1 Consanguineous marriage , past and present

Major problems can arise when a term with a quite specific scientific definition becomes part of everyday speech. A prime example of this phenomenon is the word mutation, acknowledged within science as denoting a change in genetic structure and the driving force of evolution. But to members of the general public a mutation almost inevitably denotes a change that is at best disadvantageous and in many cases is life-threatening. Unfortunately, the terms inbred and inbreeding also fall into this category and, as a result, it has become virtually impossible to persuade members of the general public that inbreeding, and by extension marriage between biological relatives, can be anything other than harmful. Yet in the animal kingdom there are many examples of deliberate inbreeding that have resulted in healthy and fertile stock, in particular the mouse strains which are routinely used in biomedical research. It has been claimed that all of the common laboratory strains of mice can be traced back to a single female (Ferris et al., 1982), and after continuous brother–sister mating for a minimum of 20 generations, it was estimated that the animals would have inherited identical gene copies from each parent at approximately 98.6% of their loci (Beck et al., 2000). Since some mouse strains have been maintained by sib-mating for more than 150 generations, in effect they now are genetically identical except for sex differences. While there is no record of such sustained close inbreeding in human populations, even in Pharaonic Egypt, the anthropological literature contains ample evidence that unions between close biological kin have been commonplace and successful in many traditional human societies. Thus, in the cross-cultural ethnographic tabulations established by G.P. Murdock of the University of Pittsburgh, 353 of the 763 societies listed either permitted or favoured firstand/or second-cousin marriage (Murdock, 1967). The continuing popularity of consanguineous unions in many presentday rural and urban populations is apparent from the detailed information presented in the Global Consanguinity DataBase (www.consang.net). Intra-familial unions between couples related as second cousins or closer are