2 BIOCHEMICAL SYSTEMATICS 



comparative biochemistry would have already established unequivo- 

 cally the same concepts of evolution which now exist. 



Four levels of biochemical unity may be recognized which, 

 collectively, provide a framework for evolutionary theory. Starting 

 with the most fundamental they are: (1) biochemical unity as ex- 

 pressed in the basic similarity of the hereditary material of all organ- 

 isms; (2) biochemical unity as expressed in the group of co-enzymes 

 which are essential to many of the basic biochemical processes; (3) 

 biochemical unity as expressed in the similarity of metabolic path- 

 ways, particularly those involved in energy exchange, of different 

 organisms; and (4) biochemical unity as expressed within major 

 taxonomic groups in the common presence of certain structural com- 

 ponents such as chitin, cellulose, and so on. At all of the levels there 

 is also some degree of diversity. For example, while deoxyribonucleic 

 acid is present in the chromosomes of diverse species, the same 

 sequence of nucleotide subunits is unlikely to be expressed even in 

 two individuals of a single species. All of this knowledge has a direct 

 bearing upon phylogeny in its broadest meaning. At least, all of the 

 facts have potential phylogenetic significance; those which emphasize 

 unity, to relate species, and those which emphasize diversity, to 

 separate species. 



In recent years a number of books have been written about 

 various aspects of the broad subject of biochemistry in relation to 

 evolution. The Molecular Basis of Evolution by Anfinsen (1959), and 

 the six volume work in preparation edited by Florkin and Mason 

 (1960) are especially noteworthy. There are also numerous individual 

 articles on the subject of biochemical evolution, treating various as- 

 pects of the subject. Speculation upon the origin of life itself is now 

 centered almost entirely upon questions relating to molecular 

 evolution (Oparin, 1959). 



Dating back many years before the beginnings of enzyme 

 chemistry and studies of metabolic pathways are numerous investiga- 

 tions of the distributions of various substances, initially in higher 

 plants and now including fungi and bacteria as well. Such investiga- 

 tions often had pharmacological and other economic objectives, but 

 some of the earliest workers were interested in correlations between 

 the distributions of substances and the taxonomic treatments of the 

 species investigated. Subsequent workers have continued to note 

 such correlations or even to make a tentative taxonomic judgment 

 based on their chemical results. Periodically, belief in the utility of 

 biochemical data for systematic purposes has been reiterated. Bio- 

 chemistry has not yet been responsible for any major advances in our 

 knowledge of phylogenetic relationships. Yet, inexorable progress in 



