Page:The New International Encyclopædia 1st ed. v. 14.djvu/326

* NATURAL SELECTION. 382 NATURAL SELECTION. nntural sikctioii, and, litiny tiaiisiuitted by heredity to subsequent generations, will be added to the previously existing type." At the present day an increasing number of evolutionists do not regard natural selection as an active cause, but rather as the result of the action of a number of other agents, comprising the J.amarckian factors of change of environment, use, disuse, isolation, and so on. Undoubtedly, as the result of compe- tition, animals have been driven to migrate, to adopt new habits, and thus to undergo modifica- tion. Many agree with Uerbcrt iSpeucer as to the inadequacy of natural selection to account for the origination of new forms. From probably a third to nearly one-half of the species of plants and animals now existing are climatic, local forms, resulting from the direct action of changes in the conditions of life, such as climate, soil, food, and the like. The great number of species of parasitic animals are the result of the young adopting a fixed or a more or less .sta- tionary mode of life. Xatural selecticm is in- operative in the case of blind or eyeless cave and deep-sea animals. OujECTioxs TO Xatural Selectio.v. The ob- jections now being urged to the special doctrine of natural selection are that, ( 1 ) to use Herbert Spencer's words, it is 'inadequate'; (2) the fa- vorable variation may be destroyed by the swamping etlects of crossing; (3) natural selec- tion is not analogous to artilicial selection; na- ture is continually eliminating monstrosities, sports, variations, instead of preserving fliem; they are constantly being bred out in wild plants and animals, or those living under natural con- ditions of existence. The otter or ancon sheep, which umler the breeder's care and watchfulness became a peculiar variety, when permitted to mingle or cross with normal sheep became ex- tinct. Xatural .selection accounts for the preser- vation rather than the origination of new or in- ci])ient forms and structures. Vur the causes of variation, it is maintained, we must look to the action of the primary factors of organic evo- lution, namely to the effects of changes in light, temperature, heat, moisture, drj-ness, altitude, food, and so on. (4) It is not necessarily the fittest or most u.seful structures or individuals which survive. Carnivorous animals in seizing or swallowing im- mense numbers of eggs, embryos, and adult ani- mals do not select this or that indiviilual. but, on the contrary, old and young, the fit and the unfit, weak and^ strong, are engulfed in the maw of the whale as it swims fhrouali a shoal of minute Crustacea; or hundreds of small fishes are indis- criminately, without reference to their fitness, swallowed by sharks. So with aphiiies existing in hundreds of thousands on some tree, the birds, like old Time of the New Kngland Primer, in- di>criniinatcly pick o(T "all. both great and small." 'Jhis niatter of the survival of the fittest and the extinction of the unfit has perhaps been somewhat exaggerated, although it is granted that competition acts unceasingly in the biologi- cal environment. (.'■>) Darwinians acknowledge, as does Wallace in his nnnrifiifini, that no one ever saw a spe- cies oriL'inated bv natural selection; Weismaim has frankly afiirmed that '"it is rcallv very dinicull to imagine this process of natural selec- tion in its details; and to this day it is impos- eible to demonstrate it in any one point" (Con- temporary /iciicir, 1893, p. 322). Yet a number of temperature species, races, or breeds have been cxi)erinu'ntally produced by changes of tempera- ture. The cases of seasonal dimorphism existing in nature have been exactly paralleled by varia- tions in moths and butterllies subjected in the pupa slate to cold, or extreme heat; and dry- season and wet-season as well as summer and winter forms have been produced aitificially. be- sides other variations supposed to be extinct phylogenetic species. ((i) The view peculiar to Darwinism is that some individual variation was nursed and pre- served, while all the others less favorable died. Some naturalists claim that the better-founded view is that of Lamarck, that the changes of en- vironment simultaneously atTected great numbers of individuals in a given region, which became modified by changes of climate, and so on, en masse. This certainly appears to be the case in local, insular, or geogra])hical races, varieties, or species. What affects one affects all the indi- viduals in a given area isolated b- mountain barriers or other natural boundaries. Where nat- ural selection appears to act is in the case of protective mimicry. The initial causes are changes in the amount of light, of shade, heat, and other physical agents, yet natural selection appears to be oi)erative in bringing out the won- derful cases of mimicry so well known. (See MniiCKY.) While therefore the Xeo-T.amarckian readily acknowledges that natural .selection re- sults after new variations have arisen, there are those who, like the Kev. Mr. Henslow, maintain that in the case of seedlings natural selection is not concerned in bringing about the survival of the fittest, adding: ".l seedling survives among others soleli) because it is vigorous." He claims that as soon as a large number of seedlings ap- pear above groun<l, "natural selection at once steps in, so to say. with the result that all those with too weak a constitution to maintain them- selves fail to withstand the struggle for existence and to come to maturity, the stnmger plants only proving themselves the best fitted to survive. This process of selection, however, is quite in- dependent of any modifications in morphological structure, by which 'varieties' or subspecies are alone recognized." The fact that the majority of olTspring always perish in infancy he calls 'const it ul ional select ii m.' (7) Darwin ex|)ressly regarded most varia- tions as indetinite. chance, fortuitous, spontane- ous or promiscuous, 'survival of the fittest.' as liomanes expressed it, "bec<miing the winnowing fan, whose fimclion it is to eliminate all the less fit in each generation, in order to preserve the good grain. <nit of which to constitute the next generation, .^nd as this process is supposed to be continuous through successive generations, its ai'tion is supposed to be cumulative, till from the eye of a worm there is gradually develr}pcd the eye of an eaj;le." dther variations Darwin called 'definite.' In the chapter of his f'arinlion of .Animals and Plants Vnder Domesfiration. en- titlerl ••Direct and IVfinite Action of the External Conditions of Life." he says: "By the term (h'finite action, as tised in this chapter. T mean an action of such a nature that, when many in- dividuals of (he same variety are exposed during several ;;enerations to any ])artieular clinnge in their conditions of life, all or nearly all the in- dividuals are modified in the same manner."