Transcending reviewed proximate theories, Van Lange et al.'s CLASH model attempts to ultimately explain the poleward declension of aggression and violence. Seasonal cold is causal, but, we contend, principally as an ecologically relevant evolutionary pressure. We further argue that futurity and restraint are life history variables, and that Life History Theory evolutionarily explains the biogeography of aggression and violence as strategic adaptation.

I identify two confusions and omissions in the target article. Confusion arises from failure to distinguish between a genetically transmitted adaptation and a conditional response to the environment, and from the elision of individual and societal adaptations. Despite points of similarity, there is no mention of Rushton's controversial theory of the climatic basis of race differences in violent crime. Sex differences are also ignored.

Van Lange et al. propose that climate affects violence via its effects on life history. That much is reasonable (and not novel), but their theory lacks causal specificity. Their foundational claim of an association between heat and violence is not well documented, and several findings that the authors themselves cite seem inconsistent with their model, rather than supportive.

We recommend extending CLASH by incorporating two evolutionary accounts of the shift toward fast life histories under harsh, unpredictable conditions. These accounts, if integrated with CLASH, make different predictions about the distributions of aggression and violence within and between societies. We discuss these predictions and propose ways of testing them.

Data from archaeology and paleoanthropology directly challenge the validity of the basic assumptions of the CLASH model. By not incorporating a “deep time” perspective, the hypothesis lacks the evolutionary baseline the authors seek to infer in validating the model.

We comment on the proposition “that lower temperatures and especially greater seasonal variation in temperature call for individuals and societies to adopt … a greater degree of self-control” (Van Lange et al., sect. 3, para. 4) for which we cannot find empirical support in a large data set with data-driven analyses. After providing greater nuance in our theoretical review, we suggest that Van Lange et al. revisit their model with an eye toward the social determinants of self-control.

We argue that the target authors focus too much on adaptive behavioral responses and not enough on actual psychological adaptations. We suggest the Dark Triad traits may represent facultative, psychological adaptations sensitive to seasonal variance and food shortages. We document that shorter distances from the equator are linked to higher national narcissism levels, whereas longer distances are associated with higher national-level machiavellianism. Dark Triad traits may serve as critical survival mechanisms when prioritizing oneself over and/or at the cost of others.

This commentary discusses the research finding that warmer temperatures are associated with more prosocial outcomes. It calls for future research and theory on climate-related variables and social behavior to allow for both positive and negative emotional and behavioral responses to warmer temperatures.

Van Lange et al. argue that variations in climate explain cross-societal variations in violence. We suggest that any approach seeking to understand cross-cultural variation in human behavior via an ecological framework must consider a wider array of ecological variables, and we find that income inequality and sex ratio are better predictors than climate of cross-societal variations in violence.

In explaining variation in violent aggression across populations, the age structures of those populations must be considered. Adolescents between the ages of 15 and 25 are disproportionately responsible for violent aggression in every society, and increases in violence tend to follow population “youth bulges.” Large numbers of adolescents in equatorial regions may account for observed relationships between geography and violence.

We agree with Van Lange et al. that climate is likely to affect individuals' social behavior in many ways. However, we suspect that its impact on physiology and psychology is so remote that its predictive power disintegrates almost completely through the causal chain underlying aggression and violence.

Considering purely climate, southern countries are less harsh and more predictable than northern countries. From a historical perspective, freezing winters resulting in fewer available resources contribute to the development of strong future orientation. The paradox is that future orientation contributes to accumulation of resources in the long run, making individuals' immediate living conditions less harsh, leading to slower life strategies.

We examined the CLASH model using the data on climate and violence from the Russian Federation. The Russian Federation is a huge country with dramatic climatic differences between regions. Our results are absolutely inconsistent with the model. We consider there are a range of climates in which the human organism functions optimally. Deviations from the range cause impulsiveness and aggression.

To support their hypothesis, the authors point to an inverse correlation between latitude and the incidence of civil conflict and crime. This observation cannot be accepted as evidence for the hypothesis, because of a weighty confounding variable: the historical geography of colonialism and its effects on the fragility of nations.

In this commentary, we address two questions: (1) Is the drive in many young men to gain status and amass resources, which frequently entails direct competition with members of outgroups, one of the key variables underlying the CLASH model? (2) Why is there so much variation in reactive aggression/violence between people living in the same environment?

The CLASH model proposed in the target article is plausible but less than parsimonious. I suggest that statistical analysis probably would find slower life history strategy, greater focus on the future, and greater self-control to be highly correlated and perhaps unifactorial, because they are all manifestations of a single underlying variable, namely, intelligence. I suggest how intelligence as a state variable plausibly could explain the differences observed by the authors.

Apparently inconsistent with the CLASH model, animal research relates predictable environments to rigid routine behaviors and aggression. However, our work on evolutionary and neural adaptations to (un)predictable environments may be able to reconcile the CLASH model with the animal research, but also suggests complexities beyond the dichotomous approach of CLASH.

Van Lange et al.'s global CLASH model overemphasizes climatic origins and underemphasizes economic origins of aggression. Our 167-country analysis of latitudinal gradients of heat, poverty, and aggression finds that heat-induced aggression is mediated by poverty and that heat tempers rather than fuels poverty-induced aggression. More importantly, the CLASH model hints at latitudinal, equatorial, and hemispheric upgradings of climato-economic modeling of human behavior.

The psychological processes that predict aggressive behaviour are also typically associated with violent self-harm (e.g., poor self-control). Yet, although human violence (towards others) appears to increase with proximity to the equator, suicide rates tend to decrease. In the light of this empirical puzzle, I argue that Van Lange et al.'s CLASH model would benefit from a broader conceptualization of human aggression.

In this commentary, we contest Van Lange and colleagues' central claim that “countries closer to the equator are generally more violent.” We point to the lack of credible empirical evidence for this assertion and suggest that the CLASH model uses the language of science to lend false credibility to a problematic sociocultural discourse.