THE THREAT OF OVERPOPULATION 191 



Many of our pests, like the corn borer and the cotton wee- 

 vil and so on, are cases in point. Nature eventually strikes 

 a new balance and keeps the newcomer in proper check, 

 but it often takes a long time. The English sparrow was in- 

 troduced into the United States toward the middle of the 

 last century and has already saturated the continent. Na- 

 ture has probably not yet worked out a proper check against 

 this bird. 



The thing to emphasize here is that the check against 

 overreproduction is death in one form or another; and star- 

 vation, w^here sheer numbers pack the habitat to "standing 

 room only," is nature's last lethal gesture. Such situations 

 do arise momentarily whenever the ordinary death check is 

 even slightly withheld, the reproductive drive being ever 

 ready to explode offspring into the habitat. Man is only now 

 beginning to realize, as v/e hope to show in this chapter, 

 that even he is not exempted from the will of nature to 

 strike a balance between births and deaths. 



Long ago Darwin was deeply impressed by this tendency 

 of all organisms to reproduce in such wild excess of mere 

 replacement. His knowledge of field biology was intimate. 

 He could literally feel the explosive pressure of jungle 

 growth, and out of this feeling came eventually his theory 

 of natural selection. He was particularly affected by the 

 overpopulation thesis of Thomas Malthus, whose dire pre- 

 dictions of human disaster will be revealed later in this 

 chapter. Darwin thought that with "variation," which he 

 took to be axiomatic in living organisms, and the tendency 

 of "overreproduction," which brings on a "struggle for 

 existence," there would be a "survival of the fittest." Nature, 

 he thought, adapted organisms to their habitats through 

 this mechanism by "natural selection." 



Biologists still feel that much of the Darwinian point of 

 view is valid when supplemented by our modern genetic 

 knowledge and by statistical studies of populations. Over- 

 population has been a factor in the evolution of all organ- 



