Teratology is the scientific study of abnormal generation and development of the embryo and the products resulting from it. This science has slowly developed out of a historical preoccupation with abnormally developed new-born animal and human infants. These "freaks of nature", such as a child born with two heads, were widely considered to forecast coming misfortunes and to result from interference by the gods with the natural order of the universe.
The earliest records show that unusual births were interpreted as signs of the gods' displeasure with the behaviour of human society. Roman law prescribed that such unfortunate new-born creatures were so dangerous to the well-being of the state that they must be drowned instantly in the nearest river. The Roman historians Livy and Tacitus recount many tales of abnormal births - two-headed animals, animals with human faces etc.
However, there were also more rational and scientific responses to these abnormal occurrences. Aristotle argued that abnormal births resulted neither from divine intervention, nor violations of natural laws, but merely represented the understandable unbalanced development resulting from an overabundance or a shortage of the essential materials of the embryo.
Aristotle's explanation was completely overshadowed in the Christian middle ages by the belief that God actively interferes in the course of nature. Freak births were interpreted as serving a dual purpose, both portentous of coming calamities, and also acting as visible signs of God's abiding interest in mankind.
As St Augustine pointed out in his City of God: "God who made the visible heavens does not disdain to work miracles whereby he may quicken souls given over to visible things, to worship even the invisible. Monsters then are not contrary to nature but only to what is known of her."
The invention of printing towards the end of the 15th century made it possible to pander to the innate human curiosity about the abnormal. Penny sheets showing woodcut illustrations of monstrous creatures, described in a brief and simple text, were eagerly consumed by a mass audience. Learned books and catalogues were also produced by antiquarians describing marvels of the day and famous prodigies of the past.
People were not above using reports of bizarre creatures to cast aspersions on rivals for their own purposes. A Venetian writer recorded the recovery of a monstrous creature from the Tiber in 1496. It had the body of a woman but the head and ears of an ass. The face of an old man appeared on its rump and its tail ended in a demon head.
AN engraved image was passed on to Martin Luther who delighted in interpreting its form as an image of Pope Paul III as the anti-Christ. Luther interpreted the ass's head as the pope and the female body as the helpless church. He called the entire creature the "Pope-ass of Rome".
With the arrival of the Renaissance, scientific curiosity in the nature of these abnormal births re-emerged. This has continued in an unbroken tradition to the present day, and we now have the scientific discipline of teratology with many journals specialising in the study of abnormal births.
The incidence of defective development of the embryo is high. About one in 14 infants that survive the neonatal period have some kind and degree of abnormality. Some types of abnormality are commoner in males and others commoner (e.g. hip displacement) in females.
Internal concealed defects are more common than external ones. Aside from relatively gross structural defects, aberrations at the molecular level also occur, principally deficiencies in one or other enzyme (biological catalysts) that cause abnormal biochemical functioning in cells.
Many types of abnormality are inherited, such as albinism and hemophilia. Other types of abnormality can arise by chance, for example Down's Syndrome.
Environmental factors are also important. Ionising radiation can induce changes in genetic material leading to birth defects. Various chemical agents have been shown experimentally to induce defects in animal embryos. The drug thalidomide has demonstrated its effectiveness in disrupting the development of human embryos.
The congenitally joined twins Chang and Eng (1811-74) gained worldwide fame because of their condition. They were born in Siam (now Thailand) and the term "Siamese twins" now universally denotes the congenitally united twin condition. Chang and Eng were joined at the waist by a tubular band of tissue about 8 cm long and 3.8 cm in diameter.
Chang and Eng travelled widely in the company of a "sponsor" around North America and Europe from 1829 to 1840 and were exhibited widely to a curious public. They then took charge of their own tours out of which they accumulated a fortune. They settled in North Carolina and took up farming. In 1843 they married a pair of sisters and maintained separate households 1.5 miles apart, spending alternate three-day periods in each household. Chang and Eng each fathered several children.
During the American Civil War they lost a lot of money and again resorted to touring Europe. Chang became moody and began to drink heavily. In 1870 he had a paralytic stroke. About four years later Chang and Eng died during the night. Chang died first and Eng three hours later.
William Reville is a senior lecturer in biochemistry and Director of Microscopy at UCC