Evolution of Personality Variation in Humans / A challenge to status quo

I’m including more of the paper in the next post: a section on the BIG 5 Personality Traits model. 

The prejudice against there being an Asperger type “personality” within the variation of “acceptable human” variation, is incredibly strong – and socially enforced – what I have encountered among “psych-psych” professionals is outright dismissal, and even “scorn” at the suggestion that an Asperger individual might not be “developmentally defective” but simply a “version” of Homo sapiens with different sensory and perceptual systems well-adapted to specific natural environments. 

Evolutionary Psychology is the branch of psychology that studies the mental adaptations of humans to a changing environment, especially differences in behavior, cognition, and brain structure.

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https://www.researchgate.net (Note; I have a direct link to the pdf, but the url of the pdf does not link to the pdf!)

by Daniel Nettle, Newcastle University in American Psychologist, 2006  Evolution and Behaviour Research Group, Division of Psychology, Henry Wellcome Building, University of Newcastle, Newcastle NE2 4HH, United Kingdom.

In recent years, there has been an extraordinary growth of interest in giving ultimate, evolutionary explanations for psychological phenomena alongside the proximate, mechanistic explanations that are psychology’s traditional fare (Barkow, Cosmides, & Tooby, 1992; Buss, 1995). The logic of ultimate explanations is that for psychological mechanisms and behavioral tendencies to have become and remain prevalent, they must serve or have served some fitness-enhancing function. (We AS types are still here, despite being a 1% minority!)

The explanatory program of evolutionary psychology has concentrated strongly on human universals, such as jealousy, sexual attraction, and reasoning about social exchange (Buss, 1989; Buss, Larsen, Westen, & Semmelroth, 1992; Cosmides, 1989). The focus has been on the central tendency of the psychology of these domains, rather than the observed variation, and explanation has been in terms of adaptations shared by all individuals. Indeed, some evolutionary psychologists have implied that one should not expect there to be any important variation in traits that have a history of selection. For example, Tooby and Cosmides (1992) argued that “human genetic variation . . . is overwhelmingly sequestered into functionally superficial biochemical differences, leaving our complex functional design universal and species typical” (p. 25). The reason invoked for this assertion is that natural selection, which is a winnowing procedure, should, if there are no counteracting forces, eventually remove all but the highest-fitness variant at a particular locus (Fisher, 1930; Tooby & Cosmides, 1990), especially because complex adaptations are built by suites of genes whose overall functioning tends to be disrupted by variation.

Because of the winnowing nature of selection, the existence of heritable variation in a trait is argued to be evidence for a trait’s not having been under natural selection: “Heritable variation in a trait generally signals a lack of adaptive significance” (Tooby & Cosmides, 1990, p. 38, italics in original). Tooby and Cosmides (1992) thus suggested that most of the genetic variation between human individuals is neutral or functionally superficial. They did, however, concede a possible role for “some thin films” (?) of functionally relevant heritable interindividual differences (Tooby & Cosmides, 1992, p. 80). The possible sources of these thin films—frequency-dependent selection and selective responses to local ecological conditions—are discussed in greater detail below. What is relevant for the present purposes is the low priority given to understanding these thin films relative to the task of describing and explaining the universal psychological mechanisms that humans undoubtedly all share.

Personality Variation and Evolutionary Psychology 

There has however, been a response from researchers seeking to marry differential and evolutionary psychology in a way that gives greater weight to the study of individual differences (see, e.g., Buss, 1991; Buss & Greiling, 1999; Figueredo et al., 2005; Gangestad & Simpson, 1990; MacDonald, 1995; Nettle, 2005). David Buss made an early contribution to this literature by enumerating possible sources of functionally important interindividual variation (Buss, 1991; see also Buss & Greiling, 1999). Most of these are mechanisms that do not rely on heritable variation in psychological mechanisms, for example, enduring situational evocation, or calibration by early life events, or calibration of behavior by the size or state of the individual. However, Buss also discussed the possibility that there are equally adaptive alternative behavioral strategies underlain by genetic polymorphisms, or continua of reactivity of psychological mechanisms, in which there is no universal optimum, and so genetic variation is maintained. The idea of continua of reactivity was taken up by Kevin MacDonald (1995). MacDonald proposed that the normal range of observed variation on personality dimensions represents a continuum of viable alternative strategies for maximizing fitness.

In this view, average fitness would be about equal across the normal range of any given personality dimension, but individuals of different personality levels might differ in the way that they achieved their fitness—for example, by investing in reproductive rather than parental effort. Implicit in MacDonald’s formulation, but perhaps not examined in enough detail, is the concept of trade-offs. The idea of trade-offs is reviewed in detail below, but the key point is that if two levels of a trait have roughly equal fitness overall and if increasing the trait increases some component of fitness, then it must also decrease other components. Every benefit produced by increasing a trait must also produce a cost. If this is not the case, there is no trade-off, and natural selection is directional toward the higher value of the trait.

The purposes of the present article are several. First, no reasonable biologist or psychologist should disagree with Tooby and Cosmides (1990, 1992) that humans’ psychological mechanisms show evidence of complex design and are largely species-specific. Nor need differential psychologists deny the importance of the branches of psychology that are devoted to the study of species-typical mechanisms. However, I argue that a more up-to-date reading of the very biology from which Tooby and Cosmides draw their inspiration leads to a rather different view of the extent and significance of variation. The films of functionally significant interindividual variation need not be particularly thin. The first purpose of this article, then, is to review interindividual variation in nonhuman species, with particular attention to the way that selection can allow variation to persist even when it is relevant to fitness. Second, although Buss’s (1991) and MacDonald’s (1995) reviews have been influential in enumerating possible evolutionary mechanisms that lie behind the persistence of personality differences, there has as yet been relatively little work in evolutionary personality psychology that actually tests the predictions of these models empirically (for some exceptions, see Figueredo et al., 2005; Gangestad &Simpson, 1990; Nettle, 2005).

The bulk of the work in personality psychology goes on uninspired by considerations of ultimate evolutionary origins. The second purpose of this article, therefore, is to build from MacDonald’s ideas of personality dimensions as alternative viable strategies, outlining a more explicit framework of costs and benefits, and to apply this framework to each of the dimensions of the five-factor model of personality. This approach allows existing studies that were done from a largely inductive, a theoretical perspective to be interpreted more coherently through the long lens of adaptive costs and benefits. In addition, the approach allows the generation of novel predictions and ideas for future research.

much, much more… 11 pages total 

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