Problems with dating 3rd cousin
Put it together and you have first cousins, twice removed. The closest relationship to the common ancestors is Charles, as a great-grandchild. But Charles and David are one generation different, so they need to be "removed" once.
Their relationship is second cousins, once removed.
As can be inferred by how common cousin marriage used to be in Europe and the United States and is still in other parts of the world, the children of cousins are not all doomed to be drooling inbreds.
In fact, the increased risk of birth defects in the children of cousins is incredibly slight. According to Islamic law as well as Indian and Pakistani custom, cousins are fair marriage game.
The social taboo against cousin marriage is a relatively new one.
In the United States, the taboo seems to have originated in highly unscientific studies that relied to eugenicist ideas.
Abe had a son named Bob; Bob had a daughter Cathy; and Cathy had a son David. Barbara and Bob have the same distance from their closest common ancestors; no "removed" is necessary. Their closest common ancestors are their great-grandparents (John and Mary).Barbara is still the closest, at grandchild, so it's still a first cousin.But David is two generations different, so he needs to be "removed" twice.Since they're not equally distant from the common ancestor, "removed" is a way to show how far apart they are.In the example below, John and Mary had two sons: Adam and Abe.
Many states only allow cousin marriage if there is no possibility of the production of children anyway. Therefore, by the age of puberty, I was required to give up hugging my male cousins and going in front of them with my head uncovered.