CAUSES OF THE EVOLUTION AND EXTINCTION OF THE TITANOTHERES 



837 



which constantly keep in touch with one another 

 through physico-chemical action, reaction, and inter- 

 action. An atypical or abnormal condition, such as 

 excess, depletion, or defect in any one of these four 

 complexes of energy, produces disturbances of some 



Figure 749. — Cumulative or favorable influence 

 of heredity, ontogeny, and environment 



kind, and the visible biocharacter ceases to be typical 

 or normal. If such disturbances of normality affect 

 many phases in the development of the biocharacter, 

 the visible organism will be extremely abnormal. 

 Thus to abnormal conditions in the germ, in the on- 



of the fourfold influences may convey its separate 

 or its combined effect upon abnormality. It is 

 equally true that departures from the typical con- 

 dition which may coincide with the adaptive direction 

 of the evolution of the biocharacter may again be 

 fourfold — that is, they may be attributable to favorable 

 predispositions in the germ, favorable modifications 

 and accommodations of the soma, favorable influences 

 of the environment in the form of physico-chemical 

 influence, favorable influences of the life environ- 

 ment in the form of food or of competition, which 

 may favor the development of certain biocharacters, 

 as, for example, the so-called habitudinal (Gulick) 

 and organic (Osborn, 1897.125) selection. 



As regards evidence, the theory of tetrakinesis in 

 evolution is quite distinct from the principle of tetra- 

 plasy in development. It is in the nature of a trial 

 hypothesis as to the causes of evolution, because we 

 do not yet understand the influence, respectively, of 

 ontogeny, environment, life environment, and selec- 

 tion upon the evolution of the germ. Therefore the 

 theory of tetrakinesis awaits further observation and 

 experiment as to the respective influence of physico- 

 chemical actions, reactions, and interactions on spe- 

 cific biocharacters of the germ. 



The following formulae, suggested by Gregory 

 (Osborn, 1912.378, p. 307), present clearly the manner 

 in which we may analyze the possible causes of incre- 

 ment — for example, quantity, intensity, plus and minus 

 variations — in any visible biocharacter wherever we 

 observe and compare members of a series. 



QUANTITATIVE INCREMENT OF THE FOUR SEPARABLE 

 FACTORS IN DEVELOPMENT AND EVOLUTION 



Let T represent the typical or normal condition of a 

 given biocharacter in the ancestral species as to recti- 



Tetraplasy Actions, Tfeactions, and Interactions 



-Diocharacters, 'Predispositions, and T^otentiatities of the Qerm 



Figure 750. — Diagram illustrating the tetraplastic theory 



Conception of a centrifugal [-^] stream of potential genes, determiners, predispositions, heritages, as passing into the life of the organism from 

 the heredity germ, both into the new reproductive organs and into every cell of the body (chromatin), and as acting, reacting, and 

 interacting with the inorganic environment, the life environment, and the ontogeny of the organism itself. At present there is com- 

 paratively little direct evidence of a centripetal [<-] or reversed current of energy such as to eflect specific changes in the heredity 

 chromatin. 



togeny, in the physical environment, or in the life 

 environment, or in all combined, are attributable 

 the visible abnormalities of the biocharacter. Each 



gradation, allometry, area, volume, degree, or inten- 

 sity of coloring, strength of muscle, or any biochar- 

 acter capable of quantitative determination. Let Tn 



