Blood, stones and genes: the new science of human evolution
A new BBC documentary presented by Alice Roberts has been charting the spread of modern humans across the globe. Is it really true that we are all Africans? Current Archaeology assesses the latest evidence.
A key stage is represented by the Ethiopian fossil skeleton known as ‘Lucy’. An advanced australopithecine who lived about 3.2 million years ago, Lucy walked upright. Though no tools have so far been found of this date, bipedalism would have freed Lucy’s arms and hands for labour. This, in turn, is likely to have caused selection in favour of higher brain capacity. Further biological evolution would then have been driven by the interaction of hand and brain, tool-making and intellect, dexterity and thought — a dynamic interaction that was to culminate in the emergence of modern humans some three million years later.
The appearance of stone tools about 2.5 million years ago — choppers made of crudely chipped pebbles — is the archaeological signature of humans: a new family of species defined by tool-making behaviour. The tools embody conceptual thought, forward planning, and manual dexterity. They represent the use of intellect and skill to modify nature so as to exploit its resources more efficiently — instead of simply taking it as it comes.
But the hominins remained a mainly African family for at least 1.5 million years. Although 1.7 million-year-old fossil remains found at Dmanisi in Georgia are proof of an early foray into Western Asia, it was not until about a million years ago that a species of archaic humans — Homo erectus — migrated from Africa and colonised much of South and East Asia. Later again, a more developed hominin — Homo heidelbergensis — settled much of Western Asia and Europe. The famous Neanderthals evolved out of heidelbergensis about 300,000 years ago.
Out of Africa: into Britain
What about Britain? Research by the Ancient Human Occupation of Britain Project (AHOB) has established that the human presence in Britain was highly episodic throughout the Palaeolithic (CA 190). The first occupation occurred around 700,000 BP (before the present), and between then and 12,000 BP — i.e. at the end of the last ice age and the beginning of the transition to the Mesolithic — hominins were in Britain for only about 20% of the time. There were at least seven abandonments, including the entire period from 180,000 to 70,000 BP. The reasons were simple: the successive advances and retreats of the glaciers, the varying availability of food, and the greater or lesser ease with which small groups of hunter-gatherers could migrate across the landscape.
The presence of Homo heidelbergensis is represented at three key sites: Pakefield (CA 201), Boxgrove (CA 153), and Swanscombe. Pakefield in Suffolk is part of an ancient buried landscape that is being revealed by coastal erosion. AHOB experts have recently recovered flint-flake tools in association with the fossil bones of extinct megafauna, and produced convincing scientific dates for this material of 700,000 BP.
These hominid occupations were ecologically specific. They provide no basis for assuming widespread occupation of diverse environments. All three sites were close to the sea or major waterways, in locations blessed with rich and varied fauna: Pakefield was in the delta of the (lost) River Bytham, Boxgrove on a coastal plain, and Swanscombe in the flood-plain of the Thames.
Each was occupied during a period of warmer weather between ice ages, typically with average temperatures several degrees higher than today. The Pakefield, Boxgrove, and Swanscombe occupations may have lasted for thousands, even tens of thousands of years: but in geological terms, there were passing moments – followed each time by the return of the ice.
This extract was taken from the article published in CA 232