Sir

Nigel Goldenfeld and Carl Woese, in their Connections Essay “Biology's next revolution” (Nature 445, 369; 2007), seek a change in concepts of 'organism, species and evolution' because of the prevalence of lateral gene transfer among bacteria. However, it has been clear for half a century that biological species are epiphenomena of sex, and exist only in sexual eukaryotes — but not in bacteria, which transfer genes laterally without sexual cell fusion. The essay exemplifies a common linguistic confusion caused by those who wish to equate microbes and prokaryotes (see Nature 445, 21; 2007).

This state of affairs acutely highlights the continued need for the classical 'concept of a bacterium' (prokaryote) put forward by R. Y. Stanier and C. B. van Niel (Arch. Mikrobiol. 42, 17–35; 1962). The inapplicability of biological species claimed for 'microbes' generally is emphatically not true for sexual protists (eukaryotic microbes). There are even more positive characters shared by all prokaryotes (for example, chromosomes attached to surface membranes) than noted by Martin and Koonin. The only circumstance in which we could reasonably abandon the term 'prokaryote' would be if the biological community as a whole were to accept the traditional use of 'bacteria' instead to embrace both archaebacteria and eubacteria.

The real need is not for a 'revolution' in language and change in the classical concept of an organism, but for molecular evolutionists to make a more serious attempt to understand it. Organisms are not mere assemblages of genes, whether inherited vertically or laterally, but cells (or integrated assemblies of cells) in which there is a mutualistic cooperation of genomes, membranes, skeletons and catalysts that together make a physically and functionally coherent unit capable of reproduction and evolution.