D i s s e r t a t i o n Approaches to an Evolutionary Personality Psychology: The Case of Sociosexuality zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) im Fach Psychologie an der Mathematisch-Naturwissenschaftlichen Fakultät II der Humboldt-Universität zu Berlin eingereicht von Dipl.-Psych. Lars Penke geb. am 02. September 1978 in Detmold Dekan: Prof. Dr. Wolfgang Coy Präsident der Humboldt-Universität zu Berlin Prof. Dr. Christoph Markschies Gutachter: 1. Prof. Dr. Jens B. Asendorpf 2. Prof. Dr. Steven W. Gangestad 3. Prof. Dr. Peter Borkenau eingereicht: 10. Mai 207 Datum der Promotion: 17. Juli 2007 This thesis is dedicated to my son Richard. Table of Contents Abstract (English) Abstract (German) Introduction Part I: The Evolutionary Genetic Approach to Personality The Evolutionary Genetics of Personality Lars Penke, Jaap J. A. Denissen and Geoffrey F. Miller 22 Open Peer Commentaries by Timothy C. Bates, Anne Campbell, Niels J. Dingemanse, Harald Euler, Aurelio José Figueredo & Paul Gladden, David C. Funder, Steven W. Gangestad, Kerry L. Jang, Wendy Johnson, Matthew C. Keller, James J. Lee, W. John Livesley, Gerald Matthews, Robert R. McCrae, Denis Réale, Irene Rebollo & Dorret I. Boomsma, Gad Saad, Andrew Sih & Alison M. Bell, Susan C. South & Robert F. Krueger, Alexander Strobel, Alfonso Troisi, and Kees van Oers Author’s Response: Genes, Evolution, and Interdisciplinary Personality Research Lars Penke, Jaap J. A. Denissen and Geoffrey F. Miller Part II: The Life History Approach to Personality Single Attribute Implicit Association Tests (SA-IAT) for the Assessment of Unipolar Constructs: The Case of Sociosexuality Lars Penke, Jan Eichstaedt and Jens B. Asendorpf Beyond Global Sociosexual Orientations: A More Differentiated Look at Sociosexuality and its Effects on Courtship and Romantic Relationships Lars Penke and Jens B. Asendorpf) Abstract Evolutionary approaches have not been as successful in personality psychology as they were in other areas of psychology, arguably because of the misfit between modern evolutionary psychology’s strong focus on universal adaptations and the study of (mostly heritable) individual differences in personality psychology. In this thesis, two alternative evolutionary approaches, which appear more suitable for personality psychology, are discussed and applied. The evolutionary genetic approach asks why genetic variance in personality differences exists. In the first part of this thesis, three evolutionary genetic mechanisms that could explain genetic variance in personality differences are assessed: selective neutrality, mutation-selection balance, and balancing selection. Based on evolutionary genetic theory and empirical results from behavior genetics and personality psychology, it is concluded that selective neutrality is largely irrelevant, that mutation- selection balance seems best at explaining genetic variance in intelligence, and that balancing selection by environmental heterogeneity seems best at explaining genetic variance in personality traits. A general model of heritable personality differences is presented, which conceptualizes intelligence as a fitness component and personality traits as individual reaction norms of genotypes across environments, with different fitness consequences in different environmental niches. Complementary to the evolutionary genetic approach, the life history approach starts with how people allocate their resources to evolutionarily relevant life tasks. It asks how individual differences in these allocation decisions emerge from the interplay of various developmental components, including personality differences. In the second part of this thesis, differences in the allocation to long- term versus short-term mating tactics (as reflected in the construct of sociosexuality) are used as a case to exemplify this approach. Two new measures for the assessment of sociosexuality components are presented. While the revised Sociosexual Orientation Inventory (SOI-R) is a questionnaire that assesses the facets Behavior, Attitude and Desire, the sociosexuality Single-Attribute Implicit Association Test (SA-IAT) is a new methodic development aimed to assess implicit sociosexuality indirectly. Both measures showed concurrent validity in online studies, but only the SOI-R facets were predictive of mating tactics, including observed flirting behavior, as well as for the number of sexual partners and changes in romantic relationship status over the following 12 months. Furthermore, distinct sex differences, developmental trends, degrees of assortative mating, and effects on a romantic partner were found for the three SOI-R facets, indicating their unique roles in the development of mating tactics. Zusammenfassung Evolutionäre Herangehensweisen hatten in der Persönlichkeitspsychologie nicht den gleichen Erfolg wie in anderen Bereichen der Psychologie, vermutlich wegen der Fehl- passung des starken Fokus auf universele Adaptationen in der modernen Evolutionspsychologie mit der Untersuchung (größtenteils erblicher) individueler Unterschiede in der Persönlichkeitspsychologie. In dieser Dissertationsschrift werden zwei alternative evolutionäre Herangehensweisen diskutiert und angewendet, welche passender für die Persönlichkeitspsychologie erscheinen. Die evolutionsgenetische Herangehensweise fragt, warum genetische Varianz in Persönlichkeitsunterschieden existiert. Im ersten Teil dieser Dissertationsschrift werden verschiedene evolutionsgenetische Mechanismen, die genetische Varianz erklären können, verglichen. Auf Grundlage evolutionsgenetischer Theorie und empirischen Befunden aus der Verhaltensgenetik und Persönlichkeitspsychologie wird geschlussfolgert, dass ein Mutations-Selektions- Gleichgewicht