in comes from the condensation
of moisture in the atmosphere, they demand of us a rain-drop from
moisture not yet condensed. If they stickle for proof and cavil on
the ninth part of a hair, as they do when we bring forward what we
deem excellent instances of the transmission of an acquired
characteristic, why may not we, too, demand at any rate some
evidence that the unmodified beetles actually did always, or nearly
always, get blown out to sea, during the reduction above referred
to, and that it is to this fact, and not to the masterly inactivity
of their fathers and mothers, that the Madeira beetles owe their
winglessness? If we begin stickling for proof in this way, our
opponents would not be long in letting us know that absolute proof
is unattainable on any subject, that reasonable presumption is our
highest certainty, and that crying out for too much evidence is as
bad as accepting too little. Truth is like a photographic
sensitized plate, which is equally ruined by over and by under
exposure, and the just exposure for which can never be absolutely
determined.

Surely if disuse can be credited with the vast powers involved in
Mr. Darwin's statement that it has probably "been the main agent in
rendering organs rudimentary," no limits are assignable to the
accumulated effects of habit, provided the effects of habit, or use
and disuse, are supposed, as Mr. Darwin supposed them, to be
inheritable at all. Darwinians have at length woke up to the
dilemma in which they are placed by the manner in which Mr. Darwin
tried to sit on the two stools of use and disuse, and natural
selection of accidental variations, at the same time. The knell of
Charles-Darwinism is rung in Mr. Wallace's present book, and in the
general perception on the part of biologists that we must either
assign to use and disuse such a predominant share in modification as
to make it the feature most proper to be insisted on, or deny that
the modifications, whether of mind or body, acquired during a single
lifetime, are ever transmitted at all. If they can be inherited at
all, they can be accumulated. If they can be accumulated at all,
they can be so, for anything that appears to the contrary, to the
extent of the specific and generic differences with which we are
surrounded. The only thing to do is to pluck them out root and
branch: they are as a cancer which, if the smallest fibre be left
unexcised, will grow again, and kill any system on to wh