Geoscientist Online

Geoscientist 18.8 August 2008

On the afternoon of 27 April 1859, two successful Englishmen businessmen made history in a gravel pit on the outskirts of Amiens on the Somme River, northern France. Joseph Prestwich, at 47 the older by 11 years, had a day job in the wine trade; but his passion was unravelling the geology of northern Europe and tracing the history of glaciations by mapping surface deposits with the evocative name of ‘drift’. His energetic and impressively bewhiskered younger companion, John Evans, was obsessed with Roman coins, and had earlier bought some from workmen digging in this very pit. He ran a paper company for his father-in-law. His wife, Harriet, had died the year before, leaving him with five young children. The eldest, Arthur, would inherit the family fortune and make his name discovering the Minoan civilisation of Crete.

Prestwich and Evans had been brought together that day by an object that lay 17 feet below the ground surface, and four and a half feet up from the base of the river terrace cut into the chalk slope. Sticking from the gravels was the edge of a worked flint tool - the first to be recorded and witnessed in situ, in gravels that had also yielded bones of extinct animals like mammoth and woolly rhino. So excited were they that they had asked for three representatives of the Société des Antiquaries de Picardie to witness its discovery, and for a photographer to record the moment when the time barrier to a human antiquity of geological proportions was conclusively broken.

 

Caption to picture

The moment when humans broke the time barrier. Who is pointing to the flint, and who is sitting in the wheel-barrow, remains a bit of a mystery. The lack of side-whiskers seems to rule Evans out, and neither figure matches pictures of Prestwich. Perhaps they are two of their French colleagues Pinsard, Dufour or Garnier? Oddly, the tool itself was never illustrated - perhaps because, as Prestwich recalled, it was ‘…rougher and more imperfect than the generality of the specimens… an unfinished implement’. Only the best artefacts were made into published plates, a costly process. Perhaps it sits today, unremarked, in a museum drawer alongside the many hand-axes Prestwich and Evans collected and bought from the workmen that day, and on later visits.

This had been a whirlwind visit. On May 1, Evans suffered a very rough crossing to join Prestwich that evening in Abbeville. They spent the morning of May 2 touring the pits in the town and examining the large collection of artefacts amassed by their host. Then during a ‘most sumptuous dejeuner à la fourchette’, as Evans recalled, a telegram arrived from Amiens 30 miles away. Workmen, briefed by Prestwich, had made a discovery that had eluded him during his own visit a few days earlier. A flint tool had been found in the section, waiting to be dug out. They quickly bid adieu to their eccentric host, boarding a fast train to meet the photographer and the French antiquaries in the pit near the seminary of St Acheul. The next day they were on the boat train, and back in London by midnight.

The following month saw some frenzied but well co-ordinated activity. Evans set off on May 6 for a business trip taking in Dublin, Belfast and Manchester, returning home a week later. In the meantime Prestwich went back to St Acheul with palaeontologist John Flower to recover more artefacts and extinct animal bones. They planned a three-pronged attack on the learned societies whose endorsement they needed if they were to establish a high antiquity for humans. Prestwich spoke first, to the Royal Society on May 26. The audience was formidable; Faraday, Murchison, Babbage, Huxley and Lyell among others. Cutting-edge science was being laid before the greatest scientists of the age. With obvious relief, Evans wrote afterwards that ‘our assertions as to the finding of the weapons seemed to be believed’. Then Evans, the expert on flint tools, gave a full account to the Society of Antiquaries of London on June 2. Flower provided further proof to the Geological Society on June 22.

But before anyone of these three rose to speak, something quite unexpected happened. Sometime between his return from Ireland and Prestwich’s talk to the Royal Society, Evans had stumbled across a short letter, illustrated with two fine engravings, which had been sent to the Society of Antiquaries in 1797 and published in Archaeologia three years later. It had been written by John Frere, a Fellow of both the Society of Antiquaries and the Royal Society, and a Suffolk landowner. His letter, accompanied by two flint handaxes, recorded their discovery in a brick pit at Hoxne. What marks his brief communication as special are his comments on their stratigraphic position, his conjecture that they were ‘weapons of war’, and his conclusion that they came from a ‘very remote period indeed; even beyond that of the present world’. Yet although politely thanked by the Antiquaries, his paper was promptly forgotten.

The re-discovery was made when Evans was waiting for some friends at the Society of Antiquaries and looking at one of the display case was “absolutely horror-struck to see in it three or four implements precisely resembling those found at Abbeville and Amiens”. These were Frere’s implements. Evans and Prestwich went immediately to Hoxne where they met an old quarry workman who referred to the handaxes as ‘fighting stones’. Not surprisingly, Hoxne figures prominently in both their papers to their respective learned societies. It was their final proof, because it repeated the same set of discoveries – bones and stones in situ – that had been made on the Somme. Frere’s letter was the key to acceptance since, as Prestwich noted, he was ‘an antiquary unfettered by geological theories’. Frere carried no hand-axe to grind about the Earth’s antiquity.

