Entire genomes with their accompanying protein synthetic systems are t
ransferred throughout the biosphere primarily as bacteria and protists
which become symbionts as they irreversibly integrate into pre-existi
ng organisms to form more complex individuals. Individualization is st
abilized by simultaneous transmission of once-separate heterologous ge
netic systems. The origin of new species is hypothesized to correlate
with the acquisition, integration and subsequent inheritance of such a
cquired microbial genomes. These processes were recognized by Mereschk
ovsky (''Symbiogenesis'' in Russian, 1909) and by Wallin (''Symbiontic
ism'', see p. 181, this issue).