observe or think of, goes on also among the millions and scores of millions of individuals which are comprised in almost every species; and must get rid of the idea that chance determines which shall live and which die. For, although in many individual cases death may be due to chance rather than to any inferiority in those which die first, yet we cannot possibly believe that this can be the case on the large scale on which nature works. A plant, for instance, cannot be increased unless there are suitable vacant places its seeds can grow in, or stations where it can overcome other less vigorous and healthy plants. The seeds of all plants, by their varied modes of dispersal, may be said to be seeking out such places in which to grow; and we cannot doubt that, in the long run, those individuals whose seeds are the most numerous, have the greatest powers of dispersal, and the greatest vigour of growth, will leave more descendants than the individuals of the same species which are inferior in all these respects, although now and then some seed of an inferior individual may chance to be carried to a spot where it can grow and survive. The same rule will apply to every period of life and to every danger to which plants or animals are exposed. The best organised, or the most healthy, or the most active, or the best protected, or the most intelligent, will inevitably, in the long run, gain an advantage over those which are inferior in these qualities; that is, the fittest will survive, the fittest being, in each particular case, those which are superior in the special qualities on which safety depends. At one period of life, or to escape one kind of danger, concealment may be necessary; at another time, to escape another danger, swiftness; at another, intelligence or cunning; at another, the power to endure rain or cold or hunger; and those which possess all these faculties in the fullest perfection will generally survive. Having fully grasped these facts in all their fulness and in their endless and complex results, we have next to consider the phenomena of variation, discussed in the third and fourth chapters; and it is here that perhaps the greatest difficulty will be felt in appreciating the full importance of the evidence as set forth. It has been so generally the practice to speak of variation as something exceptional and comparatively rare-as an abnormal deviation from the uniformity and stability of the characters of a species-and so few even among naturalists have ever compared, accurately, considerable numbers of individuals, that the conception of variability as a general characteristic of all dominant and widespread species, large in its amount and affecting, not a few, but considerable masses of the individuals which make up the species, will be to many entirely new. Equally important is the fact that the variability extends to every organ and every structure, external and internal; while perhaps most important of all is the independent variability of these several parts, each one varying without any constant or even usual dependence on, or correlation with, other parts. No doubt there is some such correlation in the differences that exist between species and species-more developed wings usually accompanying smaller feet and vice versa—but this is, generally, a useful adaptation which has been brought about by natural selection, and does not apply to the individual variability which occurs within the species. It is because these facts of variation are so important and so little understood, that they have been discussed in what will seem to some readers wearisome and unnecessary detail. Many naturalists, however, will hold that even more evidence is required; and more, to almost any amount, could easily have been given. The character and variety of that already adduced will, however, I trust, convince most readers that the facts are as stated; while they have been drawn from a sufficiently wide area to indicate a general principle through out nature. If, now, we fully realise these facts of variation, along with those of rapid multiplication and the struggle for existence, most of the difficulties in the way of comprehending how species have originated through natural selection will disappear. For whenever, through changes of climate, or of altitude, or of the nature of the soil, or of the area of the country, any species are exposed to new dangers, and have to maintain themselves and provide for the safety of their offspring under new and more arduous conditions, then, in the variability of all parts, organs, and structures, no less than of habits and intelligence, we have the means of producing modifications which will certainly bring the species into harmony with its new conditions. And if we remember that all such physical changes are slow and gradual in their operation, we shall see that the amount of variation which we know occurs in every new generation will be quite sufficient to enable modification and adaptation to go on at the same rate. Mr. Darwin was rather inclined to exaggerate the necessary slowness of the action of natural selection; but with the knowledge we now possess of the great amount and range of individual variation, there seems no difficulty in an amount of change, quite equivalent to that which usually distinguishes allied species, sometimes taking place in less than a century, should any rapid change of conditions necessitate an equally rapid adaptation. This may often have occurred, either to immigrants into a new land, or to residents whose country has been cut off by subsidence from a larger and more varied area over which they had formerly roamed. When no change of conditions occurs, species may remain unchanged for very long periods, and thus produce that appearance of stability of species which is even now often adduced as an argument against evolution by natural selection, but which is really quite in harmony with it. On the principles, and by the light of the facts, now briefly summarised, we have been able, in the present chapter, to indicate how natural selection acts, how divergence of character is set up, how adaptation to conditions at various periods of life has been effected, how it is that low forms of life continue to exist, what kind of circumstances are most favourable to the formation of new species, and, lastly, to what extent the advance of organisation to higher types is produced by natural selection. We will now pass on to consider some of the more important objections and difficulties which have been advanced by eminent naturalists. CHAPTER VI DIFFICULTIES AND OBJECTIONS Difficulty as to smallness of variations-As to the right variations occurring when required-The beginnings of important organs-The mammary glands-The eyes of flatfish-Origin of the eye-Useless or non-adaptive characters-Recent extension of the region of utility in plants-The same in animals-Uses of tails-Of the horns of deerOf the scale-ornamentation of reptiles-Instability of non-adaptive characters-Delboeuf's law-No "specific" character proved to be useless-The swamping effects of intercrossing-Isolation as preventing intercrossing-Gulick on the effects of isolation-Cases in which isolation is ineffective. IN the present chapter I propose to discuss the more obvious and often repeated objections to Darwin's theory, and to show how far they affect its character as a true and sufficient explanation of the origin of species. The more recondite difficulties, affecting such fundamental questions as the causes and laws of variability, will be left for a future chapter, after we have become better acquainted with the applications of the theory to the more important adaptations and correlations of animal and plant life. One of the earliest and most often repeated objections was, that it was difficult "to imagine a reason why variations tending in an infinitesimal degree in any special direction should be preserved," or to believe that the complex adaptation of living organisms could have been produced "by infinitesimal beginnings." Now this term "infinitesimal," used by a wellknown early critic of the Origin of Species, was never made use of by Darwin himself, who spoke only of variations being "slight," and of the "small amount" of the variations that might be selected. Even in using these terms he undoubtedly afforded grounds for the objection above made, that such small and slight variations could be of no real use, and would not determine the survival of the individuals possessing them. We have seen, however, in our third chapter, that even Darwin's terms were hardly justified; and that the variability of many important species is of considerable amount, and may very often be properly described as large. As this is found to be the case both in animals and plants, and in all their chief groups and subdivisions, and also to apply to all the separate parts. and organs that have been compared, we must take it as proved that the average amount of variability presents no difficulty whatever in the way of the action of natural selection. It may be here mentioned that, up to the time of the preparation of the last edition of The Origin of Species, Darwin had not seen the work of Mr. J. A. Allen of Harvard University (then only just published), which gave us the first body of accurate comparisons and measurements demonstrating this large amount of variability. Since then evidence of this nature has been accumulating, and we are, therefore, now in a far better position to appreciate the facilities for natural selection, in this respect, than was Mr. Darwin himself. Another objection of a similar nature is, that the chances are immensely against the right variation or combination of variations occurring just when required; and further, that no variation can be perpetuated that is not accompanied by several concomitant variations of dependent parts-greater length of a wing in a bird, for example, would be of little use if unaccompanied by increased volume or contractility of the muscles which move it. This objection seemed a very strong one so long as it was supposed that variations occurred singly and at considerable intervals; but it ceases to have any weight now we know that they occur simultaneously in various parts of the organism, and also in a large proportion of the individuals which make up the species. A considerable number of individuals will, therefore, every year possess the required combination of characters; and it may also be considered probable that when the two characters are such that they always act together, there will be such a correlation between them that they will frequently vary together. But there is another consideration that seems to show that this coincident |