514 STRUCTURE AND LIFE HISTORIES 
cunning) will survive. In pondering this hypothesis 
Darwin at once saw its larger application. 1 There are 
always more progeny produced by a plant or an animal 
than there is room and food for, should they all survive. 
Darwin showed that the descendants of a single pair of 
elephants (one of the slowest breeders of all animals) 
would, if all that were born survived, reach the enormous 
number of 19,000,000 in from 740 to 750 years. 2 But 
the total number of elephants in the world does not appre- 
ciably increase : evidently many must perish for every one 
that lives. There must therefore be an intense struggle 
for existence. Darwin 3 gives the following illustration: 
"Seedlings, also, are destroyed in vast numbers by 
various enemies; for instance, on a piece of ground 3 
feet long and 2 wide, dug and cleared, and where there 
could be no choking from other plants, I marked all the 
seedlings of our native weeds as they came up, and out of 
357 no less than 295 were destroyed, chiefly by slugs and 
insects. If turf which has long been mown, and the case 
would be the same with turf closely browsed by quadru- 
peds, be let to grow, the more vigorous plants gradually 
1 "in October 1838," says Darwin, "that is, 15 months after I had 
begun my systematic inquiry, I happened to read for amusement 'Malthus 
on Population,' and being well prepared to appreciate the struggle for 
existence which everywhere goes on from long-continued observation of 
the habits of animals and plants, it at once struck me that under these 
circumstances favorable variations would tend to be preserved, and 
unfavorable ones to be destroyed. The result of this would be the forma- 
tion of new species. Here then I had at last got a theory by which to 
work." 
J One pair of elephants produces an average of only one baby elephant 
in 10 years, and the breeding period is confined to from about the 3oth to 
the poth year. For illustrations of the prolific nature of plants, see 
paragraph 173, pp. 190-191. 
1 "Origin of Species" (New York, 1902 edition), pp. 83, 84. 
