Thoughts in a Haystack

... evolutionary speculation constitutes a kind of metascience, which has the same fascination for some biologists that metaphysical speculation possessed for some medieval scholastics. It can be considered a relatively harmless habit, like eating peanuts, unless it assumes the form of an obsession; then it becomes a vice. - cell biologist Roger Stanier, in Organization and Control in Prokaryotic Cells: Twentieth Symposium of the Society for General Microbiology, Cambridge University Press, 1970.

It might have happened thus; but we shall surely never know certainty. Evolutionary speculation constitutes a kind of metascience, which has the same fascination for some biologists that metaphysical speculation possessed for some medieval scholastics. It can be considered a relatively harmless habit, like eating peanuts, unless it assumes the form of an obsession; then it becomes a vice. The most appropriate response to such speculations (if they are plausible and logically consistent) is an Italian rejoinder, of which the amiable cynicism cannot be adequately translated:

Se non e vero, e ben trovato.

Leaving aside for the moment the special question of the origin of chloroplasts and mitochondria, do we really have good grounds for believing that eukaryotic and prokaryotic cells are branches from a common stem of cellular evolution? In other words, might they not have arisen independently from pre-cellular forms of living matter? Mazia (1965) raised this question in a specific context: namely, that of chromosome structure. I think completely separate origins are improbable, even though most of the evidences of homology are to be found only at the deepest level ( i.e. the molecular one). They include the possession of the same genetic code; common mechanisms for the replication, transcription and translation of the genetic message; and largely common mechanisms for the biosynthesis of major classes of cell-constituents. The nexus of shared properties is sufficiently complex to suggest an origin from a common ancestor which could already be described as 'cellular'.

I should certainly not object to setting up a separate kingdom for the prokaryotic microorganisms if such an operation would serve as a handy device for emphasizing the fundamental differences between these types and organisms that possess a eukaryotic cellular organization. All the introductory statement meant to imply is that both van Niel and I now consider detailed system building at the microbial level to be an essentially meaningless operation, since there is so very little information that can be drawn on for the purposes of phylogenetic reconstruction. For this reason I prefer to use common names rather than Latin ones for every bacterial group above the level of genus.

- R. Y. Stanier to R. G. E. Murray, 21 May 1962, National Archives of Canada, MG 31, accession J35, vol. 6.

In this essay, I shall develop the argument that we have at our disposal a variety of methods for ascertaining (within certain limits) relationships among the bacteria; and that where relationship can be firmly established, it affords a more satisfactory basis for the construction of taxa than does mere resemblance. As the philosopher G. C. Lichtenberg remarked 200 years ago, there is significant difference between still believing something and believing it again. It would be obtuse still to believe in the desirability of basing bacterial classification on evolutionary considerations. However, there may be solid grounds for believing it again, in the new intellectual and experimental climate which has been produced by the molecular biological revolution.

- Stanier, R.Y. 1971. Toward an evolutionary taxonomy of the bacteria, p. 595-604. In In A. Perez-Miravete and D. Peláez (ed.), Recent advances in microbiology. Int. Congr. Microbiol. Medico.