surrounding circumstances on the organism. I have, also, often personified
the word Nature; for I have found it difficult to avoid this ambiguity; but
I mean by nature only the aggregate action and product of many natural
laws,--and by laws only the ascertained sequence of events.

It has been shown from many facts that the largest amount of life can be
supported on each area, by great diversification or divergence in the
structure and constitution of its inhabitants. We have, also, seen that the
continued production of new forms through natural selection, which implies
that each new variety has some advantage over others, inevitably leads to
the extermination of the older and less improved forms. These latter are
almost necessarily intermediate in structure, as well as in descent,
between the last-produced forms and their original parent-species. Now, if
we suppose a species to produce two or more varieties, and these in the
course of time to produce other varieties, the principal of good being
derived from diversification of structure will generally lead to the
preservation of the most divergent varieties; thus the lesser differences
characteristic of varieties come to be augmented into the greater
differences characteristic of species, and, by the extermination of the
older intermediate forms, new species end by being distinctly defined
objects. Thus, also, we shall see how it is that organic beings can be
classed by what is called a natural method in distinct groups--species
under genera, and genera under families.

As all the inhabitants of each country may be said, owing to their high
rate of reproduction, to be striving to increase in numbers; as each form
comes into competition with many other forms in the struggle for life,--for
destroy any one and its place will be seized by others; as every part of
the organisation occasionally varies in some slight degree, and as natural
selection acts exclusively by the preservation of variations which are