24 
POPULAR SCIENCE REVIEW. 
Love, and Power — which he maintained to constitute insuper- 
able harriers in the development of species by natural selection 
alone. Mr. Wallace has admitted the difficulty in the case of 
the brain ; is he prepared to deny it in the case of the other 
two ? He maintains — so far as appears at present, unanswerably 
— that man cannot have been produced by the unaided power 
of natural selection : does not that raise a strong presumption 
in favour of the introduction of another agent in other cases 
also ? He has marked out very clearly and conclusively the 
limits of natural selection in the origination of species ; can he 
set any limits to the controlling and interfering Power which 
he has invoked to fill up the deficiency ? 
