The early evolution of cellular life.

Recent progress in data collection and analysis has changed the study of origin of life from an area dominated by speculation into a field abundant with testable hypotheses. This review discusses advances in the following areas: the fossil recordsd; the 'retrodiction' of biochemical pathways; and contradictions between different molecular phylogenies. The latter indicates a limited number of horizontal gene transfers during the early evolution. However, these cases of horizontal gene transfer are so infrequent that they can be detected as exceptions in an otherwise coherent picture. Cases of horizontal gene transfer can be recognized within the background of the majority consensus of molecular markers. The fusion of separate lineages to form new species is revealed by the simultaneous horizontal transfer of several independent genes.