biology. Having traced the origin and significance of sex from its lowest manifestations to a point where it becomes purely intellectual, the biologist may fairly leave the subject in the hands of the psychologist.

When this chapter was printed, several years ago, I was told by several teachers of great experience in the education of both boys and girls that their observations showed no constant difference in the intellectual powers of the two sexes. They therefore disputed the accuracy of my view.

Taking the chapter alone, this is, no doubt, a fair criticism; but I believe that any reader who will examine the subject in connection with the other chapters of this book, as a part of the whole, and not as an isolated essay, will perceive that we should not expect the intellectual differences between men and women to be so well marked and conspicuous during childhood as they become after maturity is reached.

The subject is such a fruitful source of controversy that I can hardly hope to escape adverse criticism, and I can only say that I have not approached it in a spirit of controversy, and shall gladly welcome any discussion which leads to the discovery of truth.

The acceptance of my view should put an end to all discussion as to the relative intellectual rank of men and women; for if the two sexes contribute in different ways to the welfare of the race, and fill equally important but dissimilar places, there can be no question as to relative superiority or inferiority.

CHAPTER XI.

THE THEORY OF HEREDITY CONSIDERED AS SUPPLEMENTARY TO THE THEORY OF NATURAL SELECTION.

Darwin believes that variations are purely fortuitous-Natural selection cannot give rise to permanent race modifications unless many individuals vary in nearly the same way, at about the same time-The chances against this are very great if variations are fortuitous-Argument from North British Review-Darwin acknowledges the great weight of this objection -It is removed by the theory of heredity-The co-ordinated modification of complicated organs-The time demanded by Darwin practically infinite-Murphy's argument from the complexity of the eye-Herbert Spencer's illustration—Our theory removes this difficulty-Mr. Conn's objection-Saltatory evolution-Evidence that it occurs-Spike horn buckAncon and Mauchamp sheep-Black-shouldered peacock— The theory of heredity accounts for saltatory evolutionParallel variation-Evidence of its occurrence-Evolution of the medusæ-General and special Homologies.

According to Darwin's view, variations, though determined by definite causes (for the most part unknown), are, so far as their usefulness to the organism goes, fortuitous, and he makes use of the following illustration to explain his conception:

"I have spoken of selection as the paramount power, yet its action absolutely depends upon what we in our ignorance call spontaneous or accidental variability. Let an architect be compelled to build an edifice with uncut stones, fallen from a precipice. The shape of each fragment may be called accidental, yet the shape of each has been determined by the force of gravity, the

nature of the rock, and the slope of the precipiceevents and circumstances all of which depend on natural laws; but there is no relation between these laws and the purpose for which each fragment is used by the builder. In the same manner the variations of each creature are determined by fixed and immutable laws; but these bear no relation to the living structure which is slowly built up by the power of selection, whether this be natural or artificial selection."

"If our architect succeeded in rearing a noble edifice, using the rough wedge-shaped fragments for the arches, the longer stones for the lintels, and so forth, we should admire his skill even in a higher degree than if he had used stones shaped for the purpose. So it is with selection, whether applied by man or by nature; for though variability is indisputably necessary, yet when we look at some highly complex and excellently adapted organism, variability sinks to a quite subordinate position in comparison with selection, in the same manner as the shape of each fragment used by our supposed architect is unimportant in comparison with his skill" (Variation, xxi. p. 301).

It is quite possible that Darwin may be right in attributing the modification and adaptation of organisms almost entirely to the influence of natural selection, and, at the same time, wrong in his belief that the variations are fortuitous. Several critics have pointed out that if it is true that variations have no relation whatever to the needs of the organism, there are grave difficulties in the way of natural selection; but the theory rests upon too firm a basis to be easily set aside, and these objections have hardly received the attention which they fairly deserve, for those authors who have pointed them out have, at the same time, attacked the general theory in a hostile spirit without proposing any

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