Life history theory (LHT) is a powerful evolutionary framework for understanding physiological, psychological, and behavioral variation both between and within species. Researchers and theorists are increasingly integrating LHT into evolutionary psychology, as it provides a strong foundation for research across many topical areas. Human life history variation has been represented in psychological and behavioral research in several ways, including indicators of conditions in the developmental environment, indicators of conditions in the current environment, and indicators of maturation and life milestones (e.g., menarche, initial sexual activity, first pregnancy), and in self-report survey scale measures. Survey scale measures have included constructs such as time perspective and future discounting, although the most widely used index is a constellation of indicators assessing the K-factor, thought to index general life history speed (from fast to slow). The current project examined the utility of two brief self-report survey measures assessing the life history dimensions of mating effort and parenting effort with a large undergraduate sample in the United States. Consistent with the theory, items reflected two inversely related dimensions. In regressions including the K-factor, the Mating Effort Scale proved to be a powerful predictor of other constructs and indicators related to life history variation. The Parenting Effort Scale had less predictive power overall, although it explained unique variance across several constructs and was the only unique predictor of the number of long-term (serious and committed) relationships. These scales may be valuable additions to self-report survey research projects examining life history variation.
Kruger, D.J., & Kruger, J.S. (2016). Psychometric assessment of human life history predicts health related behaviors. Psychological Topics, 25, 19-28. Invited, peer-reviewed article for special issue, Health Psychology: Current research and trends.
Life History Theory is a powerful framework that can help promote understanding of variation in health-related behavioral patterns and why they vary consistent with environmental conditions. An organism's life history reflects tradeoffs made in the allocation of effort towards specific aspects of survival and reproduction across the lifespan. This study examines the relationship between psychological indicators of life history strategy and health related behaviors in a demographically representative sample in the Midwestern USA. Slower life histories predicted higher levels of health promoting behaviors and lower levels of health adverse behaviors, even when controlling for relevant socio-demographic factors. The analyses provide a strong test of the hypothesized relationship between life history and health behavior indicators, as life history variation co-varies with these socio-demographic factors. Traditional public health efforts may be reaching their limits of effectiveness in encouraging health-promoting behaviors. Integrating an evolutionary framework may revitalize behavioral health promotion efforts.
Kruger, D.J., Nedelec, J.L., Reischl, T.M., & Zimmerman, M.A. (2015). Life history predicts perceptions of procedural justice and crime reporting intentions. Evolutionary Psychological Science, 1, 183-194.
Evolutionary life history theory (LHT) is a powerful organizing framework central to the life sciences. Interest in biosocial criminology is growing, and adoption of LHT may accelerate progress toward an integrative evolutionarily informed human science. We examined the relationship of life history to attitudes toward the police using data from a demographically representative community-wide survey in a Midwestern county with an urban center exhibiting high rates of violent crimes. As expected, life history was associated with demographic characteristics. Controlling for demographics, slower life history was associated with greater perceptions of procedural justice and police legitimacy, i.e., intentions to contact the police. LHT may promote an integrative human science and a deep theoretical framework for understanding modern social patterns.
Kruger, D.J., Fisher, M.L., De Backer, C., Kardum, I., Tetaz, M., & Tifferet, S. (2015). Human life history dimensions in reproductive strategies are intuitive across cultures. Human Ethology Bulletin, 30, 109-120.
Psychological research has been criticized for its extensive use of American university students to make broad claims about human psychology and behavior. Critics recommend a broader base of participants because there is substantial variability in experimental results across populations, and North American and Western European psychology pool participants may be outliers in comparison with the rest of the species. This challenge is especially pertinent for claims of species- universal evolved psychological architecture. One such claim has been made regarding recognition of human life history strategies. For example, previous research demonstrates that North American women and men can identify male and female characters with fast (high mating effort, low parental investment) and slow (low mating effort, high parental investment) life history strategies, make accurate predictions about their behavioral tendencies, and respond to them in ways that would facilitate participants' own reproductive success. The current project validates the understanding of fundamental life history dimensions across a wide range of cultures, therefore supporting the idea that there is a universality in human's ability to use, and perceive others' use of, life history strategies. Results for each language sample replicated patterns from North American participants. Ratings for characters clustered into two dimensions, mating effort and parental investment. Items most central to the theoretical constructs had the highest factor loadings.
Kruger, D.J., Aiyer, S.M., Caldwell, C.H., & Zimmerman, M.A. (2013). Local scarcity of adult men predicts youth assault rates. Journal of Community Psychology, 42, 119-125.
Father involvement reduces risky youth behavior at the individual level. We examine the association between the scarcity of adult men and youth violence at the Census Tract level across a small Midwestern city experiencing decades of economic adversity and high rates of violence. We calculated the ratio of men to women aged 25-64 and indicators of concentrated disadvantage across residential Census Tracts with 2000 US Decennial Census data and the average monthly assault rates for those aged 10-24 between June 2006 and December 2008 with data from the local police department. Adult male scarcity and the proportion of individuals 25 or older who had less than a high school degree were the two unique predictors of youth assault rates, together explaining 69% of the variance. Interventions promoting effective social, material, and protective support from fathers and other adult male role models may ameliorate risk for youth violence.
Kruger, D.J., Clark, J., & Vanas, S. (2013). Male scarcity is associated with higher prevalence of premature gestation and low birth weight births across the USA. American Journal of Human Biology, 25, 225-227.
Objectives: Modern adverse birth outcomes may partially result from mechanisms evolved to evaluate environmental conditions and regulate maternal investment trade-offs. Male scarcity in a population is associated with a cluster of characteristics related to higher mating effort and lower paternal investment. We predicted that modern populations with male scarcity would have shorter gestational times and lower birth weights on average.
