282 EVOLUTION OF TO-DAY. 



ous variations for successive generations in those 

 parts where change is needed. If it can be believed 

 that these laws are real ones, it is plain that a long 

 step is taken toward the solution of the problem of 

 the modification of species. The various objections 

 urged against natural selection, from the indefinite- 

 ness and minuteness of the variations, all disappear. 

 The views of those who believe in the great effect 

 of use and disuse receive much support, and even 

 the extraordinary births of Mivart are somewhat 

 more easily understood. This theory of heredity is 

 therefore an addition to all of the views we have 

 examined. 



It would be premature to attempt to draw any 

 positive conclusion in regard to this theory of 

 Brooks. There are certainly many objections which 

 arise and will preclude its acceptance in an unmodi- 

 fied form. While it very aptly explains certain series 

 of facts, it will not apply to all. But that this theory 

 may have reached one of the important laws of 

 heredity seems highly probable. 



Summary. 



The theories noticed in these two chapters are 

 not the only ones which have been advanced with a 

 like object, namely, to explain evolution. The 

 others are, however, of less importance, and need 

 not detain us. It will probably appear to many 

 readers that none of them are satisfactory, and that, 

 granting evolution to be true, the explanation is not 

 yet fully obtained, not even by a satisfactory hy- 

 pothesis. Let us notice again the problem to be 



