hich is due to Nitsche, in no way affects the fact
recognised by Darwin, that ear-forms showing the point characteristic
of the animal ear occur in man with extraordinary frequency.

Finally, there is a discussion of those rudimentary structures which
occur only in _one_ sex, such as the rudimentary mammary glands in the
male, the vesicula prostatica, which corresponds to the uterus of the
female, and others. All these facts tell in favour of the common
descent of man and all other vertebrates. The conclusion of this
section is characteristic: "_It is only our natural prejudice, and
that arrogance which made our forefathers declare that they were
descended from demi-gods, which leads us to demur to this conclusion.
But the time will before long come, when it will be thought wonderful
that naturalists, who were well acquainted with the comparative
structure and development of man, and other mammals, should have
believed that each was the work of a separate act of creation._"[92]

In the second chapter there is a more detailed discussion, again based
upon an extraordinary wealth of facts, of the problem as to the manner
in which, and the causes through which, man evolved from a lower form.
Precisely the same causes are here suggested for the origin of man, as
for the origin of species in general. Variability, which is a
necessary assumption in regard to all transformations, occurs in man
to a high degree. Moreover, the rapid multiplication of the human race
creates conditions which necessitate an energetic struggle for
existence, and thus afford scope for the intervention of natural
selection. Of the exercise of _artificial_ selection in the human
race, there is nothing to be said, unless we cite such cases as the
grenadiers of Frederick William I, or the population of ancient
Sparta. In the passages already referred to and in those which follow,
the transmission of acquired characters, upon which Darwin does not
dwell, is taken for granted. In man, direct effects of changed
conditions can be demonstrated (for instance in regard to bodily
size), and there are also proofs of the influence exerted on his
physical constitution by increased use or disuse. Reference is here
made to the fact, established by Forbes, that the Quechua Indians of
the high plateaus of Peru show a striking development of lungs and
thorax, as a result of living constantly at high altitudes.

Such special forms of variation as arrests of development