The Evolution of Organisms 155 



tistical registration of organic changes that actually 

 occur is rapidly helping us out of the slough of 

 vagueness, in which, to the physicist's contempt, 

 biology has so long floundered. It is too soon to 

 sum up the results of recent studies on variation, 

 but some facts are clear. 



(1) Variability is even greater than Darwin sup- 

 posed, and is not less among creatures living in a 

 state of nature than among those domesticated or 

 cultivated forms on which the great master con- 

 centrated his attention. Whenever we settle down 

 to measure, to identify, to describe, we find that 

 specific diagnoses are average statements, that spe- 

 cific characters require a curve of frequency for 

 their expression, that the living creature is usu- 

 ally a Proteus. It is true that there are long-lived, 

 non-plastic, conservative types, built, as it were, 

 not for a day, but for all time, like Lingula, and 

 perhaps a score of other well-known organisms, 

 where no visible variability (of hard parts, at 

 least) can be proved even in a million years. But 

 to judge from these as to the march of evolution is 

 like estimating the rush of a river from the eddies 

 of a sheltered pool. 



(2) It has become possible to distinguish be- 

 tween minute fluctuations, which seem to be of 

 general occurrence, in which the offspring has a 

 little more or a little less of a given character than 

 its parents had, and discontinuous variations or 