Their papers also neatly side-stepped the most contentious issue - the artefacts’ age. Prestwich said: ‘the evidence, as it at present stands, does not seem to me to necessitate the carrying of man back in past time, so much as the bringing forward of the extinct animals towards our own time’. They had no way to estimate how old the finds were; but as Evans wrote: ‘This much appears to be established beyond a doubt; that in a period of antiquity, remote beyond any of which we have hitherto found traces, this portion of the globe was peopled by man; and that mankind has here witnessed some of those geological changes by which these so-called diluvial beds were deposited’.

But they left nothing to chance in convincing those with the greatest scientific and social clout. In June they arranged for the doyen of British geologists, Sir Charles Lyell (until then a critic of great human antiquity) to visit the Somme. More handaxes were found - one of which survives in Edinburgh University, bearing Lyell’s name and the St Acheul location. Lyell was convinced, and at a packed session of the British Association for the Advancement of Science at Aberdeen, and in the presence of Prince Albert, he added his authority: ‘A vast lapse of ages, [separates] the era in which the fossil implements were framed and that of the invasion of Gaul by the Romans’. And that was the end of the matter.

Barely a month later, The Origin of Species created the 19th Century’s greatest publishing sensation. Darwin’s work side-stepped human evolution, but the implications were clear. Fuller discussion came with The Descent of Man (1871), published a year before the French archaeologist and political maverick Gabriel de Mortillet used St Acheul as the type site for those distinctive stone handaxes. Thus the “Acheulean”, one of the most enduring and widespread of archaeological cultural traditions, was named. Evans continued with his business and antiquarian interests, his achievements recognised with a knighthood in 1892. His massive book the Ancient Stone Implements of Great Britain (1872) established Palaeolithic archaeology. Prestwich left the wine trade in 1874 to become Professor of Geology at Oxford, a post he held for 14 years and which crowned his reputation as one of Britain’s greatest geologists. He too was knighted in 1896, the year he died.

How important are the sites of St Acheul and Hoxne for Palaeolithic archaeologists today? In the 1990s the Somme evidence was thoroughly re-assessed by a French team led by Alain Tuffreau and Pierre Antoine. Their work on the age of the deposits began with Prestwich’s sections across the valley and the staircase of river terraces that he had carefully noted. Their aim was to tie the phase of aggradation, when huge quantities of gravels were laid down, and the subsequent phase when they were cut through, making river terraces, to the timescale established independently from ocean floor drilling.

These deep sea sediments contain foraminifera, whose tiny skeletons soak up the oxygen isotopes present in the sea water and preserve the ratio between the light O16 and the heavier O18. When this ratio is plotted along the length of a core, what emerges is a wiggle-curve of changing values. These wiggles show a repeated pattern, or climate cycle. It took the inspired insight of Sir Nick Shackleton in the 1970s to see these wiggles as a signal of changing ice-age climates. When they are rich in O16, oceans were large and climate warm. When O18 dominated, it was because the lighter O16 had been evaporated off and dumped on ice sheets at the poles. Here was a deep-sea stratigraphy of climate change, comparable to the staircase of terraces cut into the Somme Valley.

Such deep-sea stratigraphy was undreamt of in 1859, just as our ability to put ages to these cycles would have been, using magnetic reversals. 790,000 years ago the Earth’s polarity switched from reversed to normal. This can be measured in volcanic rocks on land, as well as the marine sediments, and those same rocks can be dated by scientific methods that use the rate at which isotopes such as potassium and argon (K/Ar) decay. This boundary, the Brunhes-Matuyama (B-M), provides a stratigraphic marker above which eight climate cycles - each consisting of a warm interglacial and a subsequent glaciation – can be seen. Hoxne and the Amiens terrace at St Acheul sits in the fifth cycle after the B-M boundary.

Hoxne provides more detail on the interglacial section of this cycle (427,000 to 364,000 years ago). Pollen from the Hoxne lake sediments suggest a warm climate, during which conifers and cold tolerant trees gave way to deciduous forest. Of all the eight interglacials since the B-M boundary, this one bore the strongest climatic similarities to the present. However, differences are also plain. The population of England 400,000 years ago was probably 3000-5000 at most. Faunas indicate rich grazing and diverse habitats. Danielle Schreve has traced the changing fauna, and has found that at the time Hoxne was visited by early humans, the grasslands resounded to the footfall of extinct elephant and rhino varieties, horse and large fallow deer. Macaques lived in the forests and along the rivers an extinct giant beaver was building dams. Furthermore, even though no fossil evidence for the humans has yet been found at either Hoxne or the Somme, discoveries at sites of similar age reveal them to have been Homo heidelbergensis.

