Kelly E. Graf

Species-specific responses of Late Quaternary megafauna to climate and humans

Despite decades of research, the roles of climate and humans in driving the dramatic extinctions of large-bodied mammals during the Late Quaternary period remain contentious. Here we use ancient DNA, species distribution models and the human fossil record to elucidate how climate and humans shaped the demographic history of woolly rhinoceros, woolly mammoth, wild horse, reindeer, bison and musk ox. We show that climate has been a major driver of population change over the past 50,000 years. However, each species responds differently to the effects of climatic shifts, habitat redistribution and human encroachment. Although climate change alone can explain the extinction of some species, such as Eurasian musk ox and woolly rhinoceros, a combination of climatic and anthropogenic effects appears to be responsible for the extinction of others, including Eurasian steppe bison and wild horse. We find no genetic signature or any distinctive range dynamics distinguishing extinct from surviving species, emphasizing the challenges associated with predicting future responses of extant mammals to climate and human-mediated habitat change.

Upper Palaeolithic Siberian genome reveals dual ancestry of Native Americans

The origins of the First Americans remain contentious. Although Native Americans seem to be genetically most closely related to east Asians, there is no consensus with regard to which specific Old World populations they are closest to. Here we sequence the draft genome of an approximately 24,000-year-old individual (MA-1), from Mal’ta in south-central Siberia, to an average depth of 1×. To our knowledge this is the oldest anatomically modern human genome reported to date. The MA-1 mitochondrial genome belongs to haplogroup U, which has also been found at high frequency among Upper Palaeolithic and Mesolithic European hunter-gatherers, and the Y chromosome of MA-1 is basal to modern-day western Eurasians and near the root of most Native American lineages. Similarly, we find autosomal evidence that MA-1 is basal to modern-day western Eurasians and genetically closely related to modern-day Native Americans, with no close affinity to east Asians. This suggests that populations related to contemporary western Eurasians had a more north-easterly distribution 24,000 years ago than commonly thought. Furthermore, we estimate that 14 to 38% of Native American ancestry may originate through gene flow from this ancient population. This is likely to have occurred after the divergence of Native American ancestors from east Asian ancestors, but before the diversification of Native American populations in the New World. Gene flow from the MA-1 lineage into Native American ancestors could explain why several crania from the First Americans have been reported as bearing morphological characteristics that do not resemble those of east Asians. Sequencing of another south-central Siberian, Afontova Gora-2 dating to approximately 17,000 years ago, revealed similar autosomal genetic signatures as MA-1, suggesting that the region was continuously occupied by humans throughout the Last Glacial Maximum. Our findings reveal that western Eurasian genetic signatures in modern-day Native Americans derive not only from post-Columbian admixture, as commonly thought, but also from a mixed ancestry of the First Americans.

Modern Human Colonization of the Siberian Mammoth Steppe: A View from South-Central Siberia

Was the transition from the middle Upper Paleolithic (MUP) to late Upper Paleolithic (LUP) in Siberia the result of gradual, in situ cultural change or abrupt change that resulted from multiple recolonization attempts? Past studies have primarily focused on chronology and typology in attempts to reconstruct culture histories. As a result reconstruction of hunter-gatherer ecology has been limited to broad overviews and generalizations. Questions regarding the processes of human colonization have largely remained unanswered. Explaining the differences between MUP and LUP behavioral adaptations and decision-making in the Siberian mammoth steppe is critical to achieving full understanding of the process of human colonization of the North during the late Pleistocene. This study uses both radiocarbon and lithic technological data from MUP and LUP sites located in the Enisei River valley of south-central Siberia to address the problem from a more comprehensive behavioral perspective. Chronological data demonstrate the MUP and LUP in the Enisei region were separated by a 4000-year gap straddling the LGM, while lithic data suggest MUP foragers before the LGM were making different technological provisioning decisions than LUP foragers after the LGM. Results of this study indicate that the Siberian mammoth steppe was colonized during multiple dispersal events.

Dry Creek Revisited: New Excavations, Radiocarbon Dates, and Site Formation Inform on the Peopling of Eastern Beringia

The multicomponent Dry Creek site, located in the Nenana Valley, central Alaska, is arguably one of the most important archaeological sites in Beringia. Original work in the 1970s identified two separate cultural layers, called Components 1 and 2, thought to date to the terminal Pleistocene and suggesting that the site was visited by Upper Paleolithic huntergatherers between about 13,000 and 12,000 calendar years before present (cal B.P.). The oldest of these became the typeassemblage for the Nenana complex. Recently, some have questioned the geoarchaeological integrity of the sites early deposits, suggesting that the separated cultural layers resulted from natural postdepositional disturbances. In 2011, we revisited Dry Creek to independently assess the sites age and formation. Here we present our findings and reaffirm original interpretations of clear separation of two terminal Pleistocene cultural occupations. For the first time, we report direct radiocarbon dates on cultural features associated with both occupation zones, one dating to 13,485-13,305 and the other to 11,060-10,590 cal B.P.

Technology and Human Response to Environmental Change at the Pleistocene-Holocene Boundary in Eastern Beringia: A View from Owl Ridge, Central Alaska

Paleoecological records indicate that from the Allerod to early Holocene interior Alaska underwent significant climatic changes that affected local environments. How did prehistoric Alaskans respond to these shifts between 14,000 and 10,000 cal BP? This paper examines the lithic record at the Owl Ridge site, central Alaska, from a human ecological perspective to explain changes in adaptive behaviors of prehistoric Alaskans. Owl Ridge is a multicomponent site located along the Teklanika River with three cultural components dating to the late Allerod (about 13,000), end of the Younger Dryas (about 12,000), and the very beginning of the Holocene Thermal Maximum (about 11,200 cal BP). We characterize and compare toolstone procurement and selection activities between these components to explore human response to changing climate at the Pleistocene-Holocene boundary. This study shows there were differences in technological organization and land-use patterns between the first occupation and subsequent occupations of the site. Initial occupants of Owl Ridge, utilizing the Nenana technocomplex, were not as familiar with the local lithic landscape as later counterparts. Later occupants, using the Denali technocomplex, exploited a higher degree of local toolstones and had become much more familiar with the local lithic landscape. We argue these changes in lithic technology and raw material procurement and selection behaviors reflect shifting land-use strategies used by interior Alaskans as they responded to climate-induced resource distribution shifts at the very end of the Pleistocene.

3.3 – The Paleolithic of eastern Beringia from western Alaska to Canadian Yukon

Abstract There were several stages in the colonization of eastern Beringia. The initial peopling took place in the Late Pleistocene, c.12,300 BP during the late Upper Paleolithic, when humans migrated to the New World from Siberia. It seems that it occurred during the time of the amelioration of climate and spread of the bush tundra. During the Allerod, people inhabited the valleys of the Tanana and Nenana Rivers. In spite of the severe conditions of Younger Dryas, people continued to inhabit this area. In the end of this time span the northern and western areas of Alaska were populated by Paleoindian hunters on large herds of mammals. The problem of possible migration of the Paleoindians from the regions lying southward is a matter of debate. It seems that the southern part of Alaska had been settled later, in the early Holocene, by the people who had penetrated from the inner areas of Alaska.