1899] TE SCOPE OF NATURAL SELECTION 11g 
in organic evolution. So far all facts point to the conclusion that 
variations under stable conditions are definite, under unstable con- 
ditions indefinite, and this definiteness and indefiniteness occur under 
precisely those conditions which the theory of natural selection would 
lead one to expect; hence, unless definite variability can be shown to 
oceur under conditions which selection could not have produced, the 
facts adduced by the Lamarckian School are favourable rather than 
otherwise to the Neo-Darwinian position. 
To realise how far the theory of selection is capable of explaining 
the facts of organic evolution, it is necessary to bear in mind the 
postulates on which the theory is founded. 
1. It is obvious that Natural Selection can only act by preserving 
or eliminating the complete organism. Selection must therefore be 
organismal, This Darwin and other selectionists have clearly recog- 
nised. 
2. As the whole organism must survive, if the favourable variation 
or variations are to be preserved, it follows that certain minor 
unfavourable variations may also be preserved if they happen to exist 
in an individual which survives on account of its major favourable 
variations. And since no individual is completely adapted to its 
environment, it follows that there must be always a variable amount 
of residual unfavourable variability in every organism. 
3. This residual unfavourable variability may be of considerable 
utility under changed conditions. 
4. Complementary specialisation of parts, as Spencer has shown, 
is favourable to successful competition, and as it is the whole organism 
that is selected or eliminated, it follows that any weakness of one 
specialised part, since it would disturb the balance of all, would be 
detrimental. The more complex the organism, the more specialised 
the structures, the more dependent one part will be on the others for 
its existence, hence a complementary specialising tendency will be 
favoured by selection, and therefore all struggles of one part of an 
organism with another will be reduced to a minimum. 
It is clear that there must be some underlying criterion which 
determines whether any given organism shall be selected or not, and 
that criterion must be the net result of its adaptability to its environ- 
ment. One organism may conceivably survive, by its possession of a 
large number of small favourable variations, while another may survive 
in virtue of a single valuable one, but in each case it would be the 
whole value of that organism which determined its survival. This 
fact is continually disregarded by opponents of the Neo-Darwinian 
position, yet this selection of the organism as a whole is the funda- 
mental postulate from which the theory of selection starts. Thus it is 
not uncommon to read criticisms bearing on the early development of 
some organ, in which the inadequacy of selection is supposed to be 
proved by the writer demonstrating, or believing he has demonstrated, 
