od still remain as evidence of the greater magnitude of the life
which has outgrown them. Similarly every man may mark within himself
the various limits which once bounded him, but which he has since
exceeded in consequence of steady and consecutive effort. The progress
of mankind at large differs only in complexity and range. It can be
tested and determined only because identical interests persist. If men
had not in all times wanted the same things it would be impossible to
measure their attainments. Their successes and failures would be
incommensurable. But the old needs and the old hopes yet remain. The
problem of life which was from {130} the beginning is a problem still.
If it can be shown that the old needs are met more easily, along with
new needs besides, that there is better promise that the hopes will be
fulfilled, and that the general problem of life is nearer a solution,
then human progress will have been demonstrated.

II

I propose, in the first place, to discuss two general principles, the
operation of which is conducive to progress. One of these principles
is _external_, that is, it relates to the environment of life rather
than to its internal economy; and to this I shall turn first.

The external environment of life is in some respects favorable, in
other respects unfavorable. Now, strangely enough, it is the
unfavorable rather than the favorable aspect of the environment that
conduces to progress. Progress, or even the least good, would, of
course, be impossible, unless the mechanical environment was morally
plastic. The fact that nature submits to the organization which we
call life is a fundamental and constant condition of all civilization.
But there is nothing in the mere compliance of nature to press life
forward. It is the _menace_ of nature which stimulates progress. It
is because nature always remains a source of difficulty and danger
{131} that life is provoked to renew the war and achieve a more
thorough conquest. Nature will not permit life to keep what it has
unless it gains more.

The external environment of life embraces not only mechanical nature,
but also such outlying units of life as have not yet been brought into
harmonious relations. Conflict between individuals, tribes, races, or
nations operates in a manner analogous to mechanical nature. It exerts
a constant pressure in the direction of greater strength and
efficiency. In order that man shall not be robbed