The COVID-19 pandemic is but one of many instances of environmental adversities that have recurred in human history. Biobehavioral resource allocation strategies, known as fast (reproduction-focused) versus slow (development-focused) life history (LH) tradeoff strategies, evolved to deal with environmental challenges such as infectious diseases. Based on 141 young people and their mothers observed prior to (ages 9 and 13) and during (age 20) COVID-19, we investigated longitudinal relations involving slow LH strategies. The results support the adaptive role of slow LH strategies in reducing COVID-related increases in externalizing problems. In addition, the effect of early adversity on COVID-related increases in externalizing was mediated, and the effect on COVID-related increases in internalizing was moderated, by slow LH strategies.