among the dark-coloured races in elevated situations or in
cold climates. In more frequent examples such changes have
been brought about in many successive gradations, as in the
deviations which are noted among Negro and Polynesian
tribes in Africa and in the Oceanic countries. It must be
observed, moreover, that the changes alluded to do not so
often take place by alteration in the physical character of a
whole tribe simultaneously, as by the springing up in it of
some new congenital peculiarity, which is afterwards propagated
and becomes a character more or less constant in the
progeny of the individuals in whom it first appeared, and is
perhaps gradually communicated by intermarriages to a whole
stock or tribe. This, as it is obvious, can only happen in a
long course of time.
If we suppose it to be conceded that all human races are
of one species, technically so termed, and that they are
not distinguished from each other by characters ever constant
and immutable, and such as cannot have been produced in
a breed or race which had been previously destitute of
them, the question still remains, what is the- proof that all
races actually descended from one stock or one parentage?
It is not self-evident that many families of the same species
were not created at first to supply at once with human as well
as with other organised beings various regions of the earth.
This, indeed, is improbable when we take into account the
almost universally rapid increase of living species, and the surprising
efficacy of the means every where contrived by nature
both for their multiplication and dispersion, which would seem
to be superfluous, or at least much greater than could be
requisite, on the hypothesis that a multitude of each tribe
existed from the beginning. But this consideration is, perhaps,
not fully conclusive, and we require to know what has
been the law of nature in this respect.
To this problem I have endeavoured to furnish a solution
in the first volume of my work. The first book is occupied
with an investigation of facts relating to the migrations and
diffusion of different tribes of organised beings over the globe.
It would seem, cl priori, very improbable that much information
could be collected on this subject sufficiently precise and
particular to lead to satisfactory results, since we possess no
history, properly so termed, of the migrations and dispersion
of the inferior tribes, and here the resource which has so
remarkably supplied the place of historical documents in the
investigations relating to human races and their dispersion
entirely fails. But in reality the sum of information collected
since the time of Pennant in regard to the diffusion of
organised beings over different parts of the world is, when
taken altogether, remarkably extensive and accurate. It
appears, indeed, to be amply sufficient to establish, in the
most conclusive manner, one or two general facts connected
with the primitive history of living tribes, and this not in one
but in all departments of organised nature. It has been
observed in both the animal and vegetable kingdoms that
while tribes of the most simple structure are spread in the
present time and appear to have been originally diffused over
the most distant regions, races of a higher and more ela-
borate organisation exist only in places to which it is generally
obvious but always probable that they may have obtained
access from some particular spot, apparently the local centre
and primitive habitation of the tribe. Hence we derive each
tribe among the higher and more perfectly organised creatures,
whether locomotive or fixed, whether animals or plants,
from one original point and from a single stock. We are,
a fortiori, at liberty to apply this conclusion to the instance
of the human species, or to infer that the law of nature,
otherwise universal or very general in its prevalence, has not
been in this case transgressed, where such an exception
would be of all cases the most improbable. In the history of
mankind various subordinate phenomena, though necessarily
partial in their bearing, have given us confirmations of this
doctrine. Such facts have been occasionally noticed in the
course of the preceding volumes. The evidence, derived
from various investigations, applied successively to different
departments of nature, from which the general inference
above-stated was at first separately deduced, will be found,
as I have said, collected in the first book.