76 EVOLUTION 



formulae that serve to describe the activity 

 of a machine will not suffice for 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, effective 

 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 development, from 

 egg-cell to seedling, from seedling to bean- 

 stalk; from egg- cell to tadpole, from tadpole 

 to frog; it shows an orderly, correlated, regu- 

 lated 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 hi normal surroundings are effective, 

 self-preservative, usually making for better- 



