Human General Intelligence as a Domain General Psychological Adaptation

The concept of general intelligence as measured by standard IQ tests has always been a difficult fit for evolutionary psychology. This paper argues that intelligence is a set of domain general abilities which was not designed to solve any specific problem from the human evolutionary past. Rather, general intelligence equips humans to make mental models of the environment and to develop action plans based on these models. It is thus ideally suited to solve evolutionarily ancient problems of survival and reproduction, but also to solve novel problems and to create ideologies (e.g., Marxism) that guide and rationalize behavior. In the human Environment of Evolutionary Adaptedness (EEA), these action plans evolved as means of achieving affective states, such as assuaging hunger, achieving social status, or other evolved goal states. Moreover, it is argued that the most important mechanism underlying general intelligence, the executive processes of working memory, is not tied to regularities in the EEA. THE MODULARITY DEBATE IN EVOLUTIONARY PSYCHOLOGY Early on, the field of evolutionary psychology coalesced around the work of Leda Cosmides and John Tooby (1992) whose views conflicted with two aspects central to the century-long research tradition that has grown up around intelligence. First, the whole point of intelligence quotient (IQ) testing was to provide a measure of individual differences in cognitive ability. Evolutionary psychology, on the other hand, concentrated on human universals. For example, regarding personality research, Tooby and Cosmides (1990) proposed that variation in personality was non-adaptive “noise” (but see MacDonald, 1995, 2012; Penke, Denissen & Miller, 2007). In the area of intelligence, it is difficult to conceptualize individual differences as noise, since individual differences have a very large number of real world correlates that have been linked to reproductive success. Thus, in contemporary societies, IQ is linked with higher social status, and greater income and education, but negatively with fertility (Gottfredson, 2007). There is also a long tradition linking increasing hominid brain weight (corrected for body size), increasing encephalization, longevity, and a relatively K-style reproductive pattern (e.g., later age of reproduction) (see Rushton, 2004). The linkage between IQ and variation in life history patterns indicates that variation in IQ is an aspect of suite of life history traits and thus unlikely to be simply non-adaptive noise. 1 In J. Kush (Ed.), Intelligence Quotient: Testing, Role of Genetics and the Environment and Social Outcomes, pp. 35–54. Hauppauge, NY: Nova Science Publishers, Inc. 2 Send correspondence to Kevin MacDonald, Department of Psychology, California State University– Long Beach, Long Beach, CA 90840-090; [email protected] MacDonald, “Human General Intelligence as a Domain General Psychological Adaptation”