Ernst Haeckel (1834–1919) was a physician who became a fervent evolutionist after reading Charles Darwin’s On the Origin of Species, although he differed with Darwin over natural selection as the primary mode of evolution. Haeckel is best known for his attempts to tie the stages of development to the stages of evolution (“ontogeny recapitulates phylogeny”); he thought that each stage of the developmental process was a depiction of an evolutionary ancestor. Haeckel is also credited with coining the terms “phylum,” “phylogeny,” and “ecology.”