A novel predictor of bullying may be underlying regional weather conditions (i.e., climate). Bullying data support the CLASH model of aggression by suggesting that climate may moderate the forms and severity of bullying, as well as predict its prevalence across countries. Furthermore, bullying data also suggest that the CLASH model may apply to forms of aggression beyond reactive aggression.

We contend that an ecological account of violence and aggression requires consideration of societal and cultural settings. Focusing on hierarchical relations, we argue countries with higher (vs. lower) power distance are, on average, located closer to the equator, have more challenging climates (e.g., higher temperature; lower temperature variation), and have a greater prevalence of violence and aggression (e.g., higher homicide rates).

Van Lange et al. add important life history perspectives to understanding violence. However, direct links between climate and violence are unlikely because cultural institutions modify human responses. Examples are given from the Bushmen of the Kalahari and Enga of Papua New Guinea. The correlations identified may occur because many countries closer to the equator are caught in the gap between the demise of traditional cultural institutions and the rise of modern forms of governance.

A total of 80 authors working in a variety of scientific disciplines commented on the theoretical model of CLimate, Aggression, and Self-control in Humans (CLASH). The commentaries cover a wide range of issues, including the logic and assumptions of CLASH, the evidence in support of CLASH, and other possible causes of aggression and violence (e.g., wealth, income inequality, political circumstances, historic circumstances, pathogen stress). Some commentaries also provide data relevant to CLASH. Here we clarify the logic and assumptions of CLASH and discusses its extensions and boundary conditions. We also offer suggestions for future research. Regardless of whether none, some, or all of CLASH is found to be true, we hope it will stimulate future research on the link between climate and human behavior. Climate is one of the most presing issues of our time.

Integrative explanations of why obesity is more prevalent in some sectors of the human population than others are lacking. Here, we outline and evaluate one candidate explanation, the insurance hypothesis (IH). The IH is rooted in adaptive evolutionary thinking: The function of storing fat is to provide a buffer against shortfall in the food supply. Thus, individuals should store more fat when they receive cues that access to food is uncertain. Applied to humans, this implies that an important proximate driver of obesity should be food insecurity rather than food abundance per se. We integrate several distinct lines of theory and evidence that bear on this hypothesis. We present a theoretical model that shows it is optimal to store more fat when food access is uncertain, and we review the experimental literature from non-human animals showing that fat reserves increase when access to food is restricted. We provide a meta-analysis of 125 epidemiological studies of the association between perceived food insecurity and high body weight in humans. There is a robust positive association, but it is restricted to adult women in high-income countries. We explore why this could be in light of the IH and our theoretical model. We conclude that although the IH alone cannot explain the distribution of obesity in the human population, it may represent a very important component of a pluralistic explanation. We also discuss insights it may offer into the developmental origins of obesity, dieting-induced weight gain, and anorexia nervosa.

Body image distortions are common in healthy individuals and a central aspect of serious clinical conditions, such as eating disorders. This commentary explores the potential implications of body image and its distortions for the insurance hypothesis. In particular, we speculate that body image may be an intervening variable mediating the relationship between perceived food scarcity and eating behavior.

The insurance hypothesis is a reasonable explanation for the current obesity epidemic. One alternative explanation is that the marketing of high-sugar foods, especially sugar-sweetened beverages, drives the rise in obesity. Another prominent hypothesis is that obesity spreads through social influence. We offer a framework for estimating the extent to which these different models explain the rise in obesity.

Food insecurity relates to fat storage, but cannot explain fat storage in excess of levels optimal for buffering – that is, obesity. However, factors related to food unpredictability in the past, including stress, disease, micronutrient content of food, and physical activity, may cue physiological processes that change intake or fat deposition even in the absence of actual food unpredictability.

Nettle et al. evaluate evidence for the insurance hypothesis, which links obesity with the perception of food scarcity. Epidemiological findings in this area have generally been weak and inconsistent. The present commentary examines three key methodological issues arising from the literature on the association between obesity and the perception of food scarcity in humans, with suggestions for future epidemiological research.

The focus of this commentary is Nettle et al.'s insurance hypothesis linking food insecurity to a high body mass index (BMI). We discuss how the relationship between race/ethnicity and obesity in the United States is consistent with this hypothesis, then present potential ways forward to elucidate the validity of this hypothesis in humans through rigorous controlled trials.

Nettle et al.’s explanation based on the insurance hypothesis applies only to the association between food insecurity and body weight among adult women, but not to the results about there being no such associations among adult men and children. These results may be best understood when the insurance hypothesis is integrated with the life history model.

This commentary focuses on the mechanisms underlying the appraisal of food insecurity. I first describe what appraisal is and why it plays a major role in explaining how different individuals consider food supply as more or less secure. I then describe the potential reciprocal links between appraisal and obesity, based on the well-documented evidence that obesity can cause cognitive deficits.

In evaluating the insurance hypothesis as an explanation for obesity, we propose one missing piece of the puzzle. Our suggested explanation for why individuals report food insecurity is that an individual may have an impaired episodic ability to plan for the future.

Nettle et al. describe increasing food intake (relative to energy expenditure) in response to food insecurity as a key contributor to obesity. I argue that a variety of implicit psychological mechanisms underlie this process to contribute to weight gain. The biobehavioral pathways and the social nature of food selection discussed here are importantly related to food selection and obesity.

We extend Nettle et al.’s insurance hypothesis (IH) argument, drawing upon life-history theory (LHT), a developmental evolutionary perspective that documents downstream consequences of early-life exposure to unpredictable environments. We discuss novel evidence consistent with both IH and LHT, suggesting that early-life exposure to unpredictable environments is associated with reduced engagement in weight management behaviors and a greater probability of adulthood obesity.

Nettle et al. provide a useful but incomplete analysis of the drivers of obesity. In this commentary, we argue that a dual-motives conceptualization of self-control, together with insights from the psychology of (perceived and actual) scarcity, might help advance a more fine-grained mechanistic understanding of the observed association between food insecurity and obesity.

We suggest two psychological mechanisms, temporal discounting and feeling of resource scarcity, for explaining the relation between food insecurity and body overweight. We demonstrate how Nettle et al.’s findings could be explained, post hoc, by each of these accounts, suggesting that their data are not rich enough to allow identification of mechanisms that underlie food insecurity and overweight relationship.

Addressing the obesity epidemic depends on a holistic understanding of the reasons that people become and maintain excessive fat. Theories about the causes of obesity usually focus proximately or evoke evolutionary mismatches, with minimal clinical value. There is potential for substantial progress by adapting strategic body mass regulation models from evolutionary ecology to human obesity by assessing the role of information.

The target article explores the role of food insecurity as a contemporary risk factor for human overweight and obesity. The authors provide conditional support for the insurance hypothesis among adult women from high-income countries. We consider the potential contribution of additional factors in producing variation in adiposity patterns between species and across human contexts.

The target article proposes the insurance hypothesis as an explanation for higher levels of obesity among food-insecure women living in high-income countries. An alternative hypothesis based on anti-fat discrimination in marriage can also account for such correlations between poverty and obesity and is more consistent with finer-grained analyses by marital status, gender, and age.