Kinship: The Tie that Binds (Disciplines). In: Holcomb HR, editor. Conceptual Challenges in Evolutionary Psychology. Dordrecht: Springer Netherlands; 2001. pp. 19-38. [DOI: 10.1007/978-94-010-0618-7_2]

Social closeness of MZ and DZ twin parents towards nieces and nephews

Twins' marriages to non‐twins yield genetically and socially informative kinships. Monozygotic (MZ) twins' genetic identity makes them ‘genetic parents’ of their nieces/nephews, and their nieces/nephews their ‘genetic children’. The present study is the first to apply twin‐family models to study social relatedness. Analyses of twin families (MZ: N = 248; DZ: N = 75) tested evolutionary‐based concepts concerning social closeness, perceived similarity and caretaking. Hypotheses based on Hamilton's inclusive fitness theory were supported: MZ twin aunts/uncles expressed greater social closeness towards their nieces/nephews than DZ twin aunts/uncles; and female twins from same‐sex pairs expressed greater closeness towards their nieces/nephews than male twins from same‐sex pairs. This study underlines benefits of associations between behavioural‐genetic and evolutionary psychological theories, methods and interpretations. Copyright © 2007 John Wiley & Sons, Ltd.

Genetic Contributions to Loneliness and Their Relevance to the Evolutionary Theory of Loneliness

Loneliness is a negative and distressing emotional state that arises from a discrepancy between one's desired and achieved levels of social connectedness. The evolutionary theory of loneliness (ETL) posits that experiencing loneliness is an inherited adaptation that signals that salutary social relations are endangered or damaged and prompts people to reconnect to significant others. The basic tenets of the ETL has led researchers to examine the genetic underpinnings of loneliness. The current review provides an updated overview of genetic studies on loneliness and discusses the importance of genetic research for the ETL. The most recent studies suggest that the many genes that contribute to a small degree to differences in loneliness partially overlap with genes that contribute to neuroticism, but not with depression. In addition, the genetic studies discussed in this review show that genes are unlikely to have a direct effect on loneliness. Instead, environmental factors determine in a dynamic fashion how genes that contribute to loneliness are expressed. Future research on epigenetic processes, such as DNA methylation, can further elucidate the dynamic interplay between genes and the environment and how this interplay contributes to loneliness.

Examining the Acceptance of and Resistance to Evolutionary Psychology

The field of psychology remains a divided one. Several different sub-disciplines (e.g., developmental, cognitive, behaviorism, social, etc.) form what could be a unified scientific area. However, there is no widely accepted theory of unification. Charles Darwin once theorized that evolutionary theory would change the foundation of psychology; but over the years, evolutionary psychology has been met with hostile resistance from some of the prominent psychologists within the other sub-disciplines. Yet in recent years, all of the divided sub-disciplines of psychology have been slowly implementing evolutionary principles into their literature and research. This slow integration of evolutionary psychology into the other sub-disciplines indicates the possibility of a unified psychology with evolution as its foundation. This paper briefly reviews the literature within each major sub-discipline of psychology to show their implementation of evolutionary psychological theories, indicating the possibility of evolutionary psychology becoming the unifying paradigm upon which the entire field of psychology can be based. A call for action to continue this process is also discussed.

Meeting One's Twin: Perceived Social Closeness and Familiarity

Perceptions of social closeness and familiarity were assessed among 44 monozygotic (MZA) and 33 dizygotic (DZA) reunited twin pairs, and several individual twins and triplets. Significantly greater MZA than DZA closeness and familiarity were found. Closeness and familiarity ratings for co-twins exceeded those for nonbiological siblings with whom twins were raised. Correlations between perceptions of physical resemblance and social closeness and familiarity were positive and statistically significant. However, most correlations between social relatedness and contact time were non-significant. Associations between social relatedness and similarities in selected behavioral traits were also examined. The findings support various theoretical perspectives anticipating greater affiliation among close relatives than distant relatives.