374 ANIMAL BIOLOGY 



to acquire or lose by the influence of the circumstances to which 

 their race may be for a long time exposed, and consequently by the 

 influence of the predominant use of such an organ, or by that of 

 the constant lack of use of such part, it preserves by heredity and 

 passes on to the new individuals which descend from it, provided 

 that the changes thus acquired are common to both sexes, or to 

 those which have given origin to these new individuals." 



Lamarck's first law is, in general, sound, but the second — the 

 inheritance of acquired characters — is highly questionable to say 

 the least, because, as we have seen, there is no evidence that modi- 

 fications are heritable. But this weak point was not the one which 

 caused the rejection of the theory by Lamarck's contemporaries. 

 The various antagonistic influences can be summed up by saying: 

 the time was not ripe for evolution. 



2. Darwinism 



Then a generation later appeared Charles Darwin in England. 

 With a better background prepared for him, in part by headway 

 being made by the evolution theory in geology, he did two things 

 in his Origin of Species which was published in 1859. He presented 

 an overwhelming mass of facts which could be explained most 

 reasonably by assuming the origin of existing species by descent 

 with change from other species. And he offered as an explanation 

 of the origin of species the theory of "natural selection, or the 

 preservation of favoured races in the struggle for life." It was the 

 combination of the facts and the theory to account for the facts 

 that won the thinking world to organic evolution — a common 

 height from which we view the whole world of living beings. 

 (Fig. 296.) 



What, in brief, was the theory? In the first place, without 

 attempting to determine the cause of variations, Darwin showed 

 the great amount of variation in nature. And any and all kinds 

 of heritable variations were, broadly speaking, important - - though 

 he somewhat grudgingly admitted the inheritance of acquired 

 characters. 



The universality of variations established, Darwin emphasized 

 the fact that the power of reproduction of organisms far ex- 

 ceeds space for the offspring to live in and food for them to eat. 

 Some recent data will illustrate this point. A microscopic Para- 

 mecium possesses the power to eat, grow, and reproduce — to 



