The idea of evolution did not begin with Darwin...he just (just!) explained how it happened and backed it up with evidence.
"The only novelty in my work is the attempt to explain how species become modified," Darwin later wrote. He did not mean to belittle his achievement. The how, backed up by an abundance of evidence, was crucial: nature throws up endless biological variations, and they either flourish or fade away in the face of disease, hunger, predation and other factors. Darwin's term for it was "natural selection"; Wallace called it the "struggle for existence." But we often act today as if Darwin invented the idea of evolution itself, including the theory that human beings developed from an ape ancestor. And Wallace we forget altogether.
In fact, scientists had been talking about our primate origins at least since 1699, after the London physician Edward Tyson dissected a chimpanzee and documented a disturbing likeness to human anatomy. And the idea of evolution had been around for generations.