I recall that when I was a child in the 80's I saw a book in Waldenbooks, a book that made a brief splash before disappearing beneath the waves... it was book of scientific or pseudo scientific speculation about how humans might evolve in the future. I think it was a coffee-table book, although I was young enough that most books seemed pretty large to me at the time, and it had color illustrations showing scary freakish future humans. There was one image I recall as a two-page spread showing a barren landscape, with a large God Emperor of Dune type worm or slug... with a human-like face. Creeped me out.
Does anyone have a clue what book I'm talking about? Cursory Googling turns up nothing.
Edit: Man After Man by Dougal Dixon. Long out of print, fairly pricey on the old book market. Not to be confused with After Man, also by Dougal Dixon and more easily available.