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Consanguinity is basically "how close are you related?". Laws to prevent consanguinity (in other words, "don't marry your sister"), have been passed down from ancient times. The Marriage Act 1949 as amended by the Marriage (Enabling) Act 1960 establishes this list:

Many Americans may be surprised to hear that first cousins may marry, because it is forbidden in many American states, as well as other parts of the world. The Marriage Act of 1986 (Prohibited Degrees of Relationship) makes further provision for the marriage of persons related by infinity (or marriage). The reason for these prohibitions is, firstly, public policy, and secondly, the genetic risk.

Here is the list as it appeared in a Church of England Book of Common Prayer:

A Man may not marry his:     A Woman may not marry her:
  • Mother
  • Daughter
  • Father's mother
  • Mother's mother
  • Son's daughter
  • Daughter's daughter
  • Sister
  • Father's daughter
  • Mother's daughter
  • Wife's mother
  • Wife's daughter
  • Father's wife
  • Son's wife
  • Father's father's wife
  • Mother's father's wife
  • Wife's father's mother
  • Wife's mother's mother
  • Wife's son's daughter
  • Wife's daughter's daughter
  • Son's son's wife
  • Daughter's son's wife
  • Father's sister
  • Mother's sister
  • Brother's daughter
  • Sister's daughter
  • Father
  • Son
  • Father's father
  • Mother's father
  • Son's son
  • Daughter's son
  • Brother
  • Father's son
  • Mother's son
  • Husband's father
  • Husband's son
  • Mother's husband
  • Daughter's husband
  • Father's mother's husband
  • Mother's mother's husband
  • Husband's father's father
  • Husband's mother's father
  • Husband's son's son
  • Husband's daughter's son
  • Son's daughter's husband
  • Daughter's daughter's husband
  • Father's brother
  • Mother's brother
  • Brother's son
  • Sister's son

What was it like in Medieval times?

According to Ancestral Trails, by Mark D Herber, these were the "prohibited degrees" of marriage, according to the Book of Common Prayer, 1662:

  1. brother or sister (or their spouse)
  2. parent, grandparent, aunt, uncle, child, or grandchild (or their spouse)
  3. niece or nephew (or their spouse)
  4. spouse's child, grandchild, parent, aunt, uncle or grandparent.

Statutes of 1907 and 1921 made an exception at a. above, allowing people to marry the spouse of the brother or sister, if that brother or sister had died. Some further exceptions were made in 1931, 1949 and 1986 so that, for example, a man was allowed to marry his deceased wife's niece, aunt or widowed mother.

For more information, go to Guy Etchells website.

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Last updated on 18-January-2004
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