Simpsons Genetically Predisposed to Seek Out Blue Beehives?

On last night's Simpsons episode, one of Lisa's paternal ancestors looked remarkably like Lisa's mother, who is related only by marriage to the Simpsons.

Back to the Future III had a similar problem. Writer/producer Bob Gale and writer/director Robert Zemeckis were once asked to explain how the same actress ended up in two branches of Marty's family tree:

Q: Lea Thompson plays Maggie McFly, Marty's great-great-grandmother, as well as Lorraine, Marty's mom. But Lorraine's family name is "Baines". Why did Lea play Marty's paternal great-great-grandmother, when she's really not part of that family? Is there something kinky going on in the history of the McFly family?

A: Lea plays Maggie because we didn't want to make a Back to the Future Part III without having Lea in it, especially in a "Mom is that you" scene! Of course, we thought about whether it made any sense -- obviously, Maggie McFly and Lorraine Baines cannot be blood relatives. But we did come up with a satisfactory answer: It's a well known adage that "men are attracted to women who remind them of their mothers." Clearly then, when Seamus married Maggie, that insured that the McFly men would have a genetic trait that attracted them to women who bear a resemblance to Maggie or Lea Thompson (even Jennifer is the same physical type!) [Link]