Commentary: The background and outcomes of the first-cousin marriage controversy in Great Britain

During the early years of Christianity there were major social and legal differences in attitude towards consanguineous marriage in the Eastern and Western Roman empires, reflecting pre-existing divisions between the Classical Greek and Roman worlds. In Athens and Sparta first-cousin, uncle\u96niece and half-sib marriages were permissible, 1\u963 with half-sib marriage, and even full-sib marriage continuing within the ruling Ptolemaic dynasty and the settler population of Lower Egypt between the first and the third centuries AD. 4 By comparison, in Rome there was strong disapproval of first-cousin marriage, 3 and the marriage between the Emperor Claudius (41\u9654 AD) and his niece Agrippina was regarded as especially scandalous. The genetic relationships involved in these consanguineous unions are summarized in Table 1 , accompanied by the equivalent coefficients of relationship ( r) indicating the proportion of genes shared by each parent, and coefficients of inbreeding ( F), a measure of the proportion of loci at which the offspring of a consanguineous union would be expected to inherit identical gene copies from both parents. Not surprisingly, given the period in human history, none of the early judgements on the degrees of permitted and prohibited marriages between biological relatives appears to have had an especially rational scientific basis. However, by the middle of the fifth century the Church had adopted the Roman doctrine on consanguineous marriage, with the initial impact in England recounted by the Venerable Bede writing in the early eighth century. 5 According to Bede, on his installation as the first Archbishop of Canterbury, Primate Augustine had requested advice from Pope Gregory I on Church regulations with respect to first-cousin marriages. The reply from the Pope in 591, citing Leviticus 18:6, was that \u91Sacred law forbad a man to uncover the nakedness of his near kin\u92. Furthermore ..