ioo Evolution and Adaptation 



than in the following statement : " If it has taken centuries or 

 thousands of years to improve or modify most of our plants 

 up to their present standard of usefulness to man, we can 

 understand how it is that neither Australia, the Cape of 

 Good Hope, nor any other region inhabited by quite uncivil- 

 ized man has afforded us a single plant worth culture. It is 

 not that these countries, so rich in species, do not by a 

 strange chance possess the aboriginal stocks of any useful 

 plants, but that the native plants have not been improved by 

 continued selection up to a standard of perfection comparable 

 with that acquired by the plants in countries anciently 

 civilized." 



In reply to this, it may be said that if the selection of 

 fluctuating variations leads to an accumulation in the given 

 direction, it is not apparent why it should take thousands of 

 years to produce a new race, or require such a high degree 

 of skill as Darwin supposes the breeder to possess. 



The conditions favorable to artificial selection are, accord- 

 ing to Darwin : I. The possession of a large number of in- 

 dividuals, for in this way the chance of the desired variation 

 appearing is increased. 2. Prevention of intercrossing, such 

 as results when the land is enclosed, so that new forms may 

 be kept apart. 3. Changed conditions, as introducing varia- 

 bility. 4. The intercrossing of aboriginally distinct species. 

 5. The intercrossing of new breeds, " but the importance 

 of intercrossing has been much exaggerated." 6. In plants 

 propagation of bud variations by means of cuttings. The 

 chapter concludes with the statement, " Over all these 

 causes of Change, the accumulative action of Selection, 

 whether applied methodically and quickly, or unconsciously 

 and slowly, but more efficiently, seems to have been the pre- 

 dominant Power." 



Variability, Darwin says, is governed by many unknown 

 laws, and the final result is "infinitely complex." If this is 

 so, we may at least hesitate before we accept the statement 



