98 
DARWINISM 
CHAP. 
peach is unknown in a wild state, unless it is derived from 
the common almond, on which point there is much difference 
of opinion among botanists and horticulturists. 
The immense antiquity of most of our cultivated plants 
sufficiently explains 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 Variations. 
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 wide 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, which 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. 
