258 Pearl and Surface. 
have said that this was the only absolutely certain way to insure 
improvement. It is merely a statement of fact to say that even now 
the vast majority of practical breeders hold to this opinion. It is 
embodied in many maxims of practical breeding such as “breed from 
the best to get the best”, “like produces like”, etc. 
Widespread as it has always been among practical breeders this. 
view as to the effect of selection can hardly be said to have acquired 
a definite scientific status until after the publication of the “Origin 
of Species”. A great deal of the material which Darwin used in this 
work and also in the “Variation of Animals and Plants under 
Domestication” was obtained from the records and published statements 
of practical agricultural breeders. Darwin himself was firmly convinced 
of the general truth of the contention that improvement in domesticated 
animals had been brought about chiefly by the continued selection 
of small, favorable variations. This is sufficiently shown by the 
following statement: “We cannot suppose that all the breeds were 
suddenly produced as perfect and as useful as we now see them; 
indeed, in many cases we know that this has not been their history. 
The key is man’s power of accumulative selection: nature gives 
successive variations; man adds them up in certain directions useful 
to him. In this sense he may be said to have made for himself 
useful breeds.” 1) Still more definite is the following: “If selection 
consisted merely in separating some very distinct variety, and breeding 
from it, the principle would be so obvious as hardly to be worth 
notice; but its importance consists in the great effect produced by 
the accumulation in one direction, during successive generations, of 
differences absolutely inappreciable by an uneducated eye — differences. 
which I for one have vainly attempted to appreciate.” 2) 
The view that there was in practically all cases of the improvement 
of domesticated plants and animals by breeding a definitely cumulative 
effect of selection may be said to have held the field almost undisputed 
until the publication of de Vries’ “Mutationstheorie.” This investigator’s. 
searching critique of the data furnished by the results of agricultural 
breeding work showed clearly enough that certainly all the improvement 
which has taken place in plants and animals under domestication 
can not be explained as a cumulative result of the continued selection 
of favorable variations. 
1) Origin of Species. Chapter I, p. 25. 
2) Loc. cit. p. 26. 
