SPONTANEOUS GENERATION AND EVOLUTION : CONCLUSION 383 



from them, need not have turned out exactly as it has done. In that 

 case many species would never have arisen, but others would have 

 taken their place ; on the whole, the same types of species-groups 

 would have succeeded each other in the history of the earth. Let 

 us suppose that the Sandwich Islands, like manj^ other submarine 

 volcanoes, had never risen above the surface of the sea, then the 

 endemic species of snails, birds, and plants which now live there 

 could not have arisen, and if the volcanic group of the Galapagos 

 Islands had arisen from the sea not in their actual situation, but 

 forty degrees further south or north, or i,ooo kilometres further 

 west, then it would have received other colonists, and probably fewer 

 of them, and a difterent company of endemic species would be found 

 there now. But there would be terrestrial snails and land-birds none 

 the less, and on the whole we may saj?" that both the extinct and the 

 living groups of organisms would have arisen even with different 

 formations of land and sea, of heights and depths, of climatic changes, 

 of elevations and depressions of the earth's crust, at least in so far 

 as they are adaptations to the more general conditions of life and not 

 to specialized ones. The great adaptation to swimming in the sea, 

 for instance, must have - taken place in any case ; swimming worms, 

 swimming polj^ps (Medusae), swimming vertebrates, would have arisen ; 

 terrestrial animals would have evolved also, on the one hand from 

 an ancestry of worms in the form of jointed animals and land or 

 freshwater worms, and again from an ancestry of fishes. Aerial 

 animals would also undoubtedly have evolved even if the lands 

 had been quite differently formed and bounded, and I know of no 

 reason why the adaptation to flight should not have been attempted 

 in as many diflTerent ways as it has actually been by so many different 

 groups — the insects, the reptiles (the flying Saurians of the Jurassic 

 period), the extinct Archmopteryx, the birds, and the bats among 

 mammals. 



We can trace plainly in every group the attempt not only to 

 spread itself out as far as possible over as much of the surface of 

 the earth as is accessible to it, but also to adapt itself to all possible 

 conditions of life, as far as the capacity for adaptation suffices. This 

 is very obvious from the fact that such varied groups have striven 

 to rise from life on the earth to life in the air, and have succeeded 

 more or less perfectly, and we can see the same thing in all manner 

 of groups. Almost everywhere w^e find species and groups of species 

 which emancipate themselves from the general conditions of life 

 in their class, and adapt themselves to verj^ different conditions, to 

 which the structure of the class as a whole does not seem in the least 



