238 



Biology in America 



But tlie voice of the selectionist is not yet stilled. Perhaps 

 tlie chief American exponent of tlie tlieory has been Professor 

 Castle of Hai^'ard, whose work on hooded rats is well known 

 to all biologists. The hooded rat is a color variety of the 

 common brown rat, with black head and shoulders and a black 

 stripe on the middle of back and tail. By persistent selec- 

 tion of individuals with more black and more white respec- 

 tively, Castle has obtained individuals ranging all the way 

 from those with a small median stripe of white upon the belly 

 to others with only a small patch of black upon the snout. ^ 



For over twenty years a selection experiment has been 

 conducted at the experiment station at the University of Il- 

 linois, which also appears to give strong support to the the- 



" Hooded" Eats 



Showing the results of experiments by Professor Castle of Harvard in 

 selecting these animals for extent of black and white in the pattern. 

 After Castle & Phillips, "Piebald Eats and Selection," Carnegie In- 

 stitution, Publication No. 195. 



ory. In 1896, Professors Hopkins and Smith began selecting 

 seed from ears of corn which had on the one hand a high, and 

 on the other a low protein content. This continual selection 

 has resulted not only in producing grades of high and low 

 content, but each succeeding year shows on the average a wider 

 divergence in the two grades. Thus, starting in 1896 with 

 an average per cent (in weight of grain) of 10.92 they pro- 

 duced the first year a high grade of 11.10% and a low of 

 10.55% with a difference of only 0.55%. By gradually in- 

 creasing steps these figures after twenty years' selection 

 reached 14.53% for the high, 7.26% for the low and 7.27% 

 for the difference. Similar results were obtained by them in 

 selecting for oil content. 



The anti-selectionists however have explained these results 

 as due merely to the sorting out of variations already pres- 

 ent in a very mixed stock. A better understanding of the 



•Eecently Professor Castle has modified his original contentiou. 



