The Evolutionary Theory of Loneliness (ETL) proposes that loneliness is a complex psychological state shaped by evolutionary pressures. This chapter explores the assumptions and underpinnings of the ETL, examining how loneliness is related to evolutionary fitness, heritability, and potential mechanisms. It delves into the personal, behavioral, and environmental factors that affect loneliness as well as the different evolutionary purposes of loneliness and connectedness. The reciprocal nature of loneliness, its relationship with depression and self-regulation, and the role of social observational learning in evolutionary trajectories are outlined. This chapter highlights the implications of the Evolutionary Theory of Loneliness for understanding and addressing loneliness, introducing the concept of “collective connection” as a phenotype for understanding this psychological state. The recent evolution of social media and other tools has been reviewed through the lens of the ETL, aiming to understand when technology can be supportive and when it is a risk factor for developing and maintaining loneliness. Moreover, we have reviewed the recent empirical tests of the ETL and discussed the contemporary paradigms shaping our understanding of loneliness and its development. Understanding loneliness as a polygenic risk impacted by multiple genes and potentially shaped by epigenetic factors - if environmental factors alter gene expression can help design better interventions. As such, the ETL and other evolutionary assumptions can be of unique value, although critical reflection is still needed.