THE GENERAL ENVIRONMENT 



77 



ciple for all physiology, is only one phase of 

 the relationship. The environment is also 

 relatively a fit place for life. Reflection 

 indicates that both phases of this reciprocal 

 fitness are inherently imperative. The envi- 

 ronment must have been more than pas- 

 sively favorable; otherwise hfe would prob- 

 ably not have originated and persisted. This 

 is the primary fitness. The general adapta- 

 tion of organisms to their environment fol- 

 lows as a necessary corollary. 



The developing reciprocity of environ- 

 ment and organism has produced funda- 

 mental and far-reaching results. At one 

 time, probably, the atmosphere of the earth 

 consisted chiefly of water vapor and carbon 

 dioxide. Cooling caused the condensation 

 of most of the water, and geological proc- 

 esses, aided in recent geological time by 

 the action of vegetation and the fixation of 

 carbon in coal and peat, have removed 

 nearly all the carbon dioxide. This has re- 

 sulted in the evolution of an atmosphere in 

 which inert nitrogen forms the greatest 

 bulk and in which oxygen is the most im- 

 portant active chemical element. 



As a further evidence of reciprocity be- 

 tween living and nonliving nature, Ver- 

 nadsky (1929) suggests that all the free 

 oxygen of the earth (1.5 X 10" gm.) is 

 produced by life alone. Hence, not only 

 are organisms acted on by the environment, 

 but they also react upon it to produce note- 

 worthy changes to which, in turn, evolving 

 life mvist adapt itself or perish. 



In discussing the general principle of the 

 fitness of the earth's environment as the 

 basis of life, certain deficiencies must not 

 be overlooked that make it less than ideally 

 fit.* Because of the relatively high opacity 

 of water, anabolic life is confined to a 

 relatively thin film near the surface, while 

 the intermediate reaches and the vast ocean 

 bottom are sparsely inhabited by sapro- 

 phytes and scavengers, predators and para- 

 sites. 



The atmosphere, as a result of its low 

 degree of buoyancv, cannot be used as a 

 permanent habitat by organisms, and even 

 its lower reaches can be used as a passage- 

 way only bv accident or by highly special 

 ized forms. The entire ocean of air sup- 

 ports only a sparse and transient popula- 

 tion near its lower phase boundary. On 



• The discussion is based on a personal com- 

 munication from Dr. William Etkin. 



account of the same lack of buoyancy and 

 also because of the usually strong drying 

 power of the air, even earth-supported life 

 is limited to a biosphere which, as a per- 

 manent habitat for living things, never rises 

 more than a few tens of meters above 

 the earth's surface. Because of seasonal and 

 regional variations in distribution of heat 

 and water vapor, approximately half of the 

 terrestrial surface of the earth is an impos- 

 sible environment except for a sparse popu- 

 lation of specially adapted organisms. These 

 environmental deficiencies would not have 

 had their present values during much of 

 geological time (p. 8). Cold alone closes 

 almost all of the interior of one whole 

 continent, Antarctica, to endemic hfe. The 

 sparseness of water vapor results in large 

 areas being inhabited but shghtly; the Sa- 

 hara desert is an excellent example. Yet, 

 while recognizing such difficulties with the 

 earth as an environment for life, we are 

 reminded by Henderson (1917) that water 

 is more widely distributed over the face of 

 the earth than is any other known com- 

 pound. 



To continue with the disadvantages: The 

 relative stability of many carbon compounds 

 and their insolubility in water have resulted 

 in a gradual piling up of carbon in coal 

 and peat deposits, with a resulting reduction 

 in the availability of this substance as a 

 plant nutrient. The stability of nitrogen 

 closes most of the great atmospheric store to 

 use by organisms. Such facts indicate that 

 despite many niceties of fit, the properties 

 of matter can hardly be said to be gener- 

 ously above the minimum required for the 

 origin and maintenance of living systems. 



Realizing the importance of these weak- 

 nesses in the Hendersonian argument we 

 can still conclude this phase of the present 

 discussion with another quotation from 

 Henderson (1914, p. 527) : 



"Just because life must manifest itself in and 

 tlirougfh mechanism, fust because, being in this 

 world, it must inhabit a more or less durable, 

 more or less active physico-chemical system of 

 more or less complexity in its phases, com- 

 ponents and concentrations, it is conditioned. 

 The inorganic, such as it is, imposes certain 

 conditions on the organic. Accordingly, our 

 conclusion is this: The special characteristics 

 of the inorganic are the fittest for those general 

 characteristics of the organic which the general 

 characteristics of the inorganic impose upon 

 the organic. This is the one side of reciprocal 



