SELECTION: ORGANIC AND SOCIAL 201 



years 1893, 1895, and 1898, Prof. Weldon found 

 that, during the time between the first measure- 

 ment and the last, the frontal breadth of the crabs, 

 taken relatively to their length, had distinctly 

 decreased. As the amount of suspended clay and 

 sewage in Plymouth Sound had increased during 

 the same period, Prof. Weldon concluded that 

 those with broad fronts were being persistently 

 eliminated. As the experiment referred to above 

 shows, those with narrow fronts withstand the 

 muddy water better. 1 The inference was that the 

 elimination was definitely discriminate. 



Prof. Bumpus 2 relates an interesting observa- 

 tion on the house-sparrow in North America. 

 After a storm 136 were picked up and brought 

 into the laboratory, where 72 revived and 64 suc- 

 cumbed. Survivors and eliminated were measured 

 as to length, size of wing, weight, length of head, 

 length of humerus, of femur, of tibio-tarsus, width 

 of head, and length of sternum. For all but the 

 last of these characters the range of variation 

 was considerably greater in those that succumbed, 

 the extreme variants (e.g. those with longest as well 

 as shortest wing-span) were eliminated (periodic 

 selection). Moreover, the survivors were a little 

 shorter, lighter, longer in the leg, the humerus, and 

 the breast-bone. General stability of structure, Prof. 

 Bumpus says, was the essential characteristic of 

 the survivors. 



A fine proof of the efficacy of natural selection 



1 For criticism see J. T. Cunningham, in Nature (1898), vol. Iviii. 

 pp. 593-4. 



2 " The Elimination of the Unfit as Illustrated by the Introduced 

 Sparrow," by Hermon C. Bumpus, Biol. Lect. Woods Holl, Boston 

 (1898), pp. 209-26. 



