 The very identification of DNA as the material of heredity was carried out in bacterial and viral experimental systems (Avery et al. 1943; Hershey &amp; Chase 1952). Subsequently, the expansion of molecular biology into genome sequencing and metagenomics (the sequencing and analysis of whole community genomes) began and flourished in microorganisms. This broader molecular scope enabled not only methodological and technological advances (see  SEP entry on genomics and postgenomics),  but also major evolutionary and ecological insights into the evolutionary history and community dynamics of large swathes of the biosphere (Davis 2003; Handelsman 2004). Most new empirical insights into major evolutionary transitions (as discussed in  Subsection 2.2.3)  are based on these genomic and metagenomic microbial investigations.