Escape from the Man-Eating Snails: Phobias and Evolution

Is evolutionary inheritance a credible explanation of phobias?

Posted Jan 04, 2016

Conjure up an image of your ancestors from fifty thousand years ago, tirelessly migrating across continents, discovering fire, inventing the wheel, domesticating animals and building civilizations. However, during this process of social and cultural evolution they are continuously and mercilessly being hunted down by herds of giant, man-eating snails. The sick and lame are picked off one-by-one and children are consumed as mid-morning snacks as these rampant predators satisfy their appetite for food and carnage. During this particularly challenging time of pre-history, snails occupied the ecological predatory niche later to be filled by wolves, bears, tigers and alligators. Their cunning and ruthlessness knew no bounds and those humans who survived were the ones who were the first to spot the looming shadows of the giant snail herd, the percussive shrill sound of their hunting cries, their erratic rapid movements across the savanna, and their staring eyes as they fixated their human prey.

Only joking! Unfortunately, we’re unable to verify this historical scenario because giant snails left no fossil remains, but snail phobia is one of the commonest animal fears, and is often reported in the top ten animal fears worldwide. Have you ever been gardening with bare hands and – before you’re aware it’s happened – you’ve recoiled and shaken a snail or slug from your fingers? Interestingly, women also tend to be significantly more snail phobic than men – presumably because they were tastier to those ancient predatory giant snails and so had to develop stronger avoidance responses (only joking, again!).

The reason I’ve labored this fictitious example is because it helps to caricature a process that is very easy to slip into when it comes to trying to explain phobias. Most people lack an understanding of how they acquired their fears, and there is also a tendency for people to believe that they have had their fear for as long as they can remember. This failure to identify both a cause and an event that precipitated the fear can lead to the assumption that it is biologically pre-wired – “If I don’t recall it starting, then it must have been part of me forever”. This certainly rings true if the fear appears to be an adaptive one that could prevent harm, and fear of heights, water, snakes, spiders, etc. could all be construed in this way. The argument here is that heights, water, snakes and spiders have all been around for many tens of thousands of years, and could all be harmful in some way. Therefore, the genes of our ancestors who actively avoided these things would be selected for, and in this way a ‘fear’ or avoidance of them would be genetically handed down to us in the present day. This is certainly consistent with the fact that many people do exhibit fear of heights, water, snakes and spiders, but there is something disconcertingly easy about this type of explanation.

Our story about the giant snails provides one example of how this type of explanation might be fallacious. It is easy to believe how snakes and spiders (which can often be fatally venomous) might have been genuine threats to the survival and well-being of our ancestors, but surely not snails? – And snails are a very common object of phobic fears. It is also scientific bad practice to allocate a cause to an effect without providing any supportive evidence. To my knowledge there is no substantial evidence that snakes and spiders ever represented a significant survival selection pressure to our ancestors, and this would be critical for the biological pre-wiring of any fears to these animals. It is quite possible that some aspects of phobic fear are biologically determined, but it’s hard to substantiate this down to the level of individual specific phobias. For example, we have biologically pre-wired startle reflexes that react to rapid movement towards us, rapid unpredictable movement, looming shadows, loud noises, and staring eyes and that should be quite enough to help us to detect most types of predator with some urgency. So why would evolution also want to equip us with what would be redundant pre-wired templates to detect and avoid very specific predators such as snakes and spiders?

It is probably useful at this point to introduce you to a character called Pangloss from Voltaire’s novel Candide. Pangloss was someone who exhibited universal optimism, and American biologists Stephen Jay Gould and Richard Lewontin coined the term ‘Panglossian’ to refer to the misguided view that everything present in the world today exists because it has a specific purpose. So, according to the panglossian view, the task for scientists is not to discover whether a given characteristic (such as a phobia) has an adaptive function, but to clarify how the characteristic has served an adaptive function. This panglossian view (that everything that exists must be adaptive) generates what is known as the ‘adaptive fallacy’, and this fallacy is that if you’re trying to generate reasons why something might be adaptive you can do that quite easily no matter what it is you’re thinking about, and this appears to be how some psychologists have considered phobias. That is, those phobias that are most common (e.g. heights, water, spiders, snakes, blood, injury, etc.) must be so common because they have an adaptive function – that is, they enable people to successfully avoid potentially harmful and threatening things.

I have argued many times in the past against these types of panglossian views in which claim that phobias are evolutionary pre-wired adaptations – it smacks of a scientific ‘cop out’. In 1971, the famous American psychologist Martin Seligman wrote a short but very influential paper entitled “Phobias and preparedness” arguing that we hardly ever have phobias of things like pajamas, guns, electricity outlets, hammers, even though these things are likely to be associated with trauma in our world. Instead, we tend to have phobias of spiders, snakes, insects, heights, fire, deep water, etc. – things that have been around for a long time in evolutionary terms and were potentially harmful to our pre-technological ancestors. Seligman left us with the implication that most phobias are exaggerations of evolutionary adaptations that are pre-wired and that we are biologically prepared to acquire very rapidly given the appropriate learning conditions. This paper spawned a good twenty five years of research on the view that phobias were ‘biologically prepared’, and – even today – a glance at most introductory psychology textbooks shows that they still consider this evolutionary view to be an important potential theory of phobias. There was not a lot of solid evidence in Martin Seligman’s seminal paper to support the view that common phobias exist because of their adaptive evolutionary function, and as I recall, he only authored a couple of other tangential papers on this topic before moving on to other things, leaving us all to thrash around in the void trying to put some evidential flesh on these speculative bones. While adaptation through natural selection is one possible mechanism by which common modern-day phobias could exist, Gould & Lewontin also point out that some modern-day characteristics arise from random genetic sampling, and others may exist because they are associated with other structures and behaviours that do confer a selective advantage and not because they directly increase survival themselves.

To add a further element of skepticism to this adaptionist view of phobias, this view doesn’t provide a genuinely balanced picture of how phobias might be caused. If you look at the top ten list of animals that kill human beings each year you probably won’t find the spider amongst those ten (in all probability the list would be headed by the mosquito followed by other humans). But you will find animals such as lions, elephants, tigers and bears in the list – all are animals that people rarely acquire a clinical phobia to. It’s true, if you were confronted by one of these animals in a confined space you would be right to be very scared, and would be well advised to run like the wind at the first opportunity. But this adaptive fear is not the same as phobic fear. Very few people attend phobia clinics with debilitating fears of tigers or bears, hardly anyone gets a rush of fear-laden adrenaline when they hear the word lion in a conversation, and people just do not turn away in panic when shown a picture of an elephant. All of these reactions are certainly true of people with severe snake or spider phobia (and even in many cases, slug phobia!). Indeed, most of us happily send our children to bed with cuddly replicas of bears and make them watch TV programmes depicting tigers, lions and elephants as good-natured cartoon characters – hardly the stuff that would be expected if evolution was constantly telling to us beware of them.

To put this discussion into perspective, the adaptationist or evolutionary view of phobias might seem compelling because it appears to explain why common phobias focus on things that have been around for a long time (in evolutionary terms), why it might be adaptive to avoid or fear these things, and why sufferers can only rarely recall when and how their phobia started. However, it is still a highly speculative approach.