ionately to
criticise.

SECTION II

_SELECTION_

CHAPTER VII.

THE THEORY OF NATURAL SELECTION.

Thus far we have been considering the main evidences of organic
evolution considered as a fact. We now enter a new field, namely, the
evidences which thus far have been brought to light touching the causes
of organic evolution considered as a process.

As was pointed out in the opening chapter, this is obviously the
methodical course to follow: we must have some reasonable assurance that
a fact is a fact before we endeavour to explain it. Nevertheless, it is
not necessary that we should actually demonstrate a fact to be a fact
before we endeavour to explain it. Even if we have but a reasonable
presumption as to its probability, we may find it well worth while to
consider its explanation; for by so doing we may obtain additional
evidence of the fact itself. And this because, if it really is a fact,
and if we hit upon the right explanation of it, by proving the
explanation probable, we may thereby greatly increase our evidence of
the fact. In the very case before us, for example, the evidence of
evolution as a fact has from the first been largely derived from testing
Darwin's theory concerning its method. It was this theoretical
explanation of its method which first set him seriously to enquire into
the evidences of evolution as a fact; and ever since he published his
results, the evidences which he adduced in favour of natural selection
as a method have constituted some of the strongest reasons which
scientific men have felt for accepting evolution as a fact. Of course
the evidence in favour of this fact has gone on steadily growing, quite
independently of the assistance which was thus so largely lent to it by
the distinctively Darwinian theory of its method; and, indeed, so much
has this been the case, that in the present treatise we have been able
to consider such direct evidence of the fact itself, without any
reference at all to the indirect or accessory evidence which is derived
from that of natural selection as a method. From which it follows that
in most of what I am about to say in subsequent chapters on the
evidences of natural selection as a method, there will be furnished a
large addition to the evidences which have already been detailed of
evolution as a fact. But, as a matter of systematic treatment, I have
thought it desirable to keep these two branches of our subject separate.
Which means