My dear Sir,—­When I thanked you for your little pamphlet[9] the other day, I had not read it.  I have since done so with great interest.  Its leading idea is, I think, undoubtedly true, and of much importance towards an interpretation of the facts.  Though I think that there are some purely physical modifications that may be shown to result from the direct influence of civilisation, yet I think it is quite clear, as you point out, that the small amounts of physical differences that have arisen between the various human races are due to the way in which mental modifications have served in place of physical ones.

I hope you will pursue the inquiry.  It is one in which I have a direct interest, since I hope, hereafter, to make use of its results.—­Sincerely yours,

HERBERT SPENCER

* * * * *

SIR C. LYELL TO A.R.  WALLACE

53 Harley Street.  May 22, [1864].

My dear Sir,—­I have been reading with great interest your paper on the Origin of the Races of Man, in which I think the question between the two opposite parties is put with such admirable clearness and fairness that that alone is no small assistance towards clearing the way to a true theory.  The manner in which you have given Darwin the whole credit of the theory of Natural Selection is very handsome, but if anyone else had done it without allusion to your papers it would have been wrong....  With many thanks for your most admirable paper, believe me, my dear Sir, ever very truly yours,

Cha.  Lyell.

* * * * *

SIR C. LYELL TO A.R.  WALLACE

73 Harley Street.  March 19, 1867.

Dear Mr. Wallace,—­I am citing your two papers in my second volume of the new edition of the “Principles”—­that on the Physical Geography of the Malay Archipelago, 1863, and the other on Varieties of Man in ditto, 1864.  I am somewhat confounded with the marked line which you draw between the two provinces on each side of the Straits of Lombok.  It seems to me that Darwin and Hooker have scarcely given sufficient weight to the objection which it affords to some of their arguments.  First, in regard to continental extension, if these straits could form such a barrier, it would seem as if nothing short of a land communication could do much towards fusing together two distinct faunas and floras.  But here comes the question—­are there any land-quadrupeds in Bali or in Lombok?  I think you told me little was known of the plants, but perhaps you know something of the insects.  It is impossible that birds of long flight crossing over should not have conveyed the seeds and eggs of some plants, insects, mollusca, etc.  Then the currents would not be idle, and during such an eruption as that of Tomboro in Sumbawa all sorts of disturbances, aerial, aquatic and terrestrial, would have scattered animals and plants.