78 FROM THE GREEKS TO DARWIN 



Aristotle believed in a complete ascending 

 ^gradation' in Nature, a progressive development 

 corresponding with the progressive life of the 

 soul. Nature, he says, proceeds constantly by the 

 aid of gradual transitions from the most imper- 

 fect to the most perfect, while the numerous 

 analogies which we find in the various parts of 

 the animal scale show that all is governed by the 

 same laws — in other words. Nature is a unit as 

 to its causation. The lowest stage is the inor- 

 ganic, and this passes into the organic by direct 

 metamorphosis, matter being transformed into 

 life. Plants are animate as compared with min- 

 erals, and inanimate as compared with animals; 

 they have powers of nourishment and reproduc- 

 tion, but no feeling or sensibility. Then come the 

 plant-animals or zoophytes ; these are the marine 

 creatures, such as sponges and sea-anemones, 

 which leave the observer most in doubt, for they 

 grow upon rocks and die if detached. (Polyps 

 Aristotle wrongly thought were plants, while 

 sponges he rightly considered animals.) The 

 third step taken by Nature is the development of 

 animals with sensibility — hence desire for food 

 and other needs of life, and hence locomotion to 

 fulfil these desires. Here was a more complex 

 and energetic form of the original life. Man is 

 the highest point of one long and continuous as- 

 cent ; other animals have the faculty of thought ; 



