This preface is addressed to the reader who wishes to inquire into the
prevailing concepts, hypotheses and theories about development of
sensory systems and wants to know how they are exemplified in the
following chapters. I believe that science is hypothesis and theory and
that the growth and evolution of any branch of science can be measured
by the degree to which its theories have been reified. By that standard,
one must conc1ude that developmental neuro- biologie is in its infancy.
The rapid accumulation of observations which has occurred in this branch
of science in the past century leads to progress only to the extent that
the facts validate or falsify hypotheses. The following chapters show
that we have a plethora of facts but a dearth of hypotheses. Another
index of the maturity of any branch of science is its level of
historical self-awareness. Because the history of any branch of science
is essentially the history of ideas and of the rise and fall of
theories, the level of historical awareness is related to the extent to
which reification of its hypothetical constructs has advanced. It is
largely because few theories of development of sensory systems, or
indeed, of developmental neurobiology, have progressed far in the
process of reification that the his tory of developmental neurobiology
remains unwritten. The subject of this volume is hardly mentioned in the
many books devoted to the history of related disciplines.