I’ve often wondered whether, if I had grown up celebrating Christmas, I would have believed in Santa Claus. I’d like to think I wouldn’t have. There was talk of Hanukkah Harry, but even as a little kid I knew that he didn’t really show up at all the Jewish houses with Hanukkah presents. For me, the Santa stand-in was a way to smirk about how much smarter I must have been compared with all those fools who seriously believed that a giant rotund North Pole–dwelling toy manufacturer in a red suit flies around the planet on a sleigh pulled by flying reindeer, squeezes through chimneys to deliver presents, and somehow knows which kids to reward with presents and which ones deserve coal. All in one night.

Still, I can recall being pretty terrified one year because we hadn’t smeared our doorposts with lambs’ blood during Passover. If the Angel of Death was really going to pay us a visit, he’d be coming for me, since I am my parents’ first born. So I guess I would have grown up believing in Santa Claus, at least for a few years. Young children, after all, are a fairly credulous group. When a tiny human is born into the world, her main job is learn as much as she can, and most of what she learns comes from her caregivers.

Parents and teachers are prime examples of otherwise trustworthy authorities who, come December, provide information that’s not only false but also highly implausible. After all, according to tradition, Santa’s Christmas Eve activities violate principles of physics so basic that even newborn infants can intuit them. As Occidental College cognitive scientist Andrew Shtulman writes in a study soon to appear in the journal Cognitive Development, “Santa violates our expectations about spatiotemporal continuity by visiting all the world’s children in a single night; he violates expectations about containment by entering children’s houses through their narrow chimneys; and he violates expectations about support by flying through the air on a wooden sleigh.” Still, kids’ belief in Santa is stronger than nearly any other fantasy character, and that belief often persists for several years.

Even if a child doubts the plausibility of Santa Claus, it’s hard to argue when Mom, Dad, Grandma, Grandpa, and all the other authority figures in a child’s life are so remarkably consistent in their telling. Cultural messages regarding Santa, even in movies and television, are so pervasive that even kids growing up in households free of Santa, like I did, can come to believe in his existence, at least in some circumstances.

But what Shtulman wanted to understand was the process through which kids finally come to disbelieve in Santa. Some have assumed that the same cultural processes that lead to the initial belief also lead to its eventual dissolution. But that implies that children don’t become skeptical of Santa Claus on their own, and that if they were never set straight, they’d go right on believing in a team of aerial, globe-spanning ungulates.

Shtulman suspected that children grow to doubt Santa’s existence not because the cultural messages change, but rather because of their developing intellect. In other words, they simply become too smart to seriously believe that a single man, no matter how jolly, could deliver presents to all the world’s children. They eventually come to realize that reindeer will always be fully terrestrial.

To understand how those beliefs evolve, Shtulman rounded up 47 children between the ages of 3 and 9. All the kids in the study said they believed in Santa, but it turned out that they didn’t all think about Santa in the same way.

An older child who was more capable of identifying the implausibility of Santa Claus would argue, for example, that Santa could know whether every child was naughty or nice because, as one reported, “He has cameras all around the world.” Or they might suggest that Santa’s reindeer can’t actually fly; they’re held up by yarn. By contrast, younger children would simply answer that Santa’s reindeer fly thanks to magic.

The children were attempting to reconcile the folklore surrounding Santa’s superhuman abilities with their developing knowledge about the constraints of the physical reality in which they live. Some kids were already better at distinguishing the plausible from the impossible (for instance, when asked, they said that pickle-flavored ice cream is possible but unlikely, while applesauce can never be turned into an apple). These kids had also “begun to engage with the mythology surrounding Santa at a conceptual level, questioning the feasibility of Santa’s extraordinary activities while also positing provisional explanations for those activities in the absence of a known answer,” writes Shtulman.

Granted, Shtulman wasn’t necessarily interested in the question of Santa per se. Nor could he directly assess the kids’ skepticism, because provoking young kids to question the plausibility of Santa might draw the ire of their parents. Instead, he sees Santa-related lore as exactly the sort of false knowledge that’s typically transmitted to kids from people they trust most: parents and teachers. “Studying children’s beliefs about Santa can shed light on how children interpret testimony that they cannot personally verify through firsthand observation,” he says.

For most kids, at some point the weight of evidence against the likelihood of Santa being real becomes too heavy to sustain their belief, even if their parents continue to encourage it. Shtulman relates the story of one child whose mother continued to talk up Santa. Then, as she set about wrapping presents, she found a note that her son had written on the back of the paper: “If Santa uses this paper, Mom is Santa!” Clever.

Adults tell children a lot of things that defy the basic laws of physics and biology. One might think, as I did, that the growing intellect that leads a child to become suspicious of Santa-related mythology might also lead him or her to become skeptical of religious mythology in general. But Shtulman says the two sorts of fantasies are not created equal. “People openly claim that Santa is not real, as is evident from any holiday show that includes the stock character of the hard-nosed, Santa-doubting Grinch,” he told me. And part of the deal with Santa is that the adults know they’re selling a lie. At some point the adults usually stop lying, and then they ask children who have learned the truth to help perpetuate the Santa myth among children who still believe. “Testimony about religious beings, on the other hand, is much more credible among believers and much more guarded among doubters.” And he’s probably right; an adult who admitted to believing in airborne reindeer would be openly mocked. An adult who admitted to believing in God is more likely to be respected.

Shtulman says it’s an interesting question “whether children are as skeptical of the extraordinary properties of religious beings as they are of the extraordinary properties of Santa, at least later in development.” If they are, atheists who want to recruit new members to their growing movement should take note. Perhaps young children simply need to be exposed to a few more Grinches to encourage their natural skepticism.