© 2003, 2009 Walter Scheidel







Walter Scheidel






‘Incest’, in the sense of proscribed and abhorred sexual behaviour, is a cultural construct; its boundaries vary according to definitions that are specific to individual cultures (e.g., Willner 1983). However, most cultures agree on the core of what constitutes incest: sexual relations within the nuclear family. This perception corresponds to the biological fact that on average, parents and children on the one hand and brothers and sisters on the other share fifty per cent of their genes by common descent, and are therefore much more closely related than other potential mates. Over the last century, the ubiquity of the incest taboo for the nuclear family and resultant avoidance behaviour have been explained in several different and sometimes conflicting ways. Freudian theory has it that although by nature, children harbour incestuous longings, in the absence of legitimate expression these desires are suppressed into the subconscious, triggering abhorrence in adult life; the ‘family-socialization theory’ explains the incest taboo in terms of its functions in maintaining the social structure of the human family and in facilitating the process of socialization (e.g., Malinowski, Murdock, Parsons); anthropologists have argued that the need of families to exchange wives and resources in order to forge alliances militates against incestuous unions (e.g., Tylor, White, Lévi-Strauss); the ‘demographic theory’ predicts that under high mortality, siblings were compelled to find mates outside their own families. Critiques of existing views and further alternative theories continue to be published (e.g., Ember 1983; Roscoe 1994). According to the ‘indifference theory’, early childhood association results in sexual indifference and aversion between siblings and between parents and offspring; conversely, incestuous behaviour is often caused by the lack or insufficient intensity of early contacts (first propounded by Westermarck 1891; see now Shepher 1983 and Wolf 1995 for the fullest expositions). As a consequence, sexually mature family members of one sex migrate, i.e., marry, outside the nuclear family. Animal dispersal can be explained in the same fashion (e.g., Pusey 1990). From a Darwinian perspective, natural selection favoured the evolution of this instinctive preference in the first instance because of the negative genetic effects of close inbreeding, and also because of the evolutionary benefits of genetic variation (e.g., van den Berghe 1983; Thornhill, ed. 1993). By way of a gene-culture co-evolutionary process, cultural precepts tend to reinforce this behavioural pattern (Durham 1991). In spite of some criticism (Leavitt 1990), this model seems more plausible than its competitors, especially since the dangers of close inbreeding have now been amply documented and analysed with respect to both human and animal populations (e.g., Bittles & Neel 1994; Ralls, Ballou & Templeton 1988).


In reality, of course, tensions between this (supposedly innate) principle and extraneous exigencies impel compromises between inbreeding and outbreeding. With certain types of inbreeding, such as marriage of first cousins or of uncles and nieces, moderate health losses may be offset by social and economic gains (eg., Khlat 1989; Reddy 1993). Even in societies that condone close-kin unions at these levels, however, the taboo against marital relations within the nuclear family sex is usually upheld (Thornhill 1991; Bonte, ed. 1994), in keeping with the fact that the latter cause much greater damage to offspring than less close unions (esp. Seemanová 1971). This has led some distinguished researchers to declare this type of incest taboo a universal cultural constant (Murdock 1949) or to assume that it lay at the heart of human social evolution and civilization (Levi-Strauss 1969).





