Is there a Cumulative Effect of Selection? 275 
will go on laying almost continuously during the breeding season, if 
the eggs are removed as laid, and the birds are not allowed to sit.” 
He further shows that, just as with poultry, the environmental 
conditions under which the birds are kept have a marked influence 
on the egg production in ostriches. 
In general we are strongly inclined to the view that the existing 
evidence indicates that the superior egg production of present-day 
races of domestic poultry is in the main the result of the action of 
the favorable environmental influences included in the process and 
conditions of domestication, rather than an effect of the selection 
of favorable fluctuating variations through a long period of time. 
Summary. 
The data discussed in this paper were obtained from two lines 
of work. The first of these was an experiment in which for a period . 
of nine years hens have been selected for high egg production. No 
hens were used as breeders whose production in the pullet year had 
not been 160 or more eggs. The cockerels used were, after the first 
year of the experiment, invariably the sons of mothers producing 
200 or more eggs in their pullet year. 
The second source of data was an experiment in which the inheri- 
tance of egg production from mother to daughter was directly measured. 
Records of the pullet year egg production of 250 daughters of hens laying 
200 or more eggs in their (the mothers’) pullet year were obtained. 
Certain of the most important results obtained may be summarily 
stated as follows: — 
I. Selection for high egg production carried on for nine consecutive 
years did not lead to any increase in the average production of the flocks. 
3. There was no decrease in variability in egg production as a 
result of this selection. 
3. The present data give no evidence that there is a sensible 
correlation between mother and daughter in respect to egg production, 
or that egg-producing ability (fecundity) is sensibly inherited. 
4. In this experiment the daughters of “200-egg’” hens did not 
exhibit, when kept under the same environmental conditions, such 
as high average egg production as did pullets of the same age which were 
the daughters of birds whose production was less than 200 eggs per year. 
5. The daughters of “‘200-egg” hens were not less variable in 
respect to egg production than were similar birds whose mothers 
were not so closely selected. 
u gr, 18 * 
