Summary: Do we react to a loaded gun the same way we react to a venomous snake? New research indicates that while both modern and ancestral dangers produce physiological responses, threats with deep evolutionary roots provoke stronger and more distinct bodily reactions.
By recording electrodermal activity (skin resistance, a proxy for sweating) alongside participants’ self-reported fear, researchers observed that ancestral threats—especially heights and snakes—evoke more frequent and more intense involuntary responses than modern dangers such as firearms or airborne disease cues.
Key Facts
- Study design: 119 volunteers viewed images representing four threat types: venomous snakes and heights (ancestral threats) versus firearms and airborne disease (modern threats).
- Physiological measure: Electrodermal activity (skin resistance) tracked involuntary arousal. Greater sweating (lower skin resistance) signaled stronger autonomic activation.
- Snake paradox: Snakes produced the highest subjective fear ratings, yet reported fear did not always align with sweat responses, implying a powerful unconscious component to snake-related processing.
- Heights stand apart: Images of heights triggered the most frequent and distinct skin responses, indicating that not all ancestral threats are processed identically.
- Modern threats register too: Firearms and airborne disease images did provoke physiological reactions, but these were generally less intense than the responses to heights or venomous snakes.
Source: PLOS
Fear-eliciting images of modern and ancestral threats are both capable of producing physiological responses, but ancestral dangers often generate stronger skin resistance changes, according to a study published March 18, 2026 in the open-access journal PLOS One by Eva Landová and colleagues at Charles University, Czech Republic.
The research aimed to clarify whether modern threats activate our defensive systems as strongly as ancestral threats that shaped human evolution. Participants viewed photographs depicting venomous snakes, precarious heights, firearms, and airborne disease cues (for example, people wearing masks or sneezing) as well as neutral control images of leaves. For each image, the team recorded skin resistance—how strongly the skin impedes electrical current, which decreases with increased sweating—and collected subjective fear ratings.
Overall, images depicting threats produced more frequent electrodermal reactions than control images. Photos of heights provoked the most frequent responses, followed by snakes, firearms, and airborne disease. In terms of response magnitude, heights and venomous snakes produced the largest skin-resistance changes, indicating stronger physiological arousal.
Importantly, the study found subtle but meaningful distinctions among ancestral threats themselves. Responses to heights differed from responses to snakes in several respects, showing that grouping threats simply by evolutionary origin misses important differences in how the body responds.
Although participants rated snake images as the most fear-inducing overall, subjective fear did not always predict the size of the physiological reaction for snakes. By contrast, self-reported fear correlated more closely with skin-resistance changes for heights, firearms, and airborne disease images. This pattern suggests that snake-related reactions may be driven more by fast, unconscious processing than by conscious appraisal.
The authors note some limitations. Electrodermal changes develop relatively slowly; presenting many images in a short session could create overlapping responses to multiple stimuli. The experimental setup also did not permit separating purely instinctive responses from those influenced by conscious thought, which may vary across threat types.
Despite these caveats, the findings challenge a simple binary between ancestral and modern threats. Both categories can elicit autonomic responses depending on how salient or relevant the stimulus is, but certain ancient threats retain a clear physiological edge.
Eva Landová summarized: “Not all evolutionary threats are alike. We observed pronounced differences in responses to heights versus venomous snakes—these two ancestral dangers produced distinct patterns in nearly every measure.”
Iveta Štolhoferová added: “For snake images, people’s subjective fear reports often did not match their skin-resistance changes. That mismatch points to stronger unconscious processing of snakes compared with other threats.”
Markéta Janovcová reflected on stimulus selection: “Choosing images that reliably elicit reactions is surprisingly difficult. Even after years of work, predicting which pictures will provoke the strongest responses remains challenging.”
Funding: This project was supported by the Czech Scientific Foundation (GAČR), project No. 22-13381S, awarded to E.L. The funder had no role in study design, data collection, analysis, decision to publish, or manuscript preparation.
Key Questions Answered:
A: Humans evolved neural systems tuned to detect and respond quickly to certain ancient dangers like snakes. Those circuits can trigger automatic physiological reactions—such as sweating—before conscious awareness catches up. Modern threats like guns are recognized by our conscious knowledge, but they may not always engage those same deep, automatic pathways as potently.
A: Yes. Images of heights produced the most frequent and among the strongest physiological responses in this study. Avoiding a fall has been a persistent survival challenge throughout human evolution, so our bodies appear to have a pronounced and specialized alarm for gravity-related threats.
A: Many of these responses are involuntary and thus difficult to eliminate entirely. Nevertheless, modern threats do trigger physiological reactions, suggesting that learning and cultural experience can shape our responses. Therapy and repeated, controlled exposure can reduce fear for many individuals, even if baseline autonomic tendencies remain.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- The journal paper was reviewed in full.
- Additional context was added by 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
When people encounter potentially dangerous stimuli, the body and mind often launch a cascade of physiological, emotional, and cognitive responses intended to reduce harm. Whether modern threats activate this defensive system as robustly as ancestral threats has remained unclear.
This study compared skin-resistance responses to four threat categories—venomous snakes, heights, airborne disease cues, and firearms—using recordings from 119 participants and their subjective fear ratings. Threat images produced more frequent skin-resistance changes than control images, with the highest reaction probability for heights, then snakes, firearms, and airborne disease. The largest response amplitudes occurred for heights and venomous snakes. Higher subjective fear generally increased the likelihood of a skin-resistance change. Although ancestral threats showed some advantage, the distinct pattern for heights versus snakes indicates that simply labeling threats as ancestral or modern does not fully capture the complexity of human defensive responses. Both ancestral and modern stimuli can trigger similar electrodermal reactions depending on how salient and relevant the stimulus is to the observer.