Dear Sir,

Whilst thinking over Natural Selection, of the truth of which I am fully convinced, one or two ideas occurred to me which may possibly be of service to you in future editions of your works. It has often been urged that on the view of evolution the differentiation of the sexes presents a difficulty. This you have satisfactorily answered in the case of phanerogamia but I do not remember having read any explanation for animals. In your work on Orchids you arrive at the conclusion that some great unknown good is derived from the crossing of distinct individuals & it is a well known fact that as an animal advances in organization the different function of the body are carried out by organs specially constructed (using this expression metaphorically) for the purpose.¹ Some great & unknown good therefore is derived from this “division of labour” for in the long run the most highly organized species are victorious in the “struggle for existence”. The division of the sexes I would thus refer to the same cause—viz; that some great & unknown good is derived from the “division of labour”:—a species in which fertilization & development were carried out in distinct individuals having advantages over species in which these functions were performed by the same individual.

Then again about the long neck of the giraffe. St. George Mivart argues (Genesis of species) that if the lengthened neck had been produced by periodical famines (as explained in your “Origin”) we ought to find other species of the same order inhabiting the same district with elongated necks also. But his argument is I imagine unsound for on your view, all the species of a genus having descended from a common progenitor & inherited from that progenitor a similar constitution & therefore liability to vary in the same manner when exposed to the same conditions, it is not surprising that no other species of the order has a long neck for the giraffe is the only species of its genus: ordinal relationship having the common progenitor too remote to affect to any extent the constitution of allied genera.² Indeed the mere fact of the giraffe being the only species of its genus shows that extinction has been largely going on.

At p. 387 Vol. I of your last work (“Descent”) you have stated that both sexes of Hipparchiæ are alike but this is not the case—for in most species the female is more brightly coloured than the male in opposition the usual order of things.³

This however may perhaps be explained in a letter which I published in the same number of “Nature” as that in which you published your reply on Pangenesis to Mr. Galton—(about 6 or 7 weeks ago.)⁴ I hope you will pardon the liberty which as a stranger I have again taken, but my great devotion to Natural Science is my only excuse.

Yours obediently, | Raphael Meldola. F.C.S

C. Darwin Esq, MA, F.R.S.