Neo-darwinian evolution implies punctuated equilibria

The two central elements of neo-darwinian evolution^1,2 are small random variations and natural selection. In Wright's view, these lead to random drift of mean population characters in a fixed, multiply peaked 'adaptive landscape', with long periods spent near fitness peaks^3,4. Using recent theoretical results⁵, we show here that transitions between peaks are rapid and unidirectional even though (indeed, because) random variations are small and transitions initially require movement against selection. Thus, punctuated equilibrium^6,7, the palaeontological pattern^8,9 of rapid transitions between morphological equlibria, is a natural manifestation of the standard wrightian evolutionary theory and requires no special developmental, genetic or ecological mechanisms ^10-13.