THE EPIC OF EVOLUTION 527 



carriers of hereditary qualities that have come down the long ancestral 

 line through the continuous germinal stream. 



Other Theories 



It would be going too far afield to attempt here to review all of the 

 other theories that have been advanced to account for evolution in 

 whole or in part. Some of these are subsidiary to the theory of 

 natural selection, as, for instance, Darwin's own theory of Pangenesis, 

 already mentioned, and also his theory of Sexual Selection. 



Perhaps the largest group of alternative theories of descent are 

 those which center around the idea of Orthogenesis. These theories 

 hold that variation is not qualitative and random in character in 

 every direction, but quantitative, that is, either plus or minus modifi- 

 cations and in one direction only. According to this idea variations 

 form a determinative series that goes forwards or backwards relent- 

 lessly, with little reference to adaptation and in spite of environmental 

 influences. Overspecialization, as in the case of the gigantic antlers 

 of the extinct Irish elk, finds in orthogenesis an easy explanation, 

 for cumulative variations of this kind may gain such headway in one 

 direction that they overshoot the goal and lead to eventual destruc- 

 tion. 



Weismann in his supplementary theory of Germinal Selection and 

 Wilhelm Roux (1850-1924) with his Kamjpf der Teile, or struggle 

 between the parts, have transferred the struggle for existence from 

 individuals to the component parts of individuals, while various 

 vitalistic attempts, like Bergson's Elan Vital, and George Bernard 

 Shaw's Life Force, have been made, which dodge the whole issue by 

 invoking some mystical agency that is beyond the reach of scientific 

 testing by experiment. 



Conclusion 



Darwin's great service was that he formulated a plausible explana- 

 tion for the theory of descent which did not beg the whole question 

 by resorting to the supernatural. " ^Mother Nature " is not a directive 

 personality substituted by "ungodly scientists" for the supernatural 

 Creator of all things. There is no more personality in natural selec- 

 tion than there is in the wind, which "selects" the grain from the 

 chaff. Nor is there necessarily any more design, any more purpose 

 or moral bearing to natural selection than there is in the action of the 

 law of gravity, or in the shaping of water-worn rocks by the surf 



