See also:

The Origin of Life

Publications

External Links:

Early Evolution of Life (Massey University)

Were bacteria the first forms of life on earth? (Daniel Jeffares and Anthony Poole)

Looking for LUCA (Patrick Forterre)
 

The RNA World

It is widely believed that the current DNA/protein basis for life was preceeded by a stage in which RNA provided both the genome and the catalysts. This is suggested by the ability of RNA to act as both a replicating information store like DNA, and as a catalyst (a ribozyme) like protein enzymes, as well as by the central role that RNA plays in crucial, and presumably primitive, features of the cell such as protein synthesis. This stage in the development of life is known as the "RNA World".

Scientists at Massey University in New Zealand have carried out a detailed study of the roles of RNA in modern cells, and identified which of these they consider to be relics from the RNA World (Jeffares, Poole and Penny, J. Mol. Evol. 46, 18, 1998). They have used this information to construct a model for a primitive Ribo-organism they call Riborgis eigensis, which would have been the last RNA based organism before the evolution of protein synthesis. In a companion paper (Poole, Jeffares and Penny, J. Mol. Evol. 46, 1, 1998) they have also considered the evolutionary path from the RNA world to the emergence of eukaryotes and prokaryotes.

While it is generally considered that prokaryotes (bacteria and archaea) are more primitive than eukaryotes, the Massey University group reach a different conclusion. They suggest that some features of their primitive organism are more eukaryote like - for example it would have had multiple linear chromosomes rather than the single circular chromosome of prokaryotes. They argue that prokaryotes are a more streamlined architecture that developed in response to selection pressures, perhaps for survival at high temperatures.

A similar conclusion on the origin of prokaryotes has been reached by French scientist Patrick Forterre. In this model the root of the tree of life lies in the Eucarya branch, and the presence of hyperthermophiles in many deep branches of the archaea and bacteria is a subsequent adaptation rather than a property of the last common ancestor.