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 cooperation 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