1891.] Are Acquired Variations Inherited ? 197 
directly in causing the organism to vary as a whole, but none of 
the special individual variations which it also produces indirectly 
and directly can be inherited ; its influences upon the germ-plasma 
are gradual and indefinite. The lines of variation are definite so 
far as they are limited by the specific nature of the organism; 
within these limits variations must be indefinite and numerous ;¥ 
the proximate cause of variation is the combination of the diverse 
individual characters of the parents. Selection must accumulate 
minute existing variations in the required direction, and thus create 
new characters ;* it must act upon minute variations in single 
characters, as well as upon the ensemble of characters. Inherit- 
ance is the unbroken transmission of race and ancestral characters 
by subdivision of the germ-plasma; only changes which affect 
the body as a whole can be added to the characteristics of the 
germ-plasma. 
This is a mere abstract of the diverse positions upon every 
problem to which these principles of Lamarck and Weismann 
lead us. No half-way ground is tenable; the result of this in- 
quiry will be a complete rout to one side or the other. By the 
former we diminish the powers of Natural Selection, and increase 
the powers of Environment; at the same time we greatly simplify: 
the problem of Variation, and render far more complex the prob- 
lem of Inheritance. By the latter we throw the entire burden of 
Evolution upon Natural Selection, and eliminate the direct action 
of Environment; we admit definite laws or causes of general 
Variability, but no definite laws governing the variations of single 
characters ; we greatly simplify the problem of Inheritance. In 
short, the vulnerable point with the Lamarckians is in solving the 
problem of Heredity, while their opponents are weakest in solv- 
ing the problem of variation. From the purely theoretical stand- 
point both sides can offer a good working explanation of the 
process of Evolution, provided we grant all their premises ; our 
duty as professed scientific men should be, therefore, to dispassion- 
13 Biological Memoirs, p. 288. " It is the specific nature of an organism which causes it 
to respond to external influences along certain definite lines, although these may be very 
numerous.” 
1 Biological Memoirs, p. 275. 
