possible origination, so early as the Miocene, was due to my "want of appreciation of the immensity of time at our disposal, without going back beyond the Newer Pliocene."

To this objection I replied (May 24) as follows: "With regard to the probable antiquity of man, I will say a few words. First, you will see, I argue for the possibility rather than for the necessity of man having existed in Miocene times, and I still maintain this possibility, and even probability, for the following reasons. The question of time cannot be judged of positively, but only comparatively. We cannot say à priori that ten millions or a thousand millions of years would be required for any given modification in man. We must judge only by analogy, and by a comparison with the rate of change of other highly organized animals. Now, several existing genera lived in the Miocene age, and also anthropoid apes allied to Hylobates. But man is classed, even by Huxley, as a distinct family. The origin of that family—that is, its common origin with other families of the Primates must therefore date back from an earlier period than the Miocene. Now, the greater part of the family difference is manifested in the head and cranium. A being almost exactly like man in the rest of the skeleton, but with a cranium as little developed as that of a chimpanzee, would certainly not form a distinct family, only a distinct genus of Primates. My argument, therefore, is, that this great cranial difference has been slowly developing, while the rest of the skeleton has remained nearly stationary; and while the Miocene Dryopithecus has been modified into the existing gorilla, speechless and ape-brained man (but yet man) has been developed into great-brained, speech-forming man.

"The majority of Pliocene mammals, on the other hand, are, I believe, of existing genera, and as my whole argument is to show how man has undergone a more than generic change in brain and cranium, while the rest of his body has hardly changed specifically, I cannot consistently admit that all this change has been brought about in a less period than has sufficed to change most other mammals generically, except by assuming that in his case the change has been more

rapid, which may, indeed, have been so, but which we have no evidence yet to prove. I conceive, therefore, that the immensity of time, measured in years, does not affect the argument. My paper was written too hastily and too briefly to explain the subject fully and clearly, but I hope these few remarks may give my ideas on the point you have especially referred to."

In 1867, when a new edition of the "Principles of Geology" was in progress, I had much correspondence and many talks with Sir Charles, chiefly on questions relating to distribution and dispersal, in which he, like myself, was greatly interested. He was by nature so exceedingly cautious and conservative, and always gave such great weight to difficulties that occurred to himself or that were put forth by others, that it was not easy to satisfy him on any novel view upon which two opinions existed or were possible. We used often to discuss these various points, but in any case that seemed to him important he usually preferred to write to me, stating his objections, sometimes at great length, and asking me to give my views. In reply to some such inquiries I sent him my paper on the birds of the Lombok to Timor groups, and wrote to him at the same time more fully explaining its bearing, as afterwards given in my "Malay Archipelago." I also wrote him on the curious facts as to the distribution of pigs in the whole archipelago, as illustrated by facts he had himself given showing the remarkable power of swimming possessed by these animals. Another fact he wanted explained was the presence of a few non-marsupial mammals in Australia, and why there were not more of them, and why none were found in the caves. On these points I wrote to him as follows:

"MY DEAR SIR CHARLES,

"I think the fact that the only placental land mammals in Australia (truly indigenous) are the smallest of all mammals is a very suggestive fact as to how they got there. Mice would not only be carried by canoes, but they

would also be transported occasionally by floating trees carried down by floods. I think myself, however, that it is most likely they were carried by the earliest canoes of prehistoric man, and that they afford an example of rapid change of specific form, owing to the ancestral species having been subjected to a great change of conditions, both as regards climate and food, and having had an immense area of new country to roam over and multiply in, in every part of which they would be subjected to different conditions. These considerations, I think, fully meet the facts, and there ought to be no large rodents found in the caves of Australia, and no other rodents of very distinct type from those now living. When any such are found it will be time enough to consider how to account for them. It is, as you say, a most important fact that, in three such distinct localities as New Zealand, Australia, and Mauritius, no bones of extinct carnivora or other mammalia should be found along with the wingless birds and marsupials, while abundance of remains of these groups are found. We may, I think, fairly claim this as a proof that such placental mammals did not exist in those countries, and the fact that the only exception in the existing Australia fauna are mice indicates very clearly that they are a recent introduction. When all the known facts are in our favour, I do not think we need trouble ourselves to answer objections and overcome difficulties that have not yet arisen, and probably never will arise."

