322 
KIRTLEY F. MATHER 
V 
From the paleontologist’s vantage point on the reviewing 
stand, the creatures of the earth appear in this twentieth century 
to be approaching another milestone in their progress. There 
are rapids and cataracts just ahead; once again^ the stream 
of life is gathering its energies to leap forward with increasing 
velocity until it plunges swiftly over the brink of another falls. 
A crisis in life development, fully as critical as those which 
opened and closed the Age of Reptiles, is close at hand. Survi- 
val values once again have changed, but the same principles 
which selected certain groups of animals to weather those 
^devolutions” of the past will doubtless guide certain of the 
existing creatures through the dangers in the offing. The 
crisis recorded in the rocks of latest Paleozoic Age, was forced 
upon the land animals by changes in climate and environment; 
it was successfully passed by creatures who specialize in the 
adaptation of their bodies to cold and drought, and who escaped 
from the crowded confines of the sea to the almost uninhabited 
silences of the land. The ^devolution” involved in the de- 
thronement of the reptiles and the exaltation of the mammals 
at the close of the Mesozoic Era was likewise precipitated by 
external changes over which the mammals themselves had no 
control; it bettered the condition of creatures who specialized 
in the care of their young and the use of their brains. Each 
group which prospered had for some time displayed the very 
characteristics which proved efficacious in the time of stress; 
the ^devolution” afforded the opportunity for the testing and 
the rewarding of the products of progressive evolution. 
The crisis of tomorrow, already imminent, is likewise in its 
real essence the result of external conditions over which man 
has so far displayed no control. The world has lost its corners 
and shrunk into a neighborhood; but man is not to blame be- 
cause ocean highways link its farthest islands, and mountain 
barriers fail to subdivide its lands. The resources of the earth 
are proving inadequate to support a large population of idle 
rich or idle poor, without an excessive load being placed upon the 
