EVOLUTION OF INSTINCTIVE BEHAVIOUR 115 
under-acting, and the trick fails—her brood is found and 
destroyed. Does it not seem probable that such experience 
would be dearly bought, that failure would mean either death 
to the parent or death to the offspring? And is it not clear 
that natural selection is thus introduced in any case? And 
may not the selectionist pertinently ask : “ If natural selection 
is thus introduced as a factor, why halt midway between 
two hypotheses? Why not take the further step—one by 
which all the difficulties attending the intelligent acquisition 
and the biological transmission are alike avoided—of allowing 
that natural selection exercises, throughout, its influence on 
congenital variations, and not on acquired modifications of 
behaviour ?” 
There is, however, a way in which, when natural selection 
is operative, intelligence may serve to foster congenital varia- 
tions of the required nature and direction. We must re- 
member that acquired habits on the one hand, and congenital 
variations of instinctive behaviour on the other hand, are both 
working, in their different spheres, towards the same end, that 
of adjustment to the conditions of life. If, then, acquired 
accommodation and congenital adaptation reach this end by 
different methods, survival may be best secured by their co- 
operation. And the more thorough-going the co-operation 
the better the chance of survival. There would be a dis- 
tinct advantage in the struggle for existence when inherited 
tendencies of independent origin coincided in direction with 
acquired modifications of behaviour; a distinct disadvantage 
when such inherited tendencies were of such a character as to 
thwart or divert the action of intelligence. Thus any here- 
ditary variations which coincide in direction with modifications 
of behaviour due to acquired habit would be favoured and 
fostered ; while such variations as occurred on other and 
divergent lines would tend to be weeded out. Professor Mark 
Baldwin,* who has independently suggested such relation 
between modification and variation, has applied to the process 
* Professor Henry Osborn has also indicated the relationship re- 
ferred to. 
