admitting that it operated through
successive generations, it left unexplained the greater part of the
facts. Having been myself one of these few, I look back with surprise at
the way in which the facts which were congruous with the espoused view
monopolized consciousness and kept out the facts which were incongruous
with it--conspicuous though many of them were. The misjudgment was not
unnatural. Finding it impossible to accept any doctrine which implied a
breach in the uniform course of natural causation, and, by implication,
accepting as unquestionable the origin and development of all organic
forms by accumulated modifications naturally caused, that which appeared
to explain certain classes of these modifications, was supposed to be
capable of explaining the rest: the tendency being to assume that these
would eventually be similarly accounted for, though it was not clear
how.

Returning from this parenthetic remark, we are concerned here chiefly to
remember that, as said at the outset, there existed thirty years ago, no
tenable theory about the genesis of living things. Of the two
alternative beliefs, neither would bear critical examination.

* * * * *

Out of this dead lock we were released--in large measure, though not I
believe entirely--by the _Origin of Species_. That work brought into
view a further factor; or rather, such factor, recognized as in
operation by here and there an observer (as pointed out by Mr. Darwin in
his introduction to the second edition), was by him for the first time
seen to have played so immense a part in the genesis of plants and
animals.

Though laying myself open to the charge of telling a thrice-told tale, I
feel obliged here to indicate briefly the several great classes of facts
which Mr. Darwin's hypothesis explains; because otherwise that which
follows would scarcely be understood. And I feel the less hesitation in
doing this because the hypothesis which it replaced, not very widely
known at any time, has of late so completely dropped into the
background, that the majority of readers are scarcely aware of its
existence, and do not therefore understand the relation between Mr.
Darwin's successful interpretation and the preceding unsuccessful
attempt at interpretation. Of these classes of facts, four chief ones
may be here distinguished.

In the first place, such adjustments as those exemplified above are made
comprehensible. Though it is inconc