The principle influence was Darwin reading Principles of Geology
by Charles Lyell - he was given a copy by Robert Fitzroy (the
captain of the Beagle) at the start of the Beagle's voyage around
The main theme of Principles of Geology is
uniformtarianism. This is the theory that the world was
shaped by the gradual affect of observable processes. For example,
a river valley is explained by the river gradually wearing through
It is the idea of uniformtarianism that Darwin...