414 General Biology 



of evolution (which the various evolutionary theories try to explain) 

 and the course of evolution. This latter is only a description of what 

 has been found, as, for instance, the charts which show the various 

 fossil-remains of what are considered the ancestors of the horse and 

 mammoth. Such charts, of course, explain nothing. 



The Darwinians originally held to the doctrine that all variations 

 must possess some function of a survival value, but we now know that 

 characters which are a decided hindrance in the survival sense, are 

 inherited and passed on from one generation to another just as readily 

 as those which are of value. 



Two different types of organisms may often grow to be quite alike, 

 or at least certain organs may develop so as to appear alike if they 

 function alike. This growing alike is known as convergent evolution. 

 Individuals originally structurally alike, which later become dissimilar, 

 are said to do so through divergent evolution. 



From what has been said above, one is likely to agree with the 

 writer who said that every biologist seems to have his own pet theory 

 to account for the evolutionary process. 



Notwithstanding this fact, one must, however, have some kind of 

 a gauge by which to measure the plausibility of a proposed theory. 

 Otherwise there is not even an approach toward finding whether any 

 given evidence is of value. 



It is to assist the student in forming such a gauge that the following 

 seven questions are here tabulated. These must be answered by any 

 theory which is to win complete and final acceptance. 



CRITERIA FOR A SATISFACTORY EVOLUTIONARY THEORY 



These questions refer to organic evolution in its widest signification, 

 as referring to both the individual and the race. 



(1) How did life originate? 



(2) How can a more complex individual develop from ancestors 

 which were less complex? 



(3) How can an organism adapt itself to its surroundings? 



(4) What causes the so-called mechanically directed type of 

 variations known as orthogenesis? 



(5) What causes the series of the many undoubtedly purposive 

 adaptations? 



(6) What causes the factors of heredity to behave as they do? 



(7) What factors can account for mentality and intelligence 

 (which are non-physical things) arising from physical and non-mental 

 matter? 



