The coronavirus disease-2019 pandemic presents a unique opportunity to test the evolutionary hypothesis that women show stronger self-protective reactions than men to environmental threats. In their target article, Benenson et al. focus mainly on sex differences in COVID-19 mortality rates and the activation of the physiological immune system. Their argument can be expanded by analyzing sex differences in the activation of the behavioral immune system and women's emotional reactions to the risk of COVID-19 infection.
The physiological immune defense is merely reactive because it is triggered only after the infection has occurred within the body. Schaller (Reference Schaller2011) has convincingly demonstrated that selection pressures have reinforced our defenses against infections by causing the evolution of a behavioral immune system that is separate from, and complementary to, the physiological immune system. The behavioral immune system includes a set of proactive mechanisms that inhibit contact with pathogens in the first place. These mechanisms offer a sort of psychological and behavioral prophylaxis against infection. The two emotional and interrelated reactions associated with the activation of the behavioral immune system are fear of infection and pathogen disgust sensitivity (Troisi, Reference Troisi2020). Based on the evolutionary hypothesis of sex differences in self-protection, the COVID-19 pandemic is expected to have caused more intense fear of infection and pathogen disgust sensitivity in women than in men.
Data on fear of infection support the evolutionary hypothesis. A recent scoping review based on 14 studies conducted in different populations showed that female gender was the most consistent predictor of fear of COVID-19 (Quadros, Garg, Ranjan, Vijayasarathi, & Mamun, Reference Quadros, Garg, Ranjan, Vijayasarathi and Mamun2021). Compared to studies focusing on fear of infection, reports on sex differences in disgust sensitivity are fewer but their findings are anyway consistent with evolutionary predictions. Using a large nationwide Chinese sample, Ding, Yang, Ji, and Guo (Reference Ding, Yang, Ji and Guo2021) found that the COVID-19 outbreak increased levels of pathogen disgust sensitivity more in women than in men. In a large sample of Australian university students, Stevenson, Saluja, and Case (Reference Stevenson, Saluja and Case2021) found that the increase in disgust sensitivity observed during the COVID-19 pandemic was significantly greater in women than in men.
The COVID-19 outbreak is a natural experiment that not only confirms the existence of sex differences in self-protective reactions to environmental threats but also enriches our understanding of their evolutionary-developmental origin. Studies of the activation of the behavioral immune system triggered by the COVID-19 pandemic have demonstrated that evolutionary explanations of individual differences in self-protection should not be based only on parental investment and sexual selection theory, as Benenson et al. have done in their target article. A comprehensive evolutionary model of greater or lower levels of self-protection must also incorporate the individual differences that arise within each sex as a result of life history strategies and attachment patterns.
Life history theory is a mid-level evolutionary framework that explains individual differences in a variety of interrelated phenotypic traits including physiology, psychology, and behavior. At the core of the life history theory is the appreciation for the long-lasting influence of ecological information acquired in early development being utilized as a forecast in service of meeting the environmental demands of later development. Individual variation in life history strategies (i.e., different patterns of allocation of finite time and energy budgets between competing activities) can be arranged along a continuum, from “fast” to “slow” (Del Giudice, Reference Del Giudice2009). In terms of psychological attitudes and behaviors related to self-protection, slow strategists are characterized by higher levels of harm avoidance and risk averseness. Fast strategists are characterized by the opposite pattern, showing higher propensity toward impulsivity, short-term planning, and risk taking. Using an online survey tool, Corpuz, D'Alessandro, Adeyemo, Jankowski, and Kandalaft (Reference Corpuz, D'Alessandro, Adeyemo, Jankowski and Kandalaft2020) found that, among 209 U.S. adult participants interviewed during the first wave of the COVID-19 pandemic, life history orientation predicted endorsement of precautionary measures. Compared to fast strategists, slow strategists endorsed higher levels of self-protection (e.g., wearing a mask or to stay-at-home).
The attachment system is an important psychological mechanism that bridges the gap between early exposure to environmental harshness and/or unpredictability and life-history strategies enacted in adulthood (Szepsenwol & Simpson, Reference Szepsenwol and Simpson2019). Different attachment patterns (secure, preoccupied, fearful, avoidant) exert major effects on emotion regulation and, therefore, they are likely to impact individual attitudes toward self-protection. In line with such a prediction, in a sample of 101 Italian healthcare workers employed in a COVID-19 university hospital, Troisi, Croce Nanni, Riconi, Carola, and Di Cave (Reference Troisi, Croce Nanni, Riconi, Carola and Di Cave2021) found that participants with higher levels of fearful attachment reported more intense fear of infection.
Interestingly, neither the study by Corpuz et al. (Reference Corpuz, D'Alessandro, Adeyemo, Jankowski and Kandalaft2020) nor the study by Troisi et al. (Reference Troisi, Croce Nanni, Riconi, Carola and Di Cave2021) found significant relationships between sex and the dependent variables reflecting individual attitudes toward self-protection. These findings do not necessarily mean that the evolutionary hypothesis advanced by Benenson et al. in their target article is invalid. Rather, they suggest the necessity of integrating the predictions derived by asymmetrical parental investment and sexual selection theory with those based on life history theory and attachment models. Given its importance for survival and biological adaptation, the evolution of the behavioral immune system is likely to have been shaped by multiple selection pressures. A comprehensive understanding of the psychological and behavioral defenses against infection requires a conceptual framework that integrates different evolutionary subtheories: parental investment, sexual selection, life history strategies, and attachment orientations. The COVID-19 outbreak offers a unique opportunity to apply such an integrated framework to the study of self-protective behavior.
