range of
this principle was greatly over-estimated, if the great changes which have
taken place in so many organisms in the course of ages are to be
interpreted as due to this process of selection alone, since no
transformation of any importance can be evolved by itself; it is always
accompanied by a host of secondary changes. He gives the familiar example
of the Giant Stag of the Irish peat, the enormous antlers of which required
not only a much stronger skull cap, but also greater strength of the
sinews, muscles, nerves and bones of the whole anterior half of the animal,
if their mass was not to weigh down the animal altogether. It is
inconceivable, he says, that so many processes of selection should take
place _simultaneously_, and we are therefore forced to fall back on the
Lamarckian factor of the use and disuse of functional parts. And how, he
asks, could natural selection follow two opposite directions of evolution
in different parts of the body at the same time, as for instance in the
case of the kangaroo, in which the forelegs must have become shorter, while
the hind legs and the tail were becoming longer and stronger?

Spencer's main object was to substantiate the validity of the
Lamarckian principle, the cooeperation of which with selection had been
doubted by many. And it does seem as though this principle, if it
operates in nature at all, offers a ready and simple explanation of
all such secondary variations. Not only muscles, but nerves, bones,
sinews, in short all tissues which function actively, increase in
strength in proportion as they are used, and conversely they decrease
when the claims on them diminish. All the parts, therefore, which
depend on the part that varied first, as for instance the enlarged
antlers of the Irish Elk, must have been increased or decreased in
strength, in exact proportion to the claims made upon them,--just as
is actually the case.

But beautiful as this explanation would be, I regard it as untenable,
because it assumes the _transmissibility of functional modifications_
(so-called "acquired" characters), and this is not only
undemonstrable, but is scarcely theoretically conceivable, for the
secondary variations which accompany or follow the first as
correlative variations, occur also in cases in which the animals
concerned are sterile and _therefore cannot transmit anything to their
descendants_. This is true of _worker bees_, and particularly of
_ants_, and I shall here g