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news focus news focus New insights into our origins Out of Africa above micro-CT scans of a cranium from Jebel irhoud, Africa (about 300,00 years old), and of one from Qafzeh in the Levant (about 95,000 years old) reflect the evolutionary changes of the braincase from an elongated to a globular shape. modern features of Homo sapiens like this did not appear at the same time and place, suggesting that our species did not evolve from a single population or region in Africa. With newly identified evidence for the earliest hominin activity outside Africa and for the diverse roots of Homo sapiens within the continent, our understanding of migration and evolution is changing. Lucia Marchini explores some of the latest thinking. The African origin of our species Homo sapiens is widely accepted, but until recently researchers have given weight to the assumption that H. sapiens evolved from a single ancestral population or within one region in Africa. Now research into the morphology of human fossils and tools from the Middle Stone Age (a period in African prehistory between c.300,000 and 60,000-20,000 years ago) across the continent is shifting the focus away from this single origin theory, which simplifies the remarkable diversity present in the archaeological record. Combining evidence from material culture, fossils, genetics, and the ancient climate, the new study (published in Trends in Ecology & Evolution) argues the case for multiple origins of H. sapiens from different groups across Africa that went through periods of mixing and isolation as the environment around them, whether forest or desert, changed. A range of transitional groups may have lived over a vast area of the continent stretching from Morocco to South Africa between at least 300,000 and 12,000 years ago. Stone tools and other artefacts, with their distinct regional styles, complicate things for the single origin theory. The technological changes that mark the beginnings of the Middle Stone Age, like the move away from large hand-held cutting tools and to hafting and prepared-core technology, took place across Africa as early as 300,000 years ago at Jebel Irhoud in the north and Olorgesailie in the east, and about 280,000 years ago at Florisbad in the south. The current West African dates are younger, at about 180,000 years ago, but this area has not been the subject of as much investigation. Lead author Eleanor Scerri sums up the findings: ‘While there is a continental-wide trend towards more sophisticated material culture, this “modernisation” clearly doesn’t originate in one region or occur at one time period.’ i t u te I n st l a n ck Pa x G u nz / M i l i p p : P h i m Ag E S l o g y a nt h ro p o i o n a r y l u t evo fo r i / Fra n ce s co S ce r r l e a n o r : e i m Ag E S i l wo o d H e n s h i sto p h e r i co / C h r ’ e r r d RIGHT As well as diversity in the fossil record, cultural diversity seen in middle Stone Age artefacts from north and south Africa points to multiple origins of H. sapiens. 10 CurrentWorldArChAeology Issue 91
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above Excavations on the slopes of Shangchen in China have revealed signs of the earliest hominin presence outside of Africa. Z h u of Z h aoy u : co u r te sy i m ag es A quick look in the mirror will reveal some of the characteristic features of modern humans, such as small faces, chins, and globular braincases. These elements did not appear at the same time and place, however, and different ‘modern’ features can be seen in early human skeletons in diverse parts of Africa. Chris Stringer, Research Leader in Human Origins at the Natural History Museum, explained the findings from the fossils: ‘We have definite Homo sapiens fossils from Ethiopia about 150,000-200,000 years ago, but in the last two years fossils from Morocco have been published that probably take our lineage back to beyond 300,000 years, with some of the earliest traces of technologically advanced Middle Stone Age tools. So how do these new findings impact our view of the origin of our species? In the past, workers have favoured regions like East Africa or South Africa as the likely place where our species and our complex behaviours originated. Yet most of Africa is covered with variants of Middle Stone Age tools, without any fossils to show who was making those tools in regions like West or Central Africa. In contrast, our current fossil finds only come from about 5% of the area of the continent, yet they show astonishing variations in their form.’ ‘In 2002, already aware of the sparse but highly variable fossil record, I suggested that our African origins might be “multiregional”, with different areas of Africa playing a part at different times. Research over the last decade, synthesised in our new paper, supports that view. When we look at the morphology of human bones over the last 300,000 years, we see a complex mix of archaic and modern features in different places and at different times. As with the stone tools, we do see a continent-wide trend towards the modern human form, but different modern features appeared in different places at different times, and some archaic features were present until remarkably recently. The shifting nature of habitable zones in Africa meant that human populations went through many cycles of isolation – leading to local adaptation and the development of unique material culture and biological make-up – followed by genetic and cultural mixing. Other populations probably went completely extinct.’ These changes in the environment led to subdivisions in the populations of other animal species, some of which exhibit similar genetic patterns to humans in their distribution. Commenting on such patterns, Mark Thomas, Professor of Evolutionary Genetics at UCL, said: ‘It is difficult to reconcile the genetic patterns we see in living Africans, and in the DNA extracted from the bones of Africans who lived over the last 10,000 years, with the idea of there being one ancestral population. We see indicators of reduced connectivity very deep in the past, some very old genetic lineages, and levels of overall diversity that a single population would struggle to maintain.’ Into Asia Long before the emergence of H. sapiens, earlier hominin species made their way out of Africa. The earliest known evidence for the appearance of hominins outside Africa, approximately 1.85-1.78 million years ago, used to come from fossils and stone tools in Dmanisi, Georgia. A new discovery in southern China, however, has pushed the date back further to more than 2 million years ago. Archaeologists working on a steep slope at Shangchen in the Loess Plateau have excavated a largely continuous sequence of 17 artefact layers ranging from approximately 2.12 to 1.26 million years ago. While some other early hominin sites have been dated by looking at the chemical fingerprints of volcanic rocks, Shangchen has no volcanic rocks and so the researchers, led by Zhaoyu Zhu, turned to palaeomagnetic dating instead. Using this method, the team analysed each of the sediment layers – palaeosols (made up of fossilised soils) and loess (silts blown by the wind) – to establish the pattern of polarity reversals (when the Earth’s magnetic field flips at random) registered in the sediments’ magnetic materials. These can then be compared to the geomagnetic polarity timescale to establish a date. Interestingly, more artefacts were found in the palaeosol layers than in the loess layers, perhaps suggesting that the occupation of the area varied along with the climate. No hominin fossils have been found at Shangchen, but archaeologists have analysed 96 stone tools excavated from the site. These were mainly small stone flakes and cobbles that could have been sourced and transported from the Qin Mountains to the south, though further research is needed to establish this. Some of the flakes bear the marks of resharpening, while some cobbles appear to have been used as hammerstones, both traits that are shared with stone tools of a similar age found within Africa. Bones of animals from the cattle, deer, and pig families were also unearthed near the oldest tools. As Robin Dennell from the University of Exeter and co-author of this study (recently published in Nature) said: ‘Our discovery means it is necessary now to reconsider the timing of when early humans left Africa.’ below Three of the oldest stone artefacts found at Shangchen, dated to 2.1 million years ago. u p f r o n t n e w s f o c u s www.world-archaeology.com CurrentWorldArchaeology CurrentWorldArchaeology 11 11

