242 WHAT 18 LIFE 



and hybrids and "intergrades" are numerous. How- 

 ever, it is necessary to exercise extreme caution 

 in assigning similar species to a common ancestral 

 form. 



My theory brings about a curious reversal: The 

 current theory of descent grants almost unlimited 

 possibilities of evolution, demanding only the pri- 

 mary, single origin of life. To account for the origin 

 of life was thought to be impossible. According to 

 my theory of life, the origin of life is a phenomenon 

 that is bound to take place granted only a very 

 limited set of physicochemical conditions. But the 

 possibilities of evolution of any forms that arise — 

 these, it appears, are strictly limited. 



It would seem that most existing species could not 

 be other than specific and fixed in their essential 

 characteristics, the limit of their development (evo- 

 lution) having been reached long ago. Specificity 

 fixity of species, then, may not be conceived in the 

 sense of something fatal that was impressed upon a 

 life-form; but must be understood to mean merely 

 that the limit of the reactions that by reason of its 

 constitution were made possible to any newly-arisen 

 life-form (the reactions that represent an organism of 

 a certain definite species), was reached long ago. The 

 average limit of possible reactions of any form having 

 been reached, the form necessarily became rigid. 



