THE ORIGIN OF THE OLDEST FOSSILS. 373 



[N^othing- could illustrate tlie lierceness of tlie struggle for food among 

 tlie animals on a crowded sea bottom more vividly than the emptiness 

 of the water in coral sounds where the bottom is practically one enor- 

 mous mouth. The only larva^ 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 larva^ of bottom animals have retained the pelagic habit for 

 the purpose of distributing tbe species, it is more probable that it has 

 been retained ou account of its comj>arative safety. 



These facts show that competition must have come (juickly after the 

 establishment of the first fauna on the bottom, and that it soon became 

 very rigorous and led to severe selection and rajnd modification; and 

 we must also remember that life on the bottom brought with it many 

 new opportunities for divergent specialization and imi)rovement. The 

 increase in size which came with economy of energy increased the possi- 

 bilities of variation and led to the natural selection of pecnliarities 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 protective 

 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 pre- 

 served as fossils. 



Life on the bottom also introduced another inqiortant evolutionary 

 influence — competition between blood-relations. In thoseanimals 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, which, having the same habits, living 

 upon the same food, and avoiding enemies in the same way, are con- 

 stantly striving to hold exclusive possession of all that is essential to 

 their welfare. 



When a stock gives rise to two dfvergent branches, each escapes 

 competition with the other so far as they differ in structure or habits, 

 while the i^arent stock competing with both at a disadvantage is exter- 

 minated. 



Among the animals which we know best, evolution leads to a branch- 

 ing tree-like genealogy, with the topmost twigs represented by living 

 animals, while the rest of the tree is buried in the dead past. The 

 connecting form between two species must therefore be sought in 

 the records of the past or reconstructed by comparison. Even at the 

 present day things are somewhat diflerent in the open ocean, and they 

 must have been very different in the primitive ocean, for a pelagic 

 animal has no fixed home, one locality is like another, and the compet- 



