by Martin Jones
Childe was a Marxist as well as an archaeologist, passionately interested in what prehistory could contribute to a grand narrative of the human past, propelled forward in a series of revolutionary episodes. He first developed his notion of a ‘Neolithic Revolution’ in detail in his classic book, Man Makes Himself, published in 1936. In his later volume What Happened in History, he described it thus: ‘The escape from the impasse of savagery was an economic and scientific revolution that made the participants active partners with nature instead of parasites on nature’ (p. 55).
From his extensive knowledge of the archaeological data available at the time, Childe was able to give that general principle some historical substance. He placed particular emphasis on the seeds of two particular grasses, wheat and barley, and on a crescent of land running from the fertile Nile valley in the south, through Israel, south-east Anatolia and Syria, and along the foothills of the Zagros mountains in Iraq towards the west. This Fertile Crescent, bounded by less hospitable environments, was also known to yield early Neolithic sites with ancient potsherds scattered across their surfaces. Although Childe himself was not intent on narrowing his prehistoric revolution down to a single event, he effectively enabled others to do so. He set the stage for them to seek out the very first farms, with the very earliest of these critical grass seeds from which the whole enterprise had sprung.
The spotlight had also been focused upon particular regions of the world by data of a quite different kind. At about the same time as Childe was developing his narrative of prehistoric revolutions, another field was similarly moving forward. The Russian botanist Nicolai Vavilov was hard at work charting the distribution of different varieties of the world’s crop plants. He argued that where those varieties were most abundant and diverse, that was where domestication happened. Indeed, those varieties did cluster in regional concentrations, supporting his idea of ‘centres of origin’. The Vavilov hypothesis provided a set of world-wide signposts to where archaeologists might find these first farms.
During the Second World War Chicago archaeologist Robert Braidwood started formulating the research strategy that would subsequently lead him to find and excavate pioneer farmsteads at the eastern end of the Fertile Crescent. Up in the Zagros foothills, he found them at such sites as Jarmo. Kathleen Kenyon, from England, would find the ancient grass seeds deep down in her excavations of Jericho, at the western end of the Crescent. Other teams would discover candidates for pioneer agriculture at south-east Anatolian sites such as Cayonu. Before, archaeologists were working with theoretical notions of a great transition. Now, they could examine the actual harvests, the animals, and the living floors of the pioneer farmers engaged in the process. Such a proximity with actual lives sharpened the issue of what Childe’s ‘revolution’ meant in human terms.
revolution or evolution?
Childe and many archaeologists after him saw parallels between this prehistoric agricultural revolution and more recent technological revolutions that have similarly had enormous impacts on culture and society. They saw direct parallels between the Neolithic Revolution of prehistory and the Industrial Revolution of more recent times. Just as we can seek out the first steam engine and trace the spread of this radical technological advance, so we could seek out the earliest domestication and trace the ripples of that new idea across the world. This is how Childe’s Neolithic Revolution came to be perceived. A challenging natural environment had brought roaming hunter-gatherers together, to where they would make the revolutionary step of controlling plants. This in turn was linked with settling down at a single year-round location where the investment of toil had been made. It also involved some new skills, such as the firing of pots for the cooking and storage of the new foods. In time, the necessary social cohesion was controlled and consolidated in urban sites, linked together in long-distance trade of exotic goods. The settled villages of early farmers had builders, potters and traders who could bring in exotic objects and polished stone. The gatherers and hunters that preceded them inhabited much simpler material worlds. The new artefacts could be plotted across Europe, tracing arrows on the map, starting from the Middle East and eventually reaching to the north and west of Europe.
Childe’s revolution was part of a new grand narrative of the human past, a later episode in the sequence that began with the collective improvement of the hominid family, walking upright, expanding the brain and refining the dexterity of the hands. It formed the ecological foundation of the great civilizations that followed. It had a radical origin in space and time, and from that context it spread, replacing the more static and passive societies that remained under nature’s control. Much of the archaeological research that first incorporated a search for the food remains was concerned with tracking those origins down, locating the farms where this momentous power over nature was first exercised. By the time this happened, however, a quite different story was being aired.
