In short: The film Arachnophobia has had amazing staying power in spite of less than stellar reviews. How does it manage to still scare us 23 years after release? The key lies in its subject: spiders. People come prepared to be scared of spiders from birth. We explore the idea of 'preparedness' and how it helps sell tickets.
The causes of specific phobias (fear of specific things or animals, like fear of spiders) are varied and complex. A traumatic experience early on in life could trigger a phobia. If you see someone being scared of something you could grow to fear it as well. It is also genetic. The heredability of phobias to particular animals is around 45% according to a recent review published on the Journal of Anxiety Disorders. This is purely genetic effect as the researchers control for learning it from your parents and other possible ways you could get sensitised to a particular thing that causes you fear. To be clear if your mom or dad had an extreme fear of spiders you are 45% likely to have it even if you are adopted by David Attenborough.
I promise I will come back to the films, but first let me explain what preparedness is as it ties well with the bit about inheriting phobias. There is this chap called Martin Seligman. He is an American Psychologist and in 1971 he formulated his preparedness hypothesis. He observed that certain things are easier to learn than others. A good example would be how easy is to get you to fear sharks, heights, spiders, snakes and angry men and how hard it is to get you to fear cars, cigarettes and bacon double cheese burgers although these three are much more likely to kill you than any of the others. Martin speculated that the reason we find these associations easy to learn is because evolution has programmed us to fear them over million of years (not many cars 200,000 years ago when humans first walk the Earth I'm afraid). The evidence from the review I mentioned at the beginning seems to back it up.
If you want more evidence for this 'preparedness' all you have to do is look at horror films and their topics to see what we are prepared to fear: Jaws (sharks), Arachnophobia (spiders), Anaconda (snakes), Vertical Limit (heights), Friday 13th (angry men), Aliens (members of groups outside our own)... the list goes on. There is a paper that examines these key fears and the evolutionary reasons behind them. I love the name of the paper: 'Slithering snakes, angry men and out-group members: What and whom are we evolved to fear?'
The tendency in films now is to create 'superstimuli' by combining two or more of our genetic evolutionary fears: like Snakes on a Plane (snakes and heights) or Sharknados (sharks and storms). I suppose we should be looking out for Snakepider this Halloween!