Human Evolution

Human evolution is the specific evolutionary history of our own species, Homo sapiens, tracing our particular lineage backward through time through a whole succession of extinct hominin ancestors and close evolutionary relatives, a history that has been worked out patiently by palaeoanthropologists chiefly from fossil, comparative anatomical and, increasingly in recent decades, molecular genetic evidence, gathered predominantly from important fossil sites located across the African and Asian continents.

Dryopithecus and Ramapithecus were two closely related early primate genera that lived roughly 15 million years ago, and their fossils together mark an important early divergence point within primate evolution: Dryopithecus was distinctly more ape-like in its overall body build, and is generally believed, from the structure of its fossil limb bones, to have moved about chiefly on all fours, in a manner broadly resembling present-day gorillas and chimpanzees, whereas Ramapithecus, though closely related, showed several somewhat more man-like anatomical features by comparison, suggesting that this general lineage was already beginning to diverge into two separate evolutionary directions — one branch eventually leading, over many further millions of years, toward the modern great apes, and a separate branch eventually leading, over an even longer further span of time, toward the succession of hominin ancestors that would in turn eventually give rise to modern humans.

Australopithecus, which lived across the open savanna grasslands of East Africa roughly 2 million years ago, represents a significantly later and more advanced stage along the specifically human evolutionary lineage: fossil evidence, particularly the structure of the pelvis and leg bones, indicates that Australopithecus walked upright, at least to a considerable degree, on two hind limbs, a mode of locomotion called bipedalism that is one of the earliest and most distinctively human anatomical features to appear in the fossil record; associated stone tool finds further suggest that Australopithecus hunted, at least occasionally, using simple crafted stone weapons, though its overall diet is believed to have still relied more heavily on wild fruit than on meat. Despite these more human-like features of gait and behaviour, Australopithecus retained a brain that remained comparatively small, only modestly larger than that of a living ape, showing clearly that upright bipedal walking evolved substantially EARLIER, along the human lineage, than the very large brain size that would only develop considerably later.

Homo habilis, whose scientific name literally translates as 'handy man', was the first species formally classified within our own genus, Homo, and it possessed a brain capacity of roughly 650 to 800 cubic centimetres — distinctly larger than that of Australopithecus, though still considerably smaller than that of modern humans. Homo habilis is the earliest hominin species definitely and directly associated, through abundant fossil evidence found alongside its own skeletal remains, with the deliberate manufacture and habitual use of simple stone tools, chiefly used for basic tasks such as cutting and scraping, although the species is still generally believed to have relied relatively little on meat as a dietary source. Homo erectus, which appeared and spread somewhat later in the fossil record, shows a further, quite substantial increase in brain capacity, to roughly 900 cubic centimetres, and the fossil and associated archaeological evidence — including, at several sites, animal bones bearing clear butchery marks found closely associated with Homo erectus remains — suggests that this species had, by this considerably later evolutionary stage, become a noticeably more committed hunter and meat-eater, as well as a substantially more capable and more sophisticated toolmaker than its own Homo habilis predecessors.

Neanderthal man, whose fossil remains have been found distributed widely across ice-age Europe as well as parts of the Middle East, and who is generally dated to the period spanning roughly 400,000 to 40,000 years ago, possessed a brain capacity of approximately 1,400 cubic centimetres — a brain size comparable to, and by certain specific anatomical measures even somewhat exceeding, the average brain size found in modern humans today. Neanderthals possessed a notably heavily built, robust body physique that is generally interpreted as an anatomical adaptation well suited to surviving the cold glacial climate of ice-age Europe, and the archaeological evidence associated with Neanderthal sites shows several unmistakably human-like cultural and behavioural traits, including the regular use of prepared animal hides, most likely for clothing or simple shelter, and, most strikingly of all, clear evidence of the deliberate, intentional burial of the Neanderthals' own dead, a behaviour widely interpreted by palaeoanthropologists as suggesting some degree of symbolic thought, and perhaps even an early form of ritual or belief, considerably more advanced than that shown by any of the earlier hominin stages discussed above. …