Pollen: A Key Tool for Understanding Climate, Vegetation, and Human Evolution

Abstract

The analysis of ancient pollen (and spores) preserved in sedimentary sequences is a classical approach used in paleoclimatology, paleoecology and archaeology since the beginning of the twentieth century. Yet, pollen analysis is the most powerful tool to reconstruct past vegetation changes affording more precise documentation of distribution, composition and land vegetation cover than geochemical tracers only providing the wet/dry-loving plants ratio through time. Ancient pollen from deep-sea cores has allowed the direct comparison of vegetation and atmospheric conditions on land with changes in ocean and ice sheet dynamics, identifying, for instance, a strong air-sea thermal contrast at orbital and millennial time scales in the European margin favouring moisture production and transport to northern hemisphere high latitudes and the last entering in glaciation. The study of ancient pollen along with plant macro remains and modern and ancient DNA has revealed the location of cryptic refugia for temperate and boreal trees during cold periods and reduced the original velocity estimations for tree migration highlighting the difficulty for certain trees to keep pace with the on-going climate change. Pollen-based vegetation changes are of most relevance to understand human evolution as past populations were tightly dependent on plant and animal resources. Repeated and strong savannah expansion in eastern Africa contemporaneous with the onset of large northern hemisphere glaciations provided enough animal resources that allowed hominin brain increase and the emergence of early Homo. In Europe, the successive and rapid steppe-dominated cold periods punctuating the last glacial period triggered repeated increases of ungulate biomass and human demography that may explain the increase and accumulation of innovations in Homo sapiens populations.