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CHAPTER 42 



ment. [ndependence of the environment 

 would also have been advanced by the phys- 

 ical association of genes involved in different 



portions o\' a given biochemical sequence. 

 this independence leading eventually to the 

 selection of mutant genes whose function, 



other than self-replication, was to regulate 

 the functioning of other genes. Thus, in 

 addition to genes for structure, evolution 

 might well have produced genes for regula- 

 tion — operator and regulator genes — and 

 genes for synthesizing specific basic proteins 

 for the regulation of chromosome coiling, 

 replication, and functioning. 



Cosmic Chemo-evolution 



In our search for information regarding 

 either pregenetic. preorganismal evolution or 

 postgenetic, postorganismal evolution, we do 

 not have to confine ourselves to this planet. 

 The universe is about ten billion years old; 

 the earth is roughly half this age. Because 

 the universe contains an infinite number of 

 stars (suns) with planets, there must be vast 

 numbers of suns the size of our own that 

 have planets about the same size as the earth 

 and at comparable distances from their suns. 

 Some of these planets are surely younger, 

 others surely older than our own. What is 

 the possibility that a chemical and biological 

 evolution similar to ours took place on other 

 planets? The answer to this question de- 

 pends, of course, upon their chemical com- 

 position. 



Most of the universe is hydrogen and 

 helium (most of the earth's hydrogen es- 

 caped from our atmosphere in Era I, as al- 

 ready mentioned). Of the remaining ele- 

 ments, the universe has abundant oxygen 

 and nitrogen and is, in fact, richer than the 

 earth in carbon — the element essential for 

 organic compounds which have played such 

 an integral role in chemical and biological 

 evolution on earth. It is therefore likely that 

 numerous places in the universe do exist 



where a chemical evolution of biological in- 

 terest might have been successfully initiated. 

 Since the relative scarcity of carbon makes 

 the earth a rather poor place for such an 

 evolution (which nevertheless occurred), 

 most surely the universe contains numerous 

 planets in early stages of chemical evolution, 

 early stages of biological evolution, as well 

 as planets older than our own. which very 

 probably have more advanced types of or- 

 ganisms. 



Evidence has been obtained for the pres- 

 ence of organic radicals such as CH, CN, 

 CC, and CO in comets, and for organic mole- 

 cules of an asymmetric type on Mars. As- 

 tronomers have also reported variations in 

 the color and texture of Mars with changes 

 of season, which strongly suggest that Mars, 

 with an atmosphere thinner than the earth's, 

 contains appreciable quantities of organic 

 matter, although we are not yet able to de- 

 termine whether their origin is preorganismal 

 or organismal. 



Further information about the chemistry 

 of our sun and its planets will undoubtedly 

 be provided by telescopes orbiting far into 

 and above our atmosphere. Plans for in- 

 terplanetary research now underway include 

 sending additional instruments to or near 

 various planets in our solar system. Such 

 missions will be designed to record the 

 detailed chemistry of our neighboring planets 

 and, of course, to detect the presence of 

 organic compounds, of organisms, and of 

 DNA and RNA. We have already sent 

 radio signals into space in an attempt to 

 contact other organisms capable of receiving 

 and or replying. 



In any space mission it is of utmost im- 

 portance to avoid the accidental transplanta- 

 tion of terrestrial genotypes to other planets; 

 if a single bacterium such as E. coli were 

 placed on a planet containing a suitable 

 medium, its progeny would occupy a volume 

 the size of the earth in about 48 hours. Such 



