i4o THE POPULAR SCIENCE MONTHLY 



He states that most existing types arose in early Paleozoic times 

 when evolution was most rapid. Then came a period of slow changes, 

 especially slow in all races which were in the acme or most flourishing 

 period of their phylogeny. Finally, when retrogression sets in the pace 

 of evolution again becomes more rapid, and startling new modifications 

 are often introduced. 



Hyatt acknowledged that natural selection was a factor which modi- 

 fied the course of evolution, but he believed that the history of a race 

 was a predetermined thing and that natural selection played but a minor 

 role in comparison with the effects of the environment. In this latter 

 respect he was a neo-Lamarckian ; a view which is now more popular 

 than it was at the time of his death. 



He believed that when a number of more or less distantly related or 

 even unrelated forms live in the same environment they acquire a re- 

 semblance one to the other; the similarity of external conditions pro- 

 ducing a " morphological equivalence " or parallelism. 



These are the chief features of Hyatt's theories of evolution and 

 heredity. To go deeper into the subject would, I fear, only introduce 

 confusion into the mind of the reader. 



The paleontologist possesses at least one advantage over the student 

 of existing animals in that he may observe the changes that develop 

 during thousands of generations, whereas the zoologist sees the present 

 but dares not even vaguely guess upon the future of the race he studies. 

 Accordingly, Hyatt made little impression upon zoologists, but some of 

 the most brilliant paleontologists have applied his principles to the un- 

 raveling of the genealogy of fossil and living animals. We need only 

 mention the classic studies of Professor Charles Emerson Beecher upon 

 brachiopods and trilobites, or the many researches of Hyatt's former as- 

 sistant, Professor Eobert Tracy Jackson, at present one of the most pro- 

 gressive leaders of the Hyatt school, among whom are such active in- 

 vestigators as Bather, Buckman, J. M. Clarke, Cumings, G-rabau, Euede- 

 mann, Stanton, J. Perrin Smith, Burnet Smith, Schuchert and Van 

 Ingen. In the untimely death of Professor Beecher in 1904, the school 

 suffered a most serious and almost irreparable loss. The general atti- 

 tude of zoologists toward Hyatt's theory of evolution is probably best ex- 

 pressed by quoting from two of the letters which Charles Darwin wrote 

 to Professor Hyatt in 1872, in which Darwin says : 



After long reflection I can not avoid the conviction that no innate tendency 

 to progressive development exists, as is now held by so many able naturalists, 

 perhaps by yourself. . . . The longer I live the more I become convinced how 

 ignorant we are of the extent to which all sorts of structures are serviceable to 

 each species. But that characters supervening during maturity in one species 

 should appear so regularly as you state to be the case in succeeding species 

 seems to me very surprising and inexplicable. 



