But, don different societies have different rules about who is considered to be related to whom?
A. Yes. Indeed, every culture comes up with a way to deal with the exponential unwieldiness of family trees. For many purposes of daily life, you have too many relatives. The sheer numbers of ancestors, distant cousins, and potential descendents you have expand out beyond any manageable boundaries. The amount of relatives you’ll send a Christmas card to might be larger than the number you’ll volunteer to cook Thanksgiving dinner for, but, still, there’s got to be an end to everything. Many cultures have devised rules to limit who counts as a relative for the purposes of, say, inheritance. English aristocratic families didn’t want their land holdings divided up into unimpressive and inefficient parcels, so they followed the rule of primogeniture, passing the claim to be of noble blood down through the first-born son, with latter-borns falling out of the aristocracy within two generations. For instance, Mr. Winston Churchill was the first-born son of Lord Randolph Churchill, who was the
