SECTION II. ANALYSIS OF THE ENVIRONMENT 



4. THE GENERAL ENVIRONMENT 



FITNESS OF ENVIRONMENT 



We are not here concerned with an imagi- 

 nary ecology based upon a hypothetical 

 environment inhabited by fancied organ- 

 isms evolved in some vaguely conceived 

 system of life. Such a complex may exist, 

 for all we know, with a different chemical 

 and physical basis from the one we have 

 on the earth. It is sometimes amusing to 

 speculate on the possibilities of living 

 systems that may have developed under 

 conditions of low temperature that obtain, 

 for example, on the outer planets of our 

 solar system. If such life exists, its environ- 

 ment might conceivably be based upon and 

 largely determined by the properties 

 of ammonia. This substance boils at 

 —33.5° C* and has many fitnesses for 

 being the controlling element in an environ- 

 ment-organism complex which, in many 

 features, would not be too far removed 

 trom that on the earth. There is also the 

 more remote possibility of metabolizing, re- 

 producing organisms that live at tempera- 

 tures well above the upper limits of life 

 here. The organic chemistry of such 

 systems might perhaps be based on silicon 

 rather than on carbon. 



Instead of dealing with imaginary situa- 

 tions, we are confronted by the ecology of 

 the earth as we know it, populated by or- 

 ganisms that have evolved here from the 

 basis furnished principally by water car- 

 bon dioxide, and their elements, together 

 with nitrogen (Henderson, 1913). These 

 substances tend strongly to dominate and 

 control both the earth's environment and 

 the life which inhabits it. They are aided 

 bv many other elements; at least thirty-six 

 (Fearon, 1933) and probablv forty-six 

 (Hutchinson, 1943, p. 342) of the ninetv- 



* Unless otherwise stated, all temperatures 

 are given in degrees Centigrade. 



six elements that are believed to constitute 

 the universe are major or minor constituents 

 of protoplasm. There is suggestive evidence 

 that the chemical elements essential for life 

 are not a random lot, but are correlated 

 with atomic structure (Steinberg, 1938). 



On the earth, life requires the fol 

 lowing environmental conditions (Lafleui, 

 1941): 



1. An available set of chemicals that will 

 allow variation and reproduction and will 

 carry on the complex processes of metabo- 

 lism. 



2. A suitable temperature; the high tem- 

 perature on the average star excludes the 

 possibility of the organization of molecules 

 of sufficient complexity to serve as the basis 

 of life. Cold slows down chemical processes, 

 so that near absolute zero Life is as impos- 

 sible as it would be at some hundreds of 

 degrees higher temperature. Life in general 

 occurs much nearer the lowest possible 

 than the highest known temperatures; it is 

 essentially limited to relatively cold environ- 

 ments. Living protoplasm in latent stages 

 has survived temperatures as low as about 

 -270° C. and as high as 150° C. (see Fig 

 2). Practically, hfe is limited to the tern 

 peratures at which water is a relatively 

 warm solid or a cool to warm hquid, and 

 exists only in a narrow range of tempera- 

 tures far below the upper limit for inor- 

 ganic matter that reaches some thousands 

 or even millions of degrees (Huntington 

 1945) . Molten lava aside, life in some form 

 can exist at most earth temperatures. 



3. The proper range of density and pres 

 sure; the pressure of a cool "white dwarf 

 star makes molecular organization impos 

 sible. At the other extreme in the slight 

 density of a diffuse nebula, it is impossible 

 for a molecule to collect and align needed 

 chemical units. 



From the preceding three paragraphs it 



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