At the heart of the story related above was the presumed self-evident economic advantage of agriculture over gathering and hunting. Darwin had written with evident disdain about the savages he had met on the Beagle’s voyage, and the apparent poverty and brutality of their lives. It was clear to him that the sophisticated breeders of cereals, livestock, pigeons and dahlias in his own society were further up the ladder of life. Childe could still talk of the ‘impasse of savagery’ a full century after the Beagle’s voyage. This Eurocentric view persisted for a considerable time, and it was not until after Childe’s death that it was challenged with a more detailed analysis of non-agricultural societies. In 1968, R. B. Lee and I. De Vore’s volume Man the Hunter presented a picture of affluence beyond the realm of agriculture. The !Kung bushman, for example, achieved an enviable balance between labour and leisure, gathering mongongo nuts that grew wild and forgoing the endless toil of tending plots and controlling the plant’s entire life-cycle. The closer scrutiny by anthropologists of surviving hunters and gatherers was drawing attention to their sophisticated and varied interaction with nature, moving them from the status of social fossils to unique societies in their own right. By implication, the first farmers in south-west Asia did not necessarily have an easier time than their ancestors who gathered wild grasses and hunted gazelle. The hard work and narrow diet often affected early farmers’ health, and it is far from clear that their yields were any greater than what was available from the wild cereal stands. It is not self-evident that communities on the arrow’s path on one of Childe’s maps would leap at the prospect of removing entire forests. They may not have been so keen to put aside their seafood, game and fruits of the forest for bread, porridge and the endless backbreaking jobs of digging, planting, tending and weeding.
What is more, as sieving and flotation were generating a rich new data-set of ancient seeds, the new bio-archaeology was not providing an unambiguous picture of early domestication. True, some very early domesticated plants and animals were coming to light along the Fertile Crescent at the root of Childe’s arrows, and agriculture in the north and west of Europe was very much later. But here and there early domesticates were being recorded outside this core region, around the shores of the Mediterranean for example. Other regions of the world were revealing their own transitions to agriculture, which, particularly in the case of the New World, had to be independent. Another story might make better sense of all these data. A number of ecologically minded authors favoured another account, one that did not depend upon the notion of a localized technological revolution. Instead, a more widespread and diffuse process of adaptation could account for the data.
dispersed adaptation to a turbulent environment
At the same time as bio-archaeological methods were gaining hold, and the excavations in the Fertile Crescent were proceeding, considerable headway was also being made in understanding how the climate had been changing. This was achieved in large part by examining other kinds of ancient biological remains that reflected climate rather than human activity. What they demonstrated was that the peri
od around the time of early domestication in the Fertile Crescent was one of climatic turbulence. After the glacial maximum, the melting of massive ice sheets around the world was having considerable knock-on effects for world-wide temperature, vegetation patterns and animal populations, which shifted and fluctuated rapidly. Humans were not the only species that were faced with adaptation or extinction.
Our recent hominid cousins, the Neanderthals, were, like several largish mammal species, ultimately unable to adapt to the patterns of marked change that accompanied the freezing and thawing of ice on a global scale. Anatomically modern humans were different, their versatility and ability speedily to change their way of living putting them at an advantage in a changing environment. If their own mammalian prey was on the wane, hunters could switch to fishing or gathering–whatever their changed environment offered. Coastal communities across the world were adapting in this way, and coping with change by moving to a broad spectrum of dependable foods. In many parts of the world, such as the wooded margins of the south-west Asian steppes, the gathering of seeds from the herbaceous sward that spread out across the parkland steppe played a major role. Literally hundreds of different species were collected from these prolific natural harvests. In some places, certain grasses were favoured among this mixture.
At a site called Ohalo in Israel, Mordechai Kislev examined a series of blackened plant fragments and found them to be wild barley, 19,000 years old. Along with the seeds were some of the rachis fragments, displaying the clean, natural break that marked them out as wild cereals. He also noticed four rachis fragments lacking that clean break. A further 9,000 years on, at another grass gatherers’ site called Netiv Hagdud, over 100 barley rachis fragments out of a few thousand lacked the clean break. In assemblages that are more recent still, all the rachis fragments recovered would lack the clean break. The gatherers of Ohalo and Netiv Hagdud were following an ecological path rather similar to others that had been taken across the world, shifting to dependable, fast turn-around foods in changing environments. The transition from gathering wild grasses to cultivating cereals is not marked by any immediate upheaval. Gatherers and farmers continued to live within walking distance of each other in not dissimilar settlements for 2,000 years or more. The transition was apparently smooth, yet one more adaptation in a species accustomed to constant change.
The pressures of a turbulent global environment and changing vegetation patterns were favouring those communities that introduced some artificial stability into their environments. That was how humans would avoid going the way of other large mammals that failed to adapt to environmental fluctuations. It was ordinary evolution in action, not a historic triumph in the progress of culture over nature but a dispersed and varied set of adaptations, some of which have subsequently led to the world’s great crops. It did not have a single point of origin in space or time. It was happening repeatedly and all over the place, and the early generations of environmental stabilizers, if we can call them that, did not necessarily have a better life than their predecessors. It may well have been worse.