Four hundred thousand years would have been an unbelievable amount of human history to Lyell and Evans. Prestwich, as we have seen, wanted to bring things forward rather than push humans back in time; but back in time they have gone. Hominin evolution began with the split from the chimpanzees six million years ago, a date determined by the amount of genetic differences with our closest living relative. The first stone tools occur at 2.5Ma, at Gona (Ethiopia). The first appearance of our lineage, Homo, took place soon after in Africa and then beyond at Dmanisi (Republic of Georgia) by 1.8Ma. The oldest occurrence of Acheulean handaxes is currently at Olduvai Gorge in Tanzania, excavated by Mary Leakey, and dating to 1.4Ma.

But although Hoxne and St Acheul are no longer breaking Palaeolithic time-barriers, the evidence they contain is challenging another fundamental barrier to understanding the past: when hominin brains became human minds. Currently, this is a subject of fierce debate. There are those who favour a very late date indeed for this transition; during the Neolithic with its villages, crops and domestic animals, which begins some 12,000 years ago in the Near East. They see as crucial the built environment of houses, with their opportunities for secrecy, privacy and a closer connection between people and material symbols, as are found for example at the early Anatolian town of Catalhöyök (Turkey) or the crowded tell-site of Abu Hureyra on the banks of the Euphrates.

Palaeolithic archaeologists disagree. They point to an older, human revolution predating the Neolithic by at least 50,000 years. At this time, argues Richard Klein, our brains underwent significant neural changes. Paul Mellars points to the wealth of evidence for art, ritual in the form of burials and a global diaspora when Homo sapiens became the first hominin species to move out of Africa to reach Australia, the Pacific and the Americas.

Both are strong cases; but both betray an old prejudice that modern minds must be associated with Homo sapiens and not earlier hominins such as H. heidelbergensis and their descendants the Neanderthals. From this standpoint, the argument is about which Homo sapiens possessed modern minds; the hunters of the earlier human revolution, or the farmers of the Neolithic revolution, from whom we trace our own urban and industrial beginnings.

Breaking this mind-barrier involves placing the evidence in a different framework; one in which Hoxne and St Acheul occupy an important position. Hominin evolution sees the brain treble in size. Encephalisation required changes in diet and physiology, because big brains need higher quality food like meat. The question is, what selected for such an increase at such a cost?

One answer, from evolutionary biologists Robin Dunbar and Leslie Aiello, points to the social lives of our ancestors. They started by showing that brain sizes of many different monkey species correlate strongly with group size. The bigger the brain, the bigger the group. When humans and extinct hominins are added to the same graph it becomes clear that during human evolution the number of other individuals that could be remembered, monitored and engaged with had doubled; from about 70 (the primate maximum) to 150 - a number that constantly recurs in the organisation of human groups and networks, forming the building block for our demographically huge and intricately inter-connected urban world.

How did this doubling occur? Social contacts among apes are maintained by finger-tip grooming. To go beyond the limit of 60-70 contacts soon runs into problems of finding enough time in the day to groom everyone you know. The solution is to develop a different form of communication, and Aiello and Dunbar argue that language fits this need. The implication of their argument has been dramatic. The big rise in brain size between 600,000 and 400,000 years ago, when H. heidelbergensis lived at Hoxne and St Acheul, strongly suggests they had language.

Have we now broken the mind-barrier? Apparently not. After all, those Homo sapiens who painted cave walls and buried their dead festooned with beads and covered in red ochre must have had language. However, several Neolithic archaeologists still do not regard them as having “modern minds”. Our Hoxne hominins, with their much simpler cultural inventory, therefore stand no chance - yet.

The time-barrier, the acceptance of human antiquity, was broken almost 150 years ago; yet the mind-barrier is still waiting to fall. This will not depend on a single discovery but a change in outlook as we come to understand more about how our brains actually work. Even now we are seeing that emotion plays a pivotal role. The human mind is not just defined by the use of objects and symbols, but with understanding, amplifying and manipulating the emotions of others.

Those two English businessmen were excited, passionate and, yes, emotional, about their discoveries in 1859. But since then we have only allowed a rational, dry-as-dust account of the social lives of those ancestors whose antiquity they first established. Once the mind-barrier prejudice is broken, the next 150 years of anthropological endeavour look truly exciting.

And broken it will be. Antiquaries and geologists, after all, have time on their side.

*Prof. Clive Gamble, Centre for Quaternary Research, Department of Geography, Royal Holloway, University of London, Egham TW20 0EX. This article is based on a lecture given by Professor Gamble as part of the Society of Antiquaries’ Tercentenary celebrations in 2007. With thanks to Ms Jayne Phenton of the Society of Antiquaries, for locating illustrations and facilitating this article's appearance in Geoscientist.