A review of European Middle Pleistocene hominin evolution
The European Middle Pleistocene hominin record plays a central role in debates on evolutionary processes underlying the origin and emergence of the Neanderthal lineage, yet it remains characterized by pronounced morphological variability and persistent taxonomic uncertainty. Over the last decades, this record has been interpreted through a wide range of evolutionary models that differ in their assumptions about population continuity, demographic inputs and the geographical provenance of hominin groups. These models include: (1) basic continuity scenarios deriving Middle Pleistocene populations from indigenous Early Pleistocene groups; (2) total replacement models invoking complete population turnover; (3) coexistence models proposing multiple contemporaneous lineages; (4) eastern source–sink and CADE models based on recurrent dispersals from Southwest Asia; (5) west-to-east expansion models suggesting a western European origin for key Neanderthal traits; and (6) dual Acheulean-source models positing independent dispersals into different regions of Europe. We show that, despite their differences, these models often share a trait-by-trait analytical premise in which characters are treated as largely independent units. As an alternative, we outline an organismic framework in which traits are embedded in integrated developmental and functional modules. Mosaic patterns are expected because modules respond with different sensitivities and temporal dynamics to shared organism-level perturbations, not because they follow independent evolutionary trajectories. Finally, we connect mosaic outcomes to temporal sequence using the two-phase model, in which shifts in body mass/metabolism and later encephalisation/basicranial reorganisation generate coordinated yet asynchronous anatomical change. This process-oriented perspective reduces the need to invoke multiple contemporaneous MP lineages and yields testable expectations for future research on population structure and module-specific evolutionary responses.
