very different in regard to the constancy of their transmission.
In some species they ! are much more regularly
handed down to th e offspring than in others : this is a well
known fact with relation to the vegetable tribes, and it has
been already noticed and illustrated by Mr. Knight and
other writers- on the propagation of planta. In animals the
same difference is -observable : in certain races varieties are
continually springing tip, and they as speedily disappear.
Pérhaps :the sheep may serve for one instance of these mojre
variable tribes, in which likewise the varieties which arise
are more ready to become again lost. In certain species
varieties are, as it would appear, produced with greater difficulty
; and in these when once generated, they continue with
greater permanency. In some instances it is not improbable
that modifications in the form and texture of parts originating
but rarely, become in future time constant and invariable
characters. We have however in all instances sufficient, evidence
that the same law of hereditary transmission prevails
in every tribe, by which qualities belonging to individuals,
such a t least as are congenital, have a; tendency tç préserve
themselves in propagation, and to become appropriated to
whole progenies. This is the principle on. which the exists
ence of permanent varieties depends ; and we havfe already
found sufficient evidence of its agency both in human races
and in many of the tribes of animals and plants.
What has been already said in this brief recapitulation, has
reference to the subjects considered in the few immediately
preceding chapters, which treat of varieties ia.colour and the
form, chiefly, of external parts. The analogical conclusion
has been principally a negative one. I have endeavoured to
establish the general fact, that no remarkable instance of variation
is discoverable in mankind of^which a parallel may
not be found among the lower orders of the creation. Perhaps
the evidence may be nearly as complete as the nature of the
investigation could entitle us to: expect it to be. Still it i spf a
negative kind, and not so cogent of conviction as a positive argument
would be. But here I must refer my readers to the con-
clusion&obtained in the first and second chapters of the same
book ; vit. those which contained Physidlogical and Psychological
comparisOhs^ Theseconclusions carried with them some-
thing of positive evidence. In the first chapter- it was attempted
to be proVed-^the reader can judge with what degree
of sudceSs^-that tribes of animals! which belong to different
species differ from each other physically in a variety of particulars^
in-which the most- dissimilar of human- races betray
no such differences. : In the first plucfe, separate: but even
proximdte- species differ from each rother im respect- to the
principal laws of the animal economy, as those which govern
the-|durati©n- of life, the periods- of utero-gestation; the facts
ydaftiirrelate to reproduction;r Human races coincide strictly
in all these particulars. Secondly, different species :of animals
have different diseases, are subjected'^ o different pathological
lawsy if I may use such an expression. All human races are
liable; to the same diseases; at least, the varieties which exist
in these respects are such as are produced by the influence of
climate. Thirdly, distinct species do not freely intermix their
breed, and hybrid plants and animals do not propagate their
kind beyond at most a very few generations, and no real hybrid
races are perpetuated! but mixed breeds, descended
from the most distinct races of men are remarkably prolific.
The inference is obvious. If the mixed propagation of men
does not obey the .same laws which universally govern the
breeding of hybrids, the mixed breeds'of men are not really
hybrid, and the original tribes from which they descend must
be considered as varieties of the same species. In the second
chapter, which contains psychological comparisons, I endeavoured,
in the first place, to establish on a broad scale the
observation that species, even the most nearly resembling and
belonging to the same genera, are endowed with peculiar psychical
qualities which are even more distinct, and therefore more
characteristic of particular species, than peculiarities of bodily
structure'; that all species, in fact, differ from each other in
respect to their instincts, or those active principles which with
"Wonderful constancy govern the lives and habits of creatures
belonging to each kind, and give to each tribe an uniform and