SUMMARY. 285 



is insufficient to account for evolution, Nageli 

 has thought to help the explanation by the 

 assumption of an innate tendency toward progres- 

 sion, which regulates the variations and modifi- 

 cations of individuals in such a way that a con- 

 tinual advance is the result. This hypothesis is, 

 however, not only uncalled for by the facts, but it is 

 inconsistent with some of them, and it has the 

 further disadvantage of being completely incom- 

 prehensible. No one can form the slightest con- 

 ception of what a tendency is which may continue 

 to reside in animals for millions of years, and can be 

 transmitted from one generation to another. Al- 

 though we may doubtless be obliged to accept facts 

 which we don't understand, there is no need of ac- 

 cepting such a one as this unless the facts unques- 

 tionably demand it. Mivart thinks that species 

 are sudden in their appearance, having their origin 

 in extraordinary births. He further assumes, as a 

 regulation of these births, a unitary bond running 

 through nature. Of this bond he can tell us nothing, 

 not even whether it is the result of natural law or 

 not. He would probably consider it a supernatural 

 bond. This view is an evolutionary one, since it 

 admits genetic descent ; but it is, to a certain ex- 

 tent, a view of special creation, since it assumes that 

 each species has had a sudden origin regulated by 

 some unknown force. Some American naturalists 

 have resuscitated the old Lamarckian theory, that it 

 is the inherited effects of use and disuse which 

 contain the explanation sought. Consciousness and 

 effort come in here as an important factor. But, 



