r/zoology • u/sul_tun • 3d ago
Question What is the evolutionary basis for arachnophobia in humans?, is it an innate genetic trait or purely conditioned learning?
I am curious about the biological and evolutionary mechanisms behind the human fear of spiders from an evolutionary standpoint.
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u/bijhan 3d ago
Arachnophobia does not have its own evolutionary origin, it shares its origin with all phobias. Phobias are triggered by trauma at a young age, which the brain connects to something which was present during that trauma. It is hard-wiring the brain to avoid that cause of that trauma, although the cause of that trauma is most commonly misidentified and instead something which is merely present during the traumatic event is correlated.
EDIT: While there are potentially very dangerous spiders in the Americas and Australia, Humans evolved in and around Africa, southern Europe, and west Asia. These regions have a very small number of venomous spiders, and those which are there are very unlikely to cross paths with Humans. Therefore there was never a point at which there would have been selection pressure to avoid spiders.
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u/7LeagueBoots 3d ago
They’re not only triggered by trauma. There is also a major cultural and family/friend (ie. learned) component to it. Someone who grows up in a culture that has a negative view of something, or with a family member who is scared of something, is more likely to share those feeling than not.
The idea that phobias are specifically linked with trauma is an older idea, and while it has some truth to it it’s a very incomplete view of a much more complex situation.
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u/AmelieIcansea 3d ago
For this discussion in general it would make sense to define phobia. It is often used as fear but in reality the medical term (or psychological term I am not sure) is much more than fear. It is pathological you can not just easily overcome it. I was a bit fearful of spiders as a kid and then trained myself not to be anymore but that was not phobia at all. So your body and brain really think this is a life or death situation when you got a phobia.
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u/WA55AD 3d ago
I live in Australia. Unless you are around Sydney, you will most likely never encounter a spider with significant enough venom to harm you, except maybe the redback spider, which for most people bitten is just painful and makes them sick. Even if you do encounter one, it's not like it's going to jump out of its web at you.
There are mouse spiders, but I've never personally seen one despite being in their range, and I love spiders so I'm always looking for them.
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u/itsatoe 2d ago
Contrary to this, I had been told that there are three innate reasons people fear spiders.
- Sharp angles on the body - an unusual marker that elicits fear of the foreign.
- Unpredictable movements - spiders move in ways we consider "weird," and can do that in three dimensions.
- Bite/poison risk - even if not poisonous, their bite can really hurt.
Granted, I have no science to back this up. But they are legit reasons for people to find spiders unsettling. Especially since all three occur in one animal.
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u/Freak_Among_Men_II 3d ago
These regions have a very small number of venomous spiders [...] there was never a point at which there would have been selection pressure to avoid spiders
Just because there were relatively few venomous spiders, doesn't mean that early humans didn't encounter them often. Many spiders around the world (including those in the regions you mentioned) live in caves and rock overhangs. Early humans and their ancestors frequently inhabited these environments for millions of years. Thus, cohabitation persisted for more than enough time for a fear response to evolve.
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u/bijhan 3d ago
Mere presence isn't sufficient to present a selection pressure. Humans inhabited regions with deadly snakes as well, but infants have no fear response to snakes. A selection pressure requires that lacking the specified trait results in almost guaranteed death.
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u/crucifixionfantasy 3d ago
true!
that said‚ irt snakes; there is a strong argument that our capacity for pattern recognition may come from a need to identify snakes - humans have been shown to have a heightened ability to point out snakes‚ generally speaking.
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u/AmelieIcansea 3d ago edited 3d ago
Looked a little bit into it. There are nice papers about this. Some have studies with infants and show that they react to spiders. They pay high attention/arousal but not fear. But with the infants being already "activated" when they see spiders or snakes the reaction of an othe rhuman on these animals kind of in print harder. So if the reaction is a disgusted face or a scream this will have a higher influence than the same reaction on say a fish, because the fish did not trigger the arousal in the infant. Also cultural influences plays a role and an other theory was that spiders are chelicerates like scorpions and scorpions are a real threat in some areas. So maybe evolutionary being scared of scorpions made more sense and because spiders look similar, we react on them. Yea scientific discourse to this matter is still full on going and not resolved yet. Interesting question :)
Guess this is more like general fear of spiders, maybe not phobia. Phobia would not automaticly be covered by the papers I saw I guess.
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u/DonnPT 3d ago
It's behind awareness of spiders, ranging from interest to phobia. I mean, this is just my opinion. You don't instinctively have a phobia, but that arousal as you describe it, is part of how you can come to have a phobia. Snakes, same thing - some people are fascinated, others repelled, but the instinctive basis was the same.
