THE KINSHIP OF LIFE. 21 



same species, or with the individuals of distinct species, 

 or with the physical conditions of life. It is the 

 doctrine of Malthus applied with manifold force to the 

 whole animal and vegetable kingdoms; for in this case 

 there can be no artificial increase of food, and no pru- 

 dential restraint from marriage. Although some species 

 may be now increasing, more or less rapidly, in numbers, 

 all can not do so, for the world would not hold them. 

 There is no exception to the rule that every organic 

 being naturally increases at so high a rate that if not 

 destroyed the earth would soon be covered with the 

 progeny of a single pair. Even slow-breeding man has 

 doubled in twenty-five years, and, at this rate, in less 

 than a thousand years there would literally not be stand- 

 ing room for his progeny. . . . The elephant is reckoned 

 the slowest breeder of all known animals, and I have 

 taken some pains to estimate its probable minimum rate 

 of increase ; it will be safest to assume that it begins 

 breeding when thirty years old, and goes on breeding 

 until ninety years old, bringing forth six young in the 

 interval, and surviving till one hundred years old ; if 

 this be so, after a period of from seven hundred and forty 

 to eight hundred and forty years there would be nearly 

 nineteen million elephants alive, descended from the 

 first pair." 



Darwin continues : " I have found that the visits of 

 bees are necessary for the fertilization of some kinds of 



clover ; for instance, twenty heads of 

 Relation of bees white dover , Trifolium r # ens) yielded 

 to clover. * ' . 



two thousand two hundred and ninety 



seeds, but twenty other heads protected from bees pro- 

 duced not one. Again, one hundred heads of red clover 

 (Trifolium pratense) produced two thousand seven hun- 

 dred seeds, but the same number of protected heads pro- 

 duced not a single seed. Humble-bees alone visit red clo- 



