GREAT STEPS IN EVOLUTION 75 



living creatures which demand an historical 

 explanation. 



When we leave the chemical and physical 

 standpoint, and look at the living creature as 

 biologists, we recognize four chief character- 

 istics — growth, cyclical development, effec- 

 tive response, and unified behaviour. The 

 living creature grows after a fashion all its 

 own, not as a rolling snowball, by mere 

 accretion, but by a unifying incorporation; 

 not even as a crystal grows, at the expense 

 of dissolved material chemically the same as 

 itself, but at the expense of material different 

 from itself. Again, it has a cyclical develop- 

 ment, from egg-cell to seedling, from seed- 

 ling to beanstalk; from egg-cell to tadpole, 

 from tadpole to frog; it shows an orderly, 

 correlated, regulated succession of events, 

 which leads from apparent simplicity to 

 obvious complexity; but, as Huxley puts it, 

 "no sooner has the edifice, reared with such 

 exact elaboration, attained completeness, 

 than it begins to crumble." Inanimate 

 objects have a certain power of response to 

 external stimuli, as a piece of potassium 

 shows when thrown on a basin of water, but 

 the responses of a living creature in normal 

 surroundings are effective, self-preservative, 

 usually making for betterment. Lastly, the 

 living creature has a persistent unified be- 



