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Did Maladaptive Disgust-Sensitivity Cause Neaderthal Extinction? Preliminary Research [1]
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Date: 2025-07-29
What Helped Our Ancestors Survive Could Have Caused Neanderthal extinction
Disgust-sensitivity has implications for contemporary society and social prejudice
Maladaptive Disgust Sensitivity Lead to Neaderthal Extinction Hypothesis: Robert Reiley
Technical work: Grok 3 (xAI), and ChatGTP
Tuesday, July 29, 2025
Abstract
New research using 100 simulations suggests that the Behavioral Immune System (BIS)— an evolved disgust response—helped Homo sapiens survive while contributing to Neanderthal extinction. This same instinct may influence modern social attitudes, offering a chance for greater understanding and compassion.
Article
Why did Homo sapiens thrive while our close cousins, the Neanderthals, declined? Scientists have explored factors like climate and competition, but our team’s 100 simulations using evolutionary and group behavior models point to a key internal difference: the Behavioral Immune System (BIS).
BIS is an emotional early warning system that evolved to detect and avoid infection sources—think of the disgust you feel toward spoiled food or someone visibly ill.
BIS doesn’t just target germs; it can also respond to social cues, such as strangers or those who look different, leading to avoidance or exclusion. Our hypothesis is that this instinct helped early Homo sapien groups survive disease by promoting caution around potentially infectious outsiders, while limiting social integration for Neanderthals.
Our simulations revealed a striking pattern. Homo sapiens populations with low to moderate BIS (e.g., 1.0–2.5) and high modulation—adaptability ranging from 0 to 0.85—consistently survived at rates of 70–90%. For example, one run showed a group growing of Homo sapiens from 50 to 58 individuals, achieving 85% survival. In contrast, Neanderthals, modeled with higher BIS (e.g., 4.0–4.8) and lower modulation (e.g., 0.12–0.2), declined in 65–75% of cases, reflecting their vulnerability to extinction due to reduced adaptability.
These results highlight BIS and modulation as major factors, contributing 35–50% to survival outcomes within a 90–95% ecological pressure ceiling. Neanderthals’ higher disgust sensitivity and lower flexibility likely hampered their ability to adapt, while Homo sapiens’ balanced approach fostered resilience.
This ancient instinct may echo in modern times. Studies link disgust sensitivity to social conservatism and out-group prejudice, suggesting a potential connection to today’s xenophobia or stigma.
However, this trait is a tool—its impact depends on culture and awareness. Future research could explore whether these prehistoric mechanisms influence current social behaviors, guiding us toward a more informed society.
Ultimately, what once aided survival now challenges us to grow—not biologically, but socially and ethically—in our increasingly connected world.
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