454 SUMMARY OF CURRENT RESEARCHES RELATING TO 



times enough to cause instantaneous death. The rapidity of the 

 poisoning and the post-mortem appearances recalled anaphylactic shock. 



The Selection Problem.* -Raymond Pearl presses the question 

 whether selection does actually produce evolutionary change. There are 

 a few experiments (from Weidon to Harris) which agree in indicating 

 that the survivors are physically different from the eliminated. Nearly 

 as many investigations have shown an elimination which is not dis- 

 criminative. Moreover, it is necessary to have proof that the somatic 

 differences on which selection works are heritable. Pearl illustrates 

 this by referring to his recent experiments on the variation called " side- 

 sprig " in the comb of poultry, which gave no proof of the heritability 

 of the character. Furthermore, survival often depends on somatic 

 modifications. It appears that selection experiments with agents that 

 directly affect the germ-cells (e.g. alcohol on poultry) will yield valuable 

 results. 



" We find the literature of evolution cluttered with a lot of utterly 

 preposterous statements about domestic animals and plants, masquerad- 

 ing as valid evidence for the selection doctrine." Thus, "the principle 

 of the gradual accumulation by continued selection of minute somatic 

 variations has had no essential part in the origin or amelioration of 

 certainly a great many of the best varieties of agricultural plants 

 which we have to-day." For some animal breeds the same is true ; thus 

 the history of bantams " shows very clearly that Darwinian selection 

 plays an extremely minor and unimportant part." Large breeds of 

 poultry (e.g. Wyandottes and Orpingtons) may originate from hybridiza- 

 tion, followed by close inbreeding of desired segregating types. In other 

 cases (e.g. White Plymouth Rock and White Cornish) sudden mutations 

 by loss of factors have afforded the starting point. 



Controlled ad hoc experimentation on selection has yielded opposite 

 results according as to whether the hereditary factors for the character 

 which formed the basis of the selection were or were not positively 

 known to be in a homozygous condition in all the individuals of the race 

 experimented with. In " pure line " conditions the results of the con- 

 tinned selection have been on the whole negative. Notable exceptions 

 occur, however, as in Jennings' work on Difflugia, especially in the case 

 where the feature selected was the ability to produce offspring with a 

 particular character. The hopeful line of selection is a selection of 

 individuals which are demonstrably able to produce a particular kind of 

 gamete. " In ordinary Darwinian selection we select the kind of somata 

 we want, and trust blindly that a wise providence has implanted in them 

 the sort of gametes we need to get further somata like those we selected." 

 But the result is often disappointment. 



In many experiments with sexually reproducing organisms, selection 

 has been attended with an alteration of the type in the direction of the 

 selection. Of such cases there are two rival interpretations— demanding 

 further experiment. " On the one hand, it is held, because there has 

 been an alteration of type in point of time coincident with successive 



* Amer. Nat., li. (1917) pp. 65-91. 



