Denisovan in the context of "Cave painting"

Early human migrations are the earliest migrations and expansions of archaic and modern humans across continents. They are believed to have begun approximately 2 million years ago with the early expansions out of Africa by Homo erectus. This initial migration was followed by other archaic humans including H. heidelbergensis, which lived around 500,000 years ago and was the likely ancestor of Denisovans and Neanderthals as well as modern humans. Early hominids had likely crossed land bridges that have now sunk.

Within Africa, Homo sapiens dispersed around the time of its speciation, roughly 300,000 years ago. The recent African origin theory suggests that the anatomically modern humans outside of Africa descend from a population of Homo sapiens migrating from East Africa roughly 70–50,000 years ago and spreading along the southern coast of Asia and to Oceania by about 50,000 years ago. Modern humans spread across Europe about 40,000 years ago.

Homo erectus (/ˌhoʊmoʊ əˈrɛktəs/ lit. 'upright man') is an extinct species of archaic human from the Pleistocene, spanning nearly 2 million years. It is the first human species to evolve a humanlike body plan and gait, to leave Africa and colonize Asia and Europe, and to wield fire. Some populations of H. erectus were ancestors of later human species, including H. heidelbergensis — the last common ancestor of modern humans, Neanderthals, and Denisovans. As such a widely distributed species both geographically and temporally, H. erectus anatomy varies considerably. Subspecies are sometimes recognized: H. e. erectus, H. e. pekinensis, H. e. soloensis, H. e. ergaster, H. e. georgicus, and H. e. tautavelensis.

The species was first described by Eugène Dubois in 1893 as "Pithecanthropus erectus" using a skullcap, molar, and femur from Java, Indonesia. Further discoveries around East Asia were used to contend that humanity evolved out of Asia. Based on historical race concepts, it was argued that local H. erectus populations evolved directly into local modern human populations (polycentrism) rather than all humanity sharing a single anatomically modern ancestor (monogenism). As the fossil record improved over the mid-to-late 20th century, "Out of Africa" theory and monogenism became the consensus.

Interbreeding between archaic and modern humans occurred during the Middle Paleolithic and early Upper Paleolithic. The interbreeding happened in several independent events that included Neanderthals and Denisovans, as well as several unidentified hominins.

In Europe, Asia and North Africa, interbreeding between archaic humans and modern humans took place several times. The introgression events into modern humans are estimated to have happened about 47,000–65,000 years ago with Neanderthals and about 44,000–54,000 years ago with Denisovans.

Homo heidelbergensis is a species of archaic human from the Middle Pleistocene of Europe and Africa, as well as potentially Asia depending on the taxonomic convention used. The species-level classification of Homo during the Middle Pleistocene is controversial, called the "muddle in the middle", owing to the wide anatomical range of variation that populations exhibited during this time. H. heidelbergensis has been regarded as either the last common ancestor of modern humans, Neanderthals, and Denisovans; or as a completely separate lineage.

H. heidelbergensis was described by German anthropologist Otto Schoetensack in 1908 based on a jawbone, Mauer 1, from a sand pit near the village of Mauer — 10 km (6.2 mi) southeast of Heidelberg. It was the oldest identified human fossil in Europe, and Schoetensack described it as an antediluvian race (before the Great Flood) which would eventually evolve into living Europeans. By the mid-20th century, all archaic human taxa were lumped as subspecies of either H. erectus or H. sapiens, with the former evolving into the latter without any coexistence. The species was usually lumped as H. e. heidelbergensis. While its utility was complicated by its definition on a jawbone (which is rarely ever found, and otherwise bears few diagnostic features) British physical anthropologist Chris Stringer revived the species in 1983, redefining it as a Euro-African ancestor of modern humans and Neanderthals using namely Kabwe 1, Petralona 1, Bodo, and Arago. These skulls are united mainly by their supraorbital torus (brow ridge) anatomy.