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than themselves, by a process of descent with gradual 

 modification ; that all species, however different they may 

 be now, are descended from the same or perfectly similar 

 ancestors, which, like the simplest living beings now known 

 to exist, were minute gelatinous masses, without organisation 

 or structure." In his work on " The Origin of Species," 

 Darwin says that, in his belief, " animals are descended 

 from at least only four or five progenitors, and plants from 

 an equal or lesser number. Analogy would lead me one 

 step further namely, to the belief that all animals and 

 plants have descended from some one prototype." 



The theory has been thus fairly stated in outline : " All 

 organisms are more or less variable; no two leaves in a 

 forest are exactly alike, and the differences are often great 

 enough to be quite conspicuous, as in the familiar case of 

 human faces. At the same time these variations tend to 

 become hereditary. Now, if any variation is such as to give 

 its owner any advantage over other individuals of the same 

 species, the owner of such a 'favourable variation' will 

 be more likely than less favoured individuals to win a place 

 in the struggle of existence, and to leave offspring. These 

 offspring will tend to inherit the favourable variation that 

 caused their parent to survive, and the same competition 

 will go on among them. Those which possess the favour- 

 able variation in the highest degree will again survive, and 

 the improvement will go on progressing and accumulating 

 through generations. This preservation of favourable 

 variation Darwin calls ' Natural Selection.' " 



The influence of cultivation and domestication in the 

 production of changes, and the difficulty in distinguishing 

 between variations and species, are fully estimated and 

 minutely considered by Darwin in the elaboration of his 



