thing to take its place. This has not prevented Darwin himself from perceiving the weight of the criticism, but it has certainly caused the objections to be ignored or overlooked by other less candid writers.

Natural selection cannot act unless many individual vary together.

One of the most serious objections to Darwin's theory is based upon the fact that while natural selection requires. that great numbers of individuals shall vary in essentially the same way at nearly the same time, the chance against this, if variations are fortuitous in Darwin's sense, is great beyond all computation.

In 1864 the writer of what Darwin terms "an able and valuable article" in the North British Review, called attention to the fact that, according to the law of chances, slight variations, however useful, will tend to be obliterated, instead of perpetuated, by natural selection, unless they simultaneously appear in a great number of individuals. Unless we can show that the causes of variability act in such a way as to affect many individuals at the same time, and cause the same part to vary in all of them, we must regard this as a very serious objection to the theory of natural selection, and Darwin himself acknowledges (Origin of Species, p. 72) that the justice of this objection cannot be disputed. He admits in the later editions of the Origin of Species, p. 71, that until reading the able and valuable article in the North British Review, he did not appreciate how rarely single variations, whether slight or strongly marked, would be perpetuated.

The reviewer points out that it is difficult to see how a species can be changed by the survival of the descendants of a few individuals which possess some favorable

variation, even when the variation is of the very greatest advantage to its possessor; and that this difficulty is very much greater when as must usually be the case, the advantage gained is very slight.

He says: "The advantage, whatever it may be, is utterly out-balanced by numerical inferiority. A million creatures are born; ten thousand survive to produce offspring. One of the million has twice as good a chance as any other of surviving; but the chances are fifty to one against the gifted individual being one of the hundred survivors. No doubt the chances are twice as great against any one other individual, but this does not prevent their being enormously in favor of some average individual. However slight the advantage may be, if it is shared by half the individuals produced, it will probably be present in at least fifty-one of the survivors, and in a larger proportion of their offspring; but the chances are against the preservation of any one 'sport' (i.e., sudden marked variation) in a numerous tribe. The vague use of an imperfectly understood doctrine of chance has led Darwinian supporters, first, to confuse the two cases. above distinguished; and, secondly, to imagine that a very slight balance in favor of some individual sport must tend to its perpetuation. All that can be said is that in the above example the favored sport would be preserved once in fifty times. Let us consider what will be its influence on the main stock when preserved. It will breed and have a progeny of say 100; now this progeny will, on the whole, be intermediate between the average individual and the sport. The odds in favor of one of this generation of the new breed will be, say, one and a half to one as compared with the average individual; the odds in their favor will, therefore, be less than that of their parents; but, owing to their greater number, the chances

are that about one and a half of them would survive. Unless these breed together, a most improbable event, their progeny would again approach the average individual; there would be 150 of them, and their superiority would be, say, in the ratio of one and a quarter to one; the probability would now be that nearly two of them would survive and have 200 children with an eighth superiority. Rather more than two of these would survive, but the superiority would again dwindle, until after a few generations it would no longer be observed, and would count for no more in the struggle for life than any of the hundred trifling advantages which occur in the ordinary organs. An illustration will bring this conception home. Suppose a white man to have been wrecked on an island inhabited by negroes, and to have established himself in friendly relations with a powerful tribe, whose customs he has learned. Suppose him to possess the physical strength, energy and ability of a dominant white race, and let the food and climate of the island suit his constitution; grant him every advantage which we can conceive a white to possess over the native; concede that in the struggle for existence his chance of a long life will be much superior to that of the native chiefs; yet from all these admissions there does not follow the conclusion that, after a limited or unlimited number of generations, the inhabitants of the island will be white. Our shipwrecked. hero would probably become king; he would kill a great many blacks in the struggle for existence; he would have a great many wives and children. In the first generation there will be some dozens of intelligent young mulattoes, much superior in average intelligence to the negroes. We might expect the throne for some generations to be occupied by a more or less yellow king; but

can any one believe that the whole island will gradually acquire a white or even a yellow population?

"Darwin says that in the struggle for life a grain may turn the balance in favor of a given structure, which will then be preserved. But one of the weights in the scale of nature is due to the number of a given tribe. Let there be 7000 A's and 7000 E's, representing two varieties of a given animal, and let all the B's, in virtue of a slight difference of structure, have the better chance of life by a part. We must allow that there is a slight probability that the descendants of B will supplant the descendants of A; but let there be only 7001 A's against 7000 B's at first, and the chances are once more equal, while if there be 7002 A's to start, the odds would be laid on the A's. True, they stand a greater chance of being killed, but then they can better afford to be killed. The grain will only turn the scales when these are very nicely balanced, and an advantage in numbers counts for weight, even as an advantage in structure. As the numbers of the favored variety diminish, so must its relative advantages increase, if the chance of its existence is to surpass the chance of its extinction, until hardly any conceivable advantage would enable the descendants of a single pair to exterminate the descendants of many thousands, if they and their descendants are supposed to breed freely with the inferior variety, and so gradually lose their ascendancy."

Darwin acknowledges that the justice of these remarks cannot be disputed, and there is no escape from the conclusion that if variations do not appear simultaneously in a great number of individuals, the theory of natural selection fails to explain the origin of species. But the theory itself is so firmly estabished by other

facts, that the logical conclusion seems to be, not that natural selection is at fault, but that Darwin's opinion, that variations are fortuitous, is an error.

According to our view of the cause of variation, it is plain that a change in the environment, affecting many individuals of a species in the same way, will cause, in succeeding generations, variation of the same cells in all or nearly all of them. It is also clear that since a change. in one cell of an organism will disturb the harmonious adjustment of all adjacent or related cells, any variation which makes its appearance will become more marked instead of being obliterated, in the offspring of successive generations.

I think it is clear, without further discussion, that our theory of heredity entirely does away with this very serious difficulty, and furnishes a firmer basis for the theory of natural selection. It is also clear that this cannot be said of the Pangenesis hypothesis, or of any other hypothesis which has been proposed.

The Formation of Complicated Organs by the Natural Selection of Fortuitous Variations demands Unlimited Time.

There is another objection of nearly the same character, which must have struck every thinker with more or less force. How are the various organs of a highly complicated organism, or the various structures which enter into the formation of a complicated organ, kept in harmonious adjustment to each other by the selection of variations which are, in Darwin's sense, fortuitous? It is plain that, as soon as one part has varied in any direction, the harmonious adjustment of related parts will be disturbed, and that they too must vary correspondingly in order to restore the proper tone to the whole, and it is equally clear that even a slight change in a compli