Abstract <p>Sleep is a ubiquitous phenomenon throughout the animal kingdom; nonetheless, its evolutionary origins remain mostly enigmatic. Comprehending the origins of the biological systems governing sleep necessitates methodologies that extend beyond comparisons of current animals and instead investigate the profound history of their molecular underpinnings. This study used a molecular paleobiology framework toexamine the evolutionary origins of sleep-related genes by mapping their homologs onto the reconstructed genome of the Last Universal Common Ancestor (LUCA). Utilizing phylogenomic reconstruction and functional enrichment studies, we ascertain that multiple gene families crucial for human sleep, especially those governing circadian timing, fundamental metabolism, and cellular signaling, were extant in this ancient progenitor. The results substantiate the perspective that the chemical elements facilitating sleep did not arise as new innovations but rather evolved from ancient cellular systems that initially served fundamental physiological roles. Our research demonstrates a profound evolutionary pathway in which the intricacy of sleep developed through the incremental co-option and amalgamation of conserved genomic modules. This study presents a novel viewpoint on the emergence of essential physiological activities from primordial and universal biological mechanisms.</p> Graphical abstract <p></p>