from an entirely new side, and of basing the theory of descent on a
consistent system, which now goes by the name of Darwinism.

Lamarck had unsuccessfully attempted to explain the modification of
organisms that descend from a common form chiefly by the action of
habit and the use of organs, though with the aid of heredity. But
Darwin's success was complete when he independently sought to give a
mechanical explanation, on a quite new ground, of this modification of
plant and animal structures by adaptation and heredity. He was
impelled to his theory of selection on the following grounds. He
compared the origin of the various kinds of animals and plants which
we modify artificially--by the action of artificial selection in
horticulture and among domestic animals--with the origin of the
species of animals and plants in their natural state. He then found
that the agencies which we employ in the modification of forms by
artificial selection are also at work in Nature. The chief of these
agencies he held to be "the struggle for life." The gist of this
peculiarly Darwinian idea is given in this formula: The struggle for
existence produces new species without premeditated design in the life
of Nature, in the same way that the will of man consciously selects
new races in artificial conditions. The gardener or the farmer selects
new forms as he wills for his own profit, by ingeniously using the
agency of heredity and adaptation for the modification of structures;
so, in the natural state, the struggle for life is always
unconsciously modifying the various species of living things. This
struggle for life, or competition of organisms in securing the means
of subsistence, acts without any conscious design, but it is none the
less effective in modifying structures. As heredity and adaptation
enter into the closest reciprocal action under its influence, new
structures, or alterations of structure, are produced; and these are