,
moreover, the way for wisdom is made ready when men who record facts
of vast but unknown import, if asked to explain their full
significance, are willing frankly to answer that they do not know. The
research which enables us to add to the sum of complete knowledge
stands first; but second only stands the research which, while
enabling us clearly to pose the problem, also requires us to say that
with our present knowledge we can offer no complete solution.

Let me illustrate what I mean by an instance or two taken from one of
the most fascinating branches of world-history, the history of the
higher forms of life, of mammalian life, on this globe.

Geologists and astronomers are not agreed as to the length of time
necessary for the changes that have taken place. At any rate, many
hundreds of thousands of years, some millions of years, have passed by
since in the eocene, at the beginning of the tertiary period, we find
the traces of an abundant, varied, and highly developed mammalian life
on the land masses out of which have grown the continents as we see
them to-day. The ages swept by, until, with the advent of man
substantially in the physical shape in which we now know him, we also
find a mammalian fauna not essentially different in kind, though
widely differing in distribution, from that of the present day.
Throughout this immense period form succeeds form, type succeeds type,
in obedience to laws of evolution, of progress and retrogression, of
development and death, which we as yet understand only in the most
imperfect manner. As knowledge increases our wisdom is often turned
into foolishness, and many of the phenomena of evolution which seemed
clearly explicable to the learned master of science who founded these
lectures, to us nowadays seem far less satisfactorily explained. The
scientific men of most note now differ widely in their estimates of
the relative parts played in evolution by natural selection, by
mutation, by the inheritance of acquired characteristics; and we study
their writings with a growing impression that there are forces at work
which our blinded eyes wholly fail to apprehend; and where this is the
case the part of wisdom is to say that we believe we have such and
such partial explanations, but that we are not warranted in saying
that we have the whole explanation. In tracing the history of the
development of faunal life during this period, the age of mammals,
there are some facts which are cl