The Uses of Principles
We gain knowledge of the animal world not in a passive or
haphazard manner but by actively applying important guiding
principles to our investigations. Just as the exploration
of outer space is both guided and limited by available technologies,
exploration of the animal world depends critically
on our questions, methods, and principles. The body of
knowledge that we call zoology makes sense only when the
principles that we use to construct it are clear.
The principles of modern zoology have a long history
and many sources. Some principles derive from the laws of
physics and chemistry, which all living systems obey. Others
derive from the scientific method, which tells us that our
hypotheses regarding the animal world are useless unless
they guide us to gather data that potentially can refute them.
Many important principles derive from previous studies of
the living world, of which animals are one part. Principles of
heredity, variation, and organic evolution guide the study
of life from the simplest unicellular forms to the most complex
animals, fungi, and plants. Because all of life shares a
common evolutionary origin, principles learned from the
study of one group often may be applied to other groups as
well. By tracing the origins of our operating principles, we
see that zoologists are not an island unto themselves but
form an integrated part of the scientific community.
We begin our study of zoology not by focusing narrowly
within the animal world, but by searching broadly for our
most basic principles and their diverse sources. These principles
simultaneously guide our studies of animals and integrate
those studies into the broader context of human
Zoology, the scientific study of animal
life, builds on centuries of human
inquiry into the animal world. The
mythologies of nearly every human
culture document attempts to solve the
mysteries of animal life and its origin.
Zoologists now confront these same
mysteries with the most advanced
methods and technologies developed
throughout all branches of science. We
start by documenting the diversity of
animal life and organizing it in a systematic
way. This complex and exciting
process builds on the contributions of
thousands of zoologists working in all dimensions
of the biosphere (Figure 1-1).
We strive through this work to understand
how animal diversity originated
and how animals perform the basic
processes of life that permit them to
thrive in many diverse environments.
This section introduces the fundamental
properties of animal life, the
methodological principles on which
their study is based, and two important
theories that guide our research: (1)
the theory of evolution, which is the
central organizing principle of biology,
and (2) the chromosomal theory of
inheritance, which guides our study of
heredity and variation in animals.
These theories unify our knowledge of
the animal world.