The stigma attached to first-cousin marriages was supported by early studies into human genetics suggesting that "recessive" versions of a gene (which are not expressed unless there are two of them, one from each parent) are more likely to be expressed in the children of genetically related parents, as well as more likely to be defective.
Most states in America have either outlawed or restricted the practice, as has China, Taiwan and both North and South Korea.
H G Wells The science fiction author of The Time Machine and The War of the Worlds married his first cousin Isabel Mary Wells in 1891 but left her after three years to marry one of his students, with whom he had two children.
Edgar Allan Poe The American gothic poet secretly married his 13-year-old first cousin, Virginia Eliza Clemm, in 1834. Johann Sebastian Bach In 1707 Bach married his second cousin Maria Barbara Bach and had seven of his 20 children with her.
There is some evidence that communities that practise cousin marriage experience higher levels of some very rare but very serious illnesses known as recessive genetic disorders.
Alison and I were particularly close and we always stayed in contact when we went to university.There is no scientific grounding for it." In the UK, the issue came to the fore when the MP Phil Woolas, now the Immigration minister, claimed earlier this year that first-cousin marriages within Asian communities in Britain resulted in an increasing number of children with health problems."A lot of arranged marriages are with first cousins, and that produces lots of genetic problems in terms of disability [in children]," Mr Woolas said."Women over the age of 40 have a similar risk of having children with birth defects and no one is suggesting they should be prevented from reproducing," said Professor Spencer, whose co-authored study is published in the online journal Public Library of Science.First-cousin marriages were once quite common in Europe, especially among the elite – Charles Darwin married his first cousin Emma Wedgwood – but that changed in the late 19th-century as people, especially women, became more socially mobile and the risks became more evident.