l--more so than those of any domesticated animal. He
is, therefore, in the conditions most favorable to variation. Again,
man possesses more than merely animal instincts. His mental powers
permit him to devise means of locomotion, of protection, of
subsistence, far superior to those of any mere animal; and his
dominant will, insatiable in its desires, bends the bodily frame to
uses and exposes it to external influences more various than any
inferior animal can dream of. Man is also more educable and plastic in
his constitution than other animals, owing both to his being less
hemmed in by unchanging instincts, and to his physical frame being
less restricted in its adaptations. If a single species, he is also
more widely distributed than any other; and there are even single
races which exceed in their extent of distribution nearly all the
inferior animals. Nor is there anything in his structure specially to
limit him to plains, or hills, or forests, or coasts, or inland
regions. All the causes which we can suppose likely to produce
variation thus meet in man, who is himself the producer of most of the
distinct races that we observe in the lower animals. If, therefore, we
condescend to compare man with these creatures, it must be under
protest that what we learn from them must be understood with reference
to his greater capabilities.

2. The races of men are deficient in some of the essential characters
of species. It is true that they are reproduced with considerable
permanency; though a great many cases of spontaneous change, of
atavism, or return to the character of progenitors, and of slow
variation under changed conditions, have been recorded. But the most
manifest deficiency in true specific characters is in the invariable
shading-off of one race into another, and in the entire failure of
those who maintain the distinction of species in the attempt
accurately to define their number and limits. The characters run into
each other in such a manner that no natural arrangement based on the
whole can apparently be arrived at; and when one particular ground is
taken, as color, or shape of skull, the so-called species have still
no distinct limits; and all the arrangements formed differ from each
other, and from the deductions of philology and history. Thus, from
the division of Virey into two species, on the entirely arbitrary
ground of facial angle, to that of Bory de St. Vincent into fifteen,
we have a great number and v