( Ixxxvii ) 



most difficult to ascertain, and when ascertained most difficult 

 to interpret. Consider, for example, the case already alluded 

 to, the relative immunity of dark-skinned races from malarial 

 fever, which fact was made the basis of a restricted theory of 

 natural selection by Dr. Wells, in 1813. The most reason- 

 able interpretation that can be placed upon this observation is 

 that the dark-skinned races have already undergone the 

 action of natural selection by the elimination of those indi- 

 viduals most sensitive to the attack of particular micro- 

 organisms. There has thus arisen a race less liable to 

 malarial fever than the white races which have not been for 

 so long subjected to this selective process. Since the dark 

 races come from regions where malarial fever is most preva- 

 lent and fatal, dark pigmented skin has become associated 

 with immunity from this class of diseases. The immediate 

 cause of the immunity, whether, as suggested by Prof. Kay 

 Lankester, " a certain germ-slaying quality in the phagocytes," 

 or any other quality of the blood, is physiological, and natural 

 selection may therefore be considered to have acted in this 

 case by taking advantage of physiological variability. But 

 the difficulty of interpretation will appear when it is called to 

 mind that selection may have had in this instance a dark- 

 skinned race to deal with from the very beginning, so that 

 there may be no necessary correlation between the colour and 

 the power of resisting fever germs. The dark colour of the 

 skin may be a concomitant and not a correlate of the germ- 

 slaying faculty in the blood. Thus in all such cases the first 

 thing to be settled is whether a particular external character 

 is a true correlate or only an accidental concomitant of cer- 

 tain internal physiological characters. 



With respect to the action of food, a certain number of 

 instances have been recorded which appear to indicate that 

 colour, at any rate, may in certain cases be influenced by this 

 means.* The evidence, on the whole, is not very satisfactory. f 



* De Varigny, op. cit., p. 57; Romanes, "Darwin and after Darwin," 

 Vol. IL, p. 217; Beddard, " Animal Coloration, " p. 48 ; Eimer, "Organic 

 Evolution," Cunningham's Translation, pp. 147, ct seq. 



t Semper, op. cit., p. 69. Among recent workers at this subject, 

 Dr. Standfuss, after many experiments, obtained only negative results (see 



