BIOCHEMICAL EVOLUTION 345 



In many cases the biochemical systems characteristic of such and such a 

 cellular differentiation appear to be biochemical inventions the past 

 history of which we are so far unable to reconstruct. Such systems are to 

 be found among the many different biochemical modifications in Verte- 

 brates, for example, the complex enzyme systems for the degradation of 

 haemoglobin present in histiocytes, the conversion of cholesterol to bile 

 in the cells of the hepatic parenchyma, etc. The fact that we do not know 

 the systems preceding them in phylogeny does not invalidate the fact that 

 these biochemical inventions have evolved. 



Scanty as it is at the moment, our knowledge of the biochemical diversity 

 of organisms has indicated that more detailed studies could tell us much 

 about the methods according to which the extension of the biosphere has 

 been accomplished along the lines of biochemical evolution, the bio- 

 chemical diversity being, as we shall see in Part VI, as essential as the 

 biochemical unity, for the maintenance of the metabolism of the whole 

 biosphere in extension. 



REFERENCES 



Anfinsen, C. B. (1959) The Molecular Basis of Evolution, John Wiley, New 



York. 

 Bergmann, W. (1949). Comparative biochemical studies on the lipids of marine 



invertebrates, with special reference to the sterols. Sears Found. J. Marine 



Res.,%,Ul-\16. 

 Bergmann, W. (1952). Sterols. Progr. Chem. of Fats and other Lipids, 1, 18-69. 

 Florkin, M. (1944). U evolution biochimique. Masson, Paris. 

 Jones, I. C. (1957). The Adrenal Cortex. Cambridge Univ. Press. 

 Wald, G. 1951. The chemistry of rod in Fish. Science 113, 287-291. 

 YoNGE, C. M. (1937). Evolution and adaptation in the digestive system of Metazoa. 



Biol. Rev., 12, 87-115. 

 Zeller, E. a. 1948. Enzymes of snake venoms and their biological significance. 



Advanc. EnzymoL, 8, 459-495. 



