other interpretations; and, indeed, that from the very nature of
the case, demonstrative evidence one way or the other is almost
unattainable. _A priori_, I should be disposed to expect a certain
amount of infertility between some of the extreme modifications of
mankind; and still more between the offsprings of their intermixture.
_A posteriori_, I cannot discover any satisfactory proof that such
infertility exists.

From the facts of ethnology I now turn to the theories and
speculations of ethnologists, which have been devised to explain
these facts, and to furnish satisfactory answers to the inquiry--what
conditions have determined the existence of the persistent
modifications of mankind, and have caused their distribution to be
what it is?

These speculations may be grouped under three heads: firstly, the
Monogenist hypotheses; secondly, those of the Polygenists; and
thirdly, that which would result from a simple application of
Darwinian principles to mankind.

According to the Monogenists, all mankind have sprung from a single
pair, whose multitudinous progeny spread themselves over the world,
such as it now is, and became modified into the forms we meet with in
the various regions of the earth, by the effect of the climatal and
other conditions to which they were subjected.

The advocates of this hypothesis are divisible into several schools.
There are those who represent the most numerous, respectable,
and would-be orthodox of the public, and are what may be called
"Adamites," pure and simple. They believe that Adam was made out of