98 DARWINISM 



peach is unknown in a wild state, unless it is derived from 

 the common almond, on which i)oint there is much difference 

 of oi)inion among Itotanists and horticulturists. 



The immense antiquity of most of our cultivated plants 

 sufficiently exi)lains the apparent absence of such useful 

 productions in Australia and the Cape of Good Hope, not- 

 withstanding that they both possess an exceedingly rich and 

 varied flora. These countries having been, until a com- 

 paratively recent period, inhabited only by uncivilised men, 

 neither cultivation nor selection has been carried on for a 

 sufficiently long time. In North America, however, where 

 there was evidently a very ancient if low form of civilisation, 

 as indicated by the remarkable mounds, earthworks, and 

 other prehistoric remains, maize was cultivated, though it 

 was probably derived from Peru ; and the ancient civilisation 

 of that country and of Mexico has given rise to no fewer than 

 thirty-three useful cultivated plants. 



Conditions favourable to the production of Variaiians. 



In order that plants and animals may be improved and 

 modified to any considerable extent, it is of course essential 

 that suitable variations should occur with tolerable frequency. 

 There seem to be three conditions which are especially favour- 

 able to the production of variations: (1) That the particular 

 species or variety should be kept in very large numbers; (2) 

 that it should be spread over a Avide area and thus subjected 

 to a considerable diversity of physical conditions ; and (3) 

 that it should be occasionally crossed with some distinct but 

 closely allied race. The first of these conditions is perhaps 

 the most important, the chance of variations of any partic- 

 ular kind being increased in proportion to the quantity of 

 the original stock and of its annual offspring. It has been re- 

 marked that only those breeders who keep large flocks can 

 effect much improvement ; and it is for the same reason that 

 pigeons and fowls, w^hich can be so easily and rapidly increased, 

 and which have been kept in such large numbers by so great 

 a number of persons, have produced such strange and numer- 

 ous varieties. In like manner, nurserymen who grow fruit and 

 flowers in large quantities have a great advantage over private 

 amateurs in the production of new varieties. 