Some months later (November, 1867) he wrote me about the dispersal and the colours of the races of man. On the first point I replied at some length, principally to show why we should not expect the primary regions which show the great features of the distribution of birds, reptiles, and mammalia should also apply to man. On the question of colour I replied as follows: "Why the colour of man is sometimes constant over large areas while in other cases it varies, we cannot certainly tell; but we may well suppose it to be due to its being more or less correlated with constitutional characters favourable to life. By far the most common colour

of man is a warm brown, not very different from that of the American Indian. White and black are alike deviations from this, and are probably correlated with mental or physical peculiarities which have been favourable to the increase and maintenance of the particular race. I should infer, therefore, that the brown or red was the original colour of man, and that it maintains itself throughout all climates in America because accidental deviations from it have not been accompanied by any useful constitutional peculiarities. It is Bates's opinion that the Indians are recent immigrants into the tropical plains of South America, and are not yet fully acclimatized."

In the following year, when I was living at Hurstpierpoint, in a letter I wrote to Sir Charles, thanking him for the trouble he had taken in regard to the Bethnal Green Museum, I added some remarks on Darwin's new theory of "Pangenesis," which I will quote, because the disproof of it, which I thought would not be given, was not long in coming, and, with the more satisfactory theory of Weismann, led me entirely to change my opinion. I wrote (February 20, 1868): "I am reading Darwin's book ('Animals and Plants under Domestication'), and have read the 'Pangenesis' chapter first, for I could not wait. The hypothesis is sublime in its simplicity and the wonderful manner in which it explains the most mysterious of the phenomena of life. To me it is satisfying in the extreme. I feel I can never give it up, unless it be positively disproved, which is impossible, or replaced by one which better explains the facts, which is highly improbable. Darwin has here decidedly gone ahead of Spencer in generalization. I consider it the most wonderful thing he has given us, but it will not be generally appreciated."

This was written when I was fresh from the spell of this most ingenious hypothesis. Galton's experiments on blood transfusion with rabbits first staggered me, as it seemed to me to be the very disproof I had thought impossible. And later on, when Weismann adduced his views on the continuity of the germ-plasm, and the consequent non-heredity of

acquired characters; and further, when he showed that the supposed transmission of such characters, which Darwin had accepted and which the hypothesis of pangenesis was constructed to account for, was not really proved by any evidence whatever;-I was compelled to discard Darwin's view in favour of that of Weismann, which is now almost everywhere accepted as being the most probable, as well as being the most in accordance with all the facts and phenomena of heredity.

Towards the end of the year Sir Charles sent me a number of interesting papers to read, and among them was a criticism of Darwin by G. H. Lewes. When writing to thank him for them I replied to this criticism as follows:

"I have just been looking through Lewes. I think that in his great argument about the luminous and electric animals he completely fails to see their true bearing. He admits the fact that the organs producing light or electricity differ in position and form whenever the animals that bear them differ in general structure, while in their essential minute structure the (corresponding) organs closely resemble each other, however widely the animals may differ. But this is a necessary consequence of such organs being modifications of muscular tissue, which is almost identical in structure throughout the animal kingdom. If electrical and luminous organs were always identical in form and position as well as in structure, it would be a powerful argument in his favour; but as it is, I do not see that it proves anything but that the required special variation of an (almost) identical tissue occurs very rarely, and has still more rarely occurred at a time and under conditions which rendered its accumulation useful to the animal, in which case alone it would be selected and specialized so as to form a perfect electric or luminous organ.

Again, to suppose that because one single organ of a simple kind may be produced independently of common descent, therefore a combination of hundreds of organs, many of them consisting of hundreds of parts, should all be brought by the action of similar causes to an identity of form, position, and function (in different animals), appears to me absolutely