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  Teratology (Greek, ‘study of freaks’), in the life sciences, is the study of abnormal growth and development resulting in individuals with biochemical or anatomical abnormalities. The term was coined in 1822 by the French zoologist Isidore Geoffroy St Hilaire, who, continuing the work of his father Étienne, proposed that they were caused by changes in the environment of the embryo. It has subsequently become clear that the causes of abnormalities in both animals and plants are attributable to both environmental and genetic factors. Teratogenic agents include drugs such as thalidomide and alcohol, infection with pathogens such as rubella (German measles), dietary deficiencies and ionizing radiations such as X-rays.

The development of the foetus is a complex, synchronized series of processes which can easily be disrupted by environmental factors, particularly during sensitive periods; the drug thalidomide, for example, causes abnormality in babies if the mother takes the drug between the 38th and 42nd days of pregnancy. The vast majority of cases result in spontaneous abortion, usually before development has progressed very far.

In man, modern medical techniques often permit the survival of individuals who would otherwise have died in infancy as a result of abnormality; it is variously reported that between 0.3 and 4% of live human births are of abnormal infants. Yet the definition of abnormal is inherently subjective and attempts must be made to distinguish between normal variation and abnormality. In the past, abnormal animals, human in particular, were often considered to be the result of curses or unnatural matings—and ‘freaks’, both living and preserved, were eminently collectable in 19th-century Europe. RB

See also embryology; hybridization; pharmacology; radiobiology; toxicology.



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