HEREDITY AND VARIATION; LOGICAL AND 



BIOLOGICAL. 



By WILLIAM KEITH BROOKS. 

 (Read April 20, igo6.) 



One need know little of the current literature of biology to be 

 aware that many hypotheses have been proposed to account for the 

 resemblance of offspring to parent. This resemblance is commonly 

 held to be due to the transmission of a substance of inheritance, and 

 we are told that this substance is the residence of the species and the 

 bearer of its qualities. 



Reproduction is the transmission of living matter of some sort, 

 and it is part of the legitimate work of biology to discover, by the 

 scientific method of observation and experiment, what it is in the 

 transmission of which reproduction consists ; but it by no means fol- 

 lows that there is meaning in our words when we call that which is 

 thus transmitted in reproduction the substance of heredity, or the 

 bearer of the species. 



So far as the word is used inductively in biology, heredity is the 

 resemblance of child to parent, of offspring to ancestor, while the 

 difference between child and parent is called variation. These words 

 are also used metaphorically to designate the cause or the explana- 

 tion of the resemblances and differences between descendants and 

 ancestors, just as gravitation is used metaphorically to designate that 

 which makes things gravitate, geotropism that which makes roots 

 grow downwards, and selection that which brings about survival in 

 the struggle for existence. In what I have to say I shall restrict 

 myself to the inductive meaning of the words, for I know that your 

 thoughts are so free from the bonds of metaphysics that you know 

 we accomplish nothing by saying that heredity makes beings inherit, 

 or that variation makes them vary, or that selection selects. 



Let us consider the word inheritance as a term to designate the 

 resemblance between child and parent. You know that while the 

 descendant does, on the average, resemble its ancestors and collateral 



