The cuckoo that lays her eggs in strange nests gets the hard and exhausting and dangerous work of incubating done for her. whether it is unconsciously, or carelessly, or with forethought. that she does so. The advantage is the same, no matter who or what it is that puts the eggs into the strange nest. After the foster-brothers of the nestling cuckoo are destroyed. it profits by the exclusive attention of its two nurses, and so long as the conduct of cuckoos conduces to the welfare of the race. cuckoos will increase and multiply to continue in the same course. We find worldly wisdom in the habits of cuckoos. and the immorality of their conduct is shocking to our refined sense of right: but, so long as the eggs are laid in suitable nests and are hatched, the result may be expected to come about. even if the birds have no more share in the worldly wis dom than they have in the immorality.
The biologist is sometimes told that since he does not know the individual history of any organism in the past. and is even less able to foresee that of any that may exist in the future. lie only infers the fitness of living things for their environment from their survival. and can not logically 110141 the descendants acconnted for by the fitness of their ancestors: but it is our confidence in the continuity of nature, and not ability to say what it was that led to the survival of any individual organism in the past, which eimvinees us that the fittest have survived in the past, and that they will survive in the future, as they do now. While it is true that natural selection does not make anything, it does take away all signitivanee from the reasons some thinkers once thought they had for believing that a living being is anything else than a natural body with a natural history. No two objects.
living or dead. ever are exactly alike: and if we admit the endless diversity of nature, and the struggle for existence. natural selection is a fact. While we find it hard to discover any difference between individual house-flies. or ants, or bees, they no doubt differ among themselves in many ways: sonic excelling in the duration and rapid ity of their flight, while others fall below the average in size of wings, or strength of muscles, or in general coordination for flight. The in sects that inhabit wind-swept islands are in con stant danger of destruction at sea. and those that fly most are most in danger, while those that, for any reason. fly little or not at all are safest, and live longest, and have most descendants. Kerguelen 'Island is said to be one of the stormi est places on the globe. There are no trees or bushes to afford shelter on the island, which is swept by almost perpetual gales. It is inhabited by several flies, by numerous beetles, and by a moth, but all are incapable of flight, and most are entirely without wings. It is often said that they have lost their wings in order to escape danger, but this is only a figure of speech. We need not know who or what has made them de ficient in order to understand the facts. All that did fly have been exterminated, and there would not be any survivors if some bad not been de ficient in ability or in inclination to fly.