The concept of ghosts and other supernatural beings remains popular because they challenge our basic expectations about the world, according to Harvey Whitehouse, author of "Inheritance: The Evolutionary Origins of the Modern World." He explains that humans have an innate understanding of physical laws from a very young age. As infants, people expect unsupported objects to fall, move in continuous paths, and not pass through solid barriers.
Whitehouse states that these early-formed ideas help us navigate our environment. As children grow older—around three or four years old—they begin to understand that others have beliefs and desires, which can be true or false. This cognitive development also allows them to comprehend deception and lies.
"All this may sound rather abstract, but it's all you need to know if you want to build a ghost," Whitehouse says.
To create a ghostly figure, he suggests starting with a normal physical agent and then giving it one or two properties that defy intuitive physics—such as floating or passing through walls. Psychologists call such figures "Minimally Counter-Intuitive" (MCI) concepts. These are memorable because they violate just enough expectations to capture attention without being too confusing.
"As a result, simple ghost concepts have been documented all around the world but not beliefs in beings that only exist on Wednesdays or can only communicate through calculus," Whitehouse notes.
He points out that MCI ideas are widely used beyond folklore and myth. For example, Santa Claus is depicted as humanlike except for his ability to pass through chimneys (violating object solidity), fly with reindeer (defying gravity), and know the behavior of all children globally at once (challenging theory-of-mind intuitions).
"This socially salient MCI feature may well be one of the clinchers that helps to explain not only why children are enchanted but also why adults buy into it," says Whitehouse.
He adds that such concepts underpin both religious beliefs and children's stories across cultures. Their commercial impact is significant; for instance, global spending on Christmas exceeds a trillion dollars annually—more than the GDP of many countries. Similarly, Chinese New Year festivities featuring dragons and spirits generate around $150 billion each year.
"Halloween ghouls – like Santa and his sleigh – are money-spinners in America but the same kinds of ideas have universal appeal because they tap deep into our evolved psychology. America is a big country but not as big as China. Chinese New Year with its fire-breathing dragons and evil spirits is estimated to be worth around $150 billion per annum. And of course, there are countless other festivals involving MCIs all around the world," he says.
Whitehouse concludes: "The truth is that these kinds of ideas – the building blocks of religion and children’s stories alike – are universal. We all know how to build a ghost. But now we know how we know."