GREAT QUESTIONS IN LITTLE 
course. One cannot see where there is any room for 
a physical change, but the mental growth may be 
enormous, incalculable. All our theories of knowl- 
edge, all our beliefs, are founded upon the assump- 
tion that we have reached the summit of human life. 
But just as the men of a few centuries ago were 
children in the arts and sciences, compared with us, 
so we shall doubtless appear as children when com- 
pared with men a few centuries hence. The mental 
powers of man may not have increased since Aris- 
totle and Plato, but that is only a brief time. Local, 
and, as it were, accidental, causes may account for 
that. Wait five or ten thousand years, and then see. 
It is a long road and it is up and down hill. Man is 
now armed with the weapons of science as he never 
has been before, and his conquest over Nature is 
bound to be more and more complete. 
Whole tribes and families of animals have become 
extinct in the past, and others will probably become 
extinct in the future, but one can think of the race 
of man as becoming extinct only on some radical 
cosmic change in the earth, such as there has been in 
some of the other planets and in our moon. This 
change will come, but not in millions of years. 
Unless the waste of the fertility of the land into 
the sea through man’s agency is checked, the fertil- 
ity of the soil in the course of countless ages will no 
longer support the race, but this as a cause working 
against the perpetuity of the race can be and doubt- 
307 
