NATURAL selection; AND THE ANTIQUITY OF LIFE 233 



The scarcity of floating organisms can have only one explana- 

 tion. They are eaten up, and competition for food is so fierce 

 that nearly every organism which is swept in by the tide and 

 nearly every larva which is born in the sounds is snatched by 

 the tentacles around some hungry mouth. 



Nothing could illustrate the fierceness of the struggle for 

 food among the animals on a crowded sea-bottom more vividly 

 than the emptiness of the water in coral sounds where the bot- 

 tom is practically one enormous mouth. The only larvae which 

 have much chance to establish themselves for life are those which 

 are so fortunate as to be swept out into the open ocean, where 

 they can complete their larval life under the milder competition of 

 the pelagic fauna, and while it is usually stated that the larvae 

 of bottom animals have retained the pelagic habit for the purpose 

 of distributing the species, it is more probable that it has been 

 retained on account of its comparative safety. 



These facts show that competition must have come quickly 

 after the establishment of the first fauna on the bottom, and that 

 it soon became very rigorous and led to severe selection and 

 rapid modification ; and we must also remember that life on the 

 bottom brought with it many new opportunities for divergent 

 specialization and improvement. The increase in size which came 

 with economy of energy increased the possibilities of variation 

 and led to the natural selection of peculiarities which improved 

 the efficacy of the various parts of the body in their functions 

 of relation to each other, and this has been an important factor 

 in the evolution of complicated organisms. 



The new mode of life also permitted the acquisition of pro- 

 tective shells, hard-supporting skeletons, and other imperishable 

 parts, and it is therefore probable that the history of evolution in 

 later times gives no index as to the period which was required 

 to evolve from small, simple pelagic ancestors the oldest animals 

 which were likely to be preserved as fossils. 



Life on the bottom also introduced another important evolu- 

 tionary influence — competition between blood-relations. In those 

 animals which we know most intimately, divergent modification, 

 with the extinction of connecting forms, results from the fact 

 that the fiercest competitors of each animal are its closest allies. 



