520 EVOLUTION 



the parent and not of another kind, although there may be much 

 difference in size of plants, length of ears, size and shape of ker- 

 nels, etc. In spite of variations there is inheritance which is 

 an imparting of something by the parents to the offspring, 

 which as a result develop some of the parental features. Dar- 

 win also thought that not only the resemblances to parents, but 

 also whatever variations the offspring may have are inheritable. 

 Assuming that variations are transmitted to succeeding gen- 

 erations in which they may become more pronounced, he could 

 explain the origin of new characters and new species. If a 

 variation is such as to better adapt individuals to their en- 

 vironment, those individuals in which the variation is most 

 pronounced have a better opportunity to survive and propagate 

 in greater numbers than individuals in which the variation is 

 less pronounced. Thus through many successive generations in 

 which the individuals with the variation most pronounced are 

 more favored than other individuals, the variation is intensified 

 by natural selection and eventually becomes a character of a new 

 species. Darwin drew this conclusion from some of his experi- 

 ments as well as from general observations of plants and animals 

 under domestication. He observed that through selection both 

 plants and animals changed much under domestication. Starting 

 with wild forms of plants, he was able by selecting the variants 

 from the progeny for a number of generations to obtain indi- 

 viduals differing strikingly from the original wild forms. He 

 found that continuous selection gradually built up the selected 

 character until the desired result was obtained. He concluded 

 that in nature such a selective process was brought about by 

 the competition among individuals for existence; but, while 

 any character might be built up by artificial selection, only those 

 which enable the individual to withstand competition are built 

 up in nature. 



Fitness for Environment. — It is common observation that 

 different kinds of plants and animals require different condi- 

 tions under which to live. As pointed out in the discussion of 

 Ecology, some plants and animals live submerged in the water, 

 but most plants and animals can live only on land. The Cacti 

 are so constructed that they can endure the drought of the 

 desert, but Corn, Wheat, and most plants require a medium 

 amount of moisture. Again some plants which are well pro- 



