^^8 The Theory of ISIatural Selection 



in a metaphorical sense and recognized as clearly as any of 

 us do today that a large part of the struggle is a passive one. 

 He did not need to be reminded that seedlings do not poke 

 each other with elbows or step on each other's toes. No 

 one knew better, however, that the odds are all against the 

 individual attaining maturity, if we start our calculations at 

 the point where the individual comes into being. 



It has been possible, in agricultural practice, to calcu- 

 late from a study of the soil and of the climate the limiting 

 factors for a given crop. We know in advance pretty closely 

 how many stalks of corn (of a given kind) we can expect 

 to come from an acre in a given location — that is, with a 

 given soil and a given climate. We may calculate, therefore, 

 the quantity of seed and the amount of cultivation that can 

 be profitably applied to the area. Plants and animals that 

 are not under cultivation seem to have no way of making 

 these calculations in advance and they distribute their seeds 

 and eggs in a most prodigal manner with the result that 

 there is an incalculable waste involved. 



From another point of view we may say that nothing is 

 wasted since many of the seeds and eggs serve almost im- 

 mediately as food for other species. Nearly all who start 

 upon their development seem to be readily picked off by 

 their enemies at one or another stage. There is also, from 

 the point of view of preserving a species, the need for a mar- 

 gin that will fall on the proverbial stony ground. Eggs laid 

 by amphibians and fish in shallow waters cannot in all cases 

 be insured against the pool drying up. Mortalities have also 

 been due to late frost in the spring. 



The struggle for existence takes place between mem- 

 bers of a species, where there are too many for the available 

 space or food supply. There is also the conflict between one 

 species and another for space, for sunlight, for water, for 

 food. There is the struggle between each species and its 

 prey or food supply on the one hand, and its enemies on the 

 other. There is finally the struggle between each species 

 and the inanimate factors of the surroundings. 