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news focus news focus

New insights into our origins Out of Africa above micro-CT scans of a cranium from Jebel irhoud, Africa (about 300,00 years old), and of one from Qafzeh in the

Levant (about 95,000 years old) reflect the evolutionary changes of the braincase from an elongated to a globular shape. modern features of Homo sapiens like this did not appear at the same time and place, suggesting that our species did not evolve from a single population or region in Africa.

With newly identified evidence for the earliest hominin activity outside Africa and for the diverse roots of Homo sapiens within the continent, our understanding of migration and evolution is changing. Lucia Marchini explores some of the latest thinking.

The African origin of our species Homo sapiens is widely accepted, but until recently researchers have given weight to the assumption that H. sapiens evolved from a single ancestral population or within one region in Africa. Now research into the morphology of human fossils and tools from the Middle Stone Age (a period in African prehistory between c.300,000 and 60,000-20,000 years ago) across the continent is shifting the focus away from this single origin theory, which simplifies the remarkable diversity present in the archaeological record.

Combining evidence from material culture, fossils, genetics, and the ancient climate, the new study (published in Trends in Ecology & Evolution) argues the case for multiple origins of H. sapiens from different groups across Africa that went through periods of mixing and isolation as the environment around them, whether forest or desert, changed. A range of transitional groups may have lived over a vast area of the continent stretching from Morocco to South Africa between at least 300,000 and 12,000 years ago.

Stone tools and other artefacts, with their distinct regional styles, complicate things for the single origin theory. The technological changes that mark the beginnings of the Middle Stone Age, like the move away from large hand-held cutting tools and to hafting and prepared-core technology, took place across Africa as early as 300,000 years ago at Jebel Irhoud in the north and Olorgesailie in the east, and about 280,000 years ago at Florisbad in the south. The current West African dates are younger, at about 180,000 years ago, but this area has not been the subject of as much investigation. Lead author Eleanor Scerri sums up the findings: ‘While there is a continental-wide trend towards more sophisticated material culture, this “modernisation” clearly doesn’t originate in one region or occur at one time period.’

i t u te

I n st l a n ck

Pa x

G u nz / M

i l i p p

: P h i m Ag E S

l o g y a nt h ro p o i o n a r y l u t evo fo r i / Fra n ce s co

S ce r r l e a n o r

: e i m Ag E S

i l wo o d

H e n s h i sto p h e r i co / C h r

’ e r r d

RIGHT As well as diversity in the fossil record, cultural diversity seen in middle Stone Age artefacts from north and south Africa points to multiple origins of H. sapiens.

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