genetische Varianz in Intelligenzunterschieden gut erklären kann, während ausgleichende Selektion durch Umweltheterogenität die plausibelste Erklärung für genetische Unterschiede in Persönlichkeitseigenschaften ist. Es wird ein allgemeines Modell vorgeschlagen, welches Inteligenz als Fitnesskomponente konzeptualisiert und Persönlichkeitseigenschaften als individuelle Reaktionsnormen von Genotypen auffasst, welche unterschiedliche Fitnesskonsequenzen in unterschiedlichen Umweltnischen haben. Komplementär zur evolutionsgenetischen Herangehensweise beginnt die „Life History“- Herangehensweise damit, wie Menschen ihre Ressourcen in evolutionär relevante Lebensbereiche investieren. Sie fragt, wie Unterschiede in diesen Investitions- entscheidungen aus dem Zusammenspiel verschiedener Entwicklungsomponenten entstehen, einschließlich Persönlichkeitsunterschiede. Im zweiten Teil der Dissertations- schrift wird diese Herangehensweise am Beispiel von Investitionsunterschieden in Langzeit- versus Kurzzeit-Paarungstaktiken (wie im Konstrukt der Soziosexualität abgebildet) erläutert. Zwei neue Maße zur Erfassung von Soziosexualitätskomponenten werden vorgestellt. Während das revidierte Soziosexuelle Orientierungsinventar (SOI-R) ein Fragebogen zur Erfassung der Facetten „bisheriges Verhalten“, „Einstellung“ und „Begehren“ ist, wurde mit dem „Single-Attribute“ Impliziten Assoziationstest (SA-IAT) eine neue Methode zur indirekten Erfassung impliziter Soziosexualität entwickelt. Beide Maße zeigten konkurrente Validität in Onlinestudien, aber nur die SOI-R-Facetten erwiesen sich als prädiktiv für Paarungstaktiken, einschließlich beobachtetem Flirtverhalten sowie der Zahl der Sexualpartner und Veränderungen im Beziehungsstatus innerhalb der nächsten 12 Monate. Weiterhin wurden für die SOI-R-Facetten distinkte Geschlechtsunterschiede, Entwicklungsverläufe, Grade selektiver Partnerwahl, und Effekte auf den Beziehungspartner gefunden, was ihre spezifischen Rollen in der Entwicklung von Paarungstaktiken unterstreicht. 8 Introduction Over the last two decades, evolutionary approaches had a great deal of success in various branches of psychology (e.g. Buss, 2005; Dunbar & Barrett, 2007). However, personality psychology apparently withstands this general trend. While some notable theoretical attempts toward an evolutionary personality psychology have been made as early as 1990 (Buss, 1990; Tooby & Cosmides, 1990), not much has happened since then, and the current state must be regarded as unsatisfactory (Miller, 2000; Nettle, 2006). An evolutionary account for personality differences is generally acknowledged as a valuable goal for personality psychology in the long run (e.g. McAdams & Pals, 2006), but evolutionary approaches have clearly not pervaded mainstream personality research. The overarching goal of this thesis is to provide and exemplify evolutionary approaches that are suitable for personality research. One of the main reasons for the low impact that evolutionary psychology had on personality research is likely that modern evolutionary psychology has focused very much on adaptations. Adaptationistic evolutionary psychology studies domain-specific solutions to reoccurring adaptive problems in the universal design of the human species. A defining characteristic of these adaptations is that they have been fixed in the human genome, which means that they show no genetic variation. They are inherited, but not heritable (Tooby & Cosmides, 1990, 2005). This severely limits the value of the adaptationistic approach to personality research: while it can be used to explain sex differences (Mealey, 2000) and some individual differences resulting from conditional developmental reactions to environmental factors (e.g. attachment styles, e.g. Buss & Greiling, 1999), it is unable to explain heritable individual differences (Tooby & Cosmides, 1990) – and a heritable component has been established for virtually all personality differences (Plomin, DeFries, McClearn & McGuffin, 2001; Turkheimer, 2000). Alternative to the adaptationistic approach, an evolutionary genetic approach can explain genetic differences between individuals from an evolutionary perspective. Evolutionary genetics studies the effects of processes like mutation, selection, genetic drift, and migration on genetic variation between individuals and across populations (Maynard Smith, 1998; Roff, 1997).In the first part of this thesis, comprised by the theoretical target article “The evolutionary genetics of personality” (Penke, Denissen & Miller, in press a), 22 peer commentaries, and the author’s reply (Penke, Denissen & Miller, in press b), it is argued that evolutionary genetics provides a more suitable approach to personality psychology than adaptationism. While some evolutionary genetic mechanisms have already been alluded to in earlier evolutionary treatises on personality (Buss, 1990, 1991; MacDonald, 1995; Nettle, 2006; Tooby & Cosmides, 1990), these articles have not exploited the full potential of an evolutionary genetic approach. Penke et al. (in press a, b) argue that the degree of 9 elaboration of modern evolutionary genetic models and the wealth of data on human personality allows us to infer which evolutionary genetic mechanisms are most plausibly responsible for the existence and maintenance of genetic variation in personality differences. They conclude that a small set of evolutionarily independent dimensions of genetic personality differences exist in humans, of which the one underlying the g factor of intelligence is most likely maintained by a balance of new mutation and counteracting selection, while those underlying broad personality domains (as for example represented in the Five Factor Model of personality) most