OUE NATURAL INHERITANCE 77 



tion. They may appear so early that they disappear, 

 being fatal before birth. 



(g) Commoner than the inheritance of disease or 

 tendencies to disease is the inheritance of abnormal 

 peculiarities, such as colour-blindness, night-blindness, 

 deaf-mutism, well-proportioned dwarfness, brachydac- 

 tylism, polydactylism, haemophilia, baldness, obesity. 



§7. Statistical Study op Heredity 



While the great experimental work of Gregor Mendel 

 lay buried in the records of the Naturalists' Society of 

 Briinn, there was developed in Britain a statistical 

 study of inheritance, especially associated with the 

 names of Sir Francis Galton and Professor Karl Pearson. 

 It was Galton who really began to study the inheritance 

 of particular characters through successive generations, 

 and to measure quantitatively the degrees of hereditary 

 resemblance. Galton was led to the Law of Ancestral 

 Inheritance, according to which the average contribu- 

 tions to each inherited faculty are a half from the parents, 

 a quarter from the grandparents, an eighth from the 

 great-grandparents, and so on backwards, in the same 

 diminishing ratio. " The prepotencies or sub-potencies 

 of particular ancestors, in any given pedigree, are elimin- 

 ated by a law which deals only with average contribu- 

 tions, and the varying prepotencies of sex in respect 

 to different qualities are also presumably eliminated " 

 (Galton, Natural Inheritance.) The ratio of parental, 

 grandparental, great-grandparental, and other average 

 contributions worked out by Pearson is different 



