Despite the authors' acknowledgement that they are not the first to link psychology with climate and that their proposal is rooted in evolutionary psychology, there is no reference to the work of J. P. Rushton. From 1985 until his death in 2012, he wrote extensively on race and crime, arguing for an evolved life history adaptation based on temperature and climate variability as proposed in the target article. Consider, for example, the following statement:
Climate differences also influenced mental abilities. In Africa, food and warmth were available year round. To survive the cold winters, the populations migrating northwards had to become more inventive…. Making special tools, fires, clothing and shelters called for higher intelligence. Moving ‘Out of Africa’ meant moving into a K-type life-history strategy. That meant higher IQ, larger brains, slower growth, and lower hormone levels. It also meant lower levels of sexuality, aggression, and impulsive behavior. More family stability, advanced planning, self-control, rule-following, and longevity were needed. (Rushton Reference Rushton2000a, p. 41)
Given the volume of Rushton's work and the publicity that it spawned, this omission is astonishing. Whatever the merits, Rushton presented data on a far larger number of theoretically derived variables, including sexual behaviour, reproductive timing, litter size, growth rate, hormone levels, IQ, and brain volume (e.g., Rushton Reference Rushton1985a).
Although Rushton was unambiguous (and politically controversial) in proposing a genetic basis for climate-related evolved differences, the same cannot be said for Van Lange et al., who maintain an uncomfortable fence-straddling position on the issue. The majority of researchers in human life history treat fast/slow trajectories as conditional or facultative adjustments predicated on early life experiences (e.g., the intensity of local resource competition is proximally transmitted to the child through family breakdown and/or father absence). A testable hypothesis would be that harsh and unpredictable climates near the equator are associated with family dysfunction and breakdown. However, Van Lange et al. depart from this model in suggesting that temperature and seasonal variation affect temperament directly (see their Fig. 1). Yet the authors offer no account of the age at which regionally variable climatic cues are detected by the individual and how this awareness is translated into a temperamental adjustment.
Although they make a case for the “adaptiveness” of a faster life tempo in hotter climates, a glaring omission is how the psychological magic actually happens. The individual as the unit of analysis is too often occluded by nation or region. At other points in their argument, they seem to suggest a genetic basis for the adaptation (“From an evolutionary perspective, hot and cold climates have posed divergent problems to human survival, which have required distinct psycho-behavioral adaptations” [sect. 4, para. 3]). In yet other passages, the authors resolutely cling to ambiguity. Consider the following two statements: “…people's thoughts and behaviors may differ, based on the physical circumstances their ancestors faced and they themselves face” and “people coming from differing ancestral histories and living in different locations face challenges of self-control” (sect. 6, para. 3, emphasis added). By encompassing both ancestral and contemporary conditions, they create a convenient ambiguity.
Equally unclear is whether climate adaptations are proposed to occur at the individual or societal (cultural) level. In their key propositions, the two are elided, for example, “Lower temperatures, and especially larger degrees of seasonal variation in climate, call for individuals and groups to adopt a slower life history strategy, a greater focus on the future (vs. present), and a stronger focus on self-control” (abstract). This has two unfortunate consequences. First, their argument runs perilously close to the ecological fallacy by switching between units of analysis. For example, in a section purporting to address time orientation, we learn that culturally “people experience time differently across countries around the world” (sect. 3.1.2, para. 4). But the key dependent variables – acts of aggression and violence – are committed by individuals, not by cultures. Minimally, we need evidence that individuals living near the equator discount the future more steeply and are more aggressive. Despite claims that cross-cultural data on self-control are sparse (they cite only one study), the impulsiveness, self-discipline, and deliberation facets of the Big Five have been measured in 26 cultures (Costa et al. Reference Costa, Terracciano and McCrea2001). Second, the authors need to clarify the relationship between “individual” and “societal” evolution. For example, do societal constructions of time derive from individual temperaments (culture as the individual “writ large”)? Or can culture itself select for evolved individual differences in time orientation (people who experience time as moving “faster” leave more offspring)? Or do cultural ideas about time (“memes”) have an evolutionary life of their own based on contemporary popularity? Without answers, the article fails to live up to its promise of bridging “psychological processes within individuals … with social processes and outcomes at the level of groups, cultures, and societies” (sect. 6, para. 2).
Ultimately, the aim of the article is to provide an evolutionarily informed account of regional differences in aggression. But there is too much concern with region and too little with aggression. The authors fail to make a case for the functionality of heightened aggression under harsh ecological conditions. Indeed, they seem to undermine any such argument by restricting their proposal to reactive aggression rather than the instrumental aggression that would be relevant to resource competition. Is reactive aggression simply a spandrel dragged along by its association with poor self-control and short time horizons? The proposal also fails to address the well-established sex difference that is at the heart of an evolutionary approach to aggression (Campbell Reference Campbell2013; Reference Campbell and Buss2015). Worldwide, women commit less than 20% of violent offences and less than 4% of homicides. What is the correlation between men's and women's violent crime over climatic regions? If they are positively related, why are women less strongly affected by climate than men? More fundamentally, the authors fail to explicate evolutionary arguments as to the source of the sex difference or the psychological infrastructure that supports it. This is unlikely to be sex differences in either self-control or future orientation, which show small effect sizes in meta-analysis (Cross et al. Reference Cross, Copping and Campbell2011). An adequate theory of aggression should intrinsically encompass the sex difference rather than add on half the world's population as an afterthought.
