ORGANIC EVOLUTION 251 



or into new spheres of activity. Great size may entail 

 great peril in times of scarcity of food. It takes much 

 food to nourish a large organism. A dozen rabbits may 

 fatten where one buffalo would starve. Specialization 

 always means fitness for one set of conditions, and is apt 

 to be disadvantageous when conditions are suddenly 

 altered. Complexity of organization is always a peril. A 

 horse may fall and break its neck, but hardly may a hydra. 

 The mechanism with fewest parts and least complicated 

 adjustments is the one that will best stand rough usage. 



This persistence may be further illustrated by an analogy. 

 Reaping machines have had an evolution, almost within 

 our own time. The forms that have successively appeared 

 (and that have successively been dominant) are the sickle, 

 the scythe, the cradle, the reaper and the binder, and these 

 form a series, so to speak, of increasing size, efficiency and 

 complexity of structure. The advent of each new form has 

 only limited the field, has not crowded out, its predecessors. 

 All are in use still. The larger machines are adapted only 

 to broad and open fields ; the cradle that once reaped the 

 fields is now restricted to the stump-patch or rocky hill 

 slope; and the sickle finds its place in the edging of the 

 shrubbery or the corner of the garden. All persist together, 

 and the simplest of them is likely to persist longest. 



In the second place, these simple aquatic organisms have 

 remained in their primitive haunts of safety, in the ooze of 

 the bottom, or among sheltering stems or rocks, where 

 more or less out of the way of direct competition with 

 stronger forms, and where no sort of cataclasm could well 

 annihilate their whole tribe. These circumstances, combined 

 with a good reproductive capacity, make for persistence. 



Regressive development. This is the phenomenon 

 generally known as degeneration. Retrograde development 



