To be fair to Darwin, he proposed another mechanism as well, sexual selection. Also, his two mechanisms were revolutionary at the time, and many decades later

To be fair to Darwin, he proposed another mechanism as well, sexual selection. Also, his two mechanisms were revolutionary at the time, and many decades later remain the most important factors in our understanding of evolution. Yes, the general idea of evolution as "species change, rise and fall" is not a new one in Darwin's time. But today when we say "evolution" we basically mean "evolution by natural selection" which is Darwin's novelty.