sect, ii.] INTRODUCTION. 1 1 



which no one has made even a plausible surmise. All this is fa- 

 miliar to every one and every one knows the various answers that 

 have been made. 



It is not quite fair to judge such a method by the imperfection 

 of its results, but in one respect the deficiency of results obtained by 

 the Study of Adaptation is very striking, and though this has 

 often been recognized it must be again and again insisted on as a 

 thing to be kept always in view. The importance of this consider- 

 ation will be seen when the evidence of Variation is examined. 

 The Study of Adaptation ceases to help us at the exact point at 

 which help is most needed. We are seeking for the cause of the 

 differences between species and species, and it is precisely on the 

 utility of Specific Differences that the students of Adaptation are 

 silent. For, as Darwin and many others have often pointed oat, 

 the characters which visibly differentiate species are not as a rule 

 capital facts in the constitution of vital organs, but more often 

 they are just those features which seem to us useless and trivial, 

 such as the patterns of scales, the details of sculpture on chitin or 

 shells, differences in number of hairs or spines, differences between 

 the sexual prehensile organs, and so forth. These differences are 

 often complex and are strikingly constant, but their utility is in 

 almost every case problematical. For example, many suggestions 

 have been made as to the benefits which edible moths may derive 

 from their protective coloration, and as to the reasons why unpalat- 

 able butterflies in general are brightly coloured ; but as to the 

 particular benefit which one dull moth enjoys as the result of his own 

 particular pattern of dullness as compared with the closely similar 

 pattern of the next species, no suggestion is made. Nevertheless 

 these are exactly the real difficulties which beset the utilitarian 

 view of the building up of Species. We knew all along that Species 

 are approximately adapted to their circumstances ; but the diffi- 

 culty is that whereas the differences in adaptation seem to us to 

 be approximate, the differences between the structures of species 

 are frequently precise. In the early days of the Theory of Natural 

 Selection it was hoped that with searching the direct utility of 

 such small differences would be found, but time has been running 

 now and the hope is unfulfilled. 



Even as to the results which rank among the triumphant suc- 

 cesses of this method of study there is need for great reserve. 

 The adequacy of such evidence must necessarily be a matter for 

 individual judgment, but in dealing with questions of Adaptation 

 more than usual caution is needed. No disrespect is intended 

 towards those who have sought to increase our acquaintance with 

 these obscure phenomena ; but since at the present time the con- 

 clusions arrived at in this field are being allowed to pass unchal- 

 lenged to a place among the traditional beliefs of Science, it is 

 well to remember that the evidence for these beliefs is far from 

 being of the nature of proof. 



