Bart’s controversial origin story claimed that his lack of intelligence was hereditary, but Homer has seemingly forgotten this fact in The Simpsonsseason 33. Although Bart is nowhere near as bumbling as Homer in The Simpsons, he’s also not as unusually intelligent as his sister Lisa. The Simpsons once provided an in-universe explanation for this disparity, although Homer has seemingly since forgotten about this explanation.
In “Lisa The Simpson,” (season 9, episode 17), Lisa fears she is genetically predisposed to a lack of intelligence because she shares Homer’s Simpson genes. However, by the end of the episode, she is reassured that those genes only affect male Simpsons, something that briefly dismays Bart before he almost immediately stops caring. This fits with the devil-may-care attitude that leaves Bart in detention writing lines on The Simpsons' opening credits chalkboard, but the explanation was still somehow forgotten by Homer in The Simpsons season 33.
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In “Marge the Meanie” (season 33, episode 20), Homer fears that Marge’s secret propensity for pranks means Bart doesn’t have any obvious genetic connection to him. This completely ignores the earlier episode’s revelations, which Homer not only understood at the time, but also explained to a dismayed Bart. However, there might be an explanation for this that doesn’t involve The Simpsons retconning the earlier episode’s plot, which otherwise would seem to be the case. Homer may have not remembered the fact that Bart is a Simpson through and through precisely because the «Simpson gene» has made him immediately forget this information — and thus, Homer’s failure to recall the existence of the
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