living
beings had become familiar to biologists, it spread far beyond the
limits of tracing genealogical connexions between different animals and
plants. It made possible the conception of a true Science of Life, in
which every phenomenon seen in a living organism should fall into its
true place in relation to the rest, and in which also the phenomena of
life should be correlated with those discovered in the inorganic
sciences of Chemistry and Physics.

The history of the various branches of biological science in the past
sixty years reflects the general course of these tendencies. Until
shortly after 1859, the study of morphology, or the comparative
structure of animals (and of plants) was intimately related with that of
physiology, that is, with the study of function. In the years following
the appearance of the _Origin_, however, anatomists and morphologists
were seized with a new interest. For the time at least, the chief aim in
studying structure was no longer to explain function, but rather to
explain how that structure had come into being in the course of
evolution, and how it was related with homologous but different
structures in other forms. The result was a tendency to a divorce
between morphology and physiology, or at least between morphologists and
physiologists, which led to the division into two more or less distinct
sciences of what had hitherto been regarded as closely inter-related
branches of one. The greater men of the early part of the period, such
as Huxley, remained both morphologists and physiologists, but most of
their followers fell inevitably into one or the other group, and in
discussing the later phases of biological progress it will be necessary
to keep them separate.

Apart from its effect on the systematic and anatomical side of Biology,
the idea of Evolution, and especially of Darwin's theory of Natural
Selection, had important consequences on that side of the science which
may be described as Natural History. Before the appearance of Darwin's
work, Natural History consisted chiefly in the observation and
collection of facts about the habits and life-history of animals and
plants, which as a rule had no unifying principle unless they were used,
as in the Bridgewater Treatises, to illustrate 'the power, wisdom, and
goodness of God'. Now, however, a new motive was provided--that of
discovering the uses to the organism of its various colours,
structures, and habits, and the application o