It will be seen that the language used in this
volume is not the particular language of any one of these
schools. This is partly because I wish to leave seriously
controverted questions open, and partly from a feeling of
compromise, which I may explain.*
* Of recent years another compromise has been proposed between
the Lamarckians and Weismannists. It would say that the efforts
of the parent and their effect on the position of the eye--in our
case--are not inherited, but might be of use in sheltering an
embryonic variation in the direction of a displaced eye.
First, the plain issue between the Mendelians and the other two
schools--whether the passage from species to species is brought
about by a series of small variations during a long period or by
a few large variations (or "mutations") in a short period--is
open to an obvious compromise. It is quite possible that both
views are correct, in different cases, and quite impossible to
find the proportion of each class of cases. We shall see later
that in certain instances where the conditions of preservation
were good we can sometimes trace a perfectly gradual advance from
species to species.
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