Timing primate evolution: Lessons from the discordance between molecular and paleontological estimates

The molecular clock has become an increasingly important tool in evolutionary biology and biological anthropology. Nevertheless, a source of contention with respect to this method is the frequent discordance with fossil-based estimates of divergence times. The primate radiation is a case in point: Numerous studies have dated the major primate nodes (reviewed in Steiper and Young,1, 2) and there are many instances where molecular and fossil-based estimates of divergence times differ (Fig. 1). Some investigators have recently focused on phenomena such as stratigraphic dating, the stochastic nature of molecular time estimates, and other sources as potential biases in molecular clock estimates.3, 4 In this paper we do not focus on accuracy or statistical error; rather, we argue that discordance is a predictable phenomenon that provides valuable information about the tempo and mode of primate molecular and morphological evolution. Using this perspective, we reexamine the principal theoretical and methodological factors that lead to discordance between molecular and fossil estimates of the origins of taxa and discuss how a better understanding of these factors can help to improve our understanding of primate evolution.