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Old 08 October 2008, 07:23 PM
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RivkahChaya RivkahChaya is offline
 
Join Date: 14 July 2006
Location: Indiana
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IIRC, one of the arguments against making adopted children part of families, and the legal children of their parents was the problem of consanguinity. For a long time, some adoption agencies always placed children out of state to avoid this.

It probably does happen occasionally that half siblings or first cousins, or even aunt/nephew uncle/niece pairs marry without knowing they are related.

However, when a general population diverse and large, one consanguinous pair doesn't increase its incidence of birth defects. The problem of pervasive genetic defects happens in small, isolated populations, where there may not be any brother/sister couples, but everyone is at least second cousin to anyone else.
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