Early Unpublished Darwin letter on the races of man
DARWIN, CHARLES. (English) Autograph Letter Signed [to Henry Denny]
Down, Kent, June 1, 
Two pages, one leaf. Old folds, two small punch holes at foot, purple pencil notation to top. Very good condition
VERY EARLY DARWIN INVESTIGATION OF THE RACES OF MAN. In 1834 Darwin heard that head lice vary among the races of man while on the voyage of the Beagle. In his Beagle zoological diary he wrote, “Mr Martial, a surgeon of an English Whaler assures me that the Lice of the Sandwich Islanders … if they strayed to the bodies of the English in 3 or 4 days died … If these facts were verified their interest would be great.— Man springing from one stock according his varieties having different species of parasites.— It leads one into many reflections.” Intrigued by the implications of this observation, Darwin began collecting specimens for further research.
In 1844 Darwin began corresponding with entomologist Henry Denny, the recipient of this letter, who was investigating exotic species of lice. In this remarkable letter Darwin writes:
“You may remember a statement, which I communicated to you about the Sandwich Islands lice not living on Europeans. The other day, I met a passage in a foolish book: ‘White’s Regular Gradation of Men,’ which I thought you might like to know of. At p. 79 he states that he has heard that the lice on the Negroes born in N. America and who have never been in a hot country, are blacker and larger than the lice on Europeans and further that the European lice seem to refuse to live on the Negroes. It is singular if both this and my independent statement, are without any foundation.”
Darwin generously shared his findings and lice specimens with Denny, sending him a leaf of Beagle manuscript notes. Years later, Denny again took up the question of lice and variation in mankind in correspondence with Darwin, returning the Beagle notes borrowed long ago. Darwin continued to show keen interest in the subject and referred to it in The Descent of Man (Vol. I, p. 219) when discussing the question of whether the races of man might represent different species.
The “foolish” book Darwin names in this letter is Charles White’s Regular Gradation of Man (1799), which corroborated Darwin’s story about the lice and races of man. However, Darwin here rejects the book as “foolish” for its attempt to prove that human races were separate species with distinct origins.
This fascinating unpublished letter, written in the wake of the Beagle voyage, represents the earliest evidence we have seen in the market concerning Darwin’s investigations into the races of man.