, unless all these observations are erroneous, or capable of
some explanation that has not yet been pointed out, they lead, with
the strongest force of analogical reasoning, to the conclusion,
that a number of different tribes, such as the various races of
men, must either be incapable of intermixing their stock, and thus
always fated to remain separate from each other; or, if the
contrary should be the fact, that all the races to whom the remark
applies, are proved by it to belong to the same species.

"I believe it may be asserted, without the least chance of
contradiction, that mankind, of all races and varieties, are
equally capable of propagating their offspring by intermarriages,
and that such connexions are equally prolific, whether contracted
between individuals of the same or of the most dissimilar
varieties. If there is any difference, it is probably in favour of
the latter."

This conclusion is repeated a little further on.

"It appears to be unquestionable that intermediate races of men
exist and are propagated, and that no impediment whatever exists to
the perpetuation of mankind when the most dissimilar varieties are
blended together. We hence derive a conclusive proof--unless there
be, in the instance of human races, an exception to the universally
prevalent law of organized nature--that all the tribes of men are
of one family.

"Perhaps the solution of the problem which we have undertaken to
discuss might be left on this issue, or considered as obtained by
this argument. But further light may be thrown on the subject, by a
careful analysis of the facts which can be collected relative to
the nature and origination of varieties; and it may be satisfactory
to my readers to survey this field of enquiry."

Granting, then, the truth of the limitation of species to be
established, and taking as the definition of species the power of
continual propagation, we have it proved at the commencement of the
work, that "all human races are of one species;" the only question which
remains is, whether, admitting them to be of one species, the deduction
that they have a common origin is necessary; or, if not necessary,
whether it is proved in the course of the author's work. It does not
appear to us a _necessary_ conclusion; for there appears no reason _a
priori_ why the Creator should