Evolution 409 



a land-bridge which once connected Australia and America. The two 

 animals having had the same ancestry, changed their appearance because 

 of a changed geographical environment, although their general structure 

 has remained quite as it was. 



There are no native ungulates in Australia, although there is no 

 reason why there should not be if other than evolutionary methods have 

 been factors in producing new types of animals. 



Or, again, one finds, for example, on the west coast of South 

 America, peculiar animals found nowhere else in the world, while on the 

 neighboring islands there are animals resembling those on the coast 

 of the continent both in structure and habit, yet sufficiently different 

 to be called new species. 



7. Natural Selection. 



This is an attempted explanation of why present-day forms are what 

 they are, by showing that food is never equal to the possible rate of 

 increase in living forms. Such lack of food causes a struggle for exist- 

 ence, through which struggle the weakest (the ones being least adaptive) 

 go down, while the stronger (those best able to adapt themselves to 

 their environment) survive. 



Natural selection describes the causes which have prevented sur- 

 viving forms from becoming extinct. 



OPPOSING ARGUMENTS 



The arguments which are usually brought forth to oppose these 

 evidences for evolution are as follows : 



1. Paleontology. 



(a) The different kinds of plants and animals found in various 

 geological strata can only demonstrate that similar organisms were 

 either larger or smaller than others, or varied in ways which can be 

 accounted for by a difference in the temperature and food supply of 

 different ages. Examples of this are the horse and mammoth. Then, 

 too, paleontologists insist that their finds can only be explained by 

 assuming that acquired characteristics are inherited, although experi- 

 mental evidence seems to point against this being true. 



(b) The so-called increasing complexity on the part of so-called 

 "younger" fossils as compared with so-called "older" ones, may always 

 be explained by assuming that Mendelian recessive characteristics have 

 again come forth, and that consequently the so-called "new forms" are 

 really a return of old ones. 



(c) Recent fossils are like modern forms because the climatic 

 changes and the food supply have not varied much during the interval 



