96 EVOLUTION AND MAN S PLACE IN NATURE 



as to the mode of securing the result. Brooks has 

 well said: A satisfactory theory of heredity must 

 explain what it is in the structure and organisation of 

 the ovum, which determines that each ovum should 

 produce its proper organism. 1 



On this hypothesis of Pangenesis, Darwin seeks to 

 account for transmission of minute variations, along 

 with those essential to the species. Tracing the laws 

 of inheritance as these are suggested by comparative 

 biology, he gives prominence to such points as the 

 following : Two distinct elements are included under 

 the term &quot; inheritance,&quot; some appearing at birth, 

 some &quot; transmitted through the early years of life,&quot; 

 which are developed only at maturity, or during old 

 age. 2 Thus the germ life discloses its potentiality in 

 the line of growth after birth onwards to maturity. 

 Even distinctions between successive periods of life are 

 maintained in this way. A new character appearing 

 in a young animal, whether it lasts through life or is 

 only transient, will, in general, reappear in the off 

 spring at the same age, and last for the same time. 3 

 Most of our domestic races have been formed by the 

 accumulation of many slight variations. 4 All these 

 cases are intelligible on the hypothesis of pangenesis ; 

 for they depend on the gemmules of certain parts, 

 although present in both sexes, becoming, through 

 the influence of domestication, either dormant or 

 developed in either sex. 5 From these illustrations it 

 will appear how much any marked gain in structure 

 and function must depend on inheritance of acquired 



1 The Laio of Heredity, by W. K. Brooks, p. 40. 



2 The Descent of Man, p. 227. 



3 Ibid., p. 228. 4 Ibid., p. 230. 5 Ibid., p. 231. 



