The whole theory of the author of the as to organic nature has been exposed to objection in consequence of its connection with views of the general system of the universe altogether foreign to the present subject; and because of an evident inclination to the belief in a transition from inorganic to organic existence by chendeo-electric operation. The argument is also weakened by the too ready acceptance of unsubstan tiated facts, as of the transmutation of one kind of grain into another; and by resting too much on what may he reckoned the mere mistakes of naturalists, as to the forms of the lower kinds of plants and animals, of which genera and even tribes have been constituted, that have afterward been found to be mere modifications or larval stages of creatures very different in their most apparent characters. Much hostility has been also excited by the extension of the theory of development to the human species. connecting man with pre-existing and inferior forms of animal existence. All this has been avoided by Darwin, by whom, however, the chief arguments of the Votige5 are used with great scientific caution.
Darwin's views are distinguished by the introduction of what be designates the priu ciple of natural selection. He maintains the variability of species, and adduces much evidence to show that variation is continually taking place in consequence of the exter nal conditions to which plants and animals are subjected. He rests much on the diffi culty of distinguishing between varieties and species, and on the changes which are known to result from cultivation and domestication. He dwells on the selection which man makes in order to produce new breeds or varieties, and supposes a similar "selec tion" to take place in nature, iu the struggle for life, which all 'plants and animals must undergo. This struggle for life is, in fact, the foundation of his theory. He shows that every kind of plant or animal must maintain it, and in order to its continued existence, must be successful iu maintaining it not only against those other creatures which seen to make it their food, but still more in a competition with those which seek the same nutriment with itself. In this struggle the stronger, or those which possess anything peculiarly favorable in their organization, must overcome the weaker, and these must therefore cease to exist. Thus a slight variation, such as often takes place, may be per petuated; and the possessors of any advantage in the means of procuring food, or in the powers of offense or defense, may entirely displace their less favored congeners. The modifications thus taking place Darwin regards as accounting for the changes in organ ized beings from one geologic period to another, and for the great differences in the plants and animals of different parts of the world. In support of his views, he argues from the tendency to variation seen in cultivated plants and domestic animals, and the perpetuation of the forms so produced in breeds in races; and from the fact that the variations in cultivated and domestic species are in some cases greater than those which are regarded as affording grounds of specific, and sometimes even of generic or greater distinctions in a state of nature. " Can it be thought iinprobable," he says, " seeing
that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life, should sometimes occur in the course of thonsands of generations? If such do occur, can we doubt—remember ing that many more individuals are born than can possibly survive—that individuals having any advantage, however slight, over others, would have the best chance of sur viving and of procreating their kind? On the other hand, we may feel sure that any variation iu the least degree injurious would be rigidly destroyed. This preservation of fai'orable variations and the rejection of unfavorable variations, I call natural selection. Variations neither useful nor injurious would not be affected by natural selection, and would be left a fluctuating element, as perhaps we see in the species called polymorphic." He further supports these views by pointing out the favorable opportunity for the oper ation of natural selection afforded in a country undergoing great physical changes, as of climate; and particularly in an island, or a country surrounded by barriers sufficient to prevent the ready immigration of species. "In such cases," he says, " every slight modification, which in the course of ages chanced to arise, and which in any way favored the individuals of any of the species by better adapting them to their altered conditions, would tend to be preserved; and natural selection would thus have free scope for the work of improvement." Mr. Darwin supposes new variations to be continually taking place, but thb greater number of these speedily to become extinct; while others, becoming perpetuated, and perhaps causing the extinction of the original forms, again give rise to other forms, until some of them have so widely diverged that all traces of their common origin arc lost. He does not, however, commit himself to the opinion that all forms of organic life, or even all plants, or all animals, have a common origin. He completely rejects Lamarck's notion that new and simple forms are continually being produced by spontaneous gen eration. "I need hardly say," he remarks, " that science in her present state does not countenance the belief that living creature are now ever produced from inorganic mat ter," and he accounts for the existence of low forms of life by saying that "natural selection includes no necessary and universal law of advancement or development; it only takes advantage of such variations as arise and are beneficial to each creature under its complex relations of life." So that even the lowest forms might " be left by nattiral selection unimproved, or but little improved." as geology tells us of infusoria and rhizo pods which have remained for an enormous period in nearly their present state.