ess
perfect to the more perfect; the further fact that they also form a
series according as they display more or less homology of structure and
are formed according to similar types; and, lastly, that the fossil
remains of organisms found in the various strata of the earth's surface
likewise represent an ascending series from the simple to the more
complex--these three facts suggested to naturalists the thought that
living organisms were not always as we find them to-day, but that the
more perfect had developed from simpler forms through a series of
modifications. These thoughts were at first advanced with some
hesitation, and were confined to narrow circles. They received,
however, material support when, during the fourth decade of the 19th
century the splendid discovery was made (by K. E. von Baer) that every
organism is slowly developed from a germ, and in the process of
development passes through temporary lower stages to a permanent higher
one. Even at that time many naturalists believed in a corresponding
development of the whole series of organisms, without of course being
able to form a clear conception of the process. Such was the state of
affairs when Darwin in the year 1859 published his principal work,
_The Origin of Species by Means of Natural Selection_. In this
work for the first time an exhaustive attempt was made to sketch a
clear and completely detailed picture of the process of development.

Darwin started with the fact that breeders of animals and growers of
plants, having at their disposal a large number of varieties, always
diverging somewhat from each other, choose individuals possessing
characteristics which they desired to strengthen, and use only these
for procreation. In this manner the desired characteristic is gradually
made more prominent, and the breeder appears to have obtained a new
species. Similar conditions are supposed to prevail in Nature, only
that there is lacking the selecting hand of the breeder. Here the
so-called principle of Natural Selection holds automatic sway by means
of the Struggle for Existence. All the various forms of life are
warring for the means of subsistence, each striving to obtain for
itself the best nourishment, etc. In this struggle those organisms will
be victorious which possess the most favorable characteristics; all
others must succumb. Hence those only will survive which are best
adapted to their environment. But between those which survive, the
strugg