Loneliness and Depressive Symptoms Within and Across Hourly and Half-Yearly Timescales: Testing the Evolutionary Theory of Loneliness

Can feelings of loneliness and depression be adaptive for adolescents? Yes, suggests the Evolutionary Theory of Loneliness: initially, loneliness activates depressive responses for self-preservation. In turn, these feelings prepare adolescents for reaffiliation, thereby reducing loneliness (H1a: short-term balancing feedback loop). If this fails, loneliness and depressive symptoms may become long-term traits that exacerbate each other over time (H1b: long-term reinforcing feedback loop). Therefore, the short-term balancing feedback loop between loneliness and depressive symptoms may buffer against their long-term increases (H2: across-timescale influence). We tested these hypotheses in Dutch adolescents (Mage_Wave1 = 12.9, SDage_Wave1 = 0.7, 53% female) using six-wave, half-yearly panel data (N = 774; 2017-2021) and 7-day, 1.5-hourly experience sampling data (nsubsample = 84; mid-2021). Residual dynamic structural equation modeling revealed reinforcing feedback loops at both short-term (1.5-hourly) and long-term (half-yearly), supporting H1b but not H1a. Bayesian latent change score modeling supported H2: Adolescents who felt more depressed an hour after heightened loneliness showed smaller half-yearly increases in trait loneliness. However, this buffering effect was not predicted by hourly depressed-to-loneliness relation, nor did either hourly relation predict half-yearly changes in depressive symptoms. Our findings suggest that feeling depressed shortly after loneliness may protect adolescents from having long-term loneliness.