These three cycles run simultaneously, pushing the Earth’s climate in one direction or the other. Most of the time, these three cycles push and pull in different directions, and their combined effect helps to explain why each major cold or warm phase is not uniform, but is interspersed with shorter warm or cold episodes.
It was not until the 1970s that Milanković’s theory was confirmed thanks to two sources: cores taken from deep sea sediments and ice cores taken from Greenland and Antarctica. The ocean floor drilling started in the 1950s, and the ice cap drilling started in the 1970s, with research in both areas continuing today. The more recent ice core research has had an enormous impact on reconstructions of past climates because the ice cores have higher resolution, which means that they record shorter-term events, and so they have provided startling evidence for just how rapidly climate change has occurred in the past. For example, some warming events in the past 100,000 years seem to have happened over just a few decades.
In both types of cores, researchers can ‘read’ climate history from the ratio of regular oxygen atoms (16O), which are made up of eight protons and eight neutrons, to a heavier oxygen isotope (18O), which contains eight protons and ten neutrons. During glacial conditions, more of the regular (lighter) oxygen is stored in the ice caps, leaving a higher ratio of 18O/16O in the ocean and atmosphere. This ratio is then preserved in the fossilized shells of micro-organisms at the bottom of the ocean and in tiny air pockets in the ice cores. A decrease in levels of heavy oxygen (18O) in cores taken from the ocean floor indicates an interglacial, or warm period.
Research into deep sea cores and ice cores covering the past 1.2 million years or so (dating is not yet precise for the oldest parts of the sequence) has produced a series of twenty-three oxygen isotope stages (OIS for short; also called MIS for marine isotope stage, see Timeline, p. 10), in which the odd numbers represent warm periods and the even numbers represent glaciations. We are currently living in the interglacial OIS 1.
What do these cycles predict for the future of humanity? The Earth’s orbit is now in the part of the cycle where its shape approaches a perfect circle, and we can expect the current warm conditions – which are already unusually long and stable – to continue. For example, the ‘wobble’ cycle is now 6,000 years into a cooling phase and the tilt of the Earth’s axis is moving towards a minimum value, which has a cooling effect, but these cycles have been overshadowed by the warmth brought on by the shape of the orbit. Some computer models predict that the next glacial period is at least 5,000 years away.
The Holocene is already the longest stable warm spell since Homo erectus walked out of Africa. The effects of human-induced warming on such a complex system are not fully understood, but some climate scientists suggest that rather than being just 5,000 years away from the next cooling phase – which after all is just about the amount of time since the Bronze Age began or since the early phases of Stonehenge in Britain – we may have broken the cycle of glaciations for at least the next 45,000 years.
Cannibals and caves
Some of the most sensational discoveries from Palaeolithic Europe (i.e. the ‘Old Stone Age’, before the Holocene) have come from the area of Atapuerca in northern Spain since the 1990s. This has marked a change from the previous 150 years, when such countries as Germany, France and Belgium were the focus of attention. One of the directors of the Atapuerca project, Juan Luis Arsuaga, is justified in boasting, ‘Today the Iberian Peninsula occupies a very special place in European prehistory.’ For starters, it is home to Europe’s oldest known human occupation.
The Atapuerca Hills contain an extensive network of caves, parts of which were used as shelters over hundreds of thousands of years. Some of these caves were exposed by an old railway trench, cut through the hills more than 100 years ago by a mining company. Three of the sites in Atapuerca have already altered our understanding of Palaeolithic Europe: Sima del Elefante is the oldest securely dated site in Europe; Gran Dolina is the second-oldest known site in Europe and has the earliest evidence of cannibalism among hominins; overshadowing even these two extraordinary sites is Sima de los Huesos (‘Pit of the Bones’), which has produced the richest collection of hominin fossils anywhere in the world, and which we will examine in the next chapter.
Plan of the site of Atapuerca, in northern Spain. This extensive network of caves was exposed by an old railway trench, and various sites within the system have yielded extraordinary evidence of early humans, including the oldest known so far in Europe.
Why is it that we have this extraordinary accumulation of uniquely early sites and fossils in this particular formation in northern Spain? Plant and animal remains from the Atapuerca caves show that the area attracted a wide range of species. The humans shared the area with two-horned rhinoceroses, hippopotamuses, bison, sabre-toothed cats, lynxes, bears and hyenas. This diversity probably reflects the different habitats surrounding the Atapuerca Hills, such as river valleys, grasslands and forests. The caves provided commanding views over herds of animals grazing by the confluence of two rivers and thus two migration routes.
But such combinations of advantageous topography, habitat diversity and access to resources can be found in many other locations in Europe. The unique archaeological richness of the Atapuerca caves has to be attributed to good fortune in the preservation and exposure of these sites. The sediments did not suffer much destruction from natural processes, such as erosion or tectonic activity. When the roofs of the caves collapsed, the sediments were sealed, and therefore protected, until the railway was cut through them, making long sequences of archaeological layers accessible for excavation. In the case of Gran Dolina, for example, the railway trench went to a depth of 18 metres (60 ft) of archaeological deposits, exposing layers dating from 300,000 down to nearly 1 million years ago.
