Cyclic evolution of phytoplankton forced by changes in tropical seasonality.

Although the role of Earth's orbital variations in driving global climate cycles has long been recognized, their effect on evolution is hitherto unknown. The fossil remains of coccolithophores, a key calcifying phytoplankton group, enable a detailed assessment of the effect of cyclic orbital-scale climate changes on evolution because of their abundance in marine sediments and the preservation of their morphological adaptation to the changing environment. Evolutionary genetic analyses have linked broad changes in Pleistocene fossil coccolith morphology to species radiation events.