396 CELL HEREDITY 



was achieved long before living things had aecpiired huih-in regulatory 

 devices. It is illuminating that the controlling elements of gene regula- 

 tion which are now being discovered act by repression of otherwise func- 

 tioning genes. Perhaps in the earliest living forms, all the genetic 

 material functioned all the time, an awkward and wasteful situation, with 

 a tremendous selecti\e advantage accruing to any system which could 

 control this outpouring. We may even consider the possibility that the 

 primitive replicating units were cytoplasmic structures and protein- 

 forming sites, and that today some genetic information still resides in 

 the.se materials. 



Superimposed upon this rather chaotic blob of protoplasm, a very 

 orderly regulatory system was evolved, characterized by its own internal 

 organization, a controlled time and manner of replication, and a virtually 

 infinite capacity to evolve by mutation and selection — in a word, the 

 chromosomes. At this point, we may leave the alluring but shadowy 

 realm of biopoiesis and uncontrolled growth and approach the more solid 

 ground of genetic science upon which has been built the experimental 

 analysis of the evolution of life as we know it today. 



BIBLIOGRAPHY 



Horowitz, N. H., 1945. On the evohition of biochemical syntheses. Froc. Natl. 

 Acad. Sci. Wash., 31:153-157. 



Lederberg, J., 1960. E.xobiology: approaches to life beyond the earth. Science, 

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Oparin, A. I., 1953. The Origin of Life (2nd ed.). New York, Dover Publica- 

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Oparin, A. I. (ed.), 1959. International Sympu.sium on the Origin of Life on 

 the Earth. London, Pergamon Press. 



Schrodinger, E., 1945. What is Life? London, Cambridge University Press. 



Tax, S. (ed.), 1960. Evolution After Dancin. Vol. 1. The Evolution of Life. 

 620 pp. Chicago, The University of Chicago Press. 



