Answered By: Colleen Bryant Last Updated: Jul 15, 2015 Views: 230
This question is never answered in Macbeth. At least one scholar, Alfredo Leme Coelho de Carvalho, has tried to find clues in the play which reconcile Malcolm's ascent to the throne with the prophecy about Banquo's descendants. In an article in Portuguese titled "A última profecia de Macbeth" ("The final prophecy of Macbeth," Estudos anglo-Americanos (São Paulo) 1 (1977): 7-12), Carvalho "contends that Malcolm's "testing" of Macduff in Act 2 is purposely ambiguous and allows the audience to conjecture a popular revolt which will subsequently establish a new line of succession." (This précis of Carvalho's argument is taken from the World Shakespeare Bibliography Online; I have not seen the article myself.) You can decide for yourself whether you find this argument persuasive.
As you might have already discovered, there are other non-scholarly conjectures on the Internet, such as those here: