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 moditica- 
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 
