A Scoping Review of Singlehood and Mental Health: A Case For Moving From the Proximate to the Ultimate Level of Analysis

On average single individuals commonly report worse mental health outcomes than partnered individuals. With the population of single adults quickly growing it is important the mechanism that relates singlehood to worse mental health outcomes is better understood. We conducted a scoping review to summarise the literature on the relationship between singlehood and mental health, and to evaluate the extent to which ultimate level perspectives are included in the current research. Of the 181 papers, from the PsycINFO databases, included in this review the consistent finding was that single individuals reported worse mental health oucomes. An inductive thematic analysis of these sources was used to identify patterns within the literature, with four clusters of commonly associated data items reflecting different singlehood identities (Widowed & Lonely Women, Never-Partnered & Childless Women, Male Involuntary Singles and Low-Socioeconomic Status Single Parents). Similar mental health outcomes were found for single men and women but the factors influencing this relationship were sexually differentiated in ways consistent with evolutionary theory. Childlessness and age were found to be more important in the outcomes of single women, compared to sexual access and voluntariness of singlehood in the outcomes of single men. With only a small number of exceptions, the literature broadly ignores ultimate levels of analysis and evolutionary explanations for the negative impacts of singlehood and accompanying sex differences. We provide a detailed discussion of how evolutionary theory could be used to shed light on the extant literature and call for future research to consider ultimate as well as proximate perspectives.