From
the very start of living evolution certain forms dropped out of
the onward march, and have remained, to our great instruction,
what their ancestors were millions of years ago. People create a
difficulty for themselves by imagining that, if evolution is
true, all animals must evolve. A glance at our own fellows will
show the error of this. Of one family of human beings, as a
French writer has said, one only becomes a Napoleon; the others
remain Lucien, Jerome, or Joseph. Of one family of animals or
trees, some advance in one or other direction; some remain at the
original level. There is no "law of progress." The accidents of
the world and hereditary endowment impel some onward, and do not
impel others. Hence at nearly every great stage in the upward
procession through the ages some regiment of plants or animals
has dropped out, and it represents to-day the stage of life at
which it ceased to progress. In other words, when we survey the
line of the hundreds of thousands of species which we find in
nature to-day, we can trace, amid their countless variations and
branches, the line of organic evolution in the past; just as we
could, from actual instances, study the evolution of a British
house, from the prehistoric remains in Devonshire to a mansion in
Park Lane or a provincial castle.
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