This is a story not of steady northward progress, but of successive movements — including some retreats — constrained by climate change and enabled by anatomical changes and technological innovation. Hoffecker covers the paleoanthropological and archaeological record, but sets it in the context of changing climates and broader ecological trends.
Hoffecker begins with the great apes, the australopithecines, early Homo, and Homo erectus, highlighting their northernmost reach and the constraints of temperature.
"The increased consumption of meat — whether obtained primarily from scavenging or from hunting — was probably an important part of the expansion out of Africa and into higher latitudes. ... the larger body and brain size placed greater energy demands on Homo erectus. As plant food availability declined in drier and cooler habitats, the proportion of meat in the diet must have risen."
Homo heidelbergensis was in Europe from about 500,000 years ago. It is unclear what had changed: perhaps carnivore extinctions opened up a niche for them, perhaps they had adaptations to higher latitudes that have not yet been discovered, either anatomical or technological (possibly the controlled use of fire).
The Neanderthals, who emerged gradually in Europe from around 300,000 years ago, "evolved the most extreme anatomical adaptations to cold climates ever found among hominids", but they lacked key elements of modern technology such as sewing needles.
"Among recent peoples of the Arctic, clothing and shelter seem to be the most complex aspect of technology. They have always been a vital component of modern adaptation to high latitudes. Here may lie the most significant contrast between modern humans and Neanderthals — at least with respect to cold adaptation — and the critical constraint on the ability of the latter to cope with extreme cold. Although often difficult to evaluate, the evidence for Neanderthal clothing and shelter technology generally indicates a low level of complexity and effectiveness."
Modern humans came out of Africa.
"In a period of no more than 20,000 years — possibly much less — Homo sapiens occupied all the areas in southern Eurasia colonized by Homo erectus 1.8-1.4 million years ago and also invaded Australia and much of northern Eurasia."
But they were late reaching south-western Europe, perhaps because of Neanderthal competition. Anatomically equatorial, their success may have depended on technology and language, though teasing that out from traces of their art and material culture is difficult.
"The maximum cold of 24,000-20,000 years ago was an environmental disaster for modern humans in Europe and Siberia, and it brought to an end the epoch that had begun with the dispersal out of Africa."
After 20,000 years ago, the next wave of settlement was to go all the way into the Arctic. In Western Europe people followed the shrinking Fennoscandian ice sheets northwards. In Eastern Europe, the Epi-Gravettian was characterised by houses of mammoth bone. And further east expansion proceeded from the boreal forests of Russia into Siberia, Beringia, and thence into the New World.
The final chapter surveys later developments, moving from Europe eastwards: the Late Stone Age in northern Scandinavia, the Siberian Neolithic and movements to the northeast, the Paleo-Eskimo world in North America, and the expansion of the Inuit.
"The modern Inuit are the direct descendants of what archaeologists have termed the Thule culture. Thule culture was the product of a number of interrelated technological and organizational developments that began in the Bering Sea region slightly more than 2,000 years ago. These developments enabled the Alaskan ancestors of the Inuit to expand rapidly across the central and eastern Arctic after AD 1000, creating the remarkable uniformity of culture encountered by the Europeans."
There were numerous technological innovations, including maritime technology, sleds and dogs, and the use of mammal fat in lamps. Apart from a brief account of the Cold War military buildup in Arctic North America, there's no attempt to describe the recent history or culture of the modern Arctic peoples; that would really require a book in itself.
Hoffecker refrains from speculation and is fairly systematic in his coverage of finds and cultures. But his presentation is concise — just 140 pages of text, with technical details relegated to end notes — and never dull, elegantly synthesizing material from multiple disciplines. Anyone curious about early human history will find A Prehistory of the North hard to put down.