Biology is the science of living systems. It
is inherently interdisciplinary, requiring knowledge
of the physical sciences and mathematics, although
specialities may be oriented toward a group of
organisms or a level of organization. BOTANY is
concerned with plant life, ZOOLOGY with animal
life, algology with ALGAE, MYCOLOGY with
fungi, MICROBIOLOGY with microorganisms
such as protozoa and bacteria, CYTOLOGY with
CELLS, and so on. All biological specialties,
however, are concerned with life and its
characteristics. These characteristics include
cellular organization, METABOLISM, response
to stimuli, development and growth, and
reproduction. Furthermore, the information
needed to control the expression of such
characteristics is contained within each organism.
into many levels of organization--atoms,
molecules, cells, tissues, organs, organ systems,
organisms, and populations. The basic disciplines
of biology may study life at one or more of these
levels. Taxonomy attempts to arrange organisms in
natural groups based on common features. It is
concerned with the identification, naming, and
classification of organisms. The seven major
taxonomic categories, or taxa, used in
classification are kingdom, phylum, class, order,
family, genus, and species. Early systems used
only two kingdoms, plant and animal, whereas
most modern systems use five: MONERA
PROTISTA (PROTOZOA and the other
discipline of ECOLOGY is concerned with the
interrelationships of organisms, both among
themselves and between them and their
environment. Studies of the energy flow through
communities of organisms and of the environment
(the ecosystem approach) are especially valuable
in assessing the effects of human activities. An
ecologist must be knowledgeable in other
disciplines of biology. Organisms respond to
stimuli from other organisms and from the
environment; behaviorists are concerned with
these responses. Most of them study animals--as
individuals, groups, or entire species--in describing
ANIMAL BEHAVIOR patterns. These patterns
include ANIMAL MIGRATION, courtship and
mating, social organization, TERRITORIALITY,
INSTINCT, and learning. When humans are
included, biology overlaps with psychology and
sociology. Growth and orientation responses of
plants can also be studied in the discipline of
behavior, although they are traditionally
considered as belonging under development and
PHYSIOLOGY, respectively. Descriptive and
comparative EMBRYOLOGY are the classic
areas of DEVELOPMENT studies, although
postembryological development, particularly the
aging process, is also examined. The biochemical
and biophysical mechanisms that control normal
development are of particular interest when they
are related to birth defects, cancer, and other
abnormalities. Inheritance of physical and
biochemical characteristics, and the variations that
appear from generation to generation, are the
general subjects of GENETICS. The emphasis
may be on improving domestic plants and animals
through controlled breeding, or it may be on the
more fundamental questions of molecular and
cellular mechanisms of HEREDITY. A branch of
biology growing in importance since the 1940s,
molecular biology essentially developed out of
genetics and biochemistry. It seeks to explain
biological events by studying the molecules within
cells, with a special emphasis on the molecular
basis of genetics--nucleic acids in particular--and
its relationship to energy cycling and replication.
Evolution, including the appearance of new
species, the modification of existing species, and
the characteristics of extinct ones, is based on
genetic principles. Information about the structure
and distribution of fossils that is provided by
paleontologists is essential to understanding these
changes. Morphology (from the Greek, meaning
"form study") traditionally has examined the
ANATOMY of all organisms. The middle levels
of biological organization--cells, tissues, and
organs, are the usual topics--with comparisons
drawn among organisms to help establish
taxonomic and evolutionary relationships. As
important as the form of an organism are its
functions. Physiology is concerned with the life
processes of entire organisms as well as those of
cells, tissues, and organs. Metabolism and
hormonal controls are some of the special interests
of this discipline. HISTORY OF BIOLOGY
Origin and Early Development. The oldest
surviving archaeological records that indicate some
rudimentary human knowledge of biological
principles date from the Mesolithic Period. During
the NEOLITHIC PERIOD, which began almost
10,000 years ago, various human groups
developed agriculture and the medicinal use of
plants. In ancient Egypt, for example, a number of
herbs were being used medicinally and for
embalming. Early Development As a science,
however, biology did not develop until the last few
centuries BC. Although HIPPOCRATES, known
as the father of medicine, influenced the
development of medicine apart from its role in
religion, it was ARISTOTLE, a student of Plato,
who established observation and analysis as the
basic tools of biology. Of particular importance
were Aristotle\'s observations of reproduction and
his concepts for a classification system. As the
center of learning shifted from Greece to Rome
and then to Alexandria, so did the study of
biology. From the 3d century BC to the 2d
century AD, studies primarily focused on
agriculture and medicine. The Arabs dominated
the study of biology during the Middle Ages and
applied their knowledge of the Greeks\' discoveries
to medicine. The Renaissance was a period of
rapid advances, especially in Italy, France, and
Spain, where Greek culture was being
rediscovered. In the 15th and 16th centuries,
Leonardo da Vinci and Michelangelo became