The Descent of Man

accounted for by any form of selection, or by
the inherited effects of the use and disuse of
parts. We know, however, that many strange
and strongly-marked peculiarities of structure
occasionally appear in our domesticated productions,
and if their unknown causes were to
act more uniformly, they would probably become
common to all the individuals of the species.
We may hope hereafter to understand something
about the causes of such occasional
modifications, especially through the study of
monstrosities: hence the labours of experimentalists,
such as those of M. Camille Dareste, are
full of promise for the future. In general we can
only say that the cause of each slight variation
and of each monstrosity lies much more in the
constitution of the organism, than in the nature
of the surrounding conditions; though new and
changed conditions certainly play an important
part in exciting organic changes of many kinds.