Ancient Greek and Roman authors developed the scientific, ethnographic, and cosmographic interpretations of the ‘monstrous’ that were to remain influential until the end of the 17th century. However, during the Middle Ages, Greek and Roman texts were gradually lost. Only in the 13th century through contact with the works of Arabic physicians and philosophers did Europeans scholars rediscover the classical texts (including Aristotle's writings) that were to have such a profound impact on western culture.

Church Fathers also contributed to the teratological tradition. In his City of God, St. Augustine (354-430 A.D.) asked whether monsters were God's creatures, while Isidore of Seville (ca. 560-636 A.D.) attempted to classify them.

Aristotle (ca. 384-322 B.C.). De Generatione animalium. In Habentur hoc volumine haec Theodoro Gaza interprete…[Venice: in aedibus Aldi & Andreae Asulani, 1513.]

Aristotle provided one of the most important scientific discussions on the monstrous. His direct observation of nature was impressive, although in several areas his theories, like those of other ancient writers, reflected the social prejudices of his time.

Aristotle's understanding of reproduction involved two concepts: form and matter. He compared the male element, semen, to an artisan shaping the raw material provided by the female into a product. It is here that Aristotle turned his attention to monstrous births: they were created when there was either abundance or division of the semen. For Aristotle, monstrosity was not against nature per se, but simply against what usually happened in nature. “Nature makes nothing in vain” but sometimes, it did not achieve its intended goal. In that case, the outcome of a natural process was called a monster. Aristotle considered twins to be monsters because they were a rare occurrence. Because of this naturalistic explanation, Aristotle denied the existence of imaginary monsters. After his writings had been rediscovered in the 13th century, Aristotle’s theories were the accepted view of the natural order of the world.

The present edition of De Generatione Animalium, which is considered the first textbook on embryology, is a translation and commentary by Theodorus Gaza, one of the earliest translators of Aristotle's works.

Galen (131-201 A.D). De usu partium corporis humani, magna cura ad exemplaris Graeci veriritatem [sic] castigatum, universo hominum generi apprime necessarium …Paris: Simon des Colines, 1528.

Like those of Aristotle, Galen’s views remained authoritative for centuries. Galen also studied embryology and developed a theory similar to that of Hippocrates (ca. 460-ca. 377 B.C.) who had linked the cause of multiple births to the structure of the womb. Less misogynistic than Aristotle, Galen attributed an active role in reproduction to both the male and female. Both contributed semen so that the offspring could have characteristics from both parents. Galen explained that the uterus was divided into seven cells, three warmer ones on the right, which would engender males; three colder ones on the left, which would engender females; and a seventh in the middle that could produce an hermaphrodite.

Pliny, the Elder (23-79 A.D.). Historia naturalis. Venice: Joannes Alvisius, 1499.




Pliny the Elder compiled much of the cosmographical and anthropological knowledge of his time in his Natural History, which included a section on monsters. Rather than unique creatures, Pliny discussed monstrous races. The fear of the unknown led to the belief that what was the furthest away was monstrous: Pliny gave a description of supposedly monstrous races living in the remote lands of Africa and Asia. For Pliny, monstrous races were also a part of the generosity of Nature for whom nothing was impossible.


After borrowing many ideas from Pliny, St. Augustine eventually concluded that monsters were signs of original sin.

Avicenna (980-1037). Canon medicinae …Venice: Petrus Maufer et Socii, 1486.

An eminent physician of Bagdad, Avicenna attempted in his Canon to systematize and reinterpret the corpus of medical knowledge of his time according to Galenic medicine and Aristotelian natural philosophy. It was in the 13th century that his work was first read by western scholars who considered it to be an authoritative compilation for two hundred years. Avicenna’s work was concerned with the theories of Aristotle and Galen which dealt with the male and female contributions to generation. Agreeing with Aristotle’s theory on monsters, Avicenna attributed multiple births to the overabundance or division of sperm.

Saint Albertus Magnus (1193?-1280). Physica. Diui Alberti Magni Phisico[rum], siue, De phisico auditu libri octo. [Venice]: Joa[n]nem de Forliuio [et] Gregorium fratres, 1494.

Albertus Magnus, a Dominican monk, was one of the most eminent naturalists and philosophers of the thirteenth century. It was probably through the works of the Arabic physician Avicenna that Albertus assimilated Aristotle's natural philosophy. Thus, Albertus’s De Animalibus, one of the treatises in his Physica concerned with generation, is largely inspired by both Avicenna's and Aristotle's works. Albertus, like Aristotle, believed that monsters had a natural explanation.

In De Animalibus, Albertus explored in greater depth than did Aristotle the possible explanations for the production of twins. He developed a theory of the “mechanism of sexual delight for the female”, and proposed that the more pleasure a woman had in intercourse, the greater the risk of problems in reproduction. He also discussed the effects of the shape of the womb, and proposed that conjoined twins resulted from an incomplete division of semen.

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