The Quaternary Period, the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), follows the Neogene Period and spans from 2.588 ± 0.005 million years ago to the present.

Typically defined by the cyclic growth and decay of continental ice sheets driven by Milankovitch cycles and the associated climate and environmental changes that occurred, the Quaternary Period is divided into two epochs: the Pleistocene and the Holocene (eleven thousand seven hundred years ago to today).

The Pleistocene spans the world's recent period of repeated glaciations.

With the onset of the Quaternary glaciation, the first of the several ice ages to follow, decreasing oceanic evaporation results in a drier climate in East Africa and an expansion of the savanna at the expense of forests.

Reduced availability of fruits forces some Australopithecines to unlock new food sources found in the drier savanna climate, representing a move from the mostly frugivorous or omnivorous diet of Australopithecus to the carnivorous scavenging lifestyle of early Homo.

Paranthropus species are still present in the beginning of the Pleistocene, along with early human ancestors, but they disappear during the lower Paleolithic.

The Lower Paleolithic, the earliest subdivision of the Paleolithic or Old Stone Age, begins around two and a half million million years ago when the first evidence of craft and use of stone tools by hominids appears in the current archaeological record.

The genus Homo, which includes modern humans and species closely related to them, is estimated to be about two point three to two point four million years old, evolving from australopithecine ancestors with the appearance of Homo habilis.

Specifically, H. habilis is considered the direct descendant of Australopithecus garhi, a gracile species that lived about two and a half million years ago.

The most salient physiological development between the two species is the increase in cranial capacity, from about four hundred and fifty cubic centimeters (twenty-seven cubic inches) in A. garhi to six hundred cubic centimeters (thirty-seven cubic inches) in H. habilis.

The earliest known occupation of Britain by humans occurs in the Palaeolithic—the Old Stone Age.

A huge length of time, it sees many changes in the environment, encompassing several glacial and interglacial periods that greatly affect human settlement in the region.

Providing dating for this distant period is difficult and contentious.

The inhabitants of the region at this time are bands of hunter-gatherers who roam northern Europe following herds of animals, or who support themselves by fishing.

Recent (2006) scientific evidence regarding mitochondrial DNA sequences from ancient and modern Europe has shown a distinct pattern for the different time periods sampled in the course of the study.

Despite some limitations regarding sample sizes, the results were found to be non-random.

As such, the results indicate that, in addition to populations in Europe expanding from southern refugia after the last glacial maximum (especially the Franco-Cantabrian region), evidence also exists for various northern refugia.

Southern and eastern Britain at this time are linked to continental Europe by a wide land bridge allowing humans to move freely.

The current position of the English Channel is a large river flowing westwards and fed by tributaries that will later become the Thames and Seine.

Reconstructing this ancient environment has provided clues to the route first visitors took to arrive at what was then a peninsula of the Eurasian continent.

Archaeologists have found a string of early sites located close to the route of a now lost watercourse named the Bytham River, which indicate that it was exploited as the earliest route west into Britain.

There is evidence from bones and flint tools found in coastal deposits near Happisburgh in Norfolk and Pakefield in Suffolk that a species of Homo was present in what is now Britain around seven hundred thousand years ago.

Cranial capacity had again doubled within the Homo genus by six hundred thousand years ago, from H. habilis to an archaic Homo species called Homo heidelbergensis, the second human wave to be pumped from Africa into the Middle East and Western Europe.

Sites such as Boxgrove in Sussex illustrate the later arrival in the archaeological record of heidelbergensis around five hundred thousand years ago.

The cranial capacity of H. heidelbergensis overlaps with the range found in modern humans; these early peoples make Acheulean flint tools (hand axes) and hunt the large native mammals of the period.

They are thought to have driven elephants, rhinoceroses, and hippopotamuses over the tops of cliffs or into bogs to kill them more easily.

Up until the 1970s, these kill sites, often at waterholes where animals would gather to drink, were interpreted as being where Acheulean tool users killed game, butchered their carcasses, and then discarded the tools they had used.

Since the advent of zooarchaeology, which has placed greater emphasis on studying animal bones from archaeological sites, this view has changed.

Many of the animals at these kill sites have been found to have been killed by other predator animals, so it is likely that humans of the period supplemented hunting with scavenging from already dead animals.

The extreme cold of the Anglian Stage, from four hundred and seventy-eight thousand to four hundred and twenty-four thousand years ago, is likely to have driven humans out of Britain altogether and the region will apparently be unoccupied until the ice recedes during the Hoxnian Stage.

Primitive humans first migrate to the Indian subcontinent between 400,000 and 200,000 BCE; some of them possibly sail to southern India from eastern Africa.

The approximate time of divergence from the common ancestor of all modern human populations was two hundred thousand years ago, based on evidence from studies of molecular biology.

The broad study of African genetic diversity found the ǂKhomani San people to express the greatest genetic diversity among the 113 distinct populations sampled, making them one of fourteen "ancestral population clusters".

The research also located the origin of modern human migration in southwestern Africa, near the coastal border of Namibia and Angola.

Australia is possibly occupied by at least 174,000 BCE (a date suggested by archaeological fieldwork in Western Australia’s Kimberley district).

The Neanderthals move into Europe around 150,000 BCE.

The game-hunting occupants of the Grotte du Lazaret (English: Cave of Le Lazaret), now in the eastern suburbs of the French town of Nice and now overlooking the Mediterranean Sea, dating to about this time, make tents, probably of animal hides stretched over a wooden framework, with the tent entrances facing away from the cave opening.

A wolf skull is situated inside the doorway of each tent.

New, local tool traditions, including the Mousterian, appear in the frigid environment of glacial western Asia and Europe, as human populations begin to exploit a variety of habitats.

Mousterian toolmakers, including the Neandertalers, ingeniously adapt their implements to a wide variety of tasks: cutting and preparing meat, scraping hides, working wood, and many others.

Mousterian tools found in Europe and made by Neanderthals date from between 300,000 BP and 30,000 BP.

They are also produced by anatomically modern humans in Northwestern Africa and the Near East.

Assemblages produced by Neanderthals in the Levant, for example, are indistinguishable from those produced by Qafzeh type modern humans.

It may be an example of acculturation of modern humans by Neanderthals, because the culture after one hundred and thirty thousand years reaches the Levant from Europe (the first Mousterian industry appears there 200,000 BP) and the modern Qafzeh type humans appear in the Levant another hundred thousand years later.

The Moderns are taller, more slender, and less muscular than the Neanderthals, with whom they share—perhaps uneasily—the Earth.

Though their brains are smaller in overall size, they are heavier in the forebrain, a difference that may allow for more abstract thought and the development of complex speech.

Yet, the inner world of the Neanderthals remains a mystery—no one knows the depths of their thoughts or how they truly expressed them.

Homo sapiens sapiens apparently spreads rapidly from sub-Saharan Africa across the Sahara Desert and into the Near East, where the new species flourishes by 88,000 BCE.