ORIGIN OF SPECIES 229 



reproduces the leading characteristics of the species 

 to which its parents belong. Heredity has to do with 

 the preservation of traits, or characteristics, peculiar 

 in general to the species and in particular to the 

 progenitors of an offspring. The possession of special 

 traits by an individual when assignable to heredity, 

 may come as an inheritance from, or through, the 

 mother or from, or through, the father. 



It is well known that heredity does not generally 

 manifest itself in a simple reappearance in the off- 

 spring of maternal traits plus paternal traits. Slight 

 variations are the order; and these are not haphazard 

 products. The classic work of Mendel and De Vries 

 has demonstrated this experimentally. All the results 

 obtained by these investigators were secured by 

 means of artificial selection. 



Especially to the point is the unquestioned fact 

 that so far as the offspring is concerned, sexual 

 selection operates irrevocably at the moment of 

 fertilization. Hereditary traits can be transmitted 

 only at the time of fertilization. Thus fertilization 

 (when a spermatozoon is involved) is unthinkable 

 apart from heredity, and heredity is unthinkable 

 apart from fertilization. 



In fertilization, the spermatozoon then plainly has 

 the dual role of initiating specific changes in the egg 

 (which lead to cell division and growth), and of 



