Trick or treat! It’s Halloween – time for costumes, sweets and spooky fun. From aliens to zombies, stories of supernatural phenomena have been around for millennia. But now we have scientific approaches to help investigate even the creepiest of cases. So let’s have a look at a few of the usual Halloween culprits, exploring the origins and explanations for some of our deepest fears.
Let’s kick things off with the bloodsucking baddies. Any Twilight fan can tell you that vampires are cool right now, but they’ve actually remained an object of cultural fascination for the past 4000 years or so.
Stories of vampire-like creatures date back to the ancient Babylonians and Mesopotamians who attributed tragic events like miscarriages and sudden infant death syndrome to the presence of female demons who preyed on humans.
These legends spread all around the world, and by the 17th and 18th centuries, vampire hysteria had truly hit Europe. Rituals and exhumations began taking place, as terrified relatives sought to destroy ‘undead’ family members who they believed were tormenting them from the grave.
With the benefit of hindsight (and a healthy dose of scientific and historical knowledge) , we now see things from an altogether more rational perspective. So why did the vampire legend become so widespread?
First and foremost, demonic presence provided a handy explanation for unhappy circumstances, like livestock deaths, bad harvests or disease outbreaks. Without knowledge of why these things occurred, people created their own meaning.
There are also historic precedents that may have fuelled the fire of the vampire stories. In the 14th century, Prince Vladisar Basarab (aka Vlad the Impaler) became renowned for the supposed brutality with which he dispatched his enemies, later inspiring Bram Stoker’s Dracula.
About 150 years later, Countess Elizabeth Bathory of Transylvania was found to have killed up to 650 people, mostly young girls, reputedly to bathe in their blood. It’s not a big step for these real-life horror stories to become mythologised into something otherworldly.
There are also a number of medical conditions that we now recognise as the result of biological problems, but at the time could have potentially been considered supernatural. Tuberculosis can cause sufferers to become pale and cough up blood, whilst a rare condition known as porphyria can lead to mental issues and extreme sensitivity to light.
So we have history and biology to contend with, but don’t let that fool you. Vampires do exist. When villagers found cattle with their blood drained, they really were dealing with bloodsuckers. Vampire bats feed by night on the blood of other creatures. Their bites can lead to infection and, in the worst cases, death. We also have to put up with leeches, mosquitos, and bedbugs – but try not to let that keep you up at night.
Ah, zombies. They’ve shot into the pop culture spotlight in recent years with shows like The Walking Dead and paid-for zombie experiences attracting huge popularity. But the zombie myth actually has much older origins.
Legends about the living dead seem to have originated in Haiti, where voodoo is widely-practiced. Haitian folklore contains stories of people paralysed with poison so that they appear to be dead. The unfortunate victim is then buried and later dug up by evil masters, who use the brain-damaged individuals as slaves.
In the 1980s, researchers sought to investigate the stories to see if there was any truth behind the legend. They discovered that the poison supposedly used to paralyse victims contained quantities of a toxin called tetrodotoxin.
Commonly secreted by pufferfish, tetrodotoxin can cause paralysis, vomiting, respiratory failure, and death. Theories emerged that exposure to this nasty substance could to cause a victim to appear dead. Oxygen-starvation when interred in a coffin could lead to brain-damage. And then all that follows is for the poisoner to retrieve their ‘zombie’ from the ground. However no concrete evidence for this theory was ever found in practice and it has been largely dismissed by the scientific community.
But despite the disappointing lack of classic zombies, the living dead certainly do exist in the natural world. A number of bacteria and viruses can affect the behaviour of their host, sometimes causing them to become more aggressive or reckless. The theory is that this leads infected subjects to attack or be attacked by something else, so that the virus can spread to a new host.
Toxoplasmosa gondii is a parasite found in cat poo that has been linked to changes in behaviour. Prolonged exposure may also be linked to the development of schizophrenia. And it’s pretty common: some estimates suggest up to one third of people in the UK may be infected at some point in their lifetime. But don’t let that stop you petting your cat – toxoplasmosis is generally harmless and not something to be worried about.
Ladybirds are the ones who really have something to fear from zombies. Parasitic wasps like to lay their eggs inside the poor ladybird, where they grow before exploding out of the bug’s abdomen. In some cases the subservient ladybird is then forced to keep guard over the growing wasp until it’s fully developed, unable to move or act independently. Pity the poor ladybird – a real-life example of zombification.
Let’s round things up with the most perennial of spooky fascinations. Everyone loves a good ghost story. In fact, some polls suggest that about 50% of the UK public believe in ghosts. But what can science tell us about ghoulish phenomena?
Things we can’t see can have a huge influence on us. We’re affected in strange and unconscious ways by physical phenomena that we’re not even aware of. Whether it’s the environment around us or the state of our own mind, what we see is not always what’s really there.
Your mind really can play tricks on you. Normal function of the brain can be affected by both extreme physical or emotional stress, and by medical conditions such as stroke, epilepsy, cancer or migraine. Scientists have discovered that electrical stimulation of parts of brain can affect perception, causing us to experience spooky sensations or see shadow people around us.
Experiments by Michael Faraday in the 19th century demonstrated an effect known as the ideomotor response. This is where an individual, completely without conscious knowledge, performs minute muscular movements in accordance with preconceived ideas. So if you’re asked to imagine sucking a sweet, your mouth might salivate. Imagine tying shoelaces and your fingers might twitch.
This effect also accounts for ghostly phenomenon such as Ouija boards and some poltergeist activity. Perfectly honest and sane individuals can act unconsciously in response to suggestive clues and their perception of the situation.
Perhaps the most interesting scientific phenomenon commonly mistaken for paranormal activity is infrasound. People can’t hear sounds lower than 20Hz – the human ear just can’t pick them up. But we can experience the sounds as tiny, imperceptible vibrations. These vibrations can cause a sense of panic or fear in the pit of your stomach. They can even vibrate the eyeballs so that we seem to see strange things that aren’t really there.
Infrasound has been uncovered as the culprit behind more than one supposedly haunted house. The vibrations caused by nearby traffic, a current of wind, or even a simple ceiling fan can all cause terrifying experiences that seem all too real.
Still afraid of the dark?
Human beings are naturally inquisitive beings. We want to understand the world around us, and that’s why we seek answers for things that don’t quite make sense. This drive to understand can encourage myths about ghouls and demons to emerge.
But that curiosity is also the basis for scientific enquiry. Experimentation and analysis helps us to better understand the world around us, and we now have explanations for many phenomena that people once found terrifying.
So this Halloween, have some fun and get scared silly. But when the time comes to turn off the lights, remember that science has an answer for most of the things that go bump in the night.
A version of this article originally appeared on diamond.ac.uk