CAUSES OF THE EVOLUTION AND EXTINCTION OF THE TITANOTHERES 



807 



complex, and more imposing than that of Eotitanops. 

 How was the heredity germ thus enriched; how did all 

 these new predispositions of character, new qualities, 

 and new potentialities enter the germinal substance? 

 We know from comparative embryology and heredity 

 that there was a direct continuity between the heredity 

 germ of Eotitanops and that of Brontotherium (fig. 

 727); also that the germinal predispositions and 

 potentialities were handed down continuously, and 

 that while the germ flowed outward into the form and 

 fimctions of the body there is little or no Lamarckian 

 evidence that the modifications of the form and 

 functions of the body flowed inward into the germ of 

 the succeeding generation — that is, there is little 

 evidence in titanothere evolution for the Lamarck- 

 Cope-Spencer doctrine of kinetogenesis, or inherit- 

 ance of bodily modifications. 



PEINCIPIES OF TETEAPIASY IN INDIVIDUAI DEVELOP- 

 MENT; ONTOGENY 



One contrast between the causes of individual 

 bodUy development (ontogeny) and those of racial 

 (germinal) evolution (phylogeny) is that the former are 

 observedly tetraplastic, the latter are hypothetically 

 so — that is, the influences of the body and of the 

 environment on the germ are as yet hypothetic. 



We may now speak briefly of the fundamental 

 tetraplastic principles (Osborn, 1908.308) of indi- 

 vidual development, which wifl be more fully explained 

 farther on in this chapter (pp. 835-838). 



To distinguish clearly the fact that every visible 

 titanothere is the component of four physico-chemico- 

 mechanical influences and is continually subject to 

 selection in competition with other titanotheres, it is 

 necessary to keep in view the following scheme : 



Tetraplasy: Inseparable action, reaction, and interaction of Jour complexes of causes, together with natural 



selection, on development 



1. Titanothere germ evolution 



Genesis of new germinal predispositions and potentialities, giving rise to new 

 biocharacters, to new changes of form and proportion, continuous and discontinuous, 

 to the hastening or retarding of existing biocharacters in development and evolution, 

 to new predispositions to correlation and compensation of biocharacters, which give 

 rise to new germinal "mutations," "ascending mutations," " rectigradations, " 

 " allometrons," etc. 



2. Ontogeny 



The development of the body (soma) of the individual titanothere; influence 

 of habit, use, and disuse upon the germinal predispositions of function and structure; 

 genesis of new somatic modifications, of new somatic characters, of somatic chabges 

 of form and proportion, of somatic hastening and retarding of biocharacters, of 

 somatic correlation and compensation of biocharacters that may give rise to allome- 

 trons, "ontogenetic variations," "ontogenetic species," etc. 



3. Physical environment 



Geographic environment (earth, air, water, temperature, etc.). If highly 

 favorable, environment intensifies and overdevelops certain germinal predisposi- 

 tions, potentialities, tendencies of every biocharacter in the soma; if unfavorable, 

 it dwarfs, arrests, inhibits, or actually suppresses them. Environmental infiuence 

 on the appearance of new somatic biocharacters, on changing form and proportions 

 of somatic biocharacters, on the hastening and retarding of the individual develop- 

 ment of somatic biocharacters, on the correlation and compensation of somatic bio- 

 characters, concluding in extreme cases in the formation of "environmental species," 

 "climatic variations," "geographic species," "geographic variations," "geographic 

 varieties," etc. 



4. Life environment 



Plant and animal complex — flora and fauna, biota surrounding the organisms. 

 Influence of all the competing organisms on the predispositions and potentialities 

 of the titanothere germ, chemico-physical influence of different kinds of food, me- 

 chanical influence of food, and complex of the combined influence of food and of 

 habit on ontogeny. Competition with titanotheres of the same and of other varieties 

 in the search for food. 



5. "Natural selection" of Darwin; "survival 

 of the fittest" of Spencer 



Effect of competition with members of 

 the same and other species on all the 

 functions and structures developed from 

 the predispositions and potentialities of the 

 ^ germ as influenced by environment and 

 ontogeny, including the direct action of 

 selection on all biocharacters that have 

 survival value, resulting in the selection of 

 the germinal predispositions from which they 

 spring, according to the germinal selection 

 theory of Weissman, which includes, in 

 part, the "organic selection" or "coinci- 

 dent selection" of Osborn, Morgan, and 

 Baldwin. 



