CHEMICAL UNIFORMITY OF LIFE 45 



doubt these remains are from organisms fully alive, and not from 

 some borderland proto-life. 



CHEMICAL UNIFORMITY OF PRESENT MODE OF LIFE 



Returning now to the biological studies of present life, we find as a 

 salient feature of modem life the antithesis between the immense 

 variation of its morphological expression and the small number of 

 chemical reactions on which it is based. Morphologically, there is an 

 enormous number of different forms of life, species, genera, families 

 and higher systematic realms of microbes, plants and animals. Estima- 

 tes run to about one million different species existing on earth today. 

 Biochemically, in contrast, all present-day life, in all its variations, 

 is based on nucleic acids, proteins, carbohydrates and fats and some 

 minor compounds such as phosphoric esters. Although showing great 

 variation in detail, these compounds are all interrelated and built 

 upon a few scores only of basic biochemical reactions. Marine animals 

 and plants, from the smallest species of plankton drifting in the 

 currents, to huge whales, or continental plants and animals, from the 

 viruses to the elephants, aerobic or anaerobic organisms, all are based 

 on this surprisingly small number of organic compounds. 



Nature, it has been said, is so organized that any living thing forms 

 part of the food chain, can be fed on by other living things. Owing 

 to the small number of organic compounds used in building up any 

 form of life, there is always, in any organism, something digestible 

 for some other organism. Scientists are amused by this. They inter- 

 pret the biochemical similarity as an indication that all present 

 forms of life are related somehow, and consequently that all forms 

 of life have a common origin. 



The chemical compounds which build up all living forms today, 

 together form the compounds of natural organic chemistry, as op- 

 posed to inorganic chemistry. They form only a very small part, 

 however, of the organic compounds which it is possible to synthesize 

 from these same elements. Or, to use teleological jargon. Nature was 

 extremely narrow-minded in her chemical conceptions. Every chemist 

 today can make a much greater number and variety of organic 

 compounds, than Nature formed in a couple of billion years. 



If we now look more closely into this group of natural organic 

 compounds, proteins, carbohydrates, fats and some others, we find 



