My dear Darwin

Many thanks for yr clear explanation of Pallas’s views.¹ Carpenter tells me that the variations of period of gestation in cows rabbits & some other domesticated animals is said by experimenters of authority, Qy Gärtner? to vary as much as $\frac{1}{8}$ ^th. ² Nevertheless if it be true that dogs have the same period as the wolf, I sh^d infer that they all came from that wild species if we are to derive them from some one wild species of the canine genus rather than from another or from foxes or Jackalls or any other species differing in period of gestation. If some varieties of dog approach the fox, others the wolf this may have to do with “atavism”, as Decandolle calls it,³ or inheritance from their common ancestor ascending beyond any of the living wild species?

As soon as I get your book I shall attentively reread it & try to reconcile the admission with several propositions there laid down as to sterility of hybrids & laws of variation which as I read them seemed to me fundamentally opposed to the admission of our existing races of the dog coming from several wild or aboriginal canine species.

I understand you to say that selection under domestication rarely does in a shorter time what Nature might do in a longer.

I also thought, to borrow Hooker’s language, that variation was a centrifugal, & crossing or hybridism a centripetal force.⁴ This would all accord with the doctrine that after a wolf, fox & jackall existed descending from some remote prog-enitor, one of them, the wolf, might produce the Esquimaux dog, the bull dog, the Italian greyhound, the shepherd’s dog & so on, but if the three wild species above mentioned could produce any or all these races of dogs (or incipient species) by coalescing & interbreeding, I find it impossible to hope to trace any clue to the past transformations of species or their probable birthplaces

I cannot help thinking that by taking this concession, one which regards a variable species, about which we know most (little tho’ it be) an adversary may erect a battery against several of your principal rules, & in proportion as I am perverted I shall always feel inclined to withstand so serious a wavering. I marked your passage of northern species over tropical plains, & approved of it, as you may remember I once proposed to bring certain Madeira shells over Africa during the Glacial period.

C. L.