ditions have some effect.’ I am quite ready to believe it when I see any one experimental case, or such an accumulation of argument #70 as I think can be adduced cov. It is an open question, I grant. Quite so, but you must bring your case to the point! You say, ‘ you cannot see that the species has produced the same variations in all the stations,’ etc. How should I ever see whether or no, except you compare progress of individuals of some brood in each? Again, you ask, ‘If variety A succeed in locality I., why should it not succeed at locality II. if it had ever been existent there?’ My answer is that no locality II. is identical with a locality I., and that natural selection will act on an imperceptible difference—it searches where no faculty of man can follow. Consider again, and ponder well the number of individuals of a brood that die for every one that lives; multiply these by the countless generations that it must have taken to have established that amount of change which we call specific, and then reflect that if besides all this we are to have dzrect effects of local conditions, which (remember) vary in kind and amount from year to year, you will have such an accumulation of change-effecting forces that there could be no such things as recognisable species and genera. Not only every place would have different varieties, but every year in each place, and in the case of temperate plants grown in a hothouse, wet country plants in a dry house, etc., etc., we should have startling changes ever occurring. ‘‘ Another objection to my line of argument is the changes wrought in bees by either feeding or heat (as the case may be), but this again is change of individual, and is not propagated, for the queen after all lays again males and drones, not queens. Darwin, I believe, holds with you as to the influence of external conditions on the variation of the brood. I have, however, failed to be convinced by him of it, and I do not think he recognises the facts of variation to the extent I do. Indeed, I think his book would have been more convincing had he treated variation somehow so as to have impressed the unaccustomed reader and thinker to regard it as the origin of species, and natural selection as the fixer of these. As it is, in most minds the two are confused, or natural selection is supposed to szake the varieties as well as to fix them. At other times, no one more stanchly denounces the effects of external circumstances in producing variation than Darwin does. Darwin also believes in some reversion to type, which is opposed to my view of variation. You may have a single character persist or reappear, but the sum of differences goes on increasing as you depart from the parent. Variation I hold to be centrifugal; if it were not so how could it go on making species, which are only the preserved forms of each brood which circumstances favoured? Remove the circumstances which £722 the others, as man does when he cultivates (kills those that nature would have spared), and you have what you call a variety, and fancy you made it, whereas you only prevented nature killing it. ‘¢ After all, Darwin’s axiom that man has never failed in getting varieties of any species he has fairly tried, is in favour of my view that the abstract principle called variation is enough, wth time, to beget any amount of change, and by means of natural selection to retain only such as may present any amount of difference. Finally, I have come to look upon the law of variation as I do on gravitation: local circumstances may mask its

effects, but upon z¢seZf they cannot act. The power that drives the stone to the ground is “#e same whether the stone permeates water or air or vacuum, whether you let it fall straight, or throw it forwards, or even upwards. So, a certain amount of centrifugal force of variation is distributed in certain proportions amongst the twelve peas in the pod, and except to arrest or retard the progress and amount of development of the individuals or their organs (I incline to think), local circumstances are powerless. Give more nitrogen to pea No.1, and you will have more and greener leaves; but its seeds again will not be as green if they too are not supplied with nitrogen. ‘‘T think my long letter will disgust you with asking any more questions, but I should be greatly obliged if you have time and would write me again on the subject. I know no one but yourself who is really thinking out Darwin’s views to any purpose in zoology. I am sure that with you, as with me, the more you think the less occasion you will see for anything but time and natural selection to effect change; and that this view is the simplest and clearest in the present state of science, is one advantage at any rate. Indeed, I think that it is, in the present state of the inquiry, the legitimate position to take up; it is time enough to bother our heads with the second secondary cause when there is some evidence of it, or some demand for it-at present I do not see one or other, and so feel inclined to renounce any other for the present. It is not so very long since I thought differently, and that variation was the first effect of circumstances on the individual. ‘‘T hope when you next come to town you will let me know, and that we may have some more boxes of butterflies at the Linnean, and get the many curious facts you name well impressed in the languid circulation of the entomologists. ‘« Ever most truly yours, “« Jos. D. HOOKER.”

Hl. W. Bates to Dr. 3. D. Hooker.

‘KING STREET, LEICESTER, March sth, 1862.

““MY DEAR SIR,

‘*T have not been quick to answer your last, not only because most of my writing time is just now taken up by my book of Travels, but because your letter was so full of new observations on the most difficult of all natural history subjects that it required long consideration. I hope you will attend to mine only when you have nothing else to do.

“The view you propound of the origin of species—by the natural selection of varieties, which always occur as a universal condition of reproduction, in organic species, independent of the direct action of external conditions, is" simple and grand. As you say, it recommends itself by its simplicity and clearness, and is amply sufficient to explain the origin of species. But what if the real state of things is not so simple as this? Are there not some phenomena in species which seem to show that local conditions, and use and disuse, have some direct effect on individuals, the effect being propagated to the offspring, and so complicating the question of the origin of species? Whilst I was travelling I used to attribute, like many others, the production of distinct local varieties, or races, to the direct action of the local conditions;

and when I found such coming in contact with their supposed parents without intermarrying or reverting, I supposed the cause was the gradual and slow change in their constitutions which had brought them to a point when they were incapable of going back.

