CH. xiv] GENERAL DISCUSSION 167 



Yet I have been assured by one of its most eminent supporters 

 that it contains none, but rests upon proved facts. The following 

 list gives the most important assumptions : 



1. That a small structural variation may be advantageous 

 enough to call in the action of natural selection (pp. 4, 13). 



2. That a small advantageous variation may be inherited 

 (p. 4). 



3. That it mav be added to, and become more and more 

 marked in succeeding generations (pp. 4, 54, 106, 165). 



4. That the whole number of individuals upon a considerable 

 area will show the same advantageous variation, i.e. probably. 



5. That the variations are controlled by external conditions 

 (pp. 5, 165). 



6. That the whole number of individuals carrying a useful 

 variation can, and does, fight as a unit (pp. 107, 142, 144, 166). 



7. That the parent form does not also become adapted 

 (pp. 4, 13, 54). 



8. That adaptation is structural rather than functional 



(p. 4). 



9. That structural characters are the means of expression of 

 adaptation (p. 14). 



10. That differences in structure mean differences in adapta- 

 tion (pp. 52, 109). 



11. That the variety with the advantageous variation, slight 

 though it would be at first, will defeat the parent in the struggle 

 for existence (p. 4). 



12. That the new form produced by natural selection, and 

 adapted to area B, became thereby also better adapted to A, the 

 area occupied by the less well adapted parent species (p. 144). 



13. That all variations that survive must be useful, or must be 

 correlated with variations that are useful or at least that are not 

 harmful enough to be of serious disadvantage (pp. 57, 58). 



14. That the new form will invade the territory of the old, and 

 kill it out there, without being lost in hybrids (p. 143). 



15. That the defeated species w411 gradually become relics, and 

 ultimately disappear (pp. 4, 17, 91, 97-8). 



16. That fluctuating variation is irreversible. 



17. That fluctuating variation is qualitative as well as quanti- 

 tative. 



18. That fluctuating, or even small, variations can be added 

 up so that they pass the sterility line that usually divides one 

 species from the next. 



