My father is 5th cousin of himself, via a ancestor couple who seem to be unexpectedly reliable in connecting me to FF matches on my paternal side.But of course it has been a random shuffle; I, or anybody descending from the ancestral couple in question, still could have ended up getting insignificant amount of DNA from them. The genetics word "recombination" itself gives us a clue that there must be an effect of what is recombined.Anything at or above 0.0156, the coefficient for second cousins, is considered consanguineous; that includes relationships between people and their nephews and nieces. For one thing, 25 states ban marriage between first cousins, and another seven states have restrictions on it (for example, in Arizona first-cousin marriage is allowed only if both people are 65 or older, or if one is unable to reproduce).
The first-cousin marriages you’re asking about are just one type of consanguineous relationship (that’s pronounced kon-sang-gwin-ee-uh s in case you were struggling, as I was).
I have found at Ancestry DNA, that nearly half of my leaf hinted distant matches come through these cousin marriages.
It amplifies the signal; makes the algorithms estimate a closer kinship & thus "see" a lot farther.
In this case, the smaller number of generations to the common ancestor is used to determine the degree, and the difference in generations determines the number of times removed.
Note that the ages of the cousins are irrelevant to the definition of the cousin relationship.