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HUMAN EVOLUTION AND THE COLONIZATION OF THE HIGHER LATITUDES

HOFFECKER, JOHN F  INSTAAR.

Although the hominid lineage was established by 5-6 mya, early hominids—the australopithecines—did not extend their range out of the equatorial zone (to which our closest living relatives remain confined). Colonization of latitudes above 20o North took place after the appearance of the genus Homo. Over the course of roughly two million years, representatives of Homo occupied increasingly high latitudes, achieving sustained settlement above the Arctic Circle by the beginning of the Holocene.

The colonization of higher latitudes was tied closely to the evolution of the genus Homo. Expansion into areas above 20o North was linked to new anatomical or behavioral adaptations to lower temperatures, increased seasonality, and reduced biotic productivity. Most of the major episodes of expansion coincided with the appearance of new forms of Homo. Climate change, however, played a significant role in the process.

Human settlement of higher latitudes did not occur as a result of the gradual northward drift of populations and cultures. Instead, each major advance seems to have taken place relatively quickly as climate change or new adaptations suddenly opened new regions and habitats for occupation. Moreover, because of the influence of oceans and continents on terrestrial climate, many of these advances were longitudinal rather than latitudinal—movements along a climate gradient that ran from east to west as much as from north to south. This is particularly evident in northern Eurasia, where the “oceanic effect” of the North Atlantic brings milder climates to Western Europe, while colder and drier conditions prevail in Eastern Europe and Siberia.

Five major stages in the colonization of higher latitudes may be identified:

Stage 1: Occupation of the Middle Latitudes: Between roughly 1.8 and 0.8 million years ago, early humans expanded out of their tropical African base and colonized Eurasia as far as latitude 41-42o North. This stage is primarily associated with Homo erectus and changes in anatomy and behavior that allowed humans to forage across open and comparatively dry landscapes. Although perhaps rarely—if ever—exposed to subfreezing temperatures, Homo erectus populations coped with less productive and more seasonal environments than their predecessors. Their adaptations to these environments, which probably included increased consumption of meat, set the stage for subsequent expansion into higher latitudes.

Stage 2: Colonization of Western Europe: Between at least 500,000 years ago and up to roughly 250,000 years ago, humans (most of whom may be assigned to the taxon Homo heidelbergensis) occupied the continent of Europe as far east as the Danube Basin. In Britain, sites in this time range are found as far as latitude 52o North. With the possible exception of controlled fire, obvious adaptations to cold are lacking in the human fossils and archaeological sites of this interval. The initial colonization of Europe may have been largely an opportunistic expansion into the warmest parts of northern Eurasia—previously blocked by factors other than cold climate. Alternatively, some cold adaptations may remain concealed by the poverty of Homo heidelbergensis fossils and their archaeological record.

Stage 3: The Neanderthals: The Neanderthals (Homo neanderthalensis) evolved gradually in Western Europe and expanded eastward into colder and drier parts of northern Eurasia by at least 130,000 years ago (OIS 5e). They became the first humans to occupy the central East European Plain and southwestern Siberia. Unlike their predecessors in Western Europe, the Neanderthals exhibit a suite of anatomical and behavioral adaptations to cold environments. A diet high in protein and fat—obtained from the hunting of large mammals—was of critical importance. Despite their special cold-adapted traits, the Neanderthal range of climate tolerance was limited compared to that of modern humans. They probably were unable to cope with average winter temperatures much below -10o C and were generally restricted to wooded terrain.

Stage 4: Dispersal of Modern Humans: Between 45,000 and 20,000 years ago, modern humans (Homo sapiens) derived from Africa expanded into habitats and regions never occupied by early humans. The regions included Eastern Europe Siberia as far as latitude 60o North (and even farther on at least a seasonal basis). Their success was due chiefly to an ability to develop complex and innovative technology (e.g., insulated clothing, artificial shelters), some of which was essential to survival at higher latitudes during the middle of the Last Glacial period—where mean winter temperatures probably fell below -20o C. However, flexible organization may have been an important factor in sustaining a population in very cold and dry habitats, where resources were widely scattered. Both novel technology and flexible organization were probably related to syntactical language and the use of symbols. The modern humans who invaded northern Eurasia 45,000 years ago retained the warm-climate anatomy of their recent African ancestors. This may have precluded sustained settlement of the Arctic and forced them to abandon the colder parts of northern Eurasia (including most of Siberia) as the Last Glacial reached its cold maximum about 24,000 cal BP.

Stage 5: Modern Humans in the Arctic: The final stage may be divided into two sub-stages. The initial occupation of arctic environments took place between roughly 19,000 and 7,000 cal BP, as modern humans reoccupied parts of northern Eurasia abandoned during the peak of the Last Glacial. Several factors—including postglacial warming and some anatomical cold adaptations—may have triggered this event. Milder climates opened the door to northeast Asia and the Bering Land Bridge, and humans crossed into the Americas for the first time. After 7,000 years ago, humans expanded into deglaciated areas of Canada and other previously uninhabited regions of the Arctic. Much of their success was based on technological innovation (e.g., large boats, toggle-head harpoons) that facilitated a robust maritime economy.



Figure 1. Major stages in the settlement of higher latitudes by representatives of Homo during the past two million years.


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