Recapitulation and Conclusion. 321 



does group and illuminate many classes of facts which 

 are quite inexplicable without it. 



The evidence from hybrids seems to be strongly in its 

 favor, and it presents many features which are perfectly 

 simple and natural, according to our view of heredity, 

 although no other explanation of them has ever been 

 offered. 



Hybrids and mongrels are^ highly variable, as we 

 should expect from the fact that many of the cells of 

 their bodies must be placed under unnatural conditions, 

 and must therefore have a tendency to throw off gem- 

 mules. Darwin's pangenesis hypothesis accounts for 

 the variability of hybrids, but it does not account for 

 the very remarkable fact that hybrids from forms which 

 have long been cultivated or domesticated are more vari- 

 iable than those from wild species or varieties, or for the 

 .fact that the children of hybrids are more variable than 

 the hybrids themselves. 



Our view not only explains the variability of hybrids, 

 but it also accounts for the excessive variability of hy- 

 brids from domesticated forms, and of the children of 

 hybrids, for domesticated animals and plants live under 

 unnatural conditions, and they are therefore more pro- 

 lific of gemmules than wild species, and as the body of 

 a male hybrid is a new thing the cells will be much more 

 likely than those of the pure parent to throw off gem- 

 mules. 



The fact that variation is due to the male influence, 

 and that the action upon the male parent of unnatural 

 or changed conditions results in the variability of the 

 child, is well shown by crossing the hybrid with the pure 

 species, for when the male hybrid is crossed with a pure 

 female the children are much more variable than those 

 born from a hybrid mother by a pure father. 



