rmance of that action; for in each generation constant use would
better and better adapt the structures to the discharge of their
functions, and they would then be bequeathed to the next generation in
this their improved form by heredity. So that, for instance, if there
had been a thousand generations of blacksmiths, we might expect the sons
of the last of them to inherit unusually strong arms, even if these
young men had themselves taken to some other trade not requiring any
special use of their arms. Similarly, if there had been a thousand
generations of men who used their arms but slightly, we should expect
their descendants to show but a puny development of the upper
extremities. Now let us apply all this to the animal kingdom in general.
The giraffe, for instance, is a ruminant whose entire frame has been
adapted to support an enormously long neck, which is of use to the
animal in reaching the foliage of trees. The ancestors of the giraffe,
having had ordinary necks, were supposed by Lamarck to have gradually
increased the length of them, through many successive generations, by
constantly stretching to reach high foliage; and he further supposed
that, when the neck became so long as to require for its support special
changes in the general form of the animal as a whole, these special
changes would have brought about the dwindling of other parts from which
so much activity was no longer required--the general result being that
the whole organization of the animal became more and more adapted to
browsing on high foliage. And so in the cases of other animals, Lamarck
believed that the adaptation of their forms to their habits could be
explained by this simple hypothesis that the habits created the forms,
through the effects of use and disuse, coupled with heredity.

Such is what is ordinarily known as Lamarck's theory of evolution. We
may as well remember, however, that it really constitutes only one part
of his theory; for besides this hypothesis of the cumulative inheritance
of functionally-produced modifications--to which we may add the
inherited effects of any direct action exercised by surrounding
conditions of life,--Lamarck believed in some transcendental principle
tending to produce gradual improvement in pre-determined lines of
advance. Therefore it would really be more correct to designate the
former hypothesis by the name either of Erasmus Darwin, or, still
better, of Herbert Spencer. Nevertheless, in order t