THE PRESENT POSITION OF THE THEORY OP ORGANIC EVOLUTION. 97 



appearance as a sport of a crow with an enormously long beak, 

 whose offspring would found a new race, but by the preservation 

 of a large number of crows witli moderately long beaks in each 

 generation. 



It is a matter of history that in about 20 years Darwin's 

 theory won its way to wellnigh world-wide acceptance, and it 

 was then obvious that the next step to be taken in the elucida- 

 tion of biological law was the determination of the causes and 

 course of variation. To this task Darwin applied himself, and 

 in I 868 brought out his master- work, to which I have already 

 alluded, The Va/riation of Animals and Plants under Domestica- 

 tion, The compilation of this book was really the end of all his 

 labours, of which the Origin of Species was merely a preliminary 

 account; an account which the pressure of friends induced him 

 to write before he was ready to place his completed evidence 

 before the world. In his second book he takes up the question 

 of I he cause of variation, and after a survey of the whole field he 

 arrives at the tentative conclusion that variations are due to the 

 indirect effect of changes in the conditions of life, that is in the 

 environment. The indirect effect, he says advisedly, because on 

 the one hand it is well known that changes in the environment 

 often produce a direct effect on the body : thus cold stimulates 

 the growth of hair, as may be easily seen in the case of children 

 who run about bare-legged on the shore. Since, however, the 

 only bridge between parent and offspring is the tiny germ-cell, 

 it is obvious that nothing can have an hereditary effect except it 

 affects the germ-cell, and as Darwin did not see how the germ- 

 cell could be affected by a change in the body of the parent so 

 as to give rise to a corresponding change in the body of the 

 offspring, he speaks of an t: indirect effect," meaning, 1 suppose, 

 that the germ-cell is affected but not necessarily in a correspond- 

 ing manner. Yet, in spite of everything, he admits that there is 

 some evidence that the effects of use in strengthening an organ 

 and of disuse in diminishing it are handed on from one generation 

 to another in some cases. To account for this he puts forward 

 his theory of pangenesis. According to this theory, every part 

 of the body produces gemmules, and these gemmules circulate 

 in the fluids of the body and accumulate in the genital organs. 

 If an organ is altered, the gemmules which it casts off will be 

 altered — and these altered gemmules accumulating in the 

 genital cells eventually make their influence felt on the course 

 of heredity. Though this theory has been regarded as wild and 

 fantastic by many subsequent writers, and although Darwin 

 himself regarded it merely as a tentative hypothesis, it seems 



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