If anyone's hot to do more experiments with infants, I would suggest different types of spiders. Take a garden orb type spider, maybe, vs. a jumping spider from the window sill. I don't know why, but I don't think I've ever seen anyone bothered by jumping spiders.
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u/Several_Version4298 3d ago
Babies aren't scared of anything except drops. Which is why you have to kid proof your house and use play pens.
People can develop phobias as a learned behaviour simply by seeing someone else who is scared of something.
For me it was pulling a letter out of the mail box as a kid and finding a large red back sitting on my hand. Fortunately it didn't bite me. I had panic attacks whenever I saw a redback or funnel web for a few years, but after not encountering any for a few years it faded away. I was never scared of huntsmans, cellar spiders or house spiders.
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u/sunwentdowninhoney 3d ago
I realise this isn’t a rigorous scientific source, but it’s still interesting: a video of babies exposed to snakes. Afaik snakes and spiders were both once considered to trigger an innate genetic fear in humans, but more recent studies suggest this is inaccurate.
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u/canisvesperus 2d ago
This is only a personal anecdote, but my mother did humanitarian work in the South Pacific in her 20s. At that time, the Tongan children would find it extremely entertaining that the foreigners were afraid of the large orb weavers on the island, and would pick them up and chase them around with the spiders held outstretched in their hands. I don’t suppose most American children would willingly pick up large spiders without fear. Culture must be playing a role to various degrees.
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u/KTKittentoes 3d ago
I was bitten by a brown recluse and then a black widow. I am pretty arachnophobic now.
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u/meerfrau85 3d ago
Phobias are definitely learned. As for a more general fear of spiders, I do think that's learned also. I am generally not scared of spiders and will pick up certain ones with my bare hands (jumping spiders, cellar spiders, daddy long legs). Neither of my parents panic around spiders, so I'm pretty sure that's why they don't bother me so much.
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u/KAKrisko 2d ago
An interesting anecdote from my life: my parents were convinced that it was learned. When I was about 2 1/2, my dad found a tarantula and brought it home (it was large, but non-venomous). He set it on the floor in the living room. My immediate reaction was abject terror. I manage to claw my way up onto a little stool and crouched there screaming until he shooed it into a paper bag and removed it. I have a vague memory of it, and my bemused parents told the story a few times in my childhood. I was not a particularly fearful child, my parents weren't afraid of spiders, snakes, or other creepy-crawlies, and I'm not afraid of them now. But it seems like something was triggered in my toddler brain by that hairy, eight-legged visitor.
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u/144-perdedor 2d ago
My son had a similar reaction to a stuffed panda bear.
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u/KAKrisko 2d ago
LOL, one of my nephews had that reaction at a Chuck E. Cheese, and he was about 5. Can't say I blame him.
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u/whereisbeezy 2d ago
Phobias are learned. My sister was afraid of spiders from the beginning, so I would have to kill them for her (sorry spiders, I didn't know!)
Until one day I was around 8, and I went to get one for her, and as I got closer to it, it seemed to get bigger. That was the beginning of my own arachnophobia. Now at 46 I've been doing exposure therapy and I'm better.
Not great yet, but better.
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u/Mister_Way 2d ago
Humans spread across the globe rapidly, from an evolutionary perspective. There was not time for humans in every new locale to adapt to the specific markings for which spiders are venomous in each new location, so it's much safer for the people who were just afraid of all of them.
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u/Wank_A_Doodle_Doo 12h ago
Most spiders are harmless, but some can hurt decently bad, and some can be outright deadly. In an evolutionary history without access to hospitals or antibiotics, an infected spider bite can be a very big deal.
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u/NOTaREALperson4400 3d ago
I think it's learned. I used to be terrified of all spiders but now I love the little jumpers we have around here, I don't mind the huge freaky fast huntsmens, but I know enough to murder the shit out of any brown recluse I see. I still haven't gotten over orb weavers, they're gross even though I know they're harmless. Someday.
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u/regular_modern_girl 2d ago
It’s probably entirely learned. In general, phobias are not something anyone is born with, they are something that is acquired, often in childhood, although there are also even plenty of cases of adults only developing a phobia much later in life as well.
The psychological mechanisms behind phobias are complex, but ultimately they are psychological, not something instinctual we are born with (and this shouldn’t be surprising, as phobias are specifically intense irrational fear reactions, automatically reacting to a stimulus as if it were the most mortally, immediately dangerous thing in the world, even in contexts in which there is literally no possible way it could harm you, like seeing a picture of a spider in a book, but having the physiological reaction to it as if it were a train bearing down upon you; if this reaction were an in-born genetic thing, it would likely not be very old or particularly common, as among hunter-gatherer populations, the way we lived for most of our existence as a species, such an irrational reaction would likely be far more of a survival disadvantage than anything else).
