94 THE THEORY OF MUTATIONS 



modifications which are insignificant and minute, 

 whether fortuitous or not." And he proceeds : 

 " Arguments may yet be advanced in favour of 

 the view that new species have from time to time 

 manifested themselves with . . . .suddenness, by 

 modifications appearing at once (as great in degree 

 as are those which separate Hipparion from Equus), 

 the species remaining stable in the intervals of 

 such modifications : by ' stable ' being meant 

 that their variations only extend for a certain 

 degree in various directions, like oscillations in a 

 stable equilibrium. This is the conception of Mr. 

 Galton,* who compares the development of species 

 with a many-faceted spheroid tumbling over from 

 one facet, or stable equilibrium, to another." 



Whether the change takes place rapidly or 

 gradually from one facet to another, the result is 

 the production of a form widely comparatively 

 speaking widely differing from the original in- 

 dividual. Is this the production of a new species ? 

 In answering that question we are naturally con- 

 fronted with the long-standing inquiry as to what 

 after all is meant by a species. Of course in nature 

 there are no such things as species, for species are 

 only categories invented by men for the purpose 

 of aiding classification. But looked at from that 

 point of view it is by no means easy is it even 

 possible ? to say where a species ends and a 

 variety begins. It is quite easy to separate a flower- 

 ing plant from a cryptogam ; so also is it easy to 

 distinguish a member of the rose family from one 

 belonging to that of the willows. But when we 



* Hereditary Genius : An Inquire into its Laws, etc. 



