VARIATION IN DOMESTIC ANIMALS 457 
ing investigations in egg production have been carried on for about 
20 years. An attempt was made during the period from 1899 to 
1907 to increase egg production by a system of mass selection. I'or 
breeding stock, pullets were selected which had produced 160 or more 
eggs during the first year of production, and they were mated to males 
the mothers of which had produced 200 or more eggs in their first year of 
production. The results of this rigid system of selection are shown 
graphically in Fig. 185. The solid line connecting the dots represents the 
line of actual average winter egg production of the entire flock during 
the period from 1899 to 1915. “The fitted straight line for the period 
1899 to 1907 shows clearly that during this period of mass selection there 
was an actual decrease, rather than an increase, in average winter egg 
production. Pearl and Surface point out that certain environmental 
factors may have had something to do with this decrease in production, 
but even when such factors are accorded a fair maximum effect, the 
evidence favors the interpretation that this system of mass selection 
has had absolutely no effect upon the average winter production of eggs. 
That this conclusion is a sound one is also supported by correlation 
studies of egg production of mothers and daughters in these flocks. In 
Table LIX the winter egg productions of 192 daughters are entered 
Taste LIX.—CorreELATION BETWEEN DauGHTerS anp Morurrs wiTtH RESPECT 
to WintER Ecc Propuction, r = — 0.068 + 0.048 (Data of Pearl and Surface) 
Moruer’s Eaa Propuction 
Deaabieeacuseeriveicat E 2/8 i aE 8 2/5 E * E 2 ig 
AIA|S/ S/S) S| 4] Bl/S/S/R/£&}/2] 6 
ae lem |e eileen 
0-3 iba es a4 TESS 7 |: B28. | Pit) ee 
4-7 3 |.2 2/2/3/3/3/3/8]./2/1] 33 
8-11 Taso jah ape 2/5) 6| . telcos 
12-15 1:2 ee ae Tg oie heats 
16-19 1 Seales sine) 2 3)eau be 4]. 14 
20-23 1 Dy a eae alt Jeti eat ace 10 
24-27 ee lets | eteietlie anlle2 ee | 6 
28-31 1 1 ee SPS oiler a 8 
32-35 2 ee [ee poets 6 
36-39 ial L 1 4 
40-43 | it al 1 
44-47 1 1} 1 1 5 
48-51 Nal 1 eT eas 1 4 
52-55 eal Wee itieeel editable 2 
56-59 feeieead ie. 1 th ell | 6 
60-63 E lp Mestad eS est iieer eb Se 1 
64-67 eal Deztilteeatien | elie &o 
68-71 Nea alee Semeinal 
72-75 Bese alles 
76-79 sll pee ee ba 1 
Bee abe ||| | — 
motalsqnenercsecer | | 12 13 0 10 11} 20 Md nf 19 32 34] 0| 7) 4] 192 
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