The idea that humans could be related to ape-like ancestors and the rest of creation was considered subversive. If man was just an animal, then he doesn't live forever, he has no soul. And if men don't have a soul, then there's no afterlife. No heaven, no fiery deterrent of hell to keep people in line in this life. And if there's no fiery deterrent to keep people in line, "well then we might as well have hell on Earth!" the critics said.