THE DARWaNIAN THEORY 



547 



producing only two seeds a year would give rise to sixty- 

 four plants in seven years, and to 1,048,576 in twenty-one years, 

 if all lived to maturity. If an animal produced ten pairs of young 

 annually and each indi\ddual lived ten years, there would be 

 25,937,424,000 in ten years and over 700,000,000,000,000,000,000 

 in twenty years. In the elephant, one of the examples cited by 

 Darwin as a slow breeder, 

 there would be alive at the 

 end of 750 years nearly 

 19,000,000 elephants as 

 descendants of a single 

 pair, if all the indi\aduals 

 lived ninety years and each 

 female brought forth six 

 young. Examples of forms 

 that would increase much 

 more rapidly are: the 

 conger eel, which has 

 been estimated to produce 

 15,000,000 eggs annually; 

 and the herring, which may 

 produce 20,000,000. For 

 the American oyster, which 

 may produce as many as 

 60,000,000 eggs, IMarshall 

 gives the following calcu- 

 lation. If one should start 

 with a single oyster and 

 let it produce 16,000,000 

 eggs, all of which are 

 fertilized and come to ma- 

 turity, and if half of these 

 should become females and go on increasing at the same rate, 

 there would be in the third generation sLxty-four millions of 

 miUions of females and in the fifth generation thirty-three 

 thousand millions of milhons of miUions of milhons of females. 

 If to these be added an equal number of males, the bulk of 

 the shells would then be equal to more than eight times that of 

 the earth. Again, in the pedigreed cultures of the protozoan 

 paramoecium. Woodruff calculated that 3029 generations might 



Fig. 303.— Thomas Henry Huxley (1825- 

 1895), comparative anatomist and pale- 

 ontologist, and effective popular advocate 

 of organic evolution in the decades 

 following the publication of Darwin's 

 "Origin of Species." 



From Pirrson and Schuchert, "Textbook of 

 Geology," John Wiley and Sons, copyright, 

 1924. reprinted by permission.) 