‘But since I read Mr. Darwin’s book, I believe that natural selection has effected this change, operating both on structure and functions. But still the belief is strong that climatal and other causes have some slight effect. So slight, however, that of themselves they are unable to produce a race. Your letter shows me plainly that the effect must be yet slighter. I think the strongest case of the inability of local conditions acting directly to produce a race is that of the two races of man inhabiting the tropics of America and Africa. All facts go to show that the American race must have lived in Brazil many thousands of years, yet there is no approach to the negro. Yet the effect of exposure to the sun is to blacken the skin. For the nomad tribes of Amazon Indians are darker coloured than the agricultural, and the families of chiefs in Africa are lighter coloured than the rest of the tribe, etc., etc. ‘‘My studies of those curious mimetic butterflies gave me convincing proof that local physical conditions do not directly produce a race, for there I see a species exhibiting nearly a dozen varieties in one limited spot, and four or five of them, as it were, in the act of being selected and segregated; the motive for such a process being also quite plain to detect. ‘‘ A little more in corroboration of your views. On testing them by my case of the mimetic butterflies, I find they hold good. There is really no proof that the variable species originally sported in a different manner in one locality from what it did in another. Inappreciable variations or very small variations similar in all the localities, and natural selection drawing them out, as it were, would be sufficient to explain the whole case. ‘‘ The elimination of intermediate varieties formerly, and of the occasional offspring of cross-marriages between the divergent selected forms in one limited district, must have been, and must be now, very stringent and perpetually acting; probably, however, there is a moral barrier preventing frequent intermarriages, although there is not a geographical one; in other words, the selected and now somewhat widely diverged varieties refuse to intermarry. ‘“ Now for a few cases which seem to show that the modifications induced by direct action are propagated. ‘© A few sheep have been imported into the Amazons region from Portugal. The wool nearly all falls off, and the young at about two or three months old (when alone I have noticed them) have a thin coat of straight wool, more like hair than wool. I know this is an imperfect observation. I did not notice that #azy, or a tendency to hair, was produced in the lifetime of a sheep, and I did not see lambs when first born, to prove that they have this modified coating at their birth. The sheep are only kept by twos and threes, as pets, and have not been in the country for many generations, so that I do not think selection, artificial or natural, has operated. ‘‘ Dogs become lop-eared in consequence of the relaxation of muscle from disuse; puppies are born lop-eared. ‘‘Mr. Darwin’s case of tame ducks having less developed wing-bones, from disuse, seems to come under this head, but unconscious or natural

selection may have come into play here. For when ducks were first tamed, strong flyers would less readily submit than weak ones, and so forth. ‘‘The general blindness of animals in deep caverns seems to be partly owing to direct effect of external condition on individuals, leading to disuse of the organs, and collapse of muscles and nerves, reproduced in offspring.

‘But this belongs to the same class of facts as those cases which show a general similarity, in some features, amongst widely different species of animals and plants living under the same conditions; such as fleshiness of plants on sea coast, brassy tints of beetles ditto, and some similar cases which I observed in South America, such as transparency of wings in Heliconia butterflies living near either tropic; very suffused colouring on East of Andes under the equator, etc. ““Some part of this general similarity is owing to natural selection adapting one species to another in external dress; but I think there are some cases where this explanation is inapplicable. ‘‘TIt is curious in the case of negro, etc., that the colour produced by direct action should be also the one selected as most suitable by nature. ‘‘Of course the whole argument depends on this question which you put, and which I thank you for having placed so vividly before me. ‘‘Are the distinct peculiarities induced in the lifetime of an organism transmitted to its offspring? We may allow several generations for the operation. I cannot think of any facts giving affirmation to this question except the poor ones given in this letter. ‘* Even if they prove it they would not show that a race and new species could be produced by direct action; natural selection is always acting and would act, of course, on the offspring of these species. ‘©T am much, obliged to you for recalling me to order in the matter of forgetting the thousands of generations, and millions of individuals extinguished without offspring in the case of insect species. I really was not giving the full force to that. ‘«‘T have not fully answered your letter, but will finish another time. ‘‘ Would you oblige me by getting from Mr. Bentham the names of the following trees? I think Mr. Spruce may have sent them under these same native names:—Tapiriba, a stone-fruit tree (very acid, common); Acutiriba, round yellow mealy fruit; Jabuti-putré-anonacez (?), delicious wild fruit; Massarandtba, cow tree; Umari, or Mari and Uixi, two similar fruits, Upper Amazons; Pama, wild stone fruit, flavour ofcherry; Sucu-tba, of Santarem.

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