The generalization of full-fledged Upper Paleolithic traditions is often regarded as a proxy for the definitive colonization of Europe by Anatomically Modern Humans (AMH). The replacement of pre-existing populations, however, appears as a complex process illustrated by the sudden emergence of regional transitional assemblages. While aDNA studies have revealed several episodes of gene flow between Neanderthal and AMH, it becomes increasingly clear that scenarios of transition should account for several AMH dispersals prior to the establishment of the Proto-Aurignacian and Early Aurignacian techno-complexes. Initial Upper Paleolithic (IUP) assemblages, e.g. the Emirean/Bohunician technocomplex, could represent such early AMH migrations into Europe. Human groups would take advantage of the Greenland Interstadial 12 (GI 12) temperate climate to partly fill the “demographic vacuum” left by the preceding Heinrich 5 cold period.
Likewise, a single dispersal along the southern route is unlikely to account for the diversity of the Asian fossil and/or archeological record. Instead, several routes, multiple dispersals, or other mechanisms such as gene flow could be considered. The recent discovery of a 45 000 year old femur from Ust’-Ishim, Western Siberia, confirms that modern humans were halfway between the Urals and the Altai during GI 12. Chronologically, it coincides with the appearance of the Asian counterpart of the Emireo-Bohunician, the Northeast Asian IUP, documented between the Altai and Mongolia. Considered together, these lines of evidence reinforce the significance of the Eurasian steppe belt to modern human expansions into Asia.
The timing of Neandertal and AMH long range dispersals across the continental landscapes of a northern route, however, appear strongly dependent on climate oscillations and the induced ecological responses. The disappearance of the Northeast Asian IUP technocomplex around the Heinrich 4 event is consistent with the genetic data showing that the UI individual was close to the common ancestor of present-day European and Asian populations but did not have direct descendants among current populations. It would illustrate an unsuccessful AMH radiation predating the definitive colonization of Eurasia. The subsequent spread of full-fledged Upper Paleolithic traditions could correspond to the beginning of more durable settlements of populations closely related to the lineages ancestral to current Asian population.