History of incest
In ancient China, first cousins with the same surnames (i.e., those born to the father’s brothers) were not permitted to marry, while those with different surnames (i.e., maternal cousins and paternal cousins born to the father’s sisters) were.
According to the Biblical Book of Genesis, the Patriarch Abraham and his wife Sarah were half-siblings, both being children of Terah (Ge 20:12).
The fable of Oedipus, with a theme of inadvertent incest between a mother and son, ends in disaster and shows ancient taboos against incest as Oedipus is punished for incestuous actions by blinding himself. In the “sequel” to Oedipus, Antigone, his four children are also punished for their parents having been incestuous.
Incest appears in the commonly accepted version of the birth of Adonis, when his mother, Myrrha has sex with her father Cinyras during a festival, disguised as a prostitute.
Incest is mentioned and condemned in Virgil’s Aeneid Book VI: hic thalamum invasit natae vetitosque hymenaeos; “This one invaded a daughter’s room and a forbidden sex act”.
It is generally accepted that sibling marriages were widespread among all classes in Egypt during the Graeco-Roman period. Numerous papyri and the Roman census declarations attest to many husbands and wives being brother and sister. The most well known of these relationships were in the royal family, the Ptolemies; The famous Cleopatra VII was married to her younger brother, Ptolemy XIII. Her mother and father,Cleopatra V and Ptolemy XII, had also been brother and sister.
In Ancient Greece, Spartan King Leonidas I, hero of the legendary Battle of Thermopylae, was married to his niece Gorgo, daughter of his half-brother Cleomenes I. Greek law allowed marriage between a brother and sister if they had different mothers. For example, some accounts say that Elpinice was for a time married to her half-brother Cimon
Incestuous unions were frowned upon and considered as nefas (against the laws of gods and man) in ancient Rome. In AD 295 incest was explicitly forbidden by an imperial edict, which divided the concept of incestus into two categories of unequal gravity: the incestus iuris gentium, which was applied to both Romans and non-Romans in the Empire, and the incestus iuris civilis, which concerned only Roman citizens. Therefore, for example, an Egyptian could marry an aunt, but a Roman could not. Despite the act of incest being unacceptable within the Roman Empire, Roman Emperor Caligula is rumored to have had sexual relationships with all three of his sisters (Julia Livilla, Drusilla, and Agrippina the Younger).Emperor Claudius, after executing his previous wife, married his brother’s daughter Agrippina the Younger, and changed the law to allow an otherwise illegal union. The law prohibiting marrying a sister’s daughter remained. The taboo against incest in Ancient Rome is demonstrated by the fact that politicians would use charges of incest (often false charges) as insults and means of political disenfranchisement.
In Norse mythology there are themes of brother-sister marriage, a prominent example being between Njörðr and his unnamed sister (perhaps Nerthus), parents of Freyja and Freyr. Loki in turn also accuses Freyja and Freyr of having a sexual relationship.
Many European monarchs were related due to political marriages, sometimes resulting in distant cousins (and even first cousins) being married. This was especially true in the Habsburg, Hohenzollern, Savoy and Bourbon royal houses. Incestuous marriages were also seen in the royal houses of ancient Japan and Korea. Half-sibling marriages were found in ancient Japan such as the marriage of Emperor Bidatsu and his half-sister Empress Suiko. Japanese Prince Kinashi no Karu had sexual relationships with his full sister Princess Karu no Ōiratsume, although the action was regarded as foolish. In order to prevent the influence of the other families, a half-sister of Korean Goryeo Dynasty monarch Gwangjong became his wife in the 10th century. Brother-sister marriages were common during some Roman periods as some census records have shown.