Molecular clocks and explosive radiations.
Molecular data are ideal for exploring evolutionary history because of its universality, stochasticity, and abundance. These features provide a means of exploring the evolutionary history of all organisms (including those that do not tend to leave fossils), potentially within a statistical framework that allows testing of evolutionary hypotheses. However, the discrepancy between molecular and paleontological dates for three key "explosive" radiations inferred from the fossil record--the Cambrian explosion of animal phyla and the post-KT radiations of modern orders of mammals and birds--have led to a reexamination of the assumptions on which molecular dates are based. Could variation in the rate of molecular evolution, perhaps associated with "explosive" radiations, cause overestimation of diversification dates? Here I examine four hypothetical causes of fast molecular rates in explosive radiations--body size, morphological rate, speciation rate, and ecological diversification--using available empirical evidence on patterns of variation in rate of molecular evolution.
Bromham
Lindell
L
Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK. L.D.Bromham@sussex.ac.uk
D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000502:physiology; D001824:Body Constitution; D019143:Evolution, Molecular; D005580:Fossils; D008322:Mammals / Q000502:physiology; D011323:Primates / Q000502:physiology; D011827:Radiation; D013045:Species Specificity; D013995:Time