etc., have nodoubt produced some direct effect. It is also necessary to bear inmind that, owing to the law of correlation, when one part varies, andthe variations are accumulated through natural selection, othermodifications, often of the most unexpected nature, will ensue.
As we see that those variations which, under domestication, appearat any particular period of life, tend to reappear in the offspringat the same period--for instance, in the shape, size, and flavor ofthe seeds of the many varieties of our culinary and agriculturalplants; in the caterpillar and cocoon stages of the varieties of thesilkworm; in the eggs of poultry, and in the color of the down oftheir chickens; in the horns of our sheep and cattle when nearlyadult--so in a state of nature, natural selection will be enabled toact on and modify organic beings at any age, by the accumulation ofvariations profitable at that age, and by their inheritance at acorresponding age. If it profit a plant to have its seeds more andmore widely disseminated by the wind, I can see no greater difficultyin this being effected through nature selection, than in the cottonplanter increasing and improving by selection the down in the pods onhis cottontrees. Natural selection may modify and adapt the larva ofan insect to a score of contingencies, wholly different from thosewhich concern the mature insect; and these modifications may affect,through correlation, the structure of the adult. So, conversely,modification in the adult may affect the structure of the larva; butin all cases natural selection will ensure that they shall not beinjurious: for if they were so, the species would become extinct.
Natural selection will modify the structure of the young inrelation to the parent, and of the parent in relation the young. Insocial animals it will adapt the structure of each individual for thebenefit of the whole community, if the community profits by theselected change. What natural selection cannot do, is to modify thestructure of one species, without giving it any advantage, for thegood of another species, and though statements to this effect may befound in works of natural history, I cannot find one case which willbear investigation. A structure used only once in an animal's life,if of high importance to it, might be modified to any extent bynatural selection; for instance, the great jaws possessed by certaininsects, used exclusively for opening the cocoon,--or the hard tip tothe beak of unhatched birds, used for breaking the egg. It has beenasserted, that of the best short-beaked tumbler pigeons a greaternumber perish in the egg than are able to get out of it; so thatfanciers assist in the act of hatching. Now if nature had to make thebeak of a full-grown pigeon very short for the bird's own advantage,the process of modification would be very slow, and there would besimultaneously the most rigorous selection of all the young birdswithin the egg, which had the most powerful and hardest beaks, forall with weak beaks would inevitably perish; or, more delicate andmore easy broken shells might be selected, the thickness of the shellbeing known to vary like every other structure.
It may be well here to remark that with all beings there must bemuch fortuitous destruction, which can have little or no influence onthe course of natural selection. For instance a vast number of eggsor seeds are annually devoured, and these could be modified throughnatural selection only if they varied in some manner which protectedthem from their enemies. Yet many of these eggs or seeds wouldperhaps, if not destroyed, have yielded individuals better adapted totheir conditions of life than any of those which happened to survive.So again a vast number of mature animals and plants, whether or notthey be the best adapted to their conditions, must be annuallydestroyed by accidental causes, which would not be in the leastdegree mitigated by certain changes of structure or constitutionwhich would in other ways be beneficial to the species. But let thedestruction of the adults be ever so heavy, if the number which canexist in any district be not wholly kept down by such causes,--oragain let the destruction of eggs or seeds be so great that only ahundredth or a thousandth part are developed,--yet of those which dosurvive, the best adapted individuals, supposing that there is anyvariability in a favorable direction, will tend to propagate theirkind in larger numbers than the less well adapted. If the numbers bewholly kept down by the causes just indicated, as will often havebeen the case, natural selection will be powerless in certainbeneficial directions; but this is no valid objection to itsefficiency at other times and in other ways; for we are far fromhaving any reason to suppose that many species ever undergomodification and improvement at the same time in the same area.
Inasmuch as peculiarities often appear under domestication in onesex and become hereditarily attached to that sex, so no doubt it willbe under nature. Thus it is rendered possible for the two sexes to bemodified through natural selection in relation to different habits oflife, as is sometimes the case; or for one sex to be modified inrelation to the other sex, as commonly occurs. This leads me to say afew words on what I have called Sexual Selection. This form ofselection depends, not on a struggle for existence in relation toother organic beings or to external conditions, but on a strugglebetween the individuals of one sex, generally the males, for thepossession of the other sex. The result is not death to theunsuccessful competitor, but few or no offspring. Sexual selectionis, therefore, less rigorous than natural selection. Generally, themost vigorous males, those which are best fitted for their places innature, will leave most progeny. But in many cases, victory dependsnot so much on general vigor, as on having special weapons, confinedto the male sex. A hornless stag or spurless cock would have a poorchance of leaving numerous offspring. Sexual selection, by alwaysallowing the victor to breed might surely give indomitable courage,length to the spur, and strength to the wing to strike with thespurred leg, in nearly the same manner as does the brutal cockfighterby the careful selection of his best cocks. How low in the scale ofnature the law of battle descends, I know not; male alligators havebeen described as fighting, bellowing, and whirling round, likeIndians in a war dance, for the possession of the females; malesalmons have been observed fighting all day long; male stag-beetlessometimes bear wounds from the huge mandibles of other males; themales of certain hymenopterous insects have been frequently seen bythat inimitable observer, M. Fabre, fighting for a particular femalewho sits by, an apparently unconcerned beholder of the struggle andthen retires with the conqueror. The war is, perhaps, severestbetween the males of polygamous animals, and these seem oftenestprovided with special weapons. The males of carnivorous animals arealready well armed; though to them and to others, special means ofdefense may be given through means of sexual selection, as the maneto the lion, and the hooked jaw to the male salmon; for the shieldmay be as important for victory as the sword or spear.
Amongst birds, the contest is often of a more peaceful character.All those who have attended to the subject, believe that there is theseverest rivalry between the males of many species to attract, bysinging, the females. The rock thrush of Guiana, birds of paradise,and some others, congregate; and successive males display with themost elaborate care, and show off in the best manner, their gorgeousplumage; they likewise perform strange antics before the females,which, standing by as spectators, at last choose the most attractivepartner. Those who have closely attended to birds in confinement wellknow that they often take individual preferences and dislikes: thusSir R. Heron has described how a pied peacock was eminentlyattractive to all his hen birds. I cannot here enter on the necessarydetails; but if man can in a short time give beauty and an elegantcarriage to his bantams, according to his standard of beauty, I cansee no good reason to doubt that female birds, by selecting, duringthousands of generations, the most melodious or beautiful males,according to their standard of beauty, might produce a marked effect.Some wellknown laws, with respect to the plumage of male and femalebirds, in comparison with the plumage of the young, can partly beexplained through the action of sexual selection on variationsoccurring at different ages, and transmitted to the males alone or toboth sexes at corresponding ages; but I have not space here to enteron this subject.
Thus it is, as I believe, that when the males and females of anyanimal have the same general habits of life, but differ in structure,color, or ornament, such differences have been mainly caused bysexual selection: that is, by individual males having had, insuccessive generations, some slight advantage over other males, intheir weapons, means of defense, or charms, which they havetransmitted to their male offspring alone. Yet, I would not wish toattribute all sexual differences to this agency: for we see in ourdomestic animals peculiarities arising and becoming attached to themale sex, which apparently have not been augmented through selectionby man. The tuft of hair on the breast of the wild turkey cock cannotbe of any use, and it is doubtful whether it can be ornamental in theeyes of the female bird;--indeed, had the tuft appeared underdomestication, it would have been called a monstrosity.
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