Despite the authors' acknowledgement that they are not the first to link psychology with climate and that their proposal is rooted in evolutionary psychology, there is no reference to the work of J. P. Rushton. From 1985 until his death in 2012, he wrote extensively on race and crime, arguing for an evolved life history adaptation based on temperature and climate variability as proposed in the target article. Consider, for example, the following statement:
Climate differences also influenced mental abilities. In Africa, food and warmth were available year round. To survive the cold winters, the populations migrating northwards had to become more inventive…. Making special tools, fires, clothing and shelters called for higher intelligence. Moving ‘Out of Africa’ meant moving into a K-type life-history strategy. That meant higher IQ, larger brains, slower growth, and lower hormone levels. It also meant lower levels of sexuality, aggression, and impulsive behavior. More family stability, advanced planning, self-control, rule-following, and longevity were needed. (Rushton Reference Rushton2000a, p. 41)
Given the volume of Rushton's work and the publicity that it spawned, this omission is astonishing. Whatever the merits, Rushton presented data on a far larger number of theoretically derived variables, including sexual behaviour, reproductive timing, litter size, growth rate, hormone levels, IQ, and brain volume (e.g., Rushton Reference Rushton1985a).
Although Rushton was unambiguous (and politically controversial) in proposing a genetic basis for climate-related evolved differences, the same cannot be said for Van Lange et al., who maintain an uncomfortable fence-straddling position on the issue. The majority of researchers in human life history treat fast/slow trajectories as conditional or facultative adjustments predicated on early life experiences (e.g., the intensity of local resource competition is proximally transmitted to the child through family breakdown and/or father absence). A testable hypothesis would be that harsh and unpredictable climates near the equator are associated with family dysfunction and breakdown. However, Van Lange et al. depart from this model in suggesting that temperature and seasonal variation affect temperament directly (see their Fig. 1). Yet the authors offer no account of the age at which regionally variable climatic cues are detected by the individual and how this awareness is translated into a temperamental adjustment.
Although they make a case for the “adaptiveness” of a faster life tempo in hotter climates, a glaring omission is how the psychological magic actually happens. The individual as the unit of analysis is too often occluded by nation or region. At other points in their argument, they seem to suggest a genetic basis for the adaptation (“From an evolutionary perspective, hot and cold climates have posed divergent problems to human survival, which have required distinct psycho-behavioral adaptations” [sect. 4, para. 3]). In yet other passages, the authors resolutely cling to ambiguity. Consider the following two statements: “…people's thoughts and behaviors may differ, based on the physical circumstances their ancestors faced and they themselves face” and “people coming from differing ancestral histories and living in different locations face challenges of self-control” (sect. 6, para. 3, emphasis added). By encompassing both ancestral and contemporary conditions, they create a convenient ambiguity.
Equally unclear is whether climate adaptations are proposed to occur at the individual or societal (cultural) level. In their key propositions, the two are elided, for example, “Lower temperatures, and especially larger degrees of seasonal variation in climate, call for individuals and groups to adopt a slower life history strategy, a greater focus on the future (vs. present), and a stronger focus on self-control” (abstract). This has two unfortunate consequences. First, their argument runs perilously close to the ecological fallacy by switching between units of analysis. For example, in a section purporting to address time orientation, we learn that culturally “people experience time differently across countries around the world” (sect. 3.1.2, para. 4). But the key dependent variables – acts of aggression and violence – are committed by individuals, not by cultures. Minimally, we need evidence that individuals living near the equator discount the future more steeply and are more aggressive. Despite claims that cross-cultural data on self-control are sparse (they cite only one study), the impulsiveness, self-discipline, and deliberation facets of the Big Five have been measured in 26 cultures (Costa et al. Reference Costa, Terracciano and McCrea2001). Second, the authors need to clarify the relationship between “individual” and “societal” evolution. For example, do societal constructions of time derive from individual temperaments (culture as the individual “writ large”)? Or can culture itself select for evolved individual differences in time orientation (people who experience time as moving “faster” leave more offspring)? Or do cultural ideas about time (“memes”) have an evolutionary life of their own based on contemporary popularity? Without answers, the article fails to live up to its promise of bridging “psychological processes within individuals … with social processes and outcomes at the level of groups, cultures, and societies” (sect. 6, para. 2).
Ultimately, the aim of the article is to provide an evolutionarily informed account of regional differences in aggression. But there is too much concern with region and too little with aggression. The authors fail to make a case for the functionality of heightened aggression under harsh ecological conditions. Indeed, they seem to undermine any such argument by restricting their proposal to reactive aggression rather than the instrumental aggression that would be relevant to resource competition. Is reactive aggression simply a spandrel dragged along by its association with poor self-control and short time horizons? The proposal also fails to address the well-established sex difference that is at the heart of an evolutionary approach to aggression (Campbell Reference Campbell2013; Reference Campbell and Buss2015). Worldwide, women commit less than 20% of violent offences and less than 4% of homicides. What is the correlation between men's and women's violent crime over climatic regions? If they are positively related, why are women less strongly affected by climate than men? More fundamentally, the authors fail to explicate evolutionary arguments as to the source of the sex difference or the psychological infrastructure that supports it. This is unlikely to be sex differences in either self-control or future orientation, which show small effect sizes in meta-analysis (Cross et al. Reference Cross, Copping and Campbell2011). An adequate theory of aggression should intrinsically encompass the sex difference rather than add on half the world's population as an afterthought.