Earlier studies of ribosomal RNA (rRNA) sequences have concluded that the oldest living organisms were hyperthermophilic. In the May 16
It is widely accepted that rRNA sequences present a useful tool for constructing phylogenetic trees. But Brochier and Philippe claim that these data should be approached with caution, and they have used a refined strategy that uses only conserved, slowly evolving positions. Their deduced phylogeny shows late emergence of hyperthermophiles; they suggest that the earlier conclusions were biased by artifacts related to fast-evolving positions.
Brochier and Philippe found that Planctomycetales emerged at the base of the bacterial tree and suggest that "the origins of bacterial tree should be seriously reconsidered".