What is the proof that “first-cousin marriage is the most common form of marriage in the world”, as a Royalty category participant claims?

That certain participant is always posting that kind of stuff. I view it as light relief to some of the other more fanatical royalists, who still think the earth is flat.

I doubt anyone seriously makes that claim.

It is normal but no way the most common.

I actually don't think it's currently the "most common," as tentofield has recently claimed, but it remains quite common among Muslims, whose numbers in the world means it's very common in general. It was once extremely common among pretty much everyone. You might find the site below interesting, with its facts and figures.

Genetically speaking, a single first-cousin marriage isn't much of a risk. However, when such marriages repeatedly take place over the centuries, genetic problems almost inevitably arise. Over the past several years, owing to a high number of congenital problems among children in the UK Muslim community, there has been some discussion of making first-cousin marriages illegal there. Should this ever become a serious proposition, I imagine the claims of ethnic discrimination will be heard all the way to -- what is it? -- John o' Groats.

Yea, yea, yea Queen Victoria yada, yada, yada, Prince Albert blah, blah, blah, got married yada, yada, yada, first cousins blah, blah, blah!

It isn't. However, it *is* very common in the Middle East, North Africa, and India. Genetic studies suggest that in the past, something like 80% of marriages were between couples who were first or second cousins.