The spread and force of incest avoidance make cases of socially and legally condoned marital and/or sexual relations within the nuclear family all the more intriguing. Paradoxically, they have been given short shrift in global surveys of incest (Fox 1980; Arens 1983; Héritier 1994). In a number of pre-modern societies, relations of this kind were the exclusive prerogative of kings and remained forbidden to commoners. ‘Royal incest’ (Bixler 1982), which serves to emphasize the supernatural qualities of the rulers (strongly associated with mythological traditions of divine incest) and insulates ruling families against intrusions, can be found around the globe, from the Pharaohs and Ptolemies of ancient Egypt (e.g., Cerny 1954; Carney 1987) and ancient Near Eastern rulers (e.g., Elam, Persia, Phoenicia, etc.) (Kornemann 1923) to kings in Central Africa (de Heusch 1958), the Inca of Peru and the Mixtec aristocracy of Mexico (Christensen 1998), and the chiefs of pre-contact Hawaii (Davenport 1994). In other cases, mostly in tribal societies, incestuous behaviour could be imagined to confer magical powers. By contrast, habitual nuclear-family incest outside ruling families was exceedingly rare. The census returns of Roman Egypt, preserved on papyrus, provide quantifiable documentary evidence of brother-sister marriage, mostly for the 2nd and early 3rd centuries AD (Thierfelder 1960; Sidler 1971; Hopkins 1980; Shaw 1992; Scheidel 1996a). At that time, one in five attested couples in Middle Egypt consisted of brothers and sisters (Bagnall and Frier 1994). The incidence of incest in the city of Arsinoe in the Fayum was higher still, indicating that virtually every man with a living younger sister married her instead of someone from outside the family. At that level, this custom must have assumed the function of a cultural norm (Scheidel 1995). Mazdaean (‘Zoroastrian’) religious doctrine, originating from Iran, not only legitimized but encouraged and extolled sexual relations between parents and children and between siblings. The very substantial corpus of pertinent evidence combines prescriptive Zoroastrian texts (mostly from the early Middle Ages) and descriptive accounts by outsiders, ranging from the 5th century BC to the Middle Ages and from western Europe to Tibet and China (West 1882; Spooner 1966; Sidler 1971; Bucci 1978; Frye 1985; Herrenschmidt 1994; Mitterauer 1994; Frandsen 2009). Half-sibling unions are also attested for a number of other societies but have so far eluded systematic investigation (Modrzejewski 1964; Goggin & Sturtevant 1964).





The phenomenon of marriage within the nuclear family has never received comprehensive treatment. Studies of sibling marriage in Roman Egypt have failed to provide a compelling explanation of this custom (Hopkins 1980; Shaw 1992) and have usually considered this subject in separation from the cross-cultural record. Moreover, the (biologically) incestuous nature of Roman Egyptian sibling marriage has recently been called into question (Hübner 2007, with Remijsen and Clarysse 2008). This alone shows the need for comprehensive reconsideration. The evidence of Zoroastrian incest has never even been collected in an exhaustive manner, let alone properly analysed (Sidler 1971 and now Frandsen 2009 are the best efforts). Comparative evaluations – between Egypt and Iran, between incest among commoners and among kings, or between incest and less extreme forms of endogamy – simply do not exist. It is my aim to provide the first book-length study of all aspects of this subject. It will contain a cross-cultural, comparative assessment of ‘royal incest’ across the world, with due attention to religious and mythological parallels. Although folk traditions of incestuous behaviour have repeatedly been surveyed (most recently by Johnson & Price-Williams 1996), I am not aware of a complete collection of the incest motif in mythological contexts. In a second step, the Zoroastrian evidence will be gathered and discussed in full detail. My collection of pertinent evidence – in its present scope the first of its kind – covers some fifty pages. I will then return to Ptolemaic and Roman Egypt, building on my own previous research which, again for the first time, put this evidence into an interdisciplinary perspective by establishing levels of inbreeding and likely levels of inbreeding defects (Scheidel 1995, 1996a,b, 1997). Existing research on cousin marriage and similar customs (Holy 1989; Khlat 1989; Reddy 1993; cf. in general Goody 1990) offers interpretations that mutatis mutandis may also be applied to incest and thus further our understanding of this phenomenon. Furthermore, my work will draw on scientific research on the biological and psychological dimensions of close inbreeding in an attempt to embed the historical record within a broader, multidisciplinary framework.





Albeit primarily designed as an historical study, my project does not address an exotic and marginal phenomenon. As indicated above, nuclear-family incest has played a crucial rôle in influential theories of human behaviour and development throughout this century, such as psychoanalysis, structuralism, and sociobiology. Incest and its avoidance occupy prominent positions in competing approaches to the understanding of human social behaviour, for instance in nature/nurture debates. As a consequence, the phenomenon of historical incest is of interest to scholars in a wide range of different disciplines. This project offers a rare opportunity to advertise ancient history to a wider academic audience, and to meet the twofold objective of contributing to historical scholarship and of bridging institutional boundaries between different disciplines.






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