48 
THE PRINCIPLES OF BIOLOGY. 
underfed. They eat their food raw, instead of cooked, 
prepared, and selected, so that their food costs more to mas¬ 
ticate and digest. They get their food irregularly—short 
periods of gluttony alternate with long periods of want. 
Then, again, the supposed greater consumption in muscular 
action undergone by civilised men than by savages is only 
apparent. The chase is very laborious, and the uncivilised 
not only undergo great exertion in seeking and securing odds 
and ends of wild food, they lack good shelter and protection 
from cold, insects, and other sources of wear and tear. 
A kindred objection is that there are cases where there are 
high powers both of self-preservation and race-propagation. 
This result is the consequence of “ a goodness of constitution,” 
resulting in a better internal utilisation of materials. To 
illustrate this, Mr. Spencer takes the case of a steam engine. 
The fuel he compares with food, the steam employed in 
working the engine with Individuation, and the waste steam 
with Genesis. Of these conditions several variations are 
possible. There may be a structural or organic change of 
proportion by enlarging or diminishing the safety valve, &c. 
There may be a functional change of proportion owing to the 
engine having to draw a heavier load or maintain a higher 
speed, and vice-versa , and there may be coincident variations 
such as that produced by the greater quantity of steam 
supplied by the use of more or better fuel. One case of 
coincident variation is parallel with the case under consider¬ 
ation—that of the augmentation of individual expenditure 
and of reproductive energy that may be caused by a superiority 
of some organ on which the utilising of materials depends— 
it is where more steam is produced from a given weight of fuel 
by improvement of the steam generating apparatus. 
Thus far, says Mr. Spencer, “ we have observed how by 
their extremely high evolution and extremely low fertility 
mankind display the inverse variation between Individuation 
and Genesis in one of its extremes. And we have also 
observed how mankind, like other kinds, are functionally 
changed in their rates of multiplication by changes of con¬ 
ditions. But we have not observed how alteration of structure 
in man entails alteration of fertility.” This is too compli¬ 
cated a problem to be dealt with otherwise than deductively. 
Human Population in the Future. 
The Evolution of Man must be of the same nature, says 
Mr. Spencer, as Evolution in general. Structural Evolution 
may consist in greater integration, or greater differentiation, 
or both; in other words in larger size, greater heterogeneity 
