Board Thread:Questions and Answers/@comment-27491885-20151228162741/@comment-27401333-20160105155255

I'm not sure just where I found this, but I've heard before that the two are fraternal twins, or brothers given birth to (or created) at the same time. Papyrus takes on the older brother roles of cleaning, cooking, and work. Sans is super lazy and adopts the role of little brother.