GENETICS IN MODERN BIOLOGY BEADLE 411 



can go backward in the evolutionary process to simpler and simpler 

 forms until finally one begins to think of systems like present-day 

 viruses, the shnplest of which consist of little more than nucleic acid 

 cores (DNA or KNA) and protein coats. One can easily imagine 

 that before systems of this type there were smaller and smaller sys- 

 tems of nucleic acid and protein capable of replication and of muta- 

 tion which in turn had ancestors consisting of only nucleic acid. 



We know that nucleic acids can be built up from nucleotides and 

 these from simpler precursors. In a lecture delivered a few days ago 

 in this auditorium, Prof. Melvin Calvin talked about the origin of 

 some nucleotide precursors and presented evidence suggesting that 

 some such compounds, or their relatives, are found in certain meteor- 

 ites. It is assumed that these were formed by natural chemical reac- 

 tions that went on and are still going on outside living systems. 

 Presumably precursors of nucleotides were formed through such reac- 

 tions. Professor Calvin also mentioned the evidence that amino acids 

 are made from such simple inorganic molecules as methane, ammonia, 

 hydrogen, and w^ater under conditions assumed to have obtained on 

 primitive earth. It is, I believe, justifiable to make the generaliza- 

 tion that anything an organic chemist can synthesize can be made 

 without him. All he does is increase the probability that given re- 

 actions will "go." So it is quite reasonable to assume that given suffi- 

 cient time and proper conditions, nucleotides, amino acids, proteins, 

 and nucleic acids will arise by reactions that, though less probable, 

 are as inevitable as those by which the organic chemist fulfills his 

 predictions. So why not self-duplicating viruslike systems capable of 

 further evolution ? 



I should point out that nucleic acid protected with a protein coat 

 has an enormous selective advantage, for it is much more resistant to 

 destruction than is "raw" nucleic acid. Viruses can be stored for 

 years as inert chemicals without losing the capacity to reproduce 

 when placed in a proper environment. Of course present-day viruses 

 demand living host cells for multiplication, but presumably the first 

 primitive life forms inhabited environments replete with sponta- 

 neously formed building blocks from which they could build replicas. 



Before molecules like methane, hydrogen, water, and ammonia 

 there were even simpler molecules. Before that there were elements, 

 all of which nuclear physicists and astrophysicists believe have 

 evolved and are now evolving from simple hydrogen. That is why I 

 say if you believe in evolution at all there is no logical stopping place 

 short of hydrogen. At that stage I'm afraid logic, too, runs out. 



The story can, of course, be repeated in reverse, Wlien the con- 

 ditions become right, hydrogen must give rise to other elements. 

 Hydrogen fuses to form helium, helium nuclei combine to give beryl- 

 lium-8, beryllium-8 captures helium nuclei to form carbon, and carbon 



