Paper claims an conservatively estimated prevalence of 1/3652 for extreme inbreeding which equates to about 18k people, assuming a UK population size of 66 million.
Not great, but nothing world-ending.
Not great, but nothing world-ending.
Many people don’t know who their biological parents are. While not a significant issue with adoption, if a guy has multiple kids who don’t know their siblings in the same area. Then they are likely geographically close and of similar ages...
They must surely have data on simple first cousins, but it didn't jump out at me.
For example, taking Fluid Intelligence Score (basically how smart you are), in Table 3, its extrapolated effect size is -3.43, so:
First cousin (relationship coefficient 0.125, inbreeding coefficient 0.0625) would give -0.214 to FIS. To put that in context, for medication, that would be considered a small effect size. So inbreeding at that level is a bit like taking a stupid pill.
Received wisdom is that a coefficient below 0.25 doesn't cause serious deleterious effect. I have no idea if that's well supported, but I imagine it's relevant to why it wasn't studied.