It shouldn’t work, but somehow it does. Ever since Doctor Who first aired in 1963, the series has been internationally recognisable thanks to one of the most ridiculous space-creatures ever conceived; a master race of intergalactic pepperpots, armed with a sink plunger and an egg whisk, who (according to popular mythology), are hell-bent on conquering anywhere, provided it doesn’t involve stairs.

But don’t let that fool you. For more than 45 years, the Doctor’s arch-enemies, the Daleks, have been striking fear into young viewers with their chilling war-cry of “Exterminate!”. Like the Doctor himself, they have become an icon of British culture. For many, hiding behind the sofa when they appear is virtually a rite of passage.

Now, with the new season of Doctor Who nearly upon us, a Cambridge University academic has turned his mind to what makes the Daleks so terrifying. Writing in a new paper, Dr Robin Bunce – normally a researcher in intellectual history – explores why these unlikeliest of sci-fi foes bettered the rest, and became the most menacing alien ever to invade the small screen.

His answer has nothing to do with their often-cited, non-human appearance, nor their weird, electronic voices. In fact, Dr Bunce believes that the Daleks succeed because they offer us a moral lesson in what it means to be human in the first place. They terrify us because the evil they represent is a more precise definition than that of philosophers stretching from Socrates to Kant. They are chilling, he argues, because they are a vision of what we ourselves might become.

“The reason the Daleks are evil is because we recognise that they were once better,” Dr Bunce explained. “They are the nightmare future we dread.”

“According to their back-story, once they were capable of genuine emotion and real moral good. Now they are sexless, heartless brains, shut up in machines incapable of intimacy, who have forgotten what it means to laugh and no longer think of themselves as individuals. We recognise the Daleks as evil because they have lost all that we hold most dear.”

The Daleks are perhaps Doctor Who’s greatest success. After their first appearance, they boosted ratings and turned the show into a national phenomenon. “Dalekmania” became a common term and “Dalek” itself now commands its own entry in the Oxford English Dictionary.

Almost half a century later, their popularity shows little sign of subsiding. A 2008 survey by the National Trust found that while only 53% of children could identify an oak leaf, nine out of 10 could identify a Dalek. In 2010, readers of the science fiction magazine SFX voted the Dalek as the all-time greatest monster, beating both Godzilla and Gollum from The Lord Of The Rings.

Dr Bunce, a bye-fellow at St Edmund’s College, Cambridge, decided to explore what it is that makes these villains so villainous in the first place. He returned to the original 1963 script for “The Daleks”, in which they first appeared, which was written by their creator, Terry Nation. In the story, the Doctor and his companions arrive on a post-apocalyptic planet, Skaro. They encounter both Daleks and the more peaceful Thals.

His paper concludes that the Daleks are a more powerful representation of evil than most of their extra-terrestrial competitors. The fact that they are so morally repugnant is, he suggests, what makes them both frightening for viewers and (as a result) an enduring success. This stems from a very modern take on the idea of evil.

Nation’s script stresses the Daleks’ lack of humanity as the essence of their evil nature. This in itself is nothing new – since time immemorial evil people have been described as animals, because animals are not rational. Socrates had a similar view, arguing that reason and knowledge make humans good.

Daleks are different, however, because they are more rational than humans, but also far more evil. Instead of losing their capacity for rational thought, they have lost their ability to feel. As the plot of ‘The Daleks’ unfolds, we discover that after an apocalyptic “Neutronic war”, they retreated into metal shells in which their emotions withered. The fact that they were once better, Bunce says, makes them horrifying: “We dread becoming like them.”

For viewers in 1963, living shortly after the Cuban Missile Crisis, some of the connotations in Nation’s original script would have been more relevant than they are today. The surface of Skaro resembles contemporary ideas about how Earth might look after a nuclear war. The “Neutronic War” refers to the spectre of the neutron bomb – which could emit more radiation than an atomic bomb, but with a lower blast. As a result, it was more selective in wiping out humans and animal life, but not buildings and infrastructure. The Daleks represented the consequences of these very real nightmares at the time.

In the 21st century, Bunce suggests that they embody a more general fear, about the triumph of technology and science over humanity. Once creatures like us, they have mutated into something far more sinister. Inside their metal shells, they have oversized brains representing the dominance of scientific reason, at the expense of shrivelled bodies. This fear about what we might become, through scientific advancement, has existed since Victorian times. Like the Daleks, it shows little sign of abating today.

Bunce considers the Daleks a lesson in moral philosophy: “The final lesson is that moral progress is achieved by enlarging the moral imagination, not by increasing our knowledge or becoming more rational,” he said.

“Empathy is the key. We are more likely to act well when we understand that our enemy, however different they may seem, is part of a community who will grieve if they are harmed. The Thals are good because they love each other. The Daleks don’t and that’s why they’re evil.”

A peculiar breed of evil, in fact, which has also made them a terrific success.

The study appears in the book, Doctor Who and Philosophy, which is published by Open Court Books: http://www.opencourtbooks.com/books_n/doctor_who.htm