| Research in Africa and Europe shows that vegetation and climate change takes an important role in early human evolution,migration and adaptation.The scene,however,is obscure in East Asia.Qinling Mountains(QM),located in the East Asian monsoon region,is in the transition zone of the north and south China in physical geography.At the same time,various periods of hominin fossils and Paleolithic remains since 1.2 Ma in QM are discovered,particularly in-situ lithic artifacts buried in the loess deposits,making it an ideal area for study of relationship between human behaviors and environmental change.In this study,we will try to reconstruct the vegetation and climate change by pollen analysis,based on pollen preservation study for pollen assemblage correction,and then explore its impact on human activities.Pollen can be preserved in nature for a long time,but it is not non-degradable.Caution should be taken as the reconstructed paleovegetation may be biased if pollen preservation is ignored.Therefore,we firstly investigates spatio-temporal pollen preservation condition and its causal factors in Chinese loess deposits,based on studying pollen of samples in three glacial and interglacial units across a climate gradient in China.The results show that pollen concentration decreases from the cool and dry North China to warmer and wetter climate in more southerly locations at the same period.Pollen concentration in loess deposits is influenced by both pollen preservation and production,and the former one becomes the overwhelming factor where climate is quite warm and wet.Climate can influence pollen preservation by enhancing conditions for oxidation and microbial attack.Increasing temperature and moisture facilitates both the oxidation process and microbial destruction,which can result in pollen deterioration in loess deposits.In addition,a high soil pH can also cause pollen damage over time.These factors favour the relative preservation of several taxa such as Artemisia,Aster,Taraxacum,Pinus and Chenopodiaceae,and this leads to them dominating pollen spectra of Chinese loess deposits.The original pollen record suffers from the differential loss of taxa,especially toward southern loess regions and the absence of broadleaf forests or forest steppe reconstructed by pollen records may be attributable to this.Based on the available data,one scheme for correction of pollen assemblages is put forward.Based on pollen preservation and surface pollen studies,the vegetation cover and monsoon climate change since ca.1.2 Ma in QM were reconstructed by pollen analysis of several profiles in northern,middle and southern QM,combined with the existing data.Though the pollen grains underwent severe degradation and the broad-leaved tree coverage was probably underestimated,it did not alter the trend of arboreal content change on the orbital time scale.There existed mainly forest steppe with a range of open broad-leaved forest to grassland during Pleistocene in QM,with higher tree coverage,warmer-wetter climate and stronger summer monsoon southerly.On the orbital time scale,the vegetation and climate change in QM were consistent with the East Asian summer monsoon change indicated by magnetic susceptibility of loess-paleosol sequences,and the global temperature/ice volume change recorded by the deep sea oxygen isotope.The arboreal coverage was relatively higher under stronger monsoon climate during interglacial period,in contrast to glacial period.Besides the periodic changes,there were several major stages of environment change since the late Early Pleistocene.In the Early Pleistocene,many Oriental and forest-prefered mammals lived both in the southern and northern QM,indicating humid and subtropical climate.However,the climate turned to drier and cooler in the end of this period.During ca.0.8-0.3 Ma,the arboreal coverage was relatively high and monsoonal climate was strong in whole,changing with a cycle of?100 ka,similar to the loess and deep sea records.Since ca.0.3 Ma,the broadleaf trees and summer monsoon in this area became retreated,with significantly increasing fluctuation.The land cover became more open,with weaker summer monsoon in further since ca.0.07 Ma.Under the relatively strong monsoonal climate,QM became a suitable and permanent habitat in East Asia for Pleistocene human since at least 1.2 Ma,when they exploited and occupied this area.There are many advantages here,such as the warm and humid monsoonal climate,abundant forest resources for food,numerous rivers for water and various landforms for living.However,the early human were probably constrained by the environment,in that their survival,migration,evolution and adaptation were all significantly affected by both the glacial-interglacial change and stepwise trend in vegetation and climate.Early human preferred warm-humid climate and open forest/forest steppe vegetation.Before ca.0.3 Ma,the early human,termed Homo erectus,might not adapt to the relatively cool circumstance in the northern QM during glaciation,and they had to migrate southerly.At this period,the southern QM probably acted as the "source" refuge and provided the core population.Since ca.0.3 Ma,along with the worse circumstance,the early human evoluted into early Homo sapiens and changed their adaptation routine in glacial period.In particular,the further weakening of Asian summer monsoon and expansion of grassland since ca.0.07 Ma enhanced their adaptability to grassland and cool climate,through genetic alteration,technological innovation and social behaviors,and promoted them to migrate to the open plain areas.Our results show that the human behaviors in the QM are consistent with that in Europe.Combining with the research of human fossils,Paleolithic industries and genetics,we think that long-distance locomotion is among the key features of early human.The various human groups on different continents may have genetic admixture and cultural communication to help them adapt to the changing environment,and eventually make them the only cosmopolitan species. |
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