ACQUIRED ADAPTATIONS 441 



he cannot make such a sequence adequately express his idea 

 of their kinship. 



If we are warranted in supposing that all members of the 

 crowfoot family are the descendants of plants like our marsh- 

 marigold we may assume with scarcely less probability that 

 plants closely similar to these primitive marsh-marigolds 

 were the ancestors of all of the crowfoot order, and indeed 

 that from plants having very much the same primitive 

 cliaracteristics came, in the course of geological ages, all of 

 the dicotyls and perhaps all the monocot3ds as well. Our 

 mental images of ancestral forms are necessarily dim in pro- 

 portion to the remoteness of the form conceived, and are 

 likely to change as we receive new light. Yet these mental 

 diagrams of things no longer to be seen help our seeing of 

 the things about us. From the evolutionary point of view 

 all life takes on a new significance. The possibility of gaining 

 some glimpses of how the living world came to be as it is, 

 makes all life more deeply interesting. Details of structure 

 or behavior in a humble plant may lead us to some of the 

 greatest truths of life. 



166. Acquired adaptations. The belief that all existing 

 organisms are the more or less modified descendants of rel- 

 atively primitive forms, is now as generally held bj^ naturalists 

 as is the belief in universal gravitation among astronomers. 

 Yet astronomers are still striving to understand how it is 

 that the force of gravity can act as it does; likewise naturalists 

 are still debating the fundamental question as to how in- 

 herited modifications have arisen. That somehow plants 

 and animals have evolved is now taken for granted; but 

 there are wide chfferences of opinion as to the way in which 

 the changes have been wrought. 



In these few pages w^e can glance only briefly at the lead- 

 ing views now held regarding the origin of species. Each 

 theory aims to account for the appearance of those peculiari- 

 ties of structure or behavior which distinguish one group 

 from another; as for instance the climbing habit of clematis 

 and the long, mostly hairy-tailed fruit which is found no- 

 where else in the family except with certain anemonies in- 

 habiting wind-swept fields. Peculiarities of this sort are 



