58 THE MEANING OF EVOLUTION 
life and no one could foretell accidents. Mr. Dar- 
win made clear that it was not a question of chance. 
That which might happen to any individual animal 
might be what we, not knowing the process, called 
accident, and yet there could be no possible doubt 
that those who succeeded were better fitted to battle 
with life than those who failed, and that their suc- 
cess was due primarily to their being thus advantaged. 
Consequently, if generation by generation the so-called 
accidents of life are constantly eliminating the unfit 
in overwhelming proportions, not only must the posi- 
tively unfit disappear, but even the less fit. The more 
keen the struggle, the fewer could survive and the 
fitter they must be to survive at all. This is Selec- 
tion. These, then, are Darwin’s four great factors 
of evolution: Heredity, Variation, Multiplication, Se- 
lection. 
From these it results that the animals and plants 
naturally become better adapted to the situation in 
which they are placed. When, as is constantly hap- 
pening through the history of the earth, a change oc- 
curs in the physical geography of any region, when 
a plain is lifted to be a plateau, or a mountain chain 
is submerged until it becomes a row of small islands, 
this alteration will produce uncommon hardships 
among animals, even though they were well fitted to 
the old conditions. Any animal or any species of 
