Etiology (alternatively
aetiology,
aitiology) is the
study of
causation, or origination. The
word is derived from the
Greek ,
aitiologia, "giving a reason for" ( ,
aitia,
"cause"; and ,
-logia).
The word is most commonly used in medical and philosophical
theories, where it is used to refer to the study of why things
occur, or even the reasons behind the way that things act, and is
used in
philosophy,
physics,
psychology,
government,
medicine,
theology and
biology in reference to the causes of
various phenomena. An
etiological myth is a
myth intended to explain a name or create
a mythic history for a place or family.
Medicine
In medicine in particular, the term refers to the causes of
diseases or
pathologies. The first ideas about
microorganisms were those of the
Ancient Roman scholar
Marcus Terentius Varro in a 1st
century BC book titled
On Agriculture. Contemporary
medieval thinking on the etiology of disease was influenced
by
Galen and
Hippocrates. Medieval
European doctors generally held the view that disease
was related to the air and adopted a
miasmatic approach to disease
etiology. In
The Canon of
Medicine,
Avicenna discovered that
they are caused by contagion that can spread through bodily contact
or through
water and
soil.
George Sarton,
Introduction to the History of Science.
(
cf. Dr. A. Zahoor and Dr. Z. Haq (1997),
Quotations From Famous Historians of Science,
Cyberistan. He also stated that bodily
secretion is contaminated by foul foreign earthly
bodies before being infected.
Ibn Zuhr (Avenzoar) was the first physician
to provide a scientific etiology for the
inflammatory diseases of the
ear, and the first to clearly discuss the causes of
stridor. Through his
dissections, he proved that the skin disease
scabies was caused by a
parasite, a discovery which upset the
Galenic theory of
humorism,
and he was able to successfully remove the parasite from a
patient's body without any
purging or
bleeding.
When the
Black Death reached al-Andalus
in the 14th century, Ibn
Khatima proposed that infectious
diseases are caused by microscopic particles which enter the
human body. Another
Andalusian
physician,
Ibn al-Khatib (1313-1374),
wrote a treatise called
On the Plague, stating that the
contagion could spread via
garments,
vessels and
earrings.
Etiological discovery in medicine has a history in
Robert Koch's demonstration that the tubercle
bacillus (
Mycobacterium
tuberculosis complex) causes the disease
tuberculosis,
Bacillus anthracis causes
anthrax, and
Vibrio
cholerae causes
cholera. This line
of thinking and evidence is summarized in
Koch's postulates. But proof of causation
in infectious diseases is limited to individual cases that provide
experimental evidence of etiology.
In
epidemiology, several lines of
evidence together are required to infer causation.
Sir Austin Bradford-Hill demonstrated a
causal relationship between smoking and lung cancer, and summarized
the line of reasoning in the
epidemiological criteria
for causation. Dr. Al Evans, a US epidemiologist, synthesized
his predecessors' ideas in proposing the
Unified Concept of
Causation.
Further thinking in epidemiology was required to distinguish
causation from association
or statistical correlation. Events may occur together simply
due to
chance,
bias or
confounding, instead of one event being
caused by the other. It is also important to know which event is
the cause. Careful sampling and measurement are more important than
sophisticated statistical analysis to determine causation.
Experimental evidence involving interventions (providing or
removing the supposed cause) gives the most compelling evidence of
etiology.
Etiology is sometimes a part of a chain of causation. An
etiological agent of disease may require an independent co-factor,
and be subject to a promoter (increases expression) to cause
disease. An example of all the above, which was recognized late, is
that
peptic ulcer disease may
be induced by stress, requires the presence of acid secretion in
the stomach, and has primary etiology in
Helicobacter pylori infection. Many
chronic diseases of unknown cause may be studied in this framework
to explain multiple epidemiological associations or risk factors
which may or may not be causally related, and to seek the actual
etiology.
Some diseases, such as
diabetes or
hepatitis, are syndromically defined by their
signs and
symptoms, but include different
conditions with different etiologies. Conversely, a single
etiology, such as
Epstein-Barr
virus, may in different circumstances produce different
diseases such as
mononucleosis,
nasopharyngeal carcinoma,
or
Burkitt's lymphoma.
Mythology
An
etiological myth, or origin myth, is a
myth intended to explain the origins of cult
practices, natural phenomena, proper names and the like.
For
example, the name Delphi
and its
associated deity, Apollon
Delphinios, are explained in the Homeric Hymn which tells of how Apollo carried
Cretans
over the sea in the shape of a dolphin ( ) to make them his priests. While
Delphi is actually related to the word ("womb"), many etiological
myths are similarly based on
folk
etymology (the term "
Amazon", for
example). In the
Aeneid (published
circa 17 BC),
Virgil claims the descent of
Augustus Caesar's
Julian clan from the hero
Aeneas through his son Ascanius, also called
Julus.The story of
Prometheus'
sacrifice-trick in
Hesiod's
Theogony relates how Prometheus tricked
Zeus into choosing the bones and fat of the
first sacrificial animal rather than the meat to justify why, after
a sacrifice, the Greeks offered the bones wrapped in fat to the
gods while keeping the meat for themselves.
See also
References
- Discusses several examples of the medical usage of the term
etiology in the context of cleft lips and explains methods used to study
causation.
- Varro On Agriculture 1,xii Loeb
- Maimonides: an early but accurate view on the
treatment of hemorrhoids -- Magrill and Sekaran 83 (979): 352 --
Postgraduate Medical Journal
- Case study: the history and ethics clean air
- Ibrahim B. Syed, Ph.D. (2002). " Islamic Medicine: 1000 years ahead of its
times", Journal of the
Islamic Medical Association 2, p.
2-9.
- Prof. Dr. Mostafa Shehata, "The Ear, Nose and Throat in Islamic
Medicine", Journal of the International Society for the History
of Islamic Medicine, 2003 (1): 2-5 [4].
- Islamic medicine, Hutchinson Encyclopedia.
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