case, seems small; but it may partly be accounted for by the degraded
and anomalous position of the class, and by the profligacy of the
women. A certain amount of absorption of mulattoes into negroes must
always be in progress; and this would lead to an apparent diminution of
the former. The inferior vitality of mulattoes is spoken of in a
trustworthy work (13. Military and Anthropological Statistics of
American Soldiers, by B.A. Gould, 1869, p. 319.) as a well-known
phenomenon; and this, although a different consideration from their
lessened fertility, may perhaps be advanced as a proof of the specific
distinctness of the parent races. No doubt both animal and vegetable
hybrids, when produced from extremely distinct species, are liable to
premature death; but the parents of mulattoes cannot be put under the
category of extremely distinct species. The common Mule, so notorious
for long life and vigour, and yet so sterile, shews how little
necessary connection there is in hybrids between lessened fertility and
vitality; other analogous cases could be cited.
Even if it should hereafter be proved that all the races of men were
perfectly fertile together, he who was inclined from other reasons to
rank them as distinct species, might with justice argue that fertility
and sterility are not safe criterions of specific distinctness. We know
that these qualities are easily affected by changed conditions of life,
or by close inter-breeding, and that they are governed by highly
complex laws, for instance, that of the unequal fertility of converse
crosses between the same two species. With forms which must be ranked
as undoubted species, a perfect series exists from those which are
absolutely sterile when crossed, to those which are almost or
completely fertile. The degrees of sterility do not coincide strictly
with the degrees of difference between the parents in external
structure or habits of life. Man in many respects may be compared with
those animals which have long been domesticated, and a large body of
evidence can be advanced in favour of the Pallasian doctrine (14. The
Variation of Animals and Plants under Domestication, vol. ii. p. 109.
I may here remind the reader that the sterility of species when crossed
is not a specially-acquired quality, but, like the incapacity of
certain trees to be grafted together, is incidental on other acquired
differences. The nature of these differences is unknown, but they
relate more especially to the reproductive system, and much less so to
external structure or to ordinary differences in constitution. One
important element in the sterility of crossed species apparently lies
190