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Intermarriage between first cousins

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Intermarriage between first cousins

Postby ksouthall » Mon Apr 21, 2014 11:11 am

When I was growing up I was always told that intermarriage between first cousins was not a good idea as often children born to the marriage were unhealthy and some even died during infancy.

Last year, there was a study into the higher percentage of birth defects in children of first cousins: 6% compared to 3% in the general population. However this is still a very small percentage. The link below mentions the article:-

http://www.theguardian.com/science/2013 ... th-defects

A different article suggests that the risk may depend on whether or not the cousins are cross-cousins or parallel cousins. The link is below:-

http://gizmodo.com/the-science-of-marry ... 1522745684

Cross-cousins are the children of opposite sex siblings of a child's parents; i.e. children of a child's mother's brother or father's sister. Parallel cousins are children of the same sex siblings of a child's parents; i.e. mother's sister or father's brother.

The article further suggests that parallel cousins may be half-siblings if there had been any "inter-mingling among the members of an extended family".

The reason I am posting this is because I have found a number of instances where direct ancestors and also other more distant family members have married first cousins. Sometimes this has been compounded by cousins being parallel cousins and also being cousins and second or third cousins on top of that, due to an intermarriage between cousins further back in the family.

One of the instances I found was one of my great-great-great-grandfathers, George Seabrook, who appears to have been the only child of George Seabrook and his first cousin, Elizabeth Seabrook. George and Elizabeth married in 1798 by licence. They were the children of two brothers who had married two sisters, so were biologically very close!

George Seabrook senior was the son of William Seabrook and Frances Humphrey.
Elizabeth Seabrook was the daughter of George Seabrook and Elizabeth Humphrey.

As a result, instead of having 8 great-grandparents, George Seabrook junior only had 4 as they all doubled up.

I was wondering if anyone else had found intermarriages between cousins and whether or not there was a pattern in the number of surviving children.
ksouthall
 
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Re: Intermarriage between first cousins

Postby 911mama » Mon Nov 19, 2018 10:40 am

Good morning,

I came across your posting and I wondered if our Seabrooks may be the same. My George Seabrook also had a daughter Elizabeth. I'm reviewing a will from 1885. Just thought I would enquire.

Thank you for your time
Amber Lara
911mama
 
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Re: Intermarriage between first cousins

Postby Guy » Mon Nov 19, 2018 1:12 pm

There is a certain prejudice against such marriages but as animal breeding shows there can also be positive benefits in such births it is not all negative.

By the way it is the same relative increase in risk seen in births where the mother is over 34.

Very often such research simply proves what the researcher wants to concentrate on rather than give the full picture.
Cheers
Guy
As we have gained from the past, we owe the future a debt, which we pay by sharing today.
Guy
 
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Re: Intermarriage between first cousins

Postby ksouthall » Wed Nov 28, 2018 3:18 am

911mama wrote:Good morning,

I came across your posting and I wondered if our Seabrooks may be the same. My George Seabrook also had a daughter Elizabeth. I'm reviewing a will from 1885. Just thought I would enquire.

Thank you for your time
Amber Lara


Hello Amber,

Could you let me know who your Elizabeth Seabrook married, if at all, please?

Thanks,

Katherine
ksouthall
 
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Location: Sussex

Re: Intermarriage between first cousins

Postby loiseau22 » Sun Dec 09, 2018 1:13 am

My great-great grandfather John Trubshaw married his first cousin Elizabeth Trubshaw in 1834.
They had 16 children. As far as I can see, only two died before adulthood (one aged 6 and one aged 12).
loiseau22
 
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