Individual Accommodation on Evolution loi 



and 'selective value,' seem to hold in the case of reflex and 

 instinctive functions (see Chap. V., above), as against the 

 old preformist or strictly Weismannist view ; but the oper- 

 ation of organic selection, as now explained, renders these 

 objections ineffective when urged in support of Lamarck- 

 ism. * We may imagine creatures, whose hands were 

 used for holding only with the thumb and fingers on the 

 same side of the object held, to have first discovered, 

 under stress of circumstances and with variations which 

 permitted the further adjustment, how to make use of the 

 thumb for grasping opposite to the fingers, as we now do. 

 Then let us suppose that this proved of such utility that 

 all the young that did not do it were killed off ; the next 

 generation following would be plastic, intelligent, or imi- 

 tative enough to do it also. They would use the same 

 coordinations and prevent natural selection getting its 

 work in upon them ; and so instinctive " thumb-grasping " 

 might be waited for indefinitely by the species and then 

 be got as an instinct altogether apart from use-inheri- 

 tance ' (from an earlier page).^ 



5. It seems to the writer — though he hardly dares venture 

 into a field belonging so strictly to the technical biologist 

 — that this principle might not only explain many cases of 

 apparent widespread * determinate variations ' appearing 

 suddenly^ let us say, in fossil deposits, but the fact that vari- 

 ations seem often to be ^discontinuous' Suppose, for ex- 

 ample, certain animals, varying in respect to a certain 

 quality from ^ to ;^ about a mean x. The mean x would 

 be the case most likely to be preserved in fossil form, see- 

 ing that there are vastly more of them. Now suppose a 



1 Interesting cases of the operation of this principle have since been 

 cited ; cf. the extract from Headley, in Appendix B. 



