THE WORLD OF LIFE 455 



and it was at such times that the enormous population of most species 

 and their wide range over the whole continents, always secured the 

 preservation of considerable numbers of the best adapted in the most 

 favored localities. Then the rapidity of multiplication came into play, 

 so that in two or three years the population of each species became as 

 great as ever; while, as. all the least favorable variations had been 

 destroyed, the species as a whole had become better adapted to its 

 environment than before the almost catastrophic destruction of such 

 a large proportion of them. 



It is the fact of the adaptation of almost all existing species to a 

 continually fluctuating environment — fluctuating between periodical 

 extremes of great severity — that has produced an amount of adapta- 

 tion that in ordinary seasons is superfluously complete. This is shown 

 by the well-known fact that large numbers of adult animals that have 

 not only reached maturity but have also produced offspring and suc- 

 cessfully reared them, continue to live and breed for many years in 

 succession, although varying considerably from the mean, while almost 

 the whole of the inexperienced young fall victims to the various causes 

 of destruction that surround them. 



The Nature of Adaptation 



The next subject discussed was the complex nature of adaptations 

 in many cases, and probably in all; a subject of great extent and 

 difficulty. The lecturer directed special attention to the relations 

 between the superabundance of vegetation in spring and summer, the 

 enormous, but, to us, mostly invisible, hosts of the insect tribes which 

 devour this vegetation, and the great multitudes of our smaller birds 

 whose young are fed almost exclusively on these insects. Without 

 these hosts of insects the birds would soon become extinct; while 

 without the birds, the insects would increase so enormously as to de- 

 stroy a considerable amount of vegetable life, which would, in its turn, 

 lead to the destruction of much of the insect, and even of the highest 

 animal groups; leaving the world greatly impoverished in its forms of 

 life. 



The vast numbers of insects required daily and hourly to feed 

 each brood of young birds was next referred to, and the wonderful 

 adaptation of each kind of parent bird which enables it to discover 

 and to capture a sufficient quantity immediately around its nest, in 

 competition with many others engaged in the same task in every 

 copse and garden, was next pointed out. The facts were shown to 

 involve specialities of structure, agility of motions, and acuteness of 

 the senses, which could only have been attained by the preservation 

 of each successive slight variation of a beneficial character throughout 

 geological time; while the emotions of parental love must also have 



