EVOLUTION THE MASTER-KEY 



advances in biology, along lines which he discerned 

 long ago, I can hardly say. 



Make the Abbe" Mendel's discovery simple I 

 cannot, the facts being complex; but I must do 

 my best. Each of the higher animals and plants 

 is formed by the union of two cells of different 

 sex, which are called gametes; and in these the 

 problem of heredity obviously centres. The child 

 "has his father's smile," we say; and we know that 

 this character must have been transmitted in the 

 paternal gamete. Now the first question we must 

 ask is plainly this: How are the gametes formed? 

 And we know that each gamete of either sex is 

 formed by a series of cell-divisions, beginning in 

 what we may call a germ mother-cell. Now the 

 essence of Mendel's discovery is this: The germ 

 mother-cell which is about to divide and form the 

 gametes that are to reproduce any individual in 

 his or her descendants, itself contains characters 

 derived from both the parents of that individual. 

 These characters exist in the germ mother-cell in 

 opposed pairs e.g., a character corresponding to 

 the white pigmentation of the individual's father, 

 and another corresponding to the black pigmen- 

 tation of the mother and when the germ mother- 

 cells divides so as to form gametes, these pairs are 

 split up or segregated, the black character going 

 to one gamete and the white to another. Thus 

 the gametes or sex-cells of a gray individual will 

 not be potentially gray, but either black or white. 

 Observe the result. The individuals of the new 

 118 



