Associations between climate and IQ in the United States of America. "Relations between average temperature of each of the 48 contiguous states and estimates of state IQ were inspected. Additional state variables were controlled in the correlational analyses, namely gross state product, percent Hispanic, Black, and Asian in the state population, and the pupil-to-teacher ratio for each state. A significant correlation between average temperature and state IQ was found (r = -.70, p < .001). Possible explanations are discussed." Bonus excerpt from the text: "Significant negative relationships were found between state IQ and both winter (r = −.73, p < .001) and summer (r = −.53, p < .001) temperatures. Moreover, a significant negative association was found between state IQs and year-round temperatures (r = −.70, p < .001). Thus, as environmental temperature decreases, the state IQ tended to increase, congruent with the hypothesis and the findings of Templer and Arikawa (2006). While expected, these results are difficult to explain. Previous research has attributed the relationship between climate and IQ to the evolutionary process. Lynn (1991) posited that early humans who migrated from tropical climates to colder ones, were forced to undertake challenging cognitive tasks which resulted in selection for larger brain size and increased intelligence, relative to individuals and groups who remained in the warmer climates. The United States population is composed largely of immigrant groups representing a wide range of ethnicities and geographical origins, with only 1.5% indigenous peoples. Relations between state IQ and climatic data must reflect characteristics of the various ethnic groups prior to their arrival in North America. Currently there are few additional challenges related to living in colder states, so it is difficult to see why the correlation between temperature and IQ persists. Perhaps, individuals from colder climates in Europe and Asia tended to migrate to similar colder climates in the USA. Whatever the cause, studies that have examined the stratification variables of intelligence test standardization samples have reported regional differences that agree with the present findings. "
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