In the summer of 2007, the excavations of Sima del Elefante produced a combination of artifacts that is an archaeologist’s dream: chipped stone that was clearly crafted into tools by humans (as opposed to stones that may have been chipped by natural breakage); animal bones with signs that they had been cut apart by humans using those stone tools; confirmation of an exceptionally early date (between 1.1 and 1.2 million years ago) from different scientific dating methods; and, perhaps most importantly, the bones of the humans themselves. Many sites have just one or two of these kinds of evidence, leaving archaeologists to argue over key aspects such as dates, the species of hominin present or even whether the site has any conclusive signs of human activity.
The human fossils are a fragment of a lower jaw and a lower tooth. The humans probably picked up large pebbles, found within a few kilometres of the site, and knapped them in the cave, using hard stone hammers to produce simple sharp flakes which they used for defleshing animal carcasses. Some of the animal bones found at the site show cut marks from such tools, as well as percussion marks made in the process of opening up the bones to get at the marrow. The fauna and microfauna suggest that the site was used at a time when the climate was warm and humid, fitting in with the general pattern that humans at this early date had not yet shown a consistent mastery of fire and could not cope with seasonal cold.
The evidence from Gran Dolina is even more abundant than at Sima del Elefante and offers a compelling insight into the lives and minds of these early Europeans. In Gran Dolina, a layer dating to about 960,000 years ago has yielded animal bones, stone tools and fossil human bones belonging to at least six adults and children. Pollen analysis shows that the site was used at a time when climate conditions were wet and temperate. As at Sima del Elefante, the stone tools found in association with the fossils were made of local material and are simple small flakes, some of which were modified and improved, for example by making a serrated edge.
The most intriguing aspect of the Gran Dolina finds relates to the question of how the human remains came to be intermixed with food debris. The human bones are very fragmentary, and most, regardless of the age of the individual, have cut marks made by
stone tools in the process of removing the flesh from the bone. These were found along with bones of large, plant-eating mammals, and bones from both groups appear to have been defleshed in a similar manner and to have been cast aside. In other words, Gran Dolina seems to have been a food-processing site, and the humans present were eaten by other humans. How this came to be is open to speculation. A brief look at the practice of cannibalism in our own species points to some likely scenarios.
Cannibalism can be an emotive issue, because in our prosperous modern society it is almost exclusively the domain of deviants, psychopaths or people under extreme duress. Some view the notion that our ancestors practised cannibalism as defamatory. For example, Erik Trinkaus and Pat Shipman in The Neandertals (1992) trace how researchers who wished to distance Neanderthals from modern humanity have often accused them of cannibalism. But cannibalism should not surprise us, either in the Neanderthals or in more ancient hominins, because cannibalism is a well-documented part of our own species’ behaviour.
Possibly cannibalized human remains from Gran Dolina, Atapuerca, assigned by the excavators to a new species, Homo antecessor.
Perhaps the most famous modern example of human cannibalism was dramatized in the movie Alive (1993). In 1972 a plane crash stranded members of a Uruguayan rugby team and their friends high in the Andes Mountains. In desperation, the survivors resorted to cannibalism of the crash victims as they lived for more than two months far from any source of food until their incredible rescue. But it is not just in acute crises like this that modern humans have been known to eat each other. The behaviour also occurs where there is chronic protein shortage.
As we look back to the distant, pre-agricultural past, access to meat would have depended on the season, success in the hunt, location of wild herds and other factors beyond human control. A parallel can be drawn with the South Fore people of Papua New Guinea, as documented in a classic anthropological study from the 1960s by Shirley Lindenbaum and published as Kuru Sorcery (1978). The South Fore area is very remote, and it is where both traditional subsistence practices and cannibalism lasted longer than elsewhere in the region. When someone died from causes other than an infectious disease, practically the entire body would be consumed after dismemberment using bamboo and stone tools. This took place in highly ritualized ways designed to honour the dead and their families, with particular body parts reserved for close relatives. The practice only came to an end when the South Fore people suffered an epidemic of a prion disease similar to Creutzfeldt–Jakob disease (the human version of ‘mad cow’ disease), contracted from the consumption of human brains.
We cannot say whether cannibalism at Gran Dolina took place after an attack by another group, whether it reflected a simple sustenance need or if it was a routine way of honouring those who died in the course of their difficult lives. What we can say is that the act of cannibalism makes the inhabitants of Gran Dolina more, rather than less, human. Also, this site indicates that disposal of the dead by cannibalism probably predates intentional burials and burial rituals by hundreds of thousands of years. In Chapter Five we will revisit this issue in relation to cases of apparent Neanderthal cannibalism and discuss the continuing controversy.
The first Britons
The site of Pakefield on the east coast of England has been known for its fossils since before the naming of the Neanderthals in 1863. But it was only in the first decade of the 21st century that Pakefield and nearby Happisburgh brought fame to England’s East Anglia region for their prominent place in the story of the first human settlement of Europe.
