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Van Lange et al. suggest that environmental harshness and unpredictability, associated with low-latitude equatorial environments, lead to faster life history strategies, of which increased violence and aggression is one consequence. In general, we agree that factors that correlate with latitudinal climatic variation might influence relative frequencies of fast and slow life history strategies and that this could plausibly lead to different rates of aggression and violence in different regions across the world. The CLASH model, however, depends on questionable characterizations of what constitutes harsh, unpredictable environments and shaky assumptions about Life History Theory, and is inconsistent with patterns of violent crime rates in many regions of the world.
The authors make a very specific argument about environmental predictability and harshness: they equate high temperatures and low seasonal variation in temperature with high levels of harshness and unpredictability. Conversely, high seasonal variation, including the harsh winters that occur as one approaches the poles, are described as predictable, hence less harsh. Although environmental challenges apart from temperature and its annual fluctuations will undoubtedly contribute to harshness, Van Lange et al. argue that temperature is the environmental variable with the most explanatory power regarding violence and aggression, so for the moment we will limit our criticisms to that. It seems somewhat counterintuitive to us to assert that low seasonal variations in temperature automatically produce an unpredictable environment, which would render planning for the future...