Among the proponents of that alternative story was Eric Higgs, a keen advocate of the new bio-archaeology at Cambridge. In the early 1970s he encouraged his team to move their attention from a particular species and a particular time period in the Fertile Crescent. He urged them to look at different places, different times and different species, to find different manifestations of the varied story of human evolutionary adaptation. Indeed, they found there were variants to the story, early cereals and livestock turning up beyond the Fertile Crescent. Other crops were explored by bio-archaeologists in parts of the world remote from this region. Dispersed evolution and multiple origins seemed to offer a better way of accounting for human adaptation than a localized technological revolution. For any of these major resources, we could anticipate multiple routes to agriculture, as different communities experienced similar environmental problems. That was the picture from archaeology. Something quite different was coming from the molecular evidence.
an evolutionary bush
The molecular revolution in biology affected plants as much as it did humans and other animals. Rather similar molecular approaches were taken to rebuilding their family trees or phylogenies. There were some significant differences, some molecules, tissues and sub-cellular structures being found in one but not the other. Nevertheless, plant and animal cells had many similarities in molecular terms. In each case, their tissues were largely made up of proteins, carbohydrates and lipids. The genetic blueprints of plants and animals alike were stored in the form of DNA, both in the cell’s nucleus and within some of the other structures inside the cell. Just as with human genetics, the molecular revolution in crop plants first gained momentum with proteins rather than with DNA. Just as the blood proteins gave an early molecular insight into human genetics and evolution, so seed storage proteins and a group of enzymes called isozymes did the same for crop plant genetics. Minor variations between the different proteins could be used to build a phylogenetic tree for different varieties of any particular crop species. The shape and pattern within those trees could reveal to us aspects of how the past had unfolded, with a direct bearing on the contrasting models put forward by Childe and Higgs. However, a closer look at these phylogenetic trees calls into question whether ‘tree’ is the right way to describe them.
Returning for a moment to human evolution and the Neanderthal story, we were brought into contact with Mitochondrial Eve and with the family tree that springs from her. That phylogeny was more of a bush than a tree. There was no main trunk, no lofty canopy. The whole thing was a busy cluster of branches, spreading laterally rather than reaching vertically. The shape of the bush was traced by working back from the DNA sequences of living women, without prioritizing or ranking one above the other, but simply trying to make sense of the similarities and differences between them. Its form was traced by projecting backwards in time, progressively joining the shoots occupied by modern samples into minor then major branches and finally to a common stem. We need further to imagine that the bush was linked to a series of neighbouring bushes by underground stems. Those underground stems may be followed to such neighbours, allowing us to view the bush in the context of a much larger picture. In the case of the ‘human bush’ stemming from Mitochondrial Eve, some related primate such as the chimpanzee or orangutan provides a suitable neighbour through which it may be ‘rooted’. In the cases of the plant species involved in agriculture, they too have their own evolutionary bushes, rooted in relation to their own set of relatives.
The great thing about the complex pattern of prolific branching is its wealth of informative content. If we look at the form of a real bush, we learn a great deal about the history of its development. It may have grown up in a fertile environment, every branch radiating out to yield countless shoots. Or it may have been caught without water or in the shade at some point, and bear the scars of withered and dead branches to prove it. From its shady position, an odd cluster may have reached through a gap to find a shaft of light, and yielded a fresh branching cluster of young growth. All this is in the bush’s past, and yet is preserved in the patterns of its final growth form. Much the same is true of the evolutionary bushes that grow in the virtual environment of an evolutionary biologist’s computer. The pattern of their branches mirrors what happened in a species’ distant past. Nodes of prolific branching and radiation recall times when selective pressures were eased, just as a narrowing of the branching pattern can reveal the reverse, when only a few lines passed through a genetic bottleneck. The term ‘bottleneck’ refers to some geographic or demographic constriction that filtered out many of the branches, just as the heavy shade around a single shaft of light accommodated only a few branches of our living bush. These branching points and bottlenecks that we only discover through analysing similarities and building evolutionary bushes serve as virtual fossils of ancient paths in evolutionary history.
Such information is gathered by reference t
o characteristic lineages tracing a sequence of haplotypes, the genetic ‘surnames’ introduced in Chapter 3, in the context of Mitochondrial Eve. All species generate a range of haplotypes for study. In the case of domesticated animals, those haplotypes may be extremely similar to the haplotypes studied within humans. In more distantly related species such as plants, they will be distinct, but the phylogenetic analysis of the form and structure of their evolutionary bush will remain similar.
branching patterns and agricultural origins
Let us consider the two extreme versions of how agriculture might have come about, and how they will affect the form of evolutionary bush generated from the crop species involved. If we start by building that bush from all the wild relatives of that crop living today, then those relatives will form the many tips of the bush’s branches. Beneath those tips, the bush’s structure and root will be assembled by computer analysis. When it comes to adding the domesticated forms, if we take Childe’s model to its extreme, then all the domesticates will spring from a tiny portion of the evolutionary bush’s crown. This corresponds to the wild forms growing in the specific location of agriculture’s origin. If we take Higgs’s model to the extreme, the bush will look quite different. Domesticated forms will be peppered across the crown, springing from several branches and reflecting the many locations of the transition.