The evidence from these two sites indicates that by around 100,000 years after the cannibalism seen at Gran Dolina, these first Europeans travelled further north than any member of the genus Homo had ever gone. The evidence is sparse – with dozens, rather than hundreds, of crude stone tools – but this is enough to prove that hominins had reached a latitude higher than Mongolia and Calgary, Canada.
At this remote time – which the excavators put at 700,000 years ago for Pakefield and between 800,000 and 1 million years ago for Happisburgh – the English Channel had not yet formed, and Britain was connected to the rest of Europe by a land bridge. The area between Pakefield and Happisburgh is the only stretch of England’s eastern coastline from this period that is not currently submerged. Located at the bottom of a beachside cliff that is rapidly eroding into the sea, it is lucky that Pakefield has survived at all. When archaeologists unearthed a few dozen stone tools there in 2005, they had to keep a careful eye on the tides to stay safe. It is a reminder of how much important information about archaic humans has already been swallowed by the world’s oceans.
Some of the Pakefield tools, which were simple flakes made from river cobbles, were retouched (reworked by being sharpened along the cutting edge). The cores (leftover pieces from which the flakes were taken) were also found. These tools were essentially the same kind of simple cutting implements as those from Atapuerca. They were much easier to make than the handaxes that had long been in use outside Europe.
A flint tool found at Pakefield in Suffolk, England. Tools like this provide some of the earliest evidence for human presence this far north.
Pakefield was probably occupied during a mild interglacial. It is clear from the remains of particular rodents and plants that it was used at a time when the summers were warmer and drier than at present and the winters were wet with no frost. As we learned when studying in nearby Cambridge, the people there still would have had to contend with very limited daylight hours between November and February.
There are not many large mammals left in Europe, and we now associate such wildlife with nature preserves in Africa. In this period, however, despite its high northern latitudes, England was home to an array of impressive beasts. Pakefield would originally have been in the marshy floodplain of a river estuary, not far from woodland and grassland. This was an ideal feeding ground for hippos, rhinos, bison, mammoths, elephants and deer – all species identified from the animal bones at the site. They, in turn, attracted predatory animals, notably humans, who had an additional incentive to come here – the availability of flint pebbles to make stone tools.
The most startling aspect of the Pakefield stone tools when they were discovered was the unexpectedly early date of 700,000 years ago. This is now fairly secure thanks to a dating device delightfully known as the ‘vole clock’. The form of the teeth of various vole species evolved at a pace that turns out to be convenient for dating archaeological layers. The tools at Pakefield are associated with Mimomys savini, a species of vole that was also present at Gran Dolina, along with Mimomys pusillus, another vole species which seems to have gone extinct about 650,000 years ago. We know, therefore, that humans made these tools slightly before that minimum date.
Before the discovery of Pakefield, the conventional wisdom was that humans at this time were still basically a tropical or sub-tropical species which could not survive so far north. We now know that they were capable of surviving at high latitudes, and perhaps not only when the climate was extremely warm.
In 2005 Happisburgh also began to challenge what we thought we knew about early humans. Located on the banks of the ancient version of the River Thames, Happisburgh produced some eighty stone tools over five excavation seasons until 2010. As at Pakefield, the Happisburgh tools are associated with the extinct voles. But other dating evidence places it even older. The tools came from a layer in which the sand was laid down when the Earth’s magnetic poles were reversed. We know from other sites that this occurred 780,000 years ago, so this provides us with a minimum date for Happisburgh. At Gran Dolina, the human remains also come from a layer of reversed polarity.
The pollen traces discovered in the layer indicate that the area was forested and that the climate was cooler than the tropical conditions enjoyed by all humans up to that point. The excavators believe it was sufficiently cool at Happisburgh that the people who made the tools would have needed clothing and possibly also fire in
order to live through the winter. Does this mean that the first Britons were also the first humans to wear clothes? This is probably speculating too far, especially because some archaeologists argue that Happisburgh may not be quite as old as the excavators believe. But the lesson of Happisburgh and Pakefield is that our understanding of humans in these early periods is changing fast.
Who were the first Europeans?
The surest way to identify the humans who first colonized Europe is by looking at their bones, the only parts of them that have survived. But in this case, as in virtually every episode in the Neanderthal story, the fossil evidence is sufficiently ambiguous to put consensus on their meaning beyond reach. Here we have two questions. Were the first Europeans an offshoot of Asian Homo erectus or were they part of a later wave of migrations from Africa? And are they the ancestors of the Neanderthals?
The earliest human fossils in Europe are from just the sites that we have mentioned: Sima del Elefante and Gran Dolina in Spain and perhaps Ceprano in Italy (where the dating is in dispute). All together, we have fragments of around a dozen individuals, including men, women and children. We have no human bones from the British sites from this period, so it is simply a reasonable guess that the people there were part of whatever species was in the south of Europe.
The Neanderthals Rediscovered: How Modern Science is Rewriting Their Story Page 4