he causes for this fact
cannot be found in any other category than that comprising the hereditary
and congenital influences of parent upon offspring. _How_ the effect is
produced by such causes is less important in the present connection than
the natural _fact_ of congenital variation. Science, however, has learned
much about the causes in question, as we shall see at a later point.

Thus the first step which is necessary for an evolution and transformation
of organic mechanisms proves to be entirely natural when we give only
passing attention to certain obvious phenomena of life. The fact of
"becoming different" cannot be questioned without indicting our powers of
observation, and we must believe in it on account of its reality, even
though the ultimate analysis of the way variations of different kinds are
produced remains for the future.

Having learned that animals are able to change in various ways, the next
question is whether variations can be transmitted to future generations
through the operation of secondary factors. Long ago Buffon held that the
direct effects of the environment are immediately heritable, although the
mode of this inheritance was not described; it was simply assumed and
taken for granted. Thus the darker color of the skin of tropical human
races would be viewed by Buffon as the cumulative result of the sun's
direct effects. Lamarck laid greater stress upon the indirect or
functional variations due to the factors of use and disuse, and he also
assumed as self-evident that such effects were transmissible as "acquired
characters." This expression has a technical significance, for it refers
to variations that are added during individual life to the whole group of
hereditary qualities that make any animal a particular kind of organism.
If evolution takes place at all, any new kind of organism originating from
a different parental type must truly acquire its new characteristics, but
few indeed of the variations appearing during the lifetime of an animal
owe their origin to the functional and environmental influences, whose
effects only deserve the name of "acquired characters" in the special
biological sense.

In sharp contrast to Lamarckianism, so called,--although it did not
originate in the mind of the noted man of science whose name it bears,--is
the doctrine of natural selection, first proposed in its full form by
Charles Darwin. This doctrine presents a wholly natural description of the
meth