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  Around 9,000 years ago, sickles become even more common, right across the Fertile Crescent. But they’re not entirely ubiquitous – leading some archaeologists to suggest that the use of sickles may be more of a cultural preference than a total prerequisite for cereal harvesting. This isn’t as surprising as it sounds: evidence suggests that hand-plucking wheat and barley – as the Bedul Bedouin in the Valley of Petra still do – may be just as efficient as harvesting with a stone, or even a metal, tool. Perhaps the increasing use of sickles in the Near East between 9,000 and 6,000 years ago had more to do with the cultural identity – a ‘badge’ of farming – than the efficiency of the harvest itself. Nevertheless, the rising number of sickles seems to be more than just symbolic, reflecting a real increasing dependence on cereals – which initially represent just a small proportion of gathered plants, at a handful of archaeological sites. But by 7000 BCE, most sites where plant remains are preserved show cereals in the majority. And the wheat that was being cut and gathered in wasn’t just clinging on to its spikelets – the grains were larger than those of their wild predecessors. Again, something which would be a disadvantage in the wild – seeds too large to be dispersed by the wind – becomes a bonus for the farmer.

  Some increase in grain size is seen in wild wheats before the appearance of the tough-rachis feature. And then grains get bigger and bigger over three to four thousand years. Some of the increase in size is definitely down to genetic changes, but a proportion of it is probably environmental – as crops benefit from being grown in prepared soil, having to compete less with weeds, and are even well watered.

  A grain of modern, domesticated wheat comprises three important components. There’s the plant embryo or germ – this is a seed, after all. Then there’s the seed coat (the pericarp and testa) which makes up about 12 per cent of the weight of the grain, and is commonly known as bran. But by far the bulkiest part of the grain is the endosperm – making up 86 per cent of the grain weight. Like the yolk of an egg, the endosperm is there to provide sustenance to the developing wheat embryo. It contains starch – a load of starch – as well as oils and proteins. And it’s the endosperm that expanded, disproportionately, as grain size increased – packing more nutrition into each and every grain of wheat. But the embryo did increase in size as well – nowhere near as much as the endosperm, but still significantly. And there’s one really important characteristic of largegrained cereals when it comes to germination and early growth – their seedlings are much more vigorous than their small-grained counterparts.

  It seems reasonable to assume that an increase in grain size would have come about through conscious, deliberate selection of largegrained plants by early farmers. But, once again, this trait may have been selected for quite inadvertently. Early farmers were probably focused on increasing the size and productivity of their fields, rather than the size of individual grains. Larger-grained strains of wheat, with more vigorous seedlings, may simply have had an inbuilt advantage, out-competing smaller-grained varieties. Competition between seedlings – which may not have happened so much with wild, wind-scattered varieties – could have become fierce in densely sown, cultivated fields. Slowly, from summer to summer, the fields would have filled with larger-grained varieties, much to the farmers’ delight.

  These two important traits – the tough, non-shattering rachis and the larger grain size – didn’t develop at the same time in each species. They’re clearly not traits which come along as a package, like tameness and coat colour in dogs. They evolved at different rates, and for different reasons. And – rather like the initial steps towards domestication amongst the wolves who started to follow Ice Age hunter-gatherers – it seems that the process may have started off with much less forethought by humans than has often been assumed. But even without specific intent, the actions of humans produced a significant change in these cereals – making them even more productive, almost by accident. As domestication traits spread and became fixed in these plants, they became even more valuable to humans. Wheat became more and more important in ancient diets – and its future as a dietary staple was ensured.

  The protracted and complex history of domestication in wheat almost comes across like the plot-line of a romantic novel. Two potential partners – in this case, a Homo species and a Triticum species – meet. They are thrown together and then could so easily go their separate ways. But the contact has awakened something in each of them. They start to dance with each other. They grow together. Human culture changes to embrace Triticum; wheat changes, to be even more attractive to humans.

  The partnering up of humans and wheat is a little more complicated, though. For one thing, there’s not just a single type of wheat. Modern botany still recognises the three broad groups of wheat identified by Vavilov, characterised by varying numbers of sets of chromosomes. And modern genetics has revealed the complex relationships between them.

  Einkorn, both wild and domesticated, belongs to the group with a simple, double set of chromosomes: just seven pairs. It is, in the language of genetics, a diploid organism (like you and me). At some point in the distant past, there was an ancient doubling-up of chromosomes in one lineage. This happens from time to time, essentially as a mistake in cell division. The cell doubles up its chromosomes but then fails to divide in two – and persists as a single cell with double the number of chromosomes. An ancient doubling-up like this created the tetraploid wheats, with fourteen chromosome pairs (or pairs of pairs of seven chromosomes, if you prefer). This happened between 500,000 and 150,000 years ago – a very long time before the Neolithic Revolution – in the ancient, wild ancestors of emmer wheat and durum wheat.

  Then a hybridisation event occurred, involving domesticated emmer wheat (tetraploid) and wild goatgrass (diploid), producing a type of wheat with twenty-one pairs of chromosomