The Descent of Man

it shews that they graduate into each other, and
that it is hardly possible to discover clear distinctive
characters between them.
Every naturalist who has had the misfortune to
undertake the description of a group of highly
varying organisms, has encountered cases (I
speak after experience) precisely like that of
man; and if of a cautious disposition, he will
end by uniting all the forms which graduate
into each other, under a single species; for he
will say to himself that he has no right to give
names to objects which he cannot define. Cases
of this kind occur in the Order which includes
man, namely in certain genera of monkeys;
whilst in other genera, as in Cercopithecus,
most of the species can be determined with
certainty. In the American genus Cebus, the
various forms are ranked by some naturalists as
species, by others as mere geographical races.
Now if numerous specimens of Cebus were
collected from all parts of South America, and