Etiology (alternatively aetiology, aitiology) is the study of causation. The word is derived from the Greek _gr. αἰτιολογία, "aitiologia", "giving a reason for" ( _gr. αἰτία, "aitia", "cause"; and _gr. -λογία, "-logia"). [cite book | title = Aetiology | work = Oxford English Dictionary | edition = 2nd ed. | year = 2002 | publisher = Oxford University Press | isbn = 0195219422]
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, theologyand biologyin 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.
In medicine in particular, the term refers to the causes of
diseases or pathologies. [cite web | author = Greene J | url = http://www.widesmiles.org/cleftlinks/WS-364.html | title = The three C's of aetiology | work = Wide Smiles | year = 1996 | accessdate = 2007-08-20 Discusses several examples of the medical usage of the term "aetiology" in the context of cleft lips and explains methods used to study causation.] . In " The Canon of Medicine", Avicennadiscovered that they are caused by contagion that can spread through bodily contact or through waterand soil. George Sarton, "Introduction to the History of Science".
cf.Dr. A. Zahoor and Dr. Z. Haq (1997), [http://www.cyberistan.org/islamic/Introl1.html Quotations From Famous Historians of Science] , Cyberistan.] He also stated that bodily secretionis contaminated by foul foreign earthly bodies before being infected.Ibrahim B. Syed, Ph.D. (2002). " [http://www.irfi.org/articles/articles_1_50/islamic_medicine.htm Islamic Medicine: 1000 years ahead of its times] ", "Journal of the Islamic Medical Association" 2, p. 2-9.] 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. [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  .] Through his dissections, he proved that the skin disease scabieswas 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 purgingor bleeding. [http://encyclopedia.farlex.com/Islamic+medicine Islamic medicine] , " Hutchinson Encyclopedia".]
Black Death bubonic plaguereached al-Andalusin the 14th century, Ibn Khatimaposited that infectious diseases are caused by microorganisms which enter the human body. Another Andalusian physician, Ibn al-Khatib(1313-1374), wrote a treatise called "On the Plague", stating that contagioncan spread through 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-Hilldemonstrated 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
epidemiologywas required to distinguish causation from association or statistical correlation. Events may occur together simply due to chance, biasor 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 diseasemay 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
diabetesor hepatitis, are syndromically defined, by their signs and symptoms, but include different conditions with different etiologies. Conversely, one etiology, such as Epstein-Barr virus, may in different circumstances produce different diseases, such as mononucleosis, or nasopharyngeal carcinoma, or Burkitt's lymphoma.
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
Delphiand its associated deity, "Apollon Delphinios", are explained in the Homeric Hymnwhich tells of how Apollo carried Cretans over the sea in the shape of a dolphin("delphis") to make them his priests. While Delphi is actually related to the word "delphys" ("womb"), many etiological myths are similarly based on folk etymology(the term "Amazon", for example). In the " Aeneid" (published circa 17 BC), Vergilclaims the descent of Augustus Caesar's Julian clan from the hero Aeneasthrough his son Ascanius, also called Julus. Other examples of etiological myth come from the Bible, such as the setting of the rainbow in the heavens as a sign of God's covenantwith Noah(Genesis 9); or the story of Lot's wife in Genesis 19 (specifically 26), which explains why there are pillars of salt in the area of the Dead Sea. [cite book | title = Oxford Annotated Edition, Revised Standard Version of the Bible | year = 1973] The story of Prometheus' sacrifice-trick in Hesiod's " Theogony" relates how Prometheus tricked Zeusinto 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.
Just-so story(comparable to etiological myth)
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