CHAPTER VIII. 



OTHER THEORIES OF SPECIES-FORMING AND 

 DESCENT : THEORIES AUXILIARY TO SELEC- 

 TION. 



To be considered now are two categories of (mostly) 

 post-Darwinian theories, viz., those which have been offered 

 Classification as alternative theories intended to replace more 

 of other theories or less nearly entirely the selection theories, 

 alternative to* an ^ those other theories intended to serve as 

 selection. auxiliary and supporting theories for Darwin- 



ism. Obviously these two kinds of theories l emanate from 

 the two opposing biological camps. Several of these alter- 

 native and auxiliary theories of species-forming have been 

 referred to incidentally in the preceding two chapters, for 

 the replacing theories constitute part of the strength of 

 the anti-Darwinians, while the supporting theories are dis- 

 tinctly relied on to help maintain the Darwinian front. The 

 present chapter, then, is mostly a continuation of the pres- 

 entation of "Darwinism Attacked" and "Darwinism De- 

 fended," which is given a separate place because of the 

 special character of the argument with which it has directly 

 to do, namely, the synthetic or theory-building side, instead 

 of the analytic or theory-destroying side, and because of 

 the probable advantage to the student and general reader 

 wishing to understand and compare the general character 

 and significance of the various new theories of species- 

 forming with whose names, such as heterogenesis, ortho- 

 genesis, metakinesis, geographic isolation, biologic isolation, 

 organic selection, or orthoplasy, he occasionally meets in his 



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