Methods: We compared US Centers for Disease Control and Prevention county-aggregated year 2000 birth records with US Decennial Census data. We combined these data in a path model with the degree of male scarcity and known socio-economic predictors of birth outcomes as exogenous predictors of prematurity and low birth weight, with single mother households as a proportion of families with children as a mediator (N = 450).
Results: Male scarcity was directly associated with higher rates of low birth weight. Male scarcity made significant indirect predictions of rates of prematurity and low birth weight, as mediated by the proportion of families headed by single mothers. Aggregate socio-economic status also indirectly predicted birth outcomes, as mediated by the proportion of families headed by single mothers, whereas the proportion African American retained both direct and indirect predictions of adverse birth outcomes.
Conclusions: Male scarcity influences life history tradeoffs, with consequences for important social and public health issues such as adverse birth outcomes.
Kruger, D.J., & Vanas, S.B. (2012). Local scarcity of women predicts higher fertility among married couples and more single father households. Letters on Evolutionary Behavioral Science, 3, 17-20.
Influences of the sex ratio on the intensity of mating competition and selectivity for partners produce different outcomes in female biased and male biased populations because the reproductive strategies of men and women are somewhat divergent. Male scarcity enhances male mating opportunities and incentives for long-term commitment are diminished, encouraging serial and simultaneous polygyny. Paternal investment is lower in these populations, as indicated by higher divorce rates, more out-of-wedlock births, and a greater proportion of single mother households. Scarce females are more effective at securing commitment from partners and obtaining higher levels of resource investment. Women marry earlier in male biased populations. Although single father households are relatively uncommon, we expect to see higher proportions of households with children headed by single fathers where women are scarce. We also expect to see higher fertility among married couples, both because women may have greater bargaining power in reproductive decision-making and the role of woman in childbearing may be more salient and more highly valued. Data from the U.S. Census 2009 American Community Survey across 318 Metropolitan Statistical Areas supported these hypotheses.
Kruger, D. J., Munsell, M.A., & French-Turner, T. (2011). Using a life history framework to understand the relationship between neighborhood structural deterioration and adverse birth outcomes. Journal of Social, Evolutionary, and Cultural Psychology, 5, 260-274.
Life History Theory is a powerful framework for understanding how evolved functional adaptations to environmental conditions influence variation in significant life outcomes. Features indicating relatively high extrinsic mortality rates and unpredictability of future outcomes are associated with relatively faster life history strategies. Regulatory mechanisms that facilitated reproductive success in ancestral environments may contribute to adverse birth outcomes in modern technologically advanced populations. Adverse local environmental conditions may reduce maternal somatic investment in gestating offspring, consistent with long-term maternal interests. In this study, we demonstrated a relationship between neighborhood structural deterioration and adverse birth outcomes in Flint, Michigan, USA. We used Geographical Information Systems software to calculate the density of highly dilapidated structures, premature births, and low birth weight births in .25 mile square areas. Controlling for parental education and type of health coverage, the degree of structural deterioration was associated with the concentration of premature births and low birth weight births.
Kruger, D.J., Reischl, T.M., & Zimmerman, M.A. (2008). Time perspective as a mechanism for functional developmental adaptation. Journal of Social, Evolutionary, and Cultural Psychology, 2, 1-22.
Evolutionary Life History Theory (LHT) is a powerful framework that can be used for understanding behavioral strategies as functional adaptations to environmental conditions. Some evolutionary theorists have described how developmental environments can shape behavioral strategies. Theorists and previous research suggest that individuals developing in relatively less certain environments will exhibit riskier, present oriented, behavioral strategies because of the low probability of reproductive success for more cautious approaches. An evolutionary psychology approach to LHT includes the identification of psychological processes that regulate behavioral strategies as a result of developmental experiences. This paper proposes that time perspective is one psychological mechanism that may underlie functional developmental adaptation. A survey study of urban middle school students (N = 607) assessed the relationship between perceptions of local social conditions, time perspective, and risky behaviors. Structural equation model analyses indicated that present and future orientations completely mediated the relationship of positive and negative aspects of students' neighborhood social environment with reports of interpersonal aggression and illicit resource exploitation This model had a better fit to the data than competing models depicting time perspective as a byproduct of either phenotypic strategy or social-environmental experiences.
Kruger, D.J. & Fisher, M. (2008). Women's life history attributes are associated with preferences in mating relationships. Evolutionary Psychology, 6, 245-258.
Life History Theory (LHT) is a powerful framework for examining relationship choices and other behavioral strategies which integrates evolutionary, ecological, and socio-developmental perspectives. We examine the relationship between psychological and behavioral indicators of women's life history attributes and hypothetical relationship choices with characters representing short-term and long-term male sexual strategies. We demonstrate that psychological indicators of women's life history strategies are related to predicted and actual behaviors in mating relationships. Women with insecure attachment styles, especially those with negative evaluations of both themselves and others (fearful attachment), were more likely to consider men with attributes indicating short-term mating strategies for short-term and long-term relationships than women with a secure attachment style. Women with relatively unrestricted sociosexuality were more likely to predict they would have sexual affairs with men in general, with the tendency being generally stronger when considering men with attributes indicating short-term mating strategies. Those who scored high on self-monitoring were also more likely to predict having sexual affairs and short-term relationships with these men. These and other findings demonstrate the usefulness of a life history approach for understanding women's relationship choices.
See also: Evolutionary Demography
See also: Mating strategies
See also: Mortality patterns