In the target article, Van Lange et al. maintain that latitude is a strong predictor of variations in human aggression and violence and that this fact reflects adaptive “life history” variability in response to differences in climate. This is not a novel argument. The logic is essentially identical to that of Rushton (Reference Rushton1995), who proposed that people whose recent evolutionary history occurred in Africa pursue relatively “fast” life histories, whereas populations that dispersed into Europe and Asia evolved “slower” life histories. Both Rushton and Van Lange et al. hypothesize that these contrasts reflect adaptation to the “harshness” and “unpredictability” of environments at different latitudes and their associated mortality risks. The primary difference is that Rushton attributed life history variability to differential past selection on different “races,” whereas Van Lange et al. allow that the variability might reflect differences in past selection pressures, in facultative responses of a universal human nature to present cues, or both.
Aspects of this theory have an a priori plausibility. If unpredictable mortality caused by pathogens is higher in the tropics than in northern climes, for example, that alone might select for differences in age at first reproduction and other components of a fast life history (Møller Reference Møller, Clayton and Moore1997). But Van Lange et al.'s claim that climate becomes more “predictable” and less “harsh” as we move away from the equator is less plausible, and they present no supportive evidence. As in many treatments of human life history variability, the concept of environmental harshness in the target article lacks the sort of rigorous definition that would permit quantification. Do the equatorial latitudes in which we evolved really constitute a harsher environment for Homo sapiens than the extreme latitudes of Eurasia? How so, exactly? And as for predictability, does the extent to which today's temperature is predictive of tomorrow's – or is predictive of the temperature on the same date a year hence – increase with distance from the equator? That seems to be what is being proposed, but as with “harshness,” the authors provide no quantified comparisons of “predictability.” Instead, they simply assert that the strong seasonal variation in temperature at extreme latitudes is itself a sort of predictability that equatorial climates lack!
Van Lange et al.'s model also suffers from insufficient specificity. Temperature is portrayed as affecting life history, time orientation, and self-control, but how? By their own argument, the latter two are consequences of life history, not parallel constructs at the same level of analysis. The authors allude to various ways in which a relationship between climate and life history might be mediated, but do not clearly articulate the need to test among them. The theoretical chasm that presently separates the climatic inputs from the psychological outputs cries out for more explicit hypotheses about causal links, which could then be tested by structural equation modeling or path analysis. Even the premise that violence may be functional is treated obliquely: Section 3.1 hints that violent aggression is an adaptive component of a fast life history, but in ensuing sections it sounds more like a maladaptive by-product of poor self-control, leaving readers wondering whether the authors accept that aggression and violence are adaptations that are facultatively deployed (Daly Reference Daly2016; Krupp et al. Reference Krupp, Sewall, Lalumière, Sheriff and Harris2013).
Even the foundational claim that heat and violence go hand in hand is questionable. The target article's opening paragraph provides a cherry-picked contrast of “Albania, Montenegro, and Turkey” versus “Scandinavia” to illustrate how “differences in violent crime rates occur along the North-South Axis in Europe.” The trouble with this is not simply that Russia has Europe's highest homicide rate and coldest average temperature, nor even that excluding the former Soviet republics and Warsaw Pact countries moves Finland into first place. The bigger problem is that, using the same Global Study on Homicide cited by the authors (United Nations Office on Drugs and Crime 2013) and mean temperatures from 1961 to 1990 (Wikipedia 2016a), the correlation between homicide and temperature is negative across the 37 European countries with populations greater than one million (r = −0.43, 95% confidence interval: −0.66, −0.12).
The only systematic, persuasive evidence of a heat/violence association that the authors cite is in Burke et al. (Reference Burke, Hsiang and Miguel2015). Unfortunately, that study finds a much larger effect of climate on intergroup than on interpersonal aggression (see also Bell & Keys, Reference Bell and Keysin press), a result that Van Lange et al. struggle to force into their model. Are individuals with poor self-control, short time horizons, and a quarrelsome bent really better able than those with the opposite temperament to form effective coalitions in warfare (Wright et al. Reference Wright, Caspi, Moffitt and Silva1999)? This example is symptomatic of a tendency to cite results that are problematic for the authors' model as somehow supportive. They note, for example, that temperature apparently affects violent, but not nonviolent, crime; but why should poor self-control and short time horizons elevate murder rates and not elevate impulsive property crime or illicit drug use? And then there is the claim (sect. 3.1.2) that people with “present” time-orientations – people who are short on time – are the very ones who act as if they have all of the time in the world, while those with “slower” life histories move faster!
The authors maintain that their model's value is “primarily theoretical” (sect. 6, para. 3). But until their theory is grounded in explicit definitions of environmental harshness and predictability, and specifies crucial explanatory links between the climatic inputs on the one hand and the psychological outputs on the other, we do not believe that it can be helpful. Also, even with a more explicit causal model, we would still need experimental studies (contra the authors' claim in sect. 3.1.3), as well as correlational ones, to make causal sense of a complex and confusing set of cross-national patterns and associations.
