Characters as Adaptive and Specific. 231 



degrees of differentiation so frequently shade into 

 one another by indistinguishable stages (or, rather, 

 that they always do so, unless intermediate varieties 

 have perished), modern naturalists are well awake to 

 the impossibility of securing any approach to a uniform 

 standard of specific distinction. On this account 

 many of them feel a pressing need for some firmer 

 definition of a species than this one which, in 

 point of fact, scarcely deserves to be regarded as 

 a definition at all, seeing that it does not formu- 

 late any definite criterion of specific distinctness, 

 but leaves every man to follow his own standards 

 of discrimination. Now, as far as I can see, 

 there are only two definitions of a species which 

 will yield to evolutionists the steady and uniform 

 criterion required. These two definitions are as 

 follows. 



4. A group of individuals which, however many 

 characters they share with other individuals, agree in 

 presenting one or more characters of a peculiar and 

 hereditary kind, witk some certain degree of dis- 

 tinctness. 



It will be observed that this definition is exactly 

 the same as the last one, save in the addition of the 

 words "and hereditary." But, it is needless to say, 

 the addition of these words is of the highest im- 

 portance, inasmuch as it supplies exactly that objective 

 and rigid criterion of specific distinctness which the 

 preceding definition lacks. It immediately gets rid 

 of the otherwise hopeless wrangling over species as 

 "good" and "bad," or "true" and "climatic," of 

 which (as we have seen) Kerner's essay is such 

 a remarkable outcome. Therefore evolutionists have 



