68 HEREDITY AND VARIATION 



attained by the individuals of one generation tends to be 

 very nearly the same as the average character of the preceding 

 generation. This is the broad fact of specific inertia. 



A False Antithesis between Heredity and Variation. — 

 Much obscurity of thought has been due to the false antithesis 

 between heredity and variation. When we say that like tends 

 to beget Hke, that offspring tend to resemble their parents 

 and ancestors, we are stating a fact of life. But when we 

 speak of an opposition between a force or principle of heredity, 

 securing resemblance between offspring and their parents, and 

 a tendency to variability which makes offspring different from 

 their parents, we are indulging in verbiage. Heredity, as we 

 have repeatedly said, is the relation of genetic continuity between 

 successive generations, and it is such that while many characters 

 seen in parents persist in their offspring, there is also in most 

 cases a distinct individuality in these offspring. Heredity is 

 a condition of evolution, a condition of inborn variations ; it 

 is just a name for the reproductive or genetic relation between 

 parents and offspring. The inheritance which was expressed 

 in the development of the parent may be almost identical with 

 the inheritance which is expressed in the development of the 

 offspring, but in most cases the inheritance does not persist 

 in this intact way from generation to generation, and then we 

 speak of variation. The contrast is not between heredity and 

 variation, but between inertia and change, between continuity 

 or persistence and novelty or mutation, between completeness 

 of hereditary resemblance and incompleteness of hereditary 

 resemblance. 



As Prof. W. K. Brooks says (1906, p. 71) : " Living beings do 

 not exhibit unity and diversity, but unity in diversity. These 

 are not two facts, but one. The fact is the individuality in 

 kinship of living beings. Inheritance and variation are not 

 two things, but two imperfect views of a single process." 



