298 ERWIN CHARGAFF 



(4) polysaccharides. Parasitic systems (viruses, phages) apparently require the 

 presence of nucleic acids (DNA or PNA) and protein. But such a generic state- 

 ment probably is no more meaningful than if we were to say that all machines 

 consist of iron, copper, nickel, etc. For neither the knowledge of quantity' nor 

 that of quahty alone can satisfy our inquiry ; and for an understanding of what 

 is meant by organization an entirely new dimension will have to be added: a 

 dimension of which barely the foundations are discernible at present. Moreover, 

 to return to the example of the machine, it is not likely that we could learn much 

 about the 'origin of the automobile' from an inspection of the parts of a present- 

 day car; nor could such an examination help us to decide whether there did not 

 once exist an automobile made of glass, though we may conclude that, at any 

 rate under present conditions, it would hardly have survived as the fittest means 

 of locomotion. 



In any event, even if we commit the oversimpUfying fallacy of posttilating a 

 virus-like structure as the first 'Hving' molecule, we are still left to deal with a 

 nucleoprotein : a singular that conceals a multitude of possible structures. If 

 scientific facts were subject to a vote, the majority opinion would probably place 

 the nucleic acids at the top of the hierarchy and let the proteins follow; some- 

 thing like this: DNA -> PNA -^ Protein. But in my opinion it would be more 

 honest to confess that we know very little indeed about these things and to say 

 that tlie road to the future should not be uselessly cluttered up with shoddy, and 

 often entirely baseless, hypotheses. It may, however, not be tminstructive to 

 say a few words about the chemical connotations of the concept of biological 

 information. 



ON BIOLOGICAL INFORMATION 

 CHEMICALLY CONVEYED 



A biochemist, when asked to consider this problem, probably would first of all 

 translate it into the concept of chemical specificity — with which I have dealt in 

 more detail on several occasions [i, 2] — and think of a substance of an elevated 

 molecular weight, built of a number of chemically different monomers and 

 possessing chemical or physical features which are preserved without change 

 within the species, but which serve to distinguish the particular substance from 

 analogous ones produced by other species. Specific polysaccharides, specific 

 proteins, specific nucleic acids are the tyf>e of compounds that will come to mind 

 immediately; and the immunological specificity exhibited by many representa- 

 tives of the first two groups perhaps is their most striking property. The recog- 

 nition of the existence of specific nucleic acids required much more time ; but 

 their specificity, too, can now be taken to be an established fact on both chemical 

 and biological grounds [1-4]. It is, indeed, only in the fourth group of principal 

 cell constituents, namely, the lipids, that difficulties with respect to the occur- 

 rence of species specificity still are encountered. As I have pointed out recently 

 [5], one way in which the cell may be able to render lipids specific is in their 

 arrangement as prosthetic groups of lipoproteins. But there exist indications that 

 nervous tissue contains complex mucoHpids of high molecular weight which 

 could very well exhibit species specificity [6]. 



