. Biology in America. Biology. 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 bell
. Biology in America. Biology. 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 they pro- duced the first year a high grade of and a low of with a difference of only By gradually in- creasing steps these figures after twenty years' selection reached for the high, for the low and 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 stoc
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