Why, for example, is belief in invisible, supernatural agents - such as ghosts, angels, dead ancestors, and gods - so widespread? Belief in such supernatural agents appears to be a near universal feature of human societies. There is some evidence that a predisposition towards beliefs of this kind may actually be innate - part of our natural, evolutionary heritage. The Oxford psychologist Justin Barrett has suggested that the prevalence of beliefs of this kind may in part be explained by our possessing a Hyper-sensitive Agent Detection Device, or H.A.D.D.
Human beings explain features of the world around them in two very different ways. For example, we sometimes appeal to natural causes or laws in order to account for an event. Why did that apple fall from the tree? Because the wind blew and shook the branch, causing the apple to fall. Why did the water freeze in the pipes last night, because the temperature of the water fell below zero, and it is a law that water freezes below zero.
However, we also explain by appealing to agents - beings who act on the basis of their beliefs and desires in a more or less rational way. Why did the apple fall from the tree? Because Ted wanted to eat it, believed that shaking the tree would make it fall, and so shook the tree. Why are Mary's car keys on the mantelpiece? Because she wanted to remind herself not to forget them, so put them where she thought she would spot them.
Barrett suggests we have evolved to be overly sensitive to agency. We evolved in an environment containing many agents - family members, friends, rivals, predators, prey, and so on. Spotting and understanding other agents helps us survive and reproduce. So we evolved to be sensitive to them - oversensitive in fact. Hear a rustle in the bushes behind you and you instinctively spin round, looking for an agent. Most times, there's no one there - just the wind in the leaves. But, in the environment in which we evolved, on those few occasions when there was an agent present, detecting it might well save your life. Far better to avoid several imaginary predators than be eaten by a real one. Thus evolution will select for an inheritable tendency to not just detect - but over detect - agency. We have evolved to possess (or, perhaps more plausibly, to be) hyper-active agency detectors.
If we do have an H.A.D.D, that would at least partly explain the human tendency to feel there is "someone there" even when no one is observed, and so may at least partly explain our tendency to believe in the existence of invisible agents - in spirits, ghosts, angels or gods.
For example, in his book Illusion of Conscious Will, Daniel Wegner points out what he believes is the most remarkable characteristic of those using a ouija board (in which the planchette - often an upturned shot glass - on which the subjects' index fingers are gently resting appears to wander independently around the board, spelling out messages from "beyond"):
People using the board seem irresistibly drawn to the conclusion that some sort of unseen agent... is guiding the planchette movement. Not only is there a breakdown in the perception of one's own contribution to the talking board effect but a theory immediately arises to account for this breakdown: the theory of outside agency. In addition to spirits of the dead, people seem willing at times to adduce the influence of demons, angels, and even entities from the future or from outer space, depending on their personal contact with cultural theories about such effects.
Because the movement of the planchette is inexplicable and odd, it is immediately put down to the influence of an invisible agent (though notice the kind of agent invoked varies from group to group depending on their own particular, culturally-led expectations - see Piling Up The Anecdotes).
However, I am not here endorsing the H.A.D.D. explanation for widespread belief in such invisible agents (though I suspect there's some truth to it). Also, notice that, even if we do possess an H.A.D.D, that at best explains the attractiveness of only some wacky belief systems. Many - such as those involving crystal healing, palmistry or numerology - involve no invisible agents.
Note that the H.A.D.D, hypothesis does not say that there are no invisible agents. Perhaps at least some of the invisible agents people suppose exist are real. Perhaps there really are ghosts, or spirits, or gods. However, if we suppose the H.A.D.D, hypothesis does correctly explain why it is that so many people believe in the existence of invisible agents, then the fact that large numbers hold such beliefs can no longer be considered good evidence that any such agents exist. It will no longer do to say, "Surely not all these people can be so very deluded? Surely there must be some truth to these beliefs, otherwise they would not be so widespread?" The fact is, if the H.A.D.D, hypothesis is correct, we're likely to believe in the existence of such invisible agents anyway, whether or not such agents exist. But then the commonality of these beliefs is not good evidence such agents exist. If the H.A.D.D hypothesis is correct, it adds yet another nail to the coffin lid of the suggestion: "Lots of people believe it so there's got to be something to it!"