Table 1.
The evolutionary transitions
| General stages, previous | General stages, subsequent |
|---|---|
| Replicating molecules | Populations of molecules in compartments |
| Independent replicators | Chromosomes |
| RNA as gene and enzyme | DNA + protein (genetic code) |
| Prokaryotes | Eukaryotes |
| Asexual clones | Sexual populations |
| Protists | Animals, plants, fungi (cell differentiation) |
| Solitary individuals | Colonies (nonreproductive castes) |
| Primate societies | Human societies (language) |
| Animal development | |
| 1. Multicellularity (cell layers, cell adhesion, spatially controlled patterns of differentiation) | |
| 2. Defined axes of symmetry (species-specific body shape, structural repetition, origin of neurons, inner and outer epithelial germ layers) | |
| 3. Conversion of a two-germ layer body plan into a three-germ layer body plan | |
| 4. Inversion of dorsoventral patterning systems | |
| 5. Origin of vertebrates, new strategies for deploying cells in development | |
| 6. Invention of migratory lateral mesodermal cells, origin of two sets of patterned paired appendages, and anteroposterior diversification of the cranial visceral arches | |