"Though these facts are ignored by several well-known popular leaders,
they are easy to prove, and are accepted by all scientific men; on the
other hand, their importance is so great that those who have once
mastered them will, in my opinion, find few other biological
discoveries to astonish them."

We shall make it our chief task to study the evolution of man's bodily
frame and its various organs in their external form and internal
structures. But I may observe at once that this is accompanied step by
step with a study of the evolution of their functions. These two
branches of inquiry are inseparably united in the whole of
anthropology, just as in zoology (of which the former is only a
section) or general biology. Everywhere the peculiar form of the
organism and its structures, internal and external, is directly
related to the special physiological functions which the organism or
organ has to execute. This intimate connection of structure and
function, or of the instrument and the work done by it, is seen in the
science of evolution and all its parts. Hence the story of the
evolution of structures, which is our immediate concern, is also the
history of the development of functions; and this holds good of the
human organism as of any other.

At the same time, I must admit that our knowledge of the evolution of
functions is very far from being as complete as our acquaintance with
the evolution of structures. One might say, in fact, that the whole
science of evolution has almost confined itself to the study of
structures; the evolution of FUNCTIONS hardly exists even in name.
That is the fault of the physiologists, who have as yet concerned
themselves very little about evolution. It is only in recent times
that physiologists like W. Engelmann, W. Preyer, M. Verworn, and a few