98 Dynamic Theory. 



lished the Mammal as the highest animal type and perfected the de- 

 velopment of Endogens grasses and cereals necessary to sustain that 

 high type. 



Thus Geology shows in general an advance in life from age to age 

 both in the animal and vegetable kingdoms. Yet there are many 

 changes which are not advances. Genera, tribes and races by the thou- 

 sand have gone down hill and hav-e finally disappeared. But the flexi- 

 bility of organisms has always permitted their environing influences to 

 alter and adapt some of them to every new condition as it has arisen. 

 The theory of evolution requires that organic life should begin with the 

 simplest forms, and in the nature of things, no kind of differentiation 

 can take place in the simple without producing the complex. But when 

 a degree of complexit}^ has been reached it does not follow that further 

 differentiation will increase the complexity. It may diminish it. A 

 son may be inferior to his father. This point has been alluded to be- 

 fore. 



Personal development or individual growth part by part from the em- 

 bryonic germ as we have seen, is by way of a series of steps or stages, 

 each one of which is the equivalent of the permanent value of the same 

 part in an ancestor. But this general truth is more literally and 

 minutely true in the case of the lower types than in the higher. We 

 have good reason to believe that in the embryonic development of the 

 highest types many cut-offs or short cuts are taken, and steps are 

 skipped, or two or three steps condensed into one. All along the Mis- 

 sissippi river there are bayous and lagoons. These are sections of river 

 bed which the stream has abandoned. They are usually in the shape of 

 a circuitous bend, across the isthmus of which the river has cut a new 

 connection. And they remain there like atrophied rudiments. In the 

 course of time they become filled up and obliterated, while new ones 

 form elsewhere. This is something like the action in embryonic and 

 race development. The rudiments which we see left behind after the 

 embryo is complete are really but a small proportion of the whole num- 

 ber ; the majority having been aborted and obliterated during the devel- 

 opment. As in the course of race evolution these steps increase in 

 number they are crowded together, till finally many of them become 

 quasi simultaneous that were originally consecutive. And the growth 

 proceeds across the isthmus and the bend is not constructed at all. 



This modification of the track or path of development is the expres- 

 sion of new adaptations of organs and parts, which adaptations may be 

 reversions or degradations instead of advances. Thus the legs of a 

 mammal have been developed from the fins of fishes. The flippers of 

 the whale have in turn been developed from the legs of the mammal. 

 It would probably be less work to turn fins directly into flippers, than 



