XXX 



THE MENDELIAN CLUE 



IN pre-Darwinian days people spoke of Heredity 

 with a capital letter as if it were a power or 

 principle that did things just as many still 

 speak of Evolution. It was one of Darwin's 

 many services that he showed the organic linkage 

 between one generation and another to be amenable 

 to scientific inquiry and statement. To him heredity 

 was the genetic relation between successive genera- 

 tions a relation that secures, through the vehicle 

 of the germ-cells, a persistence of a large measure 

 of specificity both in form and habit, both of micro- 

 scopic architecture and chemical metabolism. His 

 particular theory (pangenesis) of what distinguished 

 the germ-cells from the specialized body-cells \vas 

 not, indeed, acceptable, but it was with Darwin 

 that the scientific study of heredity practically 

 began. To his cousin, Francis Galton, and to 

 Professor Weismann we owe the elucidation of an 

 idea which seems to have occurred to several others 

 the idea of germinal continuity that the reason 

 for like begetting like is the persistence of a specific 

 organization through a lineage of unspecialized 

 germ-cells. While most of the germinal material of 

 the fertilized ovum is used to build up the body of 



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