My dear Sir,

I have just turned out another domestic animal which I had laid aside for you—a Guinea Pig.¹ It is of the Chinese breed, and may perhaps be interesting to you for comparison with the European bred animals. I heard it asserted the other day at Cambridge that the domestic Guinea-pig would not interbreed with the Rock Cavy, it’s supposed parent-stock, and that consequently a new species had been formed by artificial selection. Have you heard of this asserted fact?² The person that gave it forth at Cambridge had it I believe on good authority. I should like much to hear your opinion on this subject.

I remain, | Dear Sir, | Your’s very truly,

Robert Swinhoe

Charles Darwin, Esq^re.