Date published: 2008/02/11
The BBC says:
Marrying a distant relative could mean a larger family, according to Icelandic researchers who studied their nation's genetic record.
The Science journal study found third and fourth cousin couples had more children than those more distantly related.
These cousins may be biologically more compatible, the specialist genetics firm deCODE concluded.
However, there was no advantage in partnerships involving first cousins.
Evidence that related couples have more children has been found before, but there has always been doubt whether this is the result of similarities in their genetic makeup, or just the result of differences in the societies in which cousin marriages are common.
The deCODE team have access to a unique genetic record which allows them to unpick the interlocking family trees of Iceland.
In addition, Icelandic society and culture has been historically uniform across its population, making it easier to rule it out as an influence on the results.
This study does not really prove that the effect they have noticed is due to "similarities in their genetic makeup". It could easily be the result of social differences between people who might marry their third or fourth cousin and people who would not. Icelandic "society and culture" might have been "historically uniform" but that does not mean that all people wanted to breed exactly the same amount as everybody else. For example, rural people might be more likely to marry third or fourth cousins (there are fewer potential partners to choose from) but might also be more likely to want bigger families.
Hopefully the deCODE team will produce more interesting and useful results than this one.
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