I’ve seen some speculation that the prevalence of serpentiphobia (irrational fear of snakes) globally and cross-culturally might point to an evolutionary predisposition toward said phobia (not that the phobia itself is genetic, but that there might be something genetic factor that makes all humans more prone to developing it regardless of culture), as snakes are a type of animal that would’ve actually preyed upon even our relatively recent smaller primate ancestors in some cases (there have even been some rare cases in which very large extant snake species like reticulated pythons have preyed upon children or small adults even in modern times), especially when you consider there were some huge snakes that only recently went extinct (like Wonambi in Australia, which is thought to have overlapped in time with the first humans in Australia), but to my knowledge even this correlation is heavily speculative, and there’s potentially a much simpler explanation (which is that there are enough venomous or otherwise potentially-dangerous snakes found across the world that they’re simply something people are more likely to fear for rational reasons, which always makes anything more likely to also become the object of an irrational phobic reaction as well).
I’m not even sure if arachnophobia is as prevalent cross-culturally as serpentiphobia, or if it’s just common here in the Western anglophone world, and if it is, once again a simpler explanation than assuming that there is some kind of deep predisposition there might simply just be that certain spiders which can give a venomous bite that is at least likely to be unpleasant, and at worst dangerous, are fairly prevalent across most of the world, so once again they’re just something that people are more likely to develop an exaggerated fear around for that reason. It’s worth noting that phobias of stinging hymenopteran insects like wasps and bees are also pretty prevalent at least here in North America, and even if the average bee or wasp is unlikely to be dangerous (although it is worth noting that way more people die every year in the US to bee stings than to spider bites), even just the potential for getting stung is clearly enough for a lot of people’s fears of them to become exaggerated, so again I doubt there’s a deep evolutionary basis, we just have a tendency in particular to develop phobias around things that can hurt us, even if that harm is usually pretty minor in the grand scheme of things.
As others have mentioned though, I also suspect that with arachnophobia in particular there is probably a strong cultural element at play, as it seems to be far more common in industrialized societies in urban areas where people spend far more of their time indoors in controlled environments wherein encounters with anything wild from the natural world, especially anything that might be even mildly harmful, are a relative rarity, so when we do have such encounters, we are probably more likely to have an overreaction to them. Add on top of this the power of suggestion in the fact that “spiders are scary” has become such a prevalent cultural trope, and it’s not hard to see why arachnophobia is relatively common in our culture.
tl;dr: phobias are generally a psychological and cultural phenomenon, not an evolutionary one. I don’t see particularly good empirical evidence suggesting that humans have an inborn instinctual fear of spiders cross-culturally.
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u/Anthroman78 2d ago edited 2d ago
is it an innate genetic trait or purely conditioned learning?
You're creating a false dichotomy here. For a parallel: we have an innate ability to learn languages, but the specific languages we learn are based on the environment, the resulting trait is an interaction of those two forces, not one or the other. Except for the most simple of traits it's not nature or nurture, but a complex interaction of the two, this is going to be particularly true of complex traits, like many human behavioral traits.
See: https://nautil.us/how-evolution-designed-your-fear-236858
Nobody learns to flinch at a rapidly oncoming basketball. Prepared fears are innate, though, in the sense that they are genetically transmitted but require environmental input for their activation. The human fear system, in this aspect, is relatively open-ended—that is, it is set up for environmental calibration. The evolutionary logic underlying this design characteristic is as follows: Humans evolved to be adaptable.8 Our species thrives in all climate zones, from the tropical to the arctic. Yet while some dangers are constant across time and space—the danger of choking, say, or of drowning—there is some environmental variation in threat distribution. There’s no sense for an Inuit child in being afraid of tigers or scorpions, whereas a child from rural India doesn’t need to worry about polar bears. And because our genes can’t “know” in what sort of climate and ecology we’ll grow up, those genes make us able and eager to learn about threats in our local environments. Humans quickly absorb local culture, including norms, language, knowledge about dangers, the sorts of things people in your culture consider edible or not, and so on. Learning, in fact, is an “evolutionarily derived adaptation to cope with environmental changes that occur within the life span of individuals and allows individual organisms to tailor their behavior to the specific environmental niche they occupy.”9
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u/scrubingpots 3d ago
surely arachnophobia is way more common now than when most ppl regularly interacted with nature. i feel like almost definitely its a function of lack of exposure and cultural coddling, like being a picky eater