94 EVOLUTION OF THE EARTH 



other part of the universe; or life arose spontaneously from 

 non-living matter at one period at least in the past as a natural 

 result of the evolution of the earth and its elements. 



THEORIES OF THE ORIGIN OF LIFE 



It will be useless to offer any extended discussion or specific 

 criticisms of the individual theories of the origin of life, for 

 each one rests on many uncertain postulates, which have a 

 greater or less degree of probability dependent, to a con- 

 siderable extent, on the personal equation of the critic. It 

 should be said, however, in justice to the authors of the theories 

 which we shall outline, that the theories are not advanced as 

 final solutions of the problem of the origin of life, but rather 

 as gropings toward a formulation of the conditions which con- 

 ceivably might have attended and contributed to its genesis. 

 The magnitude of the problem may be inferred from a recent 

 statement by the dean of American biologists that "the study 

 of the cell has on the whole seemed to widen rather than to 

 narrow the enormous gap that separates even the lowest forms 

 of life from the inorganic world." 11 



Vitalism. The vitalistic conception that life phenomena are 

 m part at least the resultant of manifestations of matter and 

 energy which transcend and differ intrinsically in kind from 

 those displayed in the inorganic world a denial, as it were, 

 in the organism of the full sufficiency of known fundamental 

 laws of matter and energy has arisen many times in the 

 development of biological thought, either as a reaction against 

 premature conclusions of the nascent sciences or from an 

 overwhelming appreciation of the complexity of life phe- 

 nomena. Vitalism goes back as far as the history of science 

 is recorded, but it attained its most concrete formulation as a 

 doctrine during the early part of the eighteenth century, 

 in opposition to the obviously inadequate explanations which 



11 Wilson, E. B., The cell in development and inheritance, 2d ed., 1900; The 

 problem of development, Science, new ser., vol. 21, 1905, pp. 281-294. 



