in the main true. These facts have as yet received no
explanation on the theory of independent Creations; they cannot be grouped
together under one point of view, but each has to be considered as an
ultimate fact. As the first origin of life on this earth, as well as the
continued life of each individual, is at present quite beyond the scope of
science, I do not wish to lay much stress on the greater simplicity of the
view of a few forms, or of only one form, having been originally created,
instead of innumerable miraculous creations having been necessary at
innumerable periods; though this more simple view accords well with
Maupertuis's philosophical axiom "of least action."

In considering how far the theory of natural selection may be {13}
extended,--that is, in determining from how many progenitors the
inhabitants of the world have descended,--we may conclude that at least all
the members of the same class have descended from a single ancestor. A
number of organic beings are included in the same class, because they
present, independently of their habits of life, the same fundamental type
of structure, and because they graduate into each other. Moreover, members
of the same class can in most cases be shown to be closely alike at an
early embryonic age. These facts can be explained on the belief of their
descent from a common form; therefore it may be safely admitted that all
the members of the same class have descended from one progenitor. But as
the members of quite distinct classes have something in common in structure
and much in common in constitution, analogy and the simplicity of the view
would lead us one step further, and to infer as probable that all living
creatures have descended from a single prototype.

I hope that the reader will pause before coming to any final and hostile
conclusion on the theory of natural selection. It is the facts and views to
be hereafter given which have convinced me of the truth of the theory. The
reader may consult my 'Origin of Species,' for a general sketch of the
whole subject; but in that work he has to take many statements on trust. In
considering the theory of natural selection, he will assuredly meet with
weighty difficulties, but these difficulties relate chiefly to
subjects--such as the degree of perfection of the geological record, the
means of distribution, the possibility of transitions in organs, &c.--on
which we are confessedly ignorant; nor do we know how ignorant