Lateral genomics (Reprinted from Trends in Biochemical Science, vol 12, Dec., 1999)

More than 20 complete prokaryotic genome sequences are now publicly availab le, each by itself an unparalleled resource for understanding organismal bi ology. Collectively, these data are even more powerful: they could force a dramatic reworking of the framework in which we understand biological evolu tion. It is possible that a single universal phylogenetic tree is not the b est way to depict relationships between all living and extinct species. Ins tead a web- or net-like pattern, reflecting the importance of horizontal or Lateral gene transfer between Lineages of organisms, might provide a more appropriate visual metaphor. Here, I ask whether this way of thinking is re ally justified, and explore its implications.