THEORY OF EXTRAORDINARY BIRTHS. 261 



much for his sudden births. That this factor may 

 have had its influence will hardly be denied by any 

 one, and in some cases new species may have arisen 

 in accordance with, these extraordinary births. This 

 theory has so many facts in its favor that it seems 

 as if it must have a certain amount of truth. But 

 at the same time it will not account for all of the 

 facts of nature and some of the difficulties which we 

 have seen are just as forcible even when we substi- 

 tute these sudden jumps for the minute variations 

 of Darwinism. While every one acknowledges that 

 natural selection is a potent factor in the modifica- 

 tion of species, scientists refuse to consider it as 

 more than one factor. And in the same way, while 

 it seems probable that sudden extraordinary births 

 may have had their influence in the origin of species, 

 here too it must be recognized that we have only 

 a single factor. 



Indeed, after all, this theory of Mivart does not 

 very much help toward a solution of the problem of 

 the origin of species, for, like the theory of Nageli, 

 it does not explain, but refers every thing to un- 

 known internal forces. To be sure, in this case, it is 

 a demonstrated fact that some internal force exists, 

 for it cannot be questioned that these extraordinary 

 births do sometimes occur. Since we believe nature 

 to be universally governed by law, even these ir- 

 regular occurrences must be under the influence of 

 some law. But of its working and significance 

 Mivart can tell us nothing. We have seen that 

 natural selection is lacking, since it is founded on 

 variations which it cannot explain. The same ob- 



