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2003 Annual Science Report

Pennsylvania State University Reporting  |  JUL 2002 – JUN 2003

A Timescale for the Evolution of Life on Earth - Nei

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

The main goal of this research is to develop statistical methods for estimating the times of origin of major groups of organisms from molecular data as well as those of major groups of gene families and infer early evolutionary events on Earth. The most relevant work from my laboratory bearing on these questions appeared earlier this year (Glazko and Nei, 2003). In that study, we compared several methods of time estimation. We examined the effects of several factors on the estimates of divergence times and reached the following conclusions: (1) It is advisable to concatenate many gene sequences and use a multigene gamma distance for estimating divergence times rather than using the individual gene approach. (2) When sequence data from many nuclear genes are available, protein sequences appear to give more robust estimates than deoxyribonucleic acid (DNA) sequences. (3) Nuclear proteins are generally more suitable than mitochondrial proteins for time estimation. (4) It is important first to construct a phylogenetic tree for a group of species using some outgroups and then estimate the branch lengths. (5) It appears to be better to use a few reliable calibration points rather than many unreliable ones.

    Masatoshi Nei Masatoshi Nei
    Project Investigator
    Galina Glazko

    Objective 1.2
    Indirect and direct astronomical observations of extrasolar habitable planets

    Objective 2.1
    Mars exploration

    Objective 3.4
    Origins of cellularity and protobiological systems

    Objective 4.1
    Earth's early biosphere

    Objective 4.2
    Foundations of complex life

    Objective 4.3
    Effects of extraterrestrial events upon the biosphere

    Objective 5.2
    Co-evolution of microbial communities

    Objective 5.3
    Biochemical adaptation to extreme environments

    Objective 7.1
    Biosignatures to be sought in Solar System materials

    Objective 7.2
    Biosignatures to be sought in nearby planetary systems