| Term | Definition |
| Darwin | English natural scientist who formulated a theory of evolution by natural selection (1809-1882) |
| Charles Lyell | explains that processes occurring now have changed Earths geological features over long periods of time, 1797-1875 - believed in uniformitarianism, that all geologic processes occur at the same rate that they always have been occurring at |
| Wallace | English naturalist who formulated a concept of evolution that resembled Charles Darwin's (1823-1913) |
| Lamarck | French naturalist who proposed that evolution resulted from the inheritance of acquired characteristics (1744-1829) |
| Malthus | an English economist who argued that increases in population would outgrow increases in the means of subsistence (1766-1834) |