SESSION I. DISCUSSION 107 



indefinite growth in tissue culture. Furthermore, there is no reason to doubt that the 

 mule itself is capable of reproducing asexually, as are most animals, by division of the 

 early embryo, giving rise to monozygotic twins. This mechanism is no different in prin- 

 ciple than that by which bacteria and other asexual organisms multiply. 



The next step in our inquiry is to attempt to define a living system chemically. What 

 is the minimal chemical system that exhibits the essential properties of living matter? 

 It is not possible to give a complete answer to this question at the present time, but from 

 the study of chemical genetics we have obtained an important fragment of the answer. 

 It will be noticed that the essential properties of living matter as I have defined them are 

 precisely the properties of the genes, as shown by experiment. Genes are mutable; they 

 reproduce by copying, as shown by the fact that mutant genes are exactly duplicated; 

 and they induce the formation of specific catalysts in their environment, as shown by 

 many examples in which gene mutation has been found to result in the permanent 

 hereditary loss of specific enzymes, or in the production of structurally novel kinds of 

 enzymes [2], It is as if the genes were the only living components of the cell, everything 

 else being — directly or indirectly — the products of genie activity. 



We are thus led to the problem of the chemical nature of genes. I cannot take up here 

 the many lines of evidence that point toward the nucleic acids as the ultimate genetic 

 material. The evidence for the genetic role of deoxyribonucleic acid has been reviewed 

 recently [3]. The question we are concerned with is whether a molecule of nucleic acid 

 could have been the first living thing on the Earth. It is tempting to believe that this 

 was so. Even if true, however, this would not solve all our problems, because we recognize 

 that no living thing can function in a vacuum. Until very recently nucleic acids were 

 known to function only within living cells. If life can be manifested only in such complex 

 systems as cells, then the problem of its origin becomes truly formidable. The recent 

 work of Kornberg [4], however, suggests that deoxyribonucleic acid reproduction may 

 occur in a rather simple system. Likewise, the synthesis of proteins in isolated systems, 

 which has been accomplished in several laboratories, suggests that the heterocatalytic 

 activity of the genes may also proceed under relatively simple conditions. If these inferences 

 are correct, then the question raised by Professor Oparin — namely, did life arise as in- 

 dividual molecules or in the form of complex poljmiolecular systems — can be answered 

 in the following way: Life arose as individual molecules in a polymolecular environment. 



California Institute of Technology , 

 Pasadena, California, U.S.A. 



REFERENCES 



1. N. H. Horowitz, Proc. nat. Acad. Sei., Wash., 31, 153, 1945. 



2. N. H. Horowitz, Fed. Proc, 15, 818, 1956. 



3. R. L. Sinsheimer, Science, 125, 1123, 1957. 



4. A. Kornberg, In: The Chemical Basis of Heredity (Ed. by McElroy & Glass). 



The Johns Hopkins Press, Baltimore, p. 579, 1957. 



V. I. Krasovskii & I. S. Shklovskii (U.S.S.R.): 



The Possible Influence of Cosmic Rays on the Origin and Evolution 

 of Life on the Earth 



It has now been proved that both the radio waves and the light rays (with a continuous 

 spectrum) of the Crab nebula were brought into being by relativistic electrons moving 

 in magnetic fields [i, 2]. This being so, we must reckon with the fact that this nebula — 

 the residue of the supernova of A.D. 1054 — contains a tremendous number of relativistic 

 particles, i.e., primary cosmic rays. The same may be said of the other nebulae which 

 are residues of supernovae. In fact the residue of the supernova of 1572 and that of the 

 supernova of 1604 are sources of radio waves [3, 4]. Recently it has been discovered that 

 radio waves are also emitted by the loop nebulae in Cygnus which are undoubtedly 



