NATURAL SELECTION; SEXUAL SELECTION 67 



the English watercress, which in its new home grows a dozen feet in 

 length, and has to be dredged out to keep navigation open, it may be 

 understood the colonials look with jaundiced eye upon suggestions 

 of any further interference with Australian nature. 



"Not to be outdone by foreign importations, the country itself 

 has shown in the humble locust a nuisance quite as potent as rabbit, 

 fox, or thistle. This bane of all men who pasture sheep on grass has 

 not been much in evidence until within the last few years, when 

 the great destruction of indigenous birds by the gun and by poisoned 

 grain strewn for rabbits has facilitated its increase. The devastation 

 caused by these insects last year was enormous, and befell a district a 

 thousand miles long and two thousand wide. For days they passed in 

 clouds that darkened the earth with the gloomy hue of an eclipse, 

 while the ground was covered with crawling millions, devouring every 

 green thing and giving to the country the appearance of being carpeted 

 with scales. It has been discovered, however, that before they attain 

 their winged state they can easily be destroyed, and energetic measures 

 will be taken against them throughout all the inhabited districts of 

 Australia whenever they make another appearance." 



The conditions of the struggle for existence are not neces- 

 sarily felt as an individual stress to the individuals which sur- 

 vive. The life they lead is the one for which they are fitted. 

 The struggle is painful or destructive only to those imperfectly 

 adapted. Men in general are fitted to the struggle endured by 

 their ancestors as they are adapted to the pressure of the air. 

 They do not recognize the pressure itself but only its fluctua- 

 tions. Hence many writers have supposed that the struggle 

 for existence belongs to animals and plants and that man is 

 or should be exempt from it. Competition has been identified 

 with injustice, fraud, or trickery, and it has been supposed that 

 it could be abolished by acts of benevolent legislation. But 

 competition is inseparable from life. The struggle for existence 

 may be hidden in social conventions or its effects more evenly 

 distributed through processes of mutual aid, but its necessity is 

 always present. Competition is the source of all progress. 



The first suggestion of the doctrine of natural selection 

 came to Darwin through the law of population as stated by 

 Thomas Malthus. The law of Malthus is in substance as fol- 

 lows: Man tends to increase by geometrical ratio that is, by 

 multiplication. The increase of food supply is by arithmetical 



