Many thanks for your note. I am very glad indeed to read remarks made by a
man who possesses such varied and odd knowledge as you do, and who is so
acute a reasoner. I have no doubt that you will detect blunders of many
kinds in my book. (411/1. "The Descent of Man.") Your MS. on the
proportion of the sexes at birth seems to me extremely curious, and I hope
that some day you will publish it. It certainly appears that the males are
decreasing in the London districts, and a most strange fact it is. Mr.
Graham, however, I observe in a note enclosed, does not seem inclined to
admit your conclusion. I have never much considered the subject of the
causes of the proportion. When I reflected on queen bees producing only
males when not impregnated, whilst some other parthenogenetic insects
produced, as far as known, only females, the subject seemed to me
hopelessly obscure. It is, however, pretty clear that you have taken the
one path for its solution. I wished only to ascertain how far with various
animals the males exceeded the females, and I have given all the facts
which I could collect. As far as I know, no other data have been
published. The equality of the sexes with race-horses is surprising. My
remarks on mankind are quite superficial, and given merely as some sort of
standard for comparison with the lower animals. M. Thury is the writer who
makes the sex depend on the period of impregnation. His pamphlet was sent
me from Geneva. (411/2. "Memoire sur la loi de Production des Sexes," 2nd
edition, 1863 (a pamphlet published by Cherbuliez, Geneva).) I can lend it
you if you like. I subsequently read an account of experiments which
convinced me that M. Thury was in error; but I cannot remember what they
were, only the impression that I might safely banish this view from my
mind. Your remarks on the less ratio of males in illegitimate births
strikes me as the most doubtful point in your MS.--requiring two
assumptions, viz. that the fathers in such cases are relatively too young,
and that the result is the same as when the father is relatively too old.