382 NATURAL SCIENCE [December 



not only of biological, but also of psychological and sociological 

 phenomena. But though this must to some degree influence his 

 judgment, he is too honest and independent an enquirer into 

 truth to champion a cause on these grounds alone. The pendu- 

 lum of biological opinion tends to swing towards a negative 

 position in this matter ; and it is a distinct gain that the arguments 

 in favour of the doctrine in question should be presented with all 

 the logical force and power of exposition which Mr Spencer has at 

 his command. And if there are many who still remain unconvinced, 

 this is not for want of fresh arguments but because they feel the 

 necessity for more facts. 



Of the three lines of evidence on which Mr Spencer in large de- 

 gree relies, the first is co-adaptation of co-operative parts. But until 

 we know more accurately than we do at present what amount of co- 

 adjustment is effected in each case by individually-acquired 

 modifications, we lack important data for discussing the problem. 

 Probably its range is very considerable. The horse runs and leaps 

 with the added weight of his rider ; and the work of all domestic 

 animals of draught and labour shows that their organization will 

 stand a strain far in excess of the normal. Granting that individual 

 coadjustment will in each generation do much (just how much 

 remains to be proved) it would seem that in the case of evolving 

 antlers the added weight will for long be within the limits of such 

 individual coadjustment. But it has been urged that the modifica- 

 tion of a structure may foster, though it may not cause, congenital 

 variations of like kind. For whereas other variations, since they 

 are out of harmony with the circumstances of life, will constantly 

 be eliminated in the struggle for existence, these are allowed free 

 play. In other words, congenital variations coincident in direction 

 with acquired modifications will be favoured. And there is no 

 necessity for them to be accurately simultaneous ; individual co- 

 adjustment will make good the deficiencies of congenital co- 

 adaptation. In view of such considerations the argument from 

 coadaptation has little weight till we have fuller knowledge of 

 the range of coadjustment. 



The second line of argument adduced by Mr Spencer is the pos- 

 session of unlike powers of discrimination by different parts of the 

 human skin. But here again we need more facts. It is assumed 

 that this discrimination is largely congenital. But we do not know 

 what proportion of it is individually acquired. We do know 

 that a comparatively short period of education in little-used areas 

 largely increases, is said to double, the power of discrimination. 

 And some psychologists contend that — as the term discrimination 

 implies — what we are really dealing with is the special application 

 of the power of central perception, not an increased delicacy of 



