THE FACTORS OF EVOLUTION 151 



have already heard on a previous occasion. I will here only recall 

 the great differences in the formation of the caecum with its 

 vermiform appendix. Whilst the appendix possesses in many 

 persons a length of 10 to 20 cm., it is in others entirely absent. 



Let us now consider the third factor, the natural breeder, the 

 struggle for existence. It is a rule without exception in Nature 

 that both animals and vegetables produce more germs than grow 

 to maturity or become capable of reproduction. If all the germs 

 of only one species of animal remained alive and reached maturity* 

 the world would soon be too small, and the quantity of food 

 insufficient for supporting this one species, for organisms multi- 

 ply in geometrical progression and thus would soon reach count- 

 less numbers. The well-known illustration of the chess-board 

 will best explain this rapid mode of multiplication. If we place 

 upon the sixty-four squares of the chess-board grains of corn in 

 the manner that we put one grain on the first, 2 on the second, 

 4 on the third, 8 on the fourth, and so on, we shall have to place 

 1,024 on the eleventh square, and on the twenty-first more than 

 a million. The thirty-ninth would require one billion grains, and 

 the last square a number of such length that is impossible to 

 pronounce it. It has been calculated that its volume would be 

 sufficient to cover the entire earth surface with a thin layer of 

 corn. If all the germs produced attained maturity and the power 

 of reproduction the multiplication of organisms would proceed in 

 the same terrifying manner. The elephant is the best known 

 example of an animal with a low ratio of increase. According to 

 Darwin, its power of reproduction begins with the thirtieth year 

 and continues to the ninetieth. As the elephant-parents have to 

 care for their young a considerable time before these reach the 

 state of independence, they produce in this long period only 

 about six young. If we assume the average life of an elephant 

 to be a hundred years we should have, if all the young elephants 

 grew up and reached the power of reproduction, after 740 to 

 750 years about nineteen million elephants as descendants of the 

 first pair. 



Among the minute organisms, the bacteria, the comma 

 bacillus, the dreaded cause of the Asiatic cholera, multiplies 

 under the most favourable conditions about every twenty minutes 

 by fission ; this would at the end of one day give the enormous 



