CHAPTER V 



FACTS OP INHERITANCE 



Progress during the Darwinian Era — Demonstration of Heritable 

 Qualities — Heredity, a Term for the Genetic Relation between 

 Successive Generations— Appreciation of Distinction between 

 Nature and Nurture — The Idea of the Continuity of Genera- 

 tions — Critical Attitude in Regard to Various Conclusions — 

 Mendelisra — Methods of Studying Heredity — Microscopical 

 Study of the Germ-cells — Statistical Study : Filial Regression 

 — Galton's Law of Ancestral Inheritance — Experimental Study 

 — Pairing of Similar Pure-bred Forms — Blending — Particulate 

 Inheritance — Exclusive Inheritance— Reversion — New Depar- 

 tures — Mendelian Inheritance — Unit Characters — The Case 

 of Andalusian Fowls — ^Waltzing Mice — Occurrence of Mendelian 

 Inheritance — Practical Importance of Mendelism — Much 

 Progress but Great Uncertainty — Transmission of Acquired 

 Characters — Disease — Facts and Possibilities — A Striking Case 

 — Logical Position of the Question — Cases where the Theory 

 of Modification-inheritance is Inapplicable — Importance of 

 Environment and Function Remains — Selection and Stimulus 

 — Indirect Importance of Modifications — Practical Import of 

 the Question as to the Transmission of Acquired Characters — 

 Inheritance of Moral Character — Three General Conclusions. 



Even in ancient times men pondered over the 

 resemblances and differences between children and 

 their parents, and wondered as to the nature of 

 the bond which links generation to generation; 

 but, although a recognition of these problems is 

 old, the precise study of them is altogether modern, 

 and may almost be called Darwinian. For it was 

 largely through Darwin's influence that the scientific 

 study of heredity began. " Before and after 

 Darwin," Professor Osborn says, " will always he 



129 9 



