Is there a cumulative Effect of Selection? 273 
continued improvement in a strain. Some improvement may possibly 
follow this method of breeding at the very start but the limits both 
in time and amount are very quickly reached. In support of this 
view of the possibilities of selective breeding the results set forth in 
the present paper furnish definite and positive confirmatory evidence. 
Our experience shows that in order to establish a strain of hens in 
which high egg production shall be a fixed characteristic it is 
necessary to do something more than simply breed from high producers. 
It will of course be understood that our investigations are not stopping 
at this point. It is proposed to test the conclusions stated in this 
paper in every possible way. 
That greatly exaggerated ideas as to the effectiveness of continued 
selection of fluctuating variations in improving stock have been widely 
held during the last half century admits of no doubt. Yet many 
practical breeders have clearly understood that something more than 
this was necessary to insure certain and definitely fixed improvement, 
In this connection a statement from a chapter on “Selection” in an 
old work!) containing much interesting matter concerning current 
opinion of the time on breeding questions is worth quoting. After 
outlining briefly the general plan of selective breeding the author 
goes on to say: “It is not merely by putting the best male to the 
best female, that the desired qualitites can be obtained; but by other 
means not clearly defined in the common practice.” May it not 
fairly be said that, as a result of the work of Nilsson, De Vries, 
Johannsen and others, some at least of these “other means” are 
now coming to be “clearly defined’’? 
The results set forth in this paper raise in one’s mind some doubt 
as to the validity of the explanation commonly given for the 
superiority of present day races of poultry over the wild Gallus 
bankiva in regard to egg production. It is generally held that 
the reason for this superiority lies in the continued selection for 
increased egg production which is assumed to have been practised 
during the centuries since the domestication of poultry began. Critical 
examination of this explanation indicates, however, that it has some 
very weak points. The following considerations are significant in 
this connection. 
1) Walker, A. Intermarriage: or the Mode in which, and the causes why, 
Beauty, Health and Intellect result from certain Unions and Deformity, Disease and 
Insanity from others: Demonstrated by ..... and by an account of corresponding 
Effects in the Breeding of Animals. American Edition, New York 1839. 
Iuduktive Abstammungs- und Vererbungslehre. II, 18 
