In a recent interview with Game Informer, Nintendo designer and director Shigeru Miyamoto discussed some unresolved issues with the series' canon, clearing up a few points of contention and putting them to rest.
On the biological controversy surrounding Bowser's children, Miyamoto admits that he does not know who Bowser Jr.'s mother is although he is a legitimate son. The rest of Bowser's seven Koopa Kids are not his children, and are essentially adopted.
In response to a question regarding the Mario characters' willingness to play tennis or race karts with each other despite constantly being at odds, Miyamoto stated that he thinks of the cast as more of "a troupe of actors."
"If you're familiar with things like Popeye and some of the old comic characters, you would oftentimes see this cast of characters that takes on different roles depending on the comic or cartoon," Miyamoto said. "They might be businessman in one [cartoon] or a pirate in another. Depending on the story that was being told, they would change roles. So, to a certain degree, I look at our characters in a similar way and feel that they can take on different roles in different games."
"He's hard-working, and certainly much more physical in nature," he said. "So, I think that a doctor is sort of an unexpected and perhaps unbelievable role for Mario. Perhaps the Dr. Mario you're thinking of was maybe, in some way, not necessarily legitimate."