132 NEW YORK STATE MUSEUM 



tion of instability, or, in other words, to the selection of adaptability, or the 

 adaptation to changeableness of environment. Selection of the first kind of 

 adaptation may have given rise to varieties, species, genera of the same 

 type of animal, and have produced spreading or diversification, while selection 

 of the second kind of adaptation may have produced the movement onward 

 and upward of all animal forms. 



The two kinds of adaptations do not always go together and selection of the 

 one may outweigh the other. It is because selection to a specific environ- 

 ment sometimes is more important than selection of adaptations to change- 

 ableness, that not all organisms have progressed in the scale of evolution 

 equally rapidly; but some have persisted in special environments with slight 

 changes of structure for very long periods, or may even have retrogressed ; 

 while other forms in which the second adaptation has been vigorously 

 selected, have moved rapidly onward and upward, and show little adaptation 

 to any special environment. 



The clearest conception of the biogenetic causes of persistence 

 we obtain, it seems to me, through Osborn's law of the four insepa- 

 rable factors. 1 This fundamental biological law is : " The life and 

 evolution or organisms continuously center around the processes 

 which we term heredity, ontogeny, environment and selection; 

 these have been inseparable and interacting from the beginning; 

 a change introduced or initiated through any one of these factors 

 causes a change in all." 



We must then infer that since no changes or but extremely slow 

 and insignificant ones are apparent in the characters of the per- 

 sistent forms, the fundamental condition of persistence is that 

 each of the four factors, heredity, ontogeny, environment and 

 selection, remains constant and no changes are originated through 

 any of them. We have already seen that environment and selec- 

 tion are processes which comprise all competition, survival or 

 elimination of individuals, and which appear under different forms 

 as important factors of persistence. Heredity is, according to 

 Osborn, by far the most conservative and stable of the four pro- 

 cesses involved in life and evolution, because it is embodied in a 

 form of matter (germ-plasm) least subject to changing external 

 influences, but it is also a fact, according to the same authority, put 

 forth through paleontological observation, that many origins of 

 new characters are through some internal action in heredity (both 



1 H. F. Osborn. Evolution as It Appears to the Paleontologist. Science, 

 n.s., 26: 744- I907- 



Also H. F. Osborn. The Four Inseparable Factors of Evolution ; theory of 

 their distinct and combined action in the transformation of the Tithanotheres, 

 an extinct family of hoofed animals in the order Perissodactyla. Science, 

 n.s., 27 : 148. 1907. 



