For most naturalists today, Charles Darwin’s “On the Origin of Species by Means of Natural Selection,” published in 1859, is a cornerstone work. It is also one that, while its propositions caused considerable stir in Darwin’s own time as well as in the decades following his death, now only seems to trouble those outside of natural history circles. His 1871 work “The Descent of Man, and Selection in Relation to Sex” is another matter indeed.