Summary: Do we fear a loaded gun the same way we fear a venomous snake? A new study suggests that while our bodies react to both, our “evolutionary” fears trigger deeper, more intense physiological responses.
By measuring skin resistance (sweat) and subjective fear, researchers found that ancient threats—specifically heights and snakes—elicit more frequent and intense physical reactions than modern threats like firearms or diseases.
Key Facts
- The Comparison: Researchers tested 119 participants against four threat categories: Venomous Snakes and Heights (Ancestral) vs. Firearms and Airborne Disease (Modern).
- Sweat as a Metric: Skin resistance (electrodermal activity) was used to measure involuntary physical arousal. Ancestral threats triggered significantly more intense sweating than modern ones.
- The “Snake” Paradox: Snakes were rated as the most subjectively terrifying, but people’s reported fear didn’t always match their physical sweat response. This suggests snakes trigger unconscious, instinctive processing that bypasses our conscious mind.
- Heights are Unique: Responses to heights were the most frequent and distinct, behaving differently from all other categories, proving that “evolutionary origin” doesn’t mean all ancient fears are processed the same way.
- Modern Fear Limitations: While firearms and diseases (like images of masks or sneezing) caused physiological reactions, they were less intense than the primal “fight-or-flight” triggered by heights or venomous animals.
Source: PLOS
Fear-eliciting images of modern and ancestral threats are equally likely to evoke physiological reactions, despite their distinct evolutionary origins, according to a study published March 18, 2026, in the open-access journal PLOS One by Eva Landová from Charles University, the Czech Republic, and colleagues.
However, ancestral threats such as heights and venomous snakes trigger greater skin resistance responses, a measure of sweating, compared to modern threats and harmless stimuli.
Fear is an adaptive emotion that can warn us and prepare us to promptly and adequately respond to threats. After encountering a potentially dangerous stimulus, the human body and mind might react with a cascade of physiological, emotional, and cognitive responses to minimize impending harm. However, whether this system can be activated by modern threats to the same extent as ancestral threats has been unclear.
To fill this knowledge gap, Landová and colleagues compared the physiological and emotional responses of 119 participants to photos of two ancestral and two modern types of threats: venomous snakes, heights, firearms, and airborne disease (e.g., pictures of medical staff or people wearing masks, sneezing, or coughing). They also presented control photos of leaves.
The researchers measured skin resistance (i.e., how much the skin impedes electrical current), which decreases with increased sweating, and the participants rated the stimuli according to the level of fear they elicited.
The researchers found that participants experienced a greater sweating reaction to photos of all presented threats compared to control photos. Reactions to photos of heights were most common, with reaction frequency being similar across snakes, firearms, and airborne disease. Reactions were observed to be most intense for heights and venomous snakes, compared to firearms and airborne disease.
Although the results suggested a slightly heightened response to the ancestral threats of heights and venomous snakes, responses to the threat of heights differed in several respects from responses to the threat of venomous snakes, demonstrating that the ancestral origin of such threats cannot fully explain all aspects of the response.
Venomous snakes were rated subjectively as the most fear-eliciting threat of those presented, though those who reported the greatest fear were not necessarily those who showed greatest physiological reactions. Subjective fear ratings correlated better with sweating responses for the heights, firearms, and airborne disease threats.
The authors note that skin resistance changes occur relatively slowly; as they presented several threats to participants within a short space of time, they might have detected overlapping physiological responses to multiple threats. Additionally, their study design did not enable separation of instinctive responses from conscious responses, which might differ by threat category.
Nonetheless, they suggest that the physiological responses they measured argue against a simple distinction between ancestral and modern threats, calling for more research to further our understanding of how we react to a range of perceived threats.
Eva Landová adds: “The key finding is already in the title: not all evolutionary threats are alike. We found clear differences in how people respond to heights and venomous snakes – in fact, their responses to these two types of threats differed in almost every aspect.”
Iveta Štolhoferová adds: “For snake images, participants’ subjective reports did not match their skin resistance responses. This suggests that reactions to snakes are influenced by unconscious processing more strongly than reactions to other threatening stimuli.”
Markéta Janovcová adds: “I always enjoy selecting the stimulus images. I often try to guess which ones will trigger the strongest reactions – but even after many years of research, it is still surprisingly hard to predict.”
Funding: This project has been supported by the Czech Scientific Foundation (GAČR), project No. 22-13381S, awarded to EL, https://www.gacr.cz/en/. The funder did not play any role in the study design, data collection, analysis, decision to publish, or preparation of the manuscript.
Key Questions Answered:
A: Your “modern” brain understands that a gun is a tool of high lethality, but your “ancient” brain has had millions of years to hardwire a specialized circuit for spotting and reacting to snakes. This study shows that the snake response is so deep it’s often unconscious—your skin starts sweating before your conscious mind even realizes you’re afraid.
A: Yes. Heights triggered the most frequent reactions in the study. Unlike a gun, which is a relatively new invention, falling from a height has been a lethal risk since our ancestors lived in trees. Our bodies have a highly refined, distinct physiological “alarm” specifically for gravity-related threats.
A: Because these reactions (like sweating) are involuntary, they are difficult to switch off. However, the study shows that modern threats do trigger physiological responses—we are beginning to evolve “scripts” for things like disease and weapons, they just aren’t as physically intense as the ones written into our DNA over eons.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this fear and evolutionary neuroscience research news
Author: Hanna Abdallah
Source: PLOS
Contact: Hanna Abdallah – PLOS
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Subjective and psychophysiological response to pictures of ancestral and modern threats: Not all evolutionary threats are alike” by Iveta Štolhoferová, Tereza Hladíková, Markéta Janovcová, Šárka Peterková, Daniel Frynta, and Eva Landová. PLOS ONE
DOI:10.1371/journal.pone.0343680
Abstract
Subjective and psychophysiological response to pictures of ancestral and modern threats: Not all evolutionary threats are alike
After encountering a potentially dangerous stimulus, the human body and mind might react with a cascade of physiological, emotional, and cognitive responses to minimize impending harm.
However, whether this system can be activated by modern (ontogenetic) threats to the same extent as by ancestral (evolutionary) threats remains uncertain, since the existing results are ambiguous.
In this study, we aimed to compare the skin resistance (SR) response to ancestral and modern threats; the focal categories were venomous snakes, heights, airborne diseases, and firearms.
We collected recordings of 119 participants, about 30 per threat category, supplemented by participants’ rating of the stimuli according to elicited fear. Results showed that participants reacted (SR change) with higher probability to all experimental categories than to control stimuli, with the most frequent reactions to photos simulating the threat of heights, followed by snakes, firearms, and airborne diseases.
The largest amplitudes, indicating response intensity, were observed for heights but also for venomous snakes. Further examination showed that higher subjective fear corresponded to an increased probability of SR change.
Although the results suggest a slight advantage for ancestral threats, responses to the threat of heights differed in several respects from responses to snakes, demonstrating that ancestrality-based categorisation cannot capture all aspects of the response.
Moreover, both ancestral and modern threats can evoke similar electrodermal responses, depending on subjective stimulus salience and/or threat relevance.
