It's just as logical, maybe moreso, that if MacBeth had an heir, he or she was not allowed to hold the throne after MacBeth was defeated by a dynasty that did not want his family to rule again at that point. Also, read about the conditions under which he rose to power... the claim that he was from a previous ruling family or family branch that returned to power, followed by a power struggle that ended in his defeat after all, in event concurrent or nearly concurrent with the aggressive Norman invasion and takeover of Britain. Albert Finley France's "House of Finley" explains the sequence of events as he understood them to be, and he claimed in 1939 to have been utilizing genealogical information given to him by a Professor John Finley at the University of Glasgow in Scotland. It would be interesting to see what, if any, records remain of Professor Finley's research. Itt has been implied in various histories that the Finleys had to go into hiding and use the name Farquharson (having descended from Farquahar), or to leave Scotland altogether at various points in time within the last 10 centuries, as it fell under rule from London, and measures were apparently taken to try to insure that the Finleys did not return to claim rule in Scotland again. However, if a later genealogy I have seen is correct, Finleys intermarried into British royal lines of later years -- during an entire millennium that has unfolded since then), at which point any residual power struggle began to come to an end, and England and Scotland were indeed unified as one. Grounds for war or division were over. I'm now working on getting Albert Finley France's 'House of Finley' text more accessible. People who have investigated the specifics in depth can argue about what Finley descendant US Navy Major A F France wrote and US Navy Rear Admiral Stout (married to a Finley). And it would be interesting trace down which Professor John Finley in Glasgow whom he wrote of.
Stout, in 'Clan Finley' indicates that A F France's research served as the foundation for his, and both admitted there were possible errors that they strove to avoid. The most obvious ones, as usual, being problems due to namesake confusion and the relatively limited ability in the 1930s to 1950s to access records.
As mentioned elsewhere, the current British royal family has indicated, on one of their websites, that Shakespeare's history of MacBeth is historically inaccurate, which may be a very diplomatic understatement, if what France wrote is true.
And if the Finleys were as influential, a thousand years and more ago, as France and Stout claimed, then the family history may have been among historical records difficult to uncover, if not destroyed by those desirous to erase the history of their influence.
I will throw these questions to the Scotland group to see what, if anything, anyone has to say, assuming they can say what they think if the subject is not still taboo. What I can say is that native Scot recently appeared to shift radically from cordiality to fear of further discussion after I mentioned my descent from the Finley 'clan', or whatever such relationships are called in the 21st century. The past is real, but you can't make it happen again, except in fantasies. The glories of monarchies are gone. But the blood, or genetics, of ancestors is not.