CHAPTER LXXXIV 

 APPLICATIONS AND THEORIES OF EVOLUTION 



494. Direct evidence of evolution. Within the memory of 

 men and women now living there have appeared new varieties 

 of potatoes, apples, plums, oranges, sheep, horses, rabbits, 

 poultry, cats, dogs, walnut trees, wheat, and so on. And the 

 new varieties of plants and animals are, at least in many 

 instances, just as truly new species as any that occur in nature. 

 It is true that very often these new species have arisen under 

 artificial conditions ; but it is also true that there is nothing 

 in these conditions that may not occur in nature, except the 

 protection of the new forms from early extermination. We 

 have, then, not only indirect evidence that evolution has taken 

 place, but direct evidence that plants and animals can behave in 

 agreement with the assumption that evolution did take place. 



In recent times within a century and a half there have 

 been many attempts to formulate a theory to explain how 

 evolution takes place. These theories may be grouped accord- 

 ing to their family resemblances, but there are only three or 

 four types of theories that are at present worth considering. 



495. Lamarckian theory. The French zoologist Lamarck 

 (1744-1829) laid emphasis on the fact that the development 

 of many organs is influenced by their activity, and on the 

 fact that many organisms (particularly animals) adjust them- 

 selves to their surroundings in the course of their lives. He 

 came to the conclusion that "all that has been acquired, 

 begun, or changed in the structure of an individual in the 

 course of its life is preserved in reproduction and transmitted 

 to the new individuals which spring from that which has 

 experienced the change." 



471 



