2006 Annual Science Report
Pennsylvania State University Reporting | JUL 2005 – JUN 2006
Genomic Record of the Earth's Early Biosphere (Hedges)
Our research involves molecular evolutionary genetics in an effort to better understand the relationship between planetary history and the evolution of life. During the past year (July 2005-June 2006) we made progress in the area of databases and empirical studies. We completed and released a database (www.timetree.net) of published divergence times among organisms (Hedges et al., 2006). It has a hierarchical structure based on the tree of life, which maximizes the utility of the data (>1100 estimates). We are expanding taxonomic coverage from tetrapods to the rest of life. In terms of empirical studies, we finished several ranging from deep divergences among animals in the Precambrian to the human-chimpanzee split. We discovered that urochordates (e.g., tunicates), not cephalachordates (e.g., amphioxus), are the closest relatives of vertebrates (Blair and Hedges, 2006); previous analyses suggesting otherwise had been plagued by sequence biases. We also unraveled the complex 300-million year history of squamate reptiles with nine nuclear genes, showing that phylogenies used during the last century were essentially upside-down, thus requiring a new classification for the group (Vidal and Hedges, 2005) and discovering an ancient clade of venomous reptiles (Fry et al., 2006). In another study focusing on Mesozoic events we found that monotreme mammals diverged from the marsupial-placental clade in the Triassic (van Rheede et al., 2006), in contrast to other sequence analyses that placed monotremes with marsupials. Our analysis of 167 genes in humans and chimpanzees resolved a relatively young 5-7 my split (Kumar et al, 2005), bearing on the evolution of intelligence and other human traits, in contrast to older estimates in other studies. We also completed several review papers, including one in press entitled “Molecular timescale of evolution in the Proterozoic” that will appear shortly in the book Neoproterozoic Geobiology and Paleobiology edited by Xiao and Kaufman (Springer, 2006).