Evolution.

Society for Experimental Biology

Date:: 1953

Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Evolution. Source: Wellcome Collection.

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440 POSTSCRIPT ON SOME PHYSICAL AND CHEMICAL ASPECTS OF EVOLUTION By J. F. DANIELLI Zoology Department, King's College, London, W.C. 2 1. BIOCHEMISTRY AND EVOLUTION The production of a reasonably comprehensive theory of any of the more complex phenomena of nature has proved exceedingly difficult. Even with relatively simple phenomena success has been very limited: e.g. the physicists have no comprehensive theory of the solid state; the chemists have no comprehensive theory of chemical reactivity. This being so, it is not surprising that we have no comprehensive theory of so complex a phenomenon as evolution, nor that the contributions to the theory of evolution on the physical and chemical levels are very limited indeed. In the field of comparative biochemistry, considered here by Baldwin, atten¬ tion has been mainly devoted to low molecular weight compounds. Up to the present time these studies suggest that there are very close similarities in the metabolic and synthetic activities of all organisms. This suggests that either these aspects of chemical evolution were largely complete before the evolution of complex organisms began, or else that the processes found in existence to-day are so remarkably more efficient than any alternatives which have existed that convergence has been practically inevitable. There appear to be no grounds available at present by which one may distinguish between these two possibilities. One is left with the impression that the great majority of organisms are potentially capable of producing all the low molecular weight compounds, and will do so at stages in their evolution at which individual compounds are valuable. Thus the array of compounds found in an organism repre¬ sents a selection of useful compounds from the enormous spectrum of compounds which are possible products of its synthetic abilities. Numerous substances have appeared, quite independently, in diverse and unrelated groups of organisms. It is unlikely that the occurrence of a low molecular weight substance A in an organism can be regarded as evidence of evolution of a new synthetic mechanism; more probably its occurrence simply indicates that at a particular stage of evolution A was useful and was within the chemical repertoire of the organism. Thus the occurrence of