e who have
other traits. To whatever extent, therefore, inheritance of this
functionally-produced modification operates, it operates independently
of natural selection.

One other point has to be noted--the relative importance of this factor.
If additional developments of muscles and bones may be transmitted--if,
as Mr. Darwin held, there are various other structural modifications
caused by use and disuse which imply inheritance of this kind--if
acquired characters are hereditary, as the Duke of Argyll believes; then
the area over which this factor of organic evolution operates is
enormous. Not every muscle only, but every nerve and nerve-centre, every
blood-vessel, every viscus, and nearly every bone, may be increased or
decreased by its influence. Excepting parts which have passive
functions, such as dermal appendages and the bones which form the skull,
the implication is that nearly every organ in the body may be modified
in successive generations by the augmented or diminished activity
required of it; and, save in the few cases where the change caused is
one which conduces to survival in a pre-eminent degree, it will be thus
modified independently of natural selection. Though this factor can
operate but little in the vegetal world, and can play but a subordinate
part in the lowest animal world; yet, seeing that all the active organs
of all animals are subject to its influence, it has an immense sphere.
The Duke of Argyll compares the claim made for this factor to "some bit
of Bumbledom setting up for Home Rule--some parochial vestry claiming
independence of a universal empire." But, far from this, the claim made
for it is to an empire, less indeed than that of natural selection, and
over a small part of which natural selection exercises concurrent power;
but of which the independent part has an area that is immense.

It seems to me, then, that the Duke of Argyll is mistaken in four of the
propositions contained in the passages I have quoted. The inheritance of
acquired characters _is_ disputed by biologists, though he thinks it is
not. It is not true that "heredity is the central idea of natural
selection." The statement that natural selection includes and covers all
the causes which can possibly operate through inheritance, is quite
erroneous. And if the inheritance of acquired characters is a factor at
all, the dominion it rules over is not insignificant but vast.

* * * * *

Her