PHYLOGENETIC RELATIONS OF ANIMAL GROUPS 885 



information concerning the ways of adaptation and phylogenetic 

 development. A significant result is the demonstration of changes 

 occurring in animals and plants. From such studies it seems quite 

 obvious that organisms now living have come to be what they are 

 by gradual change from generation to generation through a course 

 of descent from preexisting and varied ancestors, rather than by a 

 sudden and completely new development. Most of the various 

 breeds of cattle, chickens, dogs, horses, sheep, crops, etc., have been 

 developed in each case from a preexisting common ancestor. 



Darwin and Studies of Evolution 



Most discussions of organic evolution usually begin with mention 

 of Darwin's monumental work on this suljject and difficult it is to 

 get away from his fundamental basic thinking on the subject. He 

 was the first to thoroughly survey the fields of distribution, morphol- 

 ogy, embryology, and paleontology, and logically relate the data found 

 there to the theory of evolution. From his studies, many of which were 

 done along the east and west shores of South America while he was 

 naturalist of a British Naval expedition on the ship "Beagle," Darwin 

 formulated a clear-cut and definite argument for evolution on the 

 basis of Natural Selection. Beginning with Malthus' Law of Popu- 

 lation, published in 1838, Avhich stated that since man reproduces 

 in a geometric ratio, the earth would be overpopulated in a few 

 generations except for such checks as the arithmetric ratio of in- 

 crease in food production, disease, war, flood, earthquake, fire and 

 other natural catastrophes reducing population, Darwin formulated 

 the Natural Selection Theory. This theoiy includes among other 

 things the application of Malthus' law to all living organisms. The 

 four basic points on which this theory is developed, may be named in 

 order as follows: (1) overproduction, (2) struggle for existence, (3) 

 variation and heredity, and (4) survival of the fittest (natural selec- 

 tion). 



Overproduction is in operation in all thriving normal species. 

 A single codfish will produce several million eggs in one season. 

 If every codfish egg were to be fertilized, reach maturity, and repro- 

 duce with no loss from one generation to the next, it would not be 

 more than a dozen years until the entire face of the earth would be 

 covered with codfish and all other animals would be crowded out of 

 existence completely. Even a form like the elephant, which lives to 



