346 NATURALS CEENCE. May, 
of food or tissue, or to other slight advantages, may carry child or 
man through fevers otherwise fatal, or through physical dangers and 
hardships, or arduous labours and mental trials under which he would 
otherwise have succumbed. In the not very remote past, a lighter 
skull, by diminishing the weight to be moved, and so increasing a 
man’s speed and agility, may have enabied him to save his life by 
flight from enemies, or to overtake and kill a less swift and agile foe. 
Considering correlated changes and advantages, and looking at the 
many and varied tests through which our species has had to pass, at 
the critical episodes of personal strife, the occasional narrow escapes 
from natural dangers, and the innumerable diseases, parasites, 
microbes, &c., that waylay us through life, and search out the weaker 
points, it becomes almost impossible to say that any advantage has 
been so minute as never to have affected survival. Under starvation, 
wounds, disasters, illnesses, men hover on the brink of the grave, 
and a hair’s-breadth of advantage, a single grain of spare nutriment 
or lessened expenditure, may decide ultimate recovery, while any 
little disadvantage may prove the last straw that breaks the camel’s 
back. All organisms pass through kindred dangers and diseases of 
which we know little and care less. As a rule, the lower animals 
suffer far more frequently and severely from starvation and enemies 
than man does; they multiply much faster, and they are eliminated 
with proportional frequency. In view of such facts, we are by no 
means bound to suppose that small economies can never influence life 
or death in their immediate or ultimate effects. 
Darwin did not disdain to call in the effects of slight causes. He 
partly attributes the somewhat reduced size of our teeth to the prin- 
ciple of economy,” although a tooth is scarcely 3,4,,th part of the 
weight of a man’s body. Mr. Spencer, however, thinks that we 
ought to feel certain that economy, panmixia, and reversed selection, 
all put together, cannot reduce the useless, exposed, and sensitive 
eyes of the proteus and other ‘blind fish and amphibia” living in 
dark caves. We are told, indeed, that ‘‘an economy of z45th of the 
creature’s weight could not appreciably affect survival” (p. 166).% 
But if Natural Selection were really incompetent to secure economy 
in small parts, it could not secure economy in the body as a whole. 
12 Descent of Man, p. 562. 
13 Such an economy is equivalent to the saving of three-quarters of a pound in 
man. Many circumstances are conceivable in which death might be avoided and 
multiplication be favoured by slightly increased facility and quickness of motion, 
by surplus nutriment, and lessened liability to various dangers. Disused parts 
retain, or, apparently even increase, their share of liability to tumours, ulcers, and 
other diseased conditions which occasionally prove fatal by their direct or indirect 
results—of which many examples are known in man, the only animal with 
whose pathology we are really well acquainted. Probably, too, as Ray 
Lankester points out, there was a preliminary selection of animals whose im- 
perfect eyes led them into the sheltering darkness of the cave, and prevented them 
from straying from it. 
