onstitute sub-races, with a general blending of the characters of the
two parents, and only differing from fully-established races in more or
less tendency to revert to one or other of the original types. It has
been argued, on the other hand, that not all such mixed breeds are
permanent, and especially that the cross between Europeans and
Australian indigenes is almost sterile; but this assertion, when
examined with the care demanded by its bearing on the general question
of hybridity, has distinctly broken down. On the whole, the general
evidence favours the opinion that any two races may combine to produce a
new sub-race, which again may combine with any other variety. Thus, if
the existence of a small number of distinct races of mankind be taken as
a starting-point, it is obvious that their crossing would produce an
indefinite number of secondary varieties, such as the population of the
world actually presents. The working out in detail of the problem, how
far the differences among complex nations, such as those of Europe, may
have been brought about by hybridity, is still, however, a task of
almost hopeless intricacy. Among the boldest attempts to account for
distinctly-marked populations as resulting from the intermixture of two
races, are Huxley's view that the Hottentots are hybrid between the
Bushmen and the Negroes, and his more important suggestion, that the
Melanochroic peoples of southern Europe are of mixed Xanthochroic and
Australioid stock.

The problem of ascertaining how the small number of races, distinct
enough to be called primary, can have assumed their different types, has
been for years the most disputed field of anthropology, the
battle-ground of the rival schools of monogenists and polygenists. The
one has claimed all mankind to be descended from one original stock, and
generally from a single pair; the other has contended for the several
primary races being separate species of independent origin. The great
problem of the monogenist theory is to explain by what course of
variation the so different races of man have arisen from a single stock.
In ancient times little difficulty was felt in this, authorities such as
Aristotle and Vitruvius seeing in climate and circumstance the natural
cause of racial differences, the Ethiopian having been blackened by the
tropical sun, &c. Later and closer observations, however, have shown
such influences to be, at any rate, far slighter in amount and slower in