When Charles Darwin wrote The Descent of Man[i], the title was a play on words. In the context of the book, Darwin meant the word in the sense of “derivation from an ancestor”; “the fact or process of originating from an ancestral stock”; and/or “the shaping or development in nature and character by transmission from a source”.[ii] Descent, of course, can have a quite different meaning.
The word, descent, can also mean “the act or process of descending from a higher to a lower level, rank, or state”; “an inclination downward”; and/or “a downward step (as in station or value”), as in decline.
Darwin probably meant the word in this sense, also, in that philosophers and scientists and thinkers of all types before him had mostly viewed man standing apart from the rest of the natural world, standing above it (just a little lower than the angels). Darwin’s theory revealed man descending not from heaven, but descending (originating from ancestral stock) from lower life forms and ascending (evolving) from those lower life forms to the complexity the human species is today. This is the play on words.
In thinking about these things many generations after Charles Darwin coined the book title, in the context of all that has developed since his time, the subtlety and nuance of the play on words strikes me, but not in the way Darwin likely intended.