A Review: World-Power and Evolution 
40 feet in height, but with some 
trees towering to 100 feet. Schuchert 
describes it as a forest of rapid growth, 
of soft and even spongy woods, in 
which evergreen trees with compara- 
tively small, needle-like leaves were 
prominent. Associated with these were 
thickets of rushes, also of very rapid 
growth, which in habit resembled 
modern cane-brakes and bamboo 
thickets. Here and there stood majestic 
tree-like ferns, while many smaller 
ferns and similar plants thrived in the 
shady places or climbed among the 
trees. Flowers of a certain sort were 
sparingly present, but of insignificant 
size and’ unattractive color. Spores 
took the place of seeds to such a degree 
that when the trees and ferns were 
liberating them the entire forest was 
covered with a_ greenish-yellow or 
brown dust. During the Permian 
Period the sharp transitions from cold 
to warm, or from moist to dry, caused 
these ancient forests to die out. Coni- 
fers much like those of today came into 
existence. Seeds largely took the place 
of spores. These changes were accom- 
panied by a general reduction in the 
size and variety of plants, and by a 
tendency for them to become hardier 
and to have thicker and less ornate 
leaves. 
CHANGES IN ANIMAL LIFE 
“During the great climatic changes 
of the Permian, animal life suffered an 
even greater transformation than plant 
life. For example, previous to that 
time the insects had been of truly 
astonishing size. Out of the 400 forms 
known in the early and middle parts of 
the Pennsylvanian Period which pre- 
ceded the Permian, the smallest had 
wings over a third of an inch long. 
The wings of more than twenty species 
were 6 inches long, six attained. to 
nearly 8 inches, and three were giants 
of 12 inches. Imagine a spore-dusted 
forest full of insects as large as crows! 
The cold and changeable climate of 
Permian times apparently caused the 
extinction of all these forms. Their 
place was taken by small species re- 
139 
sembling those of today. Moreover, 
the very nature of insects was ‘pro- 
foundly modified by the introduction 
of metamorphosis. That is, where there 
had formerly been merely a gradual 
growth from the egg to the adult, there 
was now a growth from egg to maggot 
or caterpillar, then a resting period, 
and finally a transformation from 
maggot to fly or from caterpillar to 
butterfly. At the same time the insects 
acquired the power to become dormant 
and thus persist for months at a time. 
All these changes were apparently due 
to the necessity for adapting themselves 
to sudden periods of drought or cold 
during the time of growth in summer, 
or to the necessity for enduring long, 
severe winters. Thus the climatic varia- 
bility of the Permian Period not only 
caused a remodeling of the earth’s gar- 
ment of vegetation, but introduced a 
unique stage into the life history of 
insects. 
“For our present purpose another 
change is far more important. At this 
time apparently there occurred one of 
the most vital steps in the evolution of 
our direct ancestors, the mammals, Ex- 
treme aridity and low temperature were 
both characteristic of certain epochs of 
the Permian Period. Among the more 
progressive types of land animals 
aridity has a tendency to accelerate de- 
velopment. It places a premium upon 
the power to travel, and especially upon 
speed. As Lull puts it: ‘Not only are 
food and water scarce and _ far 
between, but the strife between 
pursuer and pursued becomes intensi- 
fied—neither can afford to be outdis- 
tanced by the other. This means in- 
creased metabolism, which in turn gen- 
erally implies not only greater motive 
powers but higher temperature. With 
increasing cold a premium would be 
placed upon such creatures as could 
maintain their activity beyond the 
limits of shortening summers, and this 
could he accomplished only by the de- 
velopment of some mechanism whereby 
a relatively constant temperature could 
be maintained within the animal regard- 
less of outside conditions.’ In other 
