The Origin and Evolution of Genetic Material 



515 



an unscheduled transplantation would doubt- 

 less be disastrous to any future plans for 

 studying either the preorganismal evolution 

 of organic compounds or any indigenous 

 organisms. As a safeguard against such con- 

 tamination, objects sent beyond our atmos- 

 phere are sterilized. Recall also that the 

 impact of a missile on a planet may cause 

 the production of organic chemical sub- 

 stances. 



Which heavenly objects likely to be in- 

 vestigated in the near future are interesting 

 from the point of view of preorganismal and 

 organismal evolution? We have already 

 mentioned Mars. Consider Venus, whose 

 unknown surface is hidden completely by an 

 opaque, highly reflecting cloud layer con- 

 taining abundant carbon dioxide and water. 

 Although estimates of Venus' temperature 

 vary widely (its surface is usually considered 

 to be dry and hot), we can assume that or- 

 ganic compounds have evolved there even 

 if biological evolution has been impossible. 

 After studying its chemistry in sufficient de- 

 tail, perhaps we might wish to colonize 

 Venus, first by placing a chlorophyll-con- 



taining microorganism in its outer atmos- 

 phere. In a short time, such an organism, 

 by utilizing great quantities of atmospheric 

 components for growth and reproduction, 

 might radically change the climate of Venus. 

 Our own satellite, the moon, has no at- 

 mosphere and probably no water. There- 

 fore, the presence of earthlike life there today 

 is almost out of the question. The moon, 

 however, may be as old as the earth and 

 may have had an organic and even a bio- 

 logical evolution similar to our own before 

 losing its atmosphere. So it will be interest- 

 ing to analyze samples of the lunar surface 

 and, particularly, its subsurface material. It 

 has been suggested that the moon acts as a 

 gravitational trap for fossil spores drifting 

 between planets. Although improbable, the 

 very possibility of an interplanetary gene flow 

 is too important to ignore in the exploration 

 and exploitation of space. Planetary re- 

 search has many motivations; but the search 

 for evidence of chemical evolution, DNA 

 and RNA, and organisms — life of any type 

 — would seem to be among the most signifi- 

 cant. 



SUMMARY AND CONCLUSIONS 



The earth has undergone a chemical evolution. This process resulted in the synthesis 

 of most types of compounds and cycles of synthesis found in present-day organisms. 

 It also resulted in the production of proteins, polynucleotides, and nucleoproteins. 

 These latter compounds evolved to a stage where a nucleic acid was able to replicate 

 itself as well as some of its changed forms and so could be identified as genetic ma- 

 terial. Chemo-evolutionary drive on earth is based largely upon protein since nucleic 

 acids provide much less chemical diversity; therefore we hypothesize that nucleic acid 

 evolution (which presumably went from RNA to DNA) was subservient to evolution 

 directed primarily toward the stabilization and synthesis of protein. 



DNA has been the primary genetic material on earth for about a billion years. 

 During this time DNA and its associated materials have undergone a structural evolu- 

 tion leading to the establishment of chromosomes and mechanisms for genetic recom- 

 bination and regulation of mutability. Also, genes have probably undergone a func- 

 tional evolution, which proceeded from genes which serve structurally (specifying the 

 synthesis or organization of nongenetic compounds) to those which serve functionally 

 (regulating gene action). 



