ABSTRACT
Comparative studies of protein structure suggested the molecular-clock hypothesis to E. Zuckerkandl and L. Pauling in 1962: that proteins evolve at statistically constant rates and that a simple algorithm might, therefore, relate the amount of protein difference between two species and the time since divergence of those species from their last common ancestor. It presents a sharp contrast to anatomical evolution, in which rates of evolution are usually related to environmental exigencies and may fluctuate widely. The concept of a molecular clock was used by V. Sarich and A. Wilson in 1967 to modify earlier assumptions about the remoteness of common ancestry between humans and the African apes.
