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 fofty 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 
white clover (Zvifoltum repens) yielded 
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- 
Relation of bees 
to clover. 
