Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

4 ON THE LAW WHICH HAS REGULATED
acquainted, or has been able to observe himself.
These have all served to convince him of the correctness of his hypothesis. Fully to enter into such a
subject would occupy much space, and it is only in
consequence of some views having been lately promulgated, he believes, in a wrong direction, that he
now ventures to present his ideas to the public, with
only such obvious illustrations of the arguments and
results as occur to him in a place far removed from
all means of reference and exact information.
A Law deduced from well-known Geograp7hical and
Geological Facts.
The following propositions in Organic Geography
and Geology give the main facts on which the
hypothesis is founded.
Geography.
1. Large groups, such as classes and orders, are
generally spread over the whole earth, while smaller
ones, such as families and genera, are frequently
confined to one portion, often to a very limited district.
2. In widely distributed families the genera are
often limited in range; in widely distributed genera,
well marked groups of species are peculiar to each
geographical district.
3. When a group is confined to one district, and
is rich in species, it is almost invariably the case
that the most closely allied species are found in the
same locality or in closely adjoining localities, and