The coronavirus disease-2019 pandemic presents a unique opportunity to test the evolutionary hypothesis that women show stronger self-protective reactions than men to environmental threats. In their target article, Benenson et al. focus mainly on sex differences in COVID-19 mortality rates and the activation of the physiological immune system. Their argument can be expanded by analyzing sex differences in the activation of the behavioral immune system and women's emotional reactions to the risk of COVID-19 infection.
The physiological immune defense is merely reactive because it is triggered only after the infection has occurred within the body. Schaller (Reference Schaller2011) has convincingly demonstrated that selection pressures have reinforced our defenses against infections by causing the evolution of a behavioral immune system that is separate from, and complementary to, the physiological immune system. The behavioral immune system includes a set of proactive mechanisms that inhibit contact with pathogens in the first place. These mechanisms offer a sort of psychological and behavioral prophylaxis against infection. The two emotional and interrelated reactions associated with the activation of the behavioral immune system are fear of infection and pathogen disgust sensitivity (Troisi, Reference Troisi2020). Based on the evolutionary hypothesis of sex differences in self-protection, the COVID-19 pandemic is expected to have caused more intense fear of infection and pathogen disgust sensitivity in women than in men.
Data on fear of infection support the evolutionary hypothesis. A recent scoping review based on 14 studies conducted in different populations showed that female gender was the most consistent predictor of fear of COVID-19 (Quadros, Garg, Ranjan, Vijayasarathi, & Mamun, Reference Quadros, Garg, Ranjan, Vijayasarathi and Mamun2021). Compared to studies focusing on fear of infection, reports on sex differences in disgust sensitivity are fewer but their findings are anyway consistent with evolutionary predictions. Using a large nationwide Chinese sample, Ding, Yang, Ji, and Guo (Reference Ding, Yang, Ji and Guo2021) found that the COVID-19 outbreak increased levels of pathogen disgust sensitivity more in women than in men. In a large sample of Australian university students, Stevenson, Saluja, and Case (Reference Stevenson, Saluja and Case2021) found that the increase in disgust sensitivity observed during the COVID-19 pandemic was significantly greater in women than in men.
The COVID-19 outbreak is a natural experiment that not only confirms the existence of sex differences in self-protective reactions to environmental threats but also enriches our understanding of their evolutionary-developmental origin. Studies of the activation of the behavioral immune system triggered by the COVID-19 pandemic have demonstrated that evolutionary explanations of individual differences in self-protection should not be based only on parental investment and sexual selection theory, as Benenson et al. have done in their target article. A comprehensive evolutionary model of greater or lower levels of self-protection must also incorporate the individual differences that arise within each sex as a result of life history strategies and attachment patterns.
Life history theory is a mid-level evolutionary framework that explains individual differences in a variety of interrelated phenotypic traits including physiology, psychology, and behavior. At the core of the life history theory is the appreciation for the long-lasting influence of ecological information acquired in early development being utilized as a forecast in service of meeting the environmental demands of later development. Individual variation in life history strategies (i.e., different patterns of allocation of finite time and energy budgets between competing activities) can be arranged along a continuum, from “fast” to “slow” (Del Giudice, Reference Del Giudice2009). In terms of psychological attitudes and behaviors related to self-protection, slow strategists are characterized by higher levels of harm avoidance and risk averseness. Fast strategists are characterized by the opposite pattern, showing higher propensity toward impulsivity, short-term planning, and risk taking. Using an online survey tool, Corpuz, D'Alessandro, Adeyemo, Jankowski, and Kandalaft (Reference Corpuz, D'Alessandro, Adeyemo, Jankowski and Kandalaft2020) found that, among 209 U.S. adult participants interviewed during the first wave of the COVID-19 pandemic, life history orientation predicted endorsement of precautionary measures. Compared to fast strategists, slow strategists endorsed higher levels of self-protection (e.g., wearing a mask or to stay-at-home).
The attachment system is an important psychological mechanism that bridges the gap between early exposure to environmental harshness and/or unpredictability and life-history strategies enacted in adulthood (Szepsenwol & Simpson, Reference Szepsenwol and Simpson2019). Different attachment patterns (secure, preoccupied, fearful, avoidant) exert major effects on emotion regulation and, therefore, they are likely to impact individual attitudes toward self-protection. In line with such a prediction, in a sample of 101 Italian healthcare workers employed in a COVID-19 university hospital, Troisi, Croce Nanni, Riconi, Carola, and Di Cave (Reference Troisi, Croce Nanni, Riconi, Carola and Di Cave2021) found that participants with higher levels of fearful attachment reported more intense fear of infection.
Interestingly, neither the study by Corpuz et al. (Reference Corpuz, D'Alessandro, Adeyemo, Jankowski and Kandalaft2020) nor the study by Troisi et al. (Reference Troisi, Croce Nanni, Riconi, Carola and Di Cave2021) found significant relationships between sex and the dependent variables reflecting individual attitudes toward self-protection. These findings do not necessarily mean that the evolutionary hypothesis advanced by Benenson et al. in their target article is invalid. Rather, they suggest the necessity of integrating the predictions derived by asymmetrical parental investment and sexual selection theory with those based on life history theory and attachment models. Given its importance for survival and biological adaptation, the evolution of the behavioral immune system is likely to have been shaped by multiple selection pressures. A comprehensive understanding of the psychological and behavioral defenses against infection requires a conceptual framework that integrates different evolutionary subtheories: parental investment, sexual selection, life history strategies, and attachment orientations. The COVID-19 outbreak offers a unique opportunity to apply such an integrated framework to the study of self-protective behavior.
Financial support
This research received no specific grant from any funding agency, commercial, or not-for-profit sectors.
Conflict of interest
None.