The Phenotype of Loneliness.

Goossens' (in press) review nicely maps the progression of scientific research from its early focus on loneliness as a dysphoric state that results from the discrepancy between a person's ideal and actual social relationships to its current emphasis on the centrality of loneliness to our very nature as a social species, and he argues that developmental science throughout Europe has a great deal to contribute to our understanding of this construct. He concludes that psychologists should care about research on loneliness for five reasons: (i) it is a well-defined phenotype, (ii) it shows both high stability and individual differences in rates of change across years, (iii) it has adaptive value and evolutionary significance, (iv) it has a genetic substrate that is moderated by social environments, and (v) it has self-maintaining features that can lead to adverse mental health outcomes. Goossen's (2012) review is rife with information and ideas. We focus here on two additional important reasons and on the phenotype of loneliness.