32 DARWINISM TO-DAY. 



ence acting on the germ-plasm from which the embryo is 

 derived. 



Now the natural selection theory, in its Darwinian and 



neo-Darwinian form, presupposes fortuitously occurring 



congenital variations of practically infinite 



Darwinian, or var i e ty in all parts of all organisms. Actual 



continuous, varia- 

 tion according to observation shows that all parts of all organ- 



chanc7 f isms do vary and that they vary congenitally, 

 that is, independently of any immediate in- 

 fluence during development exercised from without by 

 environmental conditions, as well as in response to these 

 environmental influences, and finally that in many cases this 

 variation is fortuitous, that is, that it occurs according to 

 the laws 8 of chance. The industrious statistical study of 

 variations, including the tabulation of the variation con- 

 dition in long series of individuals of the same species or 

 race and the mathematical formulation of this variation 

 condition, have shown that in many specific cases, studied 

 in numerous kinds of animal and plant forms, the character 

 of the variation in any particular character may be truly 

 represented (with close approximation) by the mathematical 

 expression and curve which would exactly define the condi- 

 tion in which the variation would exist if it actually followed 

 the law of error. It is these continuous series of slight 

 variations, these variously called fluctuating, individual, or 

 Darwinian variations, occurring in all organisms at all times 

 and often following, in their occurrence, the laws of chance, 

 on which Darwin's theory of species-forming by natural 

 selection is based. But this same industrious statistical 

 and quantitative study of variation, which has proved 

 that some variations do occur regularly, fluctuating 

 around a mean or mode, has shown, as well, that in 

 many cases the variations distinctly tend to heap up 

 on one side or the other of the mean, that is, that they 

 tend to occur along certain lines or toward certain direc- 



