One of Family Guy's biggest lingering plot holes is Brian's son Dylan, who seems to be entirely human despite his father being a dog in the show.

Family Guy has opened a Pandora’s box of confusing animal and human relationships, but Brian fathering a human son is an ever-present plot hole. In season 6, the series introduced Dylan, Brian’s long-lost teenage offspring. Dylan is not only a human character but weirdly older than his dad.

In Family Guy season 6, episode 11, “The Former Life of Brian,” Brian discovers he’s fathered a son with his ex-girlfriend Tracy Flannigan (voiced by Rachael MacFarlane), who, after introducing Dylan (Seth Green) to Brian (Seth MacFarlane), sends the kid to the Griffin’s front door. Brian initially rebukes his son but later in the episode becomes overly protective of him. Defying nature as a hard-drinking, hindleg walking egotist, Brian is one of few dogs who can speak in Family Guy as well as attempt to write novels and screenplays. Brian’s personality traits define his relationship with his son. When Dylan returns in season 12, episode 11, “Brian’s a Bad Father,” Brian reveals he's willing to exploit his flesh and blood when he extorts a screenwriting gig from Dylan’s new Disney show, Parent Boppers.

Convincing human behaviors make it easy for audiences to look past Brian’s animalistic inclinations. After twenty years on-air, Brian’s pseudo-human status has rarely been questioned. Yet, for all of Family Guy’s persuasive storytelling, the confusion surrounding Brian’s fathering a full-on human being remains one of the series’ biggest question marks. Clearly, Family Guy is no stranger to testing nature’s boundaries.

When Vinny the replacement dog was introduced as Brian’s short-lived successor in season 12, episode 6, “The Life of Brian,” he tells Peter (Seth MacFarlane) that he’s “one-sixteenth cat.” Vinny, voiced by The Sopranos’ Tony Sirico, is just one example of the series’ regular crossbreeding gags. In fact, Family Guy has a habit of injecting hybrid animals into its cutaways. From season 4’s notable Noah’s Ark cutaway featuring a crossbred elephant and penguin to a human-esque female frog dancing to Bon Jovi in season 13’s “Stewie Is Enceinte,” Family Guy routinely mates species for humor. The problem is there’s not much rhyme or reason to the experimentation, which still leaves Dylan’s purely human roots unanswered.

A memorable plotline that does more to muddle Dylan’s origins comes from another one of Family Guy’s darkest episodes, season 13’s “This Little Piggy.” Stewie (Seth MacFarlane) gives birth to a litter of crossbred puppies fathered by Brian. In this instance, the offspring are half-human and half-dog. The sickly state of the brood results in their early demise, and by the episode’s end, Brian is grimly back to a single heir. Why Brian’s chromosomes would result in partially human children with Stewie when he produced an entirely human offspring years before is never addressed. Dylan wasn’t Brian’s only child, but he was Brian’s only human child.

Finally, the age difference between Brian and Dylan isn’t a reality that seems to faze Family Guy writers. Brian is approximately eight years old during season 6 and Brian having a 13-year-old son is physically impossible unless Family Guy later reveals some Brian and Stewie time travel trickery to help smooth out the plot hole. This may be the only way the series can answer the question of Dylan’s origin.

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