purposive in the sense that they serve the organism when formed, but
they were produced without any pre-conceived aim.

This simple idea is the central thought of Darwinism, or the theory of
selection. Darwin conceived this idea at an early date, and then, for
more than twenty years, worked at the collection of empirical evidence
in support of it before he published his theory. His grandfather,
Erasmus Darwin, was an able scientist of the older school of natural
philosophy, who published a number of natural-philosophic works about
the end of the eighteenth century. The most important of them is his
Zoonomia, published in 1794, in which he expounds views similar to
those of Goethe and Lamarck, without really knowing anything of the
work of these contemporaries. However, in the writings of the
grandfather the plastic imagination rather outran the judgment, while
in Charles Darwin the two were better balanced.

Darwin did not publish any account of his theory until 1858, when
Alfred Russel Wallace, who had independently reached the same theory
of selection, published his own work. In the following year appeared
the Origin of Species, in which he develops it at length and supports
it with a mass of proof. Wallace had reached the same conclusion, but
he had not so clear a perception as Darwin of the effectiveness of
natural selection in forming species, and did not develop the theory
so fully. Nevertheless, Wallace's writings, especially those on
mimicry, etc., and an admirable work on The Geographical Distribution
of Animals, contain many fine original contributions to the theory of
selection. Unfortunately, this gifted scientist has since devoted
himself to spiritism.* (* Darwin and Wallace arrived at the theory
quite independently. Vide Wallace's Contributions to the Theory of
Natural Selection (1870) and Darwinism (1891).)