412 GENERAL BIOLOGY 



Now, it is probably from such evidence as this that one biologist, at 

 least, draws the conclusion that just as there are undoubtedly thousands 

 of colors which no human eye can see, and thousands of sounds no human 

 ear can hear, so there must be thousands of factors in every explanation 

 which the human mind cannot grasp. This being true, it follows that 

 if we can find any explanation which is plausible, and which fits in with 

 every nook and crevice of our mind, we know that such a theory is not 

 likely to be true, because there are thousands of points that we must 

 necessarily have neglected taking into consideration due to our sheer 

 intellectual inability. Thus even the most plausible arguments are 

 vitiated. 



SUMMARY 



We have presented practically all of the important arguments for 

 and against evolution itself and the various theories which attempt to 

 account for it, because it is just as essential for a well-educated man to 

 know the opposing arguments in any given case as it is for him to know 

 the supporting ones. The theories which the student is to accept are 

 those which he finds sufficient evidence for in his work throughout his 

 laboratory course. 



Regardless of what one may believe the evidence has brought forth, 

 all biological workers must accept evolution as a scientific hypothesis, 

 though this does not mean' that they must accept ( any of the theories 

 propounded to account for it. The above statement is true, because there 

 is much more evidence to show that an evolution has taken place than 

 there is to show how and why it took place. 



Then, too, the student must note the difference between the cause 

 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 is 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 in- 

 herited 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 func- 

 tion alike. This growing alike is known as convergent evolution. In- 

 dividuals 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 ac- 

 count for the evolutionary process. 