likely still exist because spatial or temporal heterogeneity in our (physical and social) environment causes balanced selection pressures on them. Penke et al. (in press a, b) also provide insights into how an evolutionary perspective might help to understand the complex interplay between genes and environmental factors in producing personality phenotypes. Evolutionary genetics thus offers a “bottom-up” approach to an evolutionary personality psychology, one where the genetic level is linked to individual differences in abstract behavioral dispositions (i.e., personality traits and abilities). However, such dispositions can only be evolutionarily relevant if they translate into consequential behaviors. More specifically, they have to influence how well people are able to extract resources (ultimately energy) from their environments, and how they invest these resources into conflicting life domains of evolutionary relevance (i.e., growth, survival, reproduction, and the support of genetic relatives). These potentials and allocation decisions, which influence reproductive success and ultimately fitness, are studied in evolutionary anthropology and behavioral ecology within the framework of life history theory (Kaplan & Gangestad, 2005). The life history approach thus deals with individual differences in highly complex behavioral and developmental strategies and tactics for the allocation of resources across the lifespan. Life history strategies and tactics can be conceptualized as the final outcome of (1) interacting systems of adaptations (Kaplan & Gangestad, 2005, 2007; White, Dill & Crawford, 2007), which are often sensitive to an individual’s own potential (i.e., condition) and to the environment (e.g. Gangestad & Simpson, 2000), and (2) genetic differences within these systems (Roff, 2002). However, the step from broad and complex strategies and tactics to domain-specific adaptations and genetic differences is a big one - from the very “downstream” to the very “upstream” in terms of the watershed model that Penke et al. (in press a) adopted from Cannon and Keller (2005). Therefore, it might be worthwhile (if not necessary) to take an intermediate step and start with studying the mid-level components of life-history strategies and tactics, as well as their interactions with each other and with relevant environmental factors across the lifespan. Since these mid-level developmental components include personality differences (both heritable and environmental-contingent), life history theory offers a “top-down” approach to an evolutionary personality psychology. 10 The life history approach is thus complementary to the evolutionary genetic “bottom-up” approach: While the former connects personality to fitness, the latter connects genes to personality. The second part of this thesis uses the life history trade-off between long-term and short- term mating tactics as an exemplary case for the life history approach to personality. Long- term mating tactics include developing and protecting an exclusive and committedromantic relationship, usually accompanied by high levels of parental investment in potential offspring. In contrast, short-term mating tactics include investing greater efforts in finding and courting potential mates, in order to have sexual affairs with either many mates or mates of especially high quality. Individual differences along this dimension of mating tactics are often equated with sociosexual orientations, which describes individual differences in the willingness to have uncommitted sex (Simpson et al., 2004). Both papers in the second part of this thesis were aimed to contribute to a dissection of this broad life history trait into its mid-level components. Penke and Asendorpf (2007) developed a revised version of the Sociosexual Orientation Inventory (SOI; Simpson & Gangestad, 1991), a short self-report questionnaire which is the most established measure of sociosexuality. The new SOI-R assesses three facets of global sociosexuality (desire, attitude, and past behavioral experiences). Penke, Eichstaedt and Asendorpf (2006) deviated from the usual reliance on self-reports and attempted to develop an indirect measure of implicit sociosexuality. This latter work was inspired by the recent trend in social psychology to explain behavior as the outcome of two different cognitive systems, distinguished by their reliance on automatic versus reflective information processing. It has been argued that the automatic systems is more involved in the generation of spontaneous, impulsive behavior, while the reflective system is responsible for deliberate behavior (Strack & Deutsch, 2004). Since Implicit Association Tests (IATs) are assumed to be capable of assessing individual differences in implicit personality self-concepts (Schnabel, Greenwald & Asendorpf, in press), and have indeed shown incremental validity over explicit self-report measures in the prediction of spontaneous behavior in some studies (e.g. Asendorpf, Banse & Mücke, 2002), Penke et al. (2006) developed a variant of the IAT procedure, the Single-Attribute IAT (SA-IAT), for the assessment of implicit sociosexuality. The rationale here was that if some of the psychological components that influence mating tactics operate on the automatic level, they might be better captured by an indirect measure like the sociosexuality SA-IAT than by an explicit self-repot measure like the SOI or SOI-R. (Note that, while Barrett, Frederick, Haselton and Kurzban, 2006, recently argued that evolved psychological mechanisms do not have to operate at the automatic level, it is possible that some of them do. Characterizing the level of operation for psychological adaptations might help us to understand them better.)