Have you ever been wandering around an art museum and found yourself chuckling at the angry middle-aged-man heads on Medieval babies? "Wow, those Medieval artists were terrible at painting children!" You probably thought to yourself. But the joke is actually on you: These artists wanted their paintings to feature mini versions of that guy from one cubicle over.

Vox spoke to Matthew Averett, an art history professor at Creighton University who edited the anthology The Early Modern Child in Art and History, to find out why this trend towards intentionally old-looking babies abounded during the Middle Ages—and what caused the shift during the Renaissance toward the chubby-cheeked cherubic faces we recognize as babies.

The reasoning, like all things artistic in the Middle Ages, has to do with Jesus. Back then, the Church commissioned most of the portraits of babies and children. And they didn't want just any old baby—they wanted the baby Jesus (or other biblical kids). Medieval artists subscribed to the concept of homunculus, which literally means "little man," or the belief that Jesus was born "perfectly formed and unchanged," Averett said.

This homuncular, adult-looking baby Jesus became the standard for all children, an exemplar that stuck in the Middle Ages because artists at the time had, according to Averett, a "lack of interest in naturalism, and they veered more toward expressionistic conventions."

During the Renaissance, however, non-religious art flourished, and wealthy patrons wanted portraits of their darling children that were cute—not Benjamin Button-esque. Add a greater attention to realism, and babies began shifting away from the hyper-stylized homuncular.