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In the target article, Van Lange et al. maintain that latitude is a strong predictor of variations in human aggression and violence and that this fact reflects adaptive “life history” variability in response to differences in climate. This is not a novel argument. The logic is essentially identical to that of Rushton (Reference Rushton1995), who proposed that people whose recent evolutionary history occurred in Africa pursue relatively “fast” life histories, whereas populations that dispersed into Europe and Asia evolved “slower” life histories. Both Rushton and Van Lange et al. hypothesize that these contrasts reflect adaptation to the “harshness” and “unpredictability” of environments at different latitudes and their associated mortality risks. The primary difference is that Rushton attributed life history variability to differential past selection on different “races,” whereas Van Lange et al. allow that the variability might reflect differences in past selection pressures, in facultative responses of a universal human nature to present cues, or both.
Aspects of this theory have an a priori plausibility. If unpredictable mortality caused by pathogens is higher in the tropics than in northern climes, for example, that alone might select for differences in age at first reproduction and other components of a fast life history (Møller Reference Møller, Clayton and Moore1997). But Van Lange et al.'s claim that climate becomes more “predictable” and less “harsh” as we move away from the equator is less plausible, and they present no supportive evidence. As in many treatments of human life history variability, the concept of environmental harshness in the target article lacks the sort of rigorous definition that would permit quantification. Do the equatorial latitudes in which we evolved really constitute a harsher environment for Homo sapiens than the extreme latitudes of Eurasia? How so, exactly? And as for predictability, does the extent to which today's temperature is predictive of tomorrow's – or is predictive of the temperature on the same date a year hence – increase with distance from the equator? That seems to be what is being proposed, but as with “harshness,” the authors provide no quantified comparisons of “predictability.” Instead, they simply assert that the strong seasonal variation in temperature at extreme latitudes is itself a sort of predictability that equatorial climates lack!
Van Lange et al.'s model also suffers from insufficient specificity. Temperature is portrayed as affecting life history, time orientation, and self-control, but how? By their own argument, the latter two are consequences of life history, not parallel constructs at the same level of analysis. The authors allude to various ways in which a relationship between climate and life history might be mediated, but do not clearly articulate the need to test among them. The theoretical chasm that presently separates the climatic inputs from the psychological outputs cries out for more explicit hypotheses about causal links, which could then be tested by structural equation modeling or path analysis. Even the premise that violence may be functional is treated obliquely: Section 3.1 hints that violent aggression is an adaptive component of a fast life history, but in ensuing sections it sounds more like a maladaptive by-product of poor self-control, leaving readers wondering whether the authors accept that aggression and violence are adaptations that are facultatively deployed (Daly Reference Daly2016; Krupp et al. Reference Krupp, Sewall, Lalumière, Sheriff and Harris2013).
Even the foundational claim that heat and violence go hand in hand is questionable. The target article's opening paragraph provides a cherry-picked contrast of “Albania, Montenegro, and Turkey” versus “Scandinavia” to illustrate how “differences in violent crime rates occur along the North-South Axis in Europe.” The trouble with this is not simply that Russia has Europe's highest homicide rate and coldest average temperature, nor even that excluding the former Soviet republics and Warsaw Pact countries moves Finland into first place. The bigger problem is that, using the same Global Study on Homicide cited by the authors (United Nations Office on Drugs and Crime 2013) and mean temperatures from 1961 to 1990 (Wikipedia 2016a), the correlation between homicide and temperature is negative across the 37 European countries with populations greater than one million (r = −0.43, 95% confidence interval: −0.66, −0.12).
The only systematic, persuasive evidence of a heat/violence association that the authors cite is in Burke et al. (Reference Burke, Hsiang and Miguel2015). Unfortunately, that study finds a much larger effect of climate on intergroup than on interpersonal aggression (see also Bell & Keys, Reference Bell and Keysin press), a result that Van Lange et al. struggle to force into their model. Are individuals with poor self-control, short time horizons, and a quarrelsome bent really better able than those with the opposite temperament to form effective coalitions in warfare (Wright et al. Reference Wright, Caspi, Moffitt and Silva1999)? This example is symptomatic of a tendency to cite results that are problematic for the authors' model as somehow supportive. They note, for example, that temperature apparently affects violent, but not nonviolent, crime; but why should poor self-control and short time horizons elevate murder rates and not elevate impulsive property crime or illicit drug use? And then there is the claim (sect. 3.1.2) that people with “present” time-orientations – people who are short on time – are the very ones who act as if they have all of the time in the world, while those with “slower” life histories move faster!
The authors maintain that their model's value is “primarily theoretical” (sect. 6, para. 3). But until their theory is grounded in explicit definitions of environmental harshness and predictability, and specifies crucial explanatory links between the climatic inputs on the one hand and the psychological outputs on the other, we do not believe that it can be helpful. Also, even with a more explicit causal model, we would still need experimental studies (contra the authors' claim in sect. 3.1.3), as well as correlational ones, to make causal sense of a complex and confusing set of cross-national patterns and associations.