he biologist may not hope to solve the ultimate problems
of life any more than the chemist and physicist may hope to penetrate
the final mysteries of existence in the non-living world. What he can
do is to observe, compare and experiment with phenomena, to resolve
more complex phenomena into simpler components, and to this extent, as
he says, to "explain" them; but he knows in advance that his
explanations will never be in the full sense of the word final or
complete. Investigation can do no more than push forward the limits of
knowledge.

The task of the biologist is a double one. His more immediate effort is
to inquire into the nature of the existing organism, to ascertain in
what measure the complex phenomena of life as they now appear are
capable of resolution into simpler factors or components, and to
determine as far as he can what is the relation of these factors to
other natural phenomena. It is often practically convenient to consider
the organism as presenting two different aspects--a structural or
morphological one, and a functional or physiological--and biologists
often call themselves accordingly morphologists or physiologists.
Morphological investigation has in the past largely followed the method
of observation and comparison, physiological investigation that of
experiment; but it is one of the best signs of progress that in recent
years the fact has come clearly into view that morphology and
physiology are really inseparable, and in consequence the distinctions
between them, in respect both to subject matter and to method, have
largely disappeared in a greater community of aim. Morphology and
physiology alike were profoundly transformed by the introduction into
biological studies of the genetic or historical point of view by
Darwin, who did more than any other to establish the fact, suspected by
many earlier naturalists, that existing vital phenomena are the outcome
of a definite process of evolution; and it was he who first fully
brought home to us how defective and one-sided is our view of the
organism so long as we do not consider it as a product of the past. It
is the second and perhaps greater task of the biologist to study the
organism from the historical point of view, considering it as the
product of a continuous process of evolution that has been in operation
since life began. In its widest scope this genetic inquiry involves
not only the evolution of higher forms from lower ones, but also the