44 Life: Its Nature and Origin 



the cell to a culmination in those processes which ultimately re- 

 duplicate the protamines and nucleic acids in the nucleus. 



Environment 



Life, however, cannot be considered apart from its environment 

 because this must provide both nutrients and other suitable condi- 

 tions for life's existence. These two environmental items may there- 

 fore be of interest in a consideration of plausible pre-biological 

 conditions. 



If, as seems to be the case, primeval life came into existence 

 before photosynthesis had evolved, we may assume that its minimum 

 nutritional requirements were those common to all but the green 

 plants. It is significant that these minimum requirements are strik- 

 ingly similar for bacteria, protozoa, insects, and mammals (Trager, 

 1953; Johnson, 1956; Lea, Dimond, and DeLong, 1956). Using 

 these minimum requirements as a basis, the needs of our primeval 

 cell were (1) water (the first cell presumably originated in an 

 aqueous environment); (2) a large selection of amino acids; (3) 

 some nucleic acid derivatives such as guanine or cytidine; (4) a 

 number of vitamins, generally at least six and commonly many more; 

 and (5) a large number of inorganic substances including phos- 

 phorus, potassium, iron, copper, zinc, cobalt, and calcium. Although 

 the energy foods (carbohydrates and fats) are used by many or- 

 ganisms, some of the other organic compounds may be "burned" 

 by the tissues for energy. Except for water, our cell requires build- 

 ing blocks from which protein and nucleic acid are manufactured 

 and a few other elements and compounds vital to the chemical 

 reactions of such manufacture. 



Suitable factors for the existence of life in water, which is the 

 habitat of pre-biological interest, comprise chiefly temperature and 

 chemical composition. The upper temperature limit for most known 

 living aquatic organisms ranges from slightly above 0°C (32°F) 

 to about 48°C (120°F), but a few algae living in thermal springs 

 tolerate 85°C (185°F). Individual species in water vary greatly in 

 chemical tolerances. In general, each species can tolerate only cer- 

 tain concentrations of various ions in solution. Above or below 

 these critical values, the organism loses or absorbs too much water 

 to maintain a proper internal organization or sufi^ers other losses 

 or absorptions which produce the same effect. Thus the highly 

 ionized metallic salts or inorganic acids such as sodium chloride 

 or sulphuric acid produce much greater environmental effects than 



