Responds to CD’s queries on polygamy in birds and orang.
Discusses sexual selection and secondary characters; colours and sexual preference.
Expresses his admiration for Pangenesis; it is superior to Herbert Spencer’s theory.
ARW differs somewhat with CD’s chapter on causes of variability [ch. 22 in Variation]. Thinks several of CD’s arguments are unsound.
Briefly discusses how natural selection might aid in producing sterility between allied species.