Three main classes of evidence for evolution:

1. Direct observation on the small scale. Small-scale observations work most powerfully against the idea of species fixity; they are almost equally good evidence for evolution and for transformism. They show, by uniformitarian extrapolation, that evolution at least could have produced the whole history of life.

2. Homologies. Most classical morphological homologies strongly suggest a common ancestor for classificatory groups. The more recently discovered molecular homologies, such as the universal genetic code, extend the argument to the whole of life - and favor evolution over both transformism and creationism

3. The fossil record. Strong arguments for large-scale evolution come from classification and the fossil record. The geological succession of the major groups suggest a common ancestor.