41 [Vol. xli. 



Secondly, under normal conditions, no species will ever 

 exterminate the species (be it {)lant, insect, or animal) on 

 which it preys. This second law is obviously a corollary 

 ol the first, since as the species preyed upon becomes 

 scarce, so also will the attacker increase less rapidly and 

 the relative balance between the two species remains un- 

 altered, and a fortiori if the preyed upon species bt'came 

 extinct the attacking species would also have become 

 extinct, unless it had turned its attention to other prey. 



A third law i?, that i£ birds are granted absolute safety 

 during the breeding season for themselves and their young, 

 man may destroy all he can during the rest of the year 

 without appreciably affecting their numbers. This is one 

 rea^^on why e^g-collecting is more harmful than skin- 

 collecting, and also, as I shall attempt to show later, gives us 

 a lead as to the most imp">rtant period in which to concentrate 

 our efforts for the protection or destruction of any particular 

 species. 



Bearing these points in mind, it is obvious that man must 

 be continually at war with Nature. 



For instance, man is largely dependent on wheat as his 

 chief food — science and civilisation enable him to grow large 

 ti-acts of wheat to the exclusion of other plants; ihese large 

 and concentrated areas of wheat bring about a lare'e increase 

 of grain-feeding birds, more particularly the House-Sparrow, 

 and we should also get an equally large increase of the 

 Sparrows' enemies, e. g., the Hawks. In this country, 

 however, that is not the case : 1st, because Hawks find 

 chickens, pheasants, and partridges, when being artificially 

 reared, a much easier prey, so that they themselves have 

 been largely kept down in the interests of sport and against 

 the interests of Agriculture. 2nd, because the Sparrow is 

 essentially a town bird, where Hawks dare not follow him, 

 migrating into the wheat fields when the corn is ripe. Thus 

 we see to what depths of com[)lexity we immediately beconie 

 involved when thinking out what looks at the outset as a 

 simple problem. 



In formulating the second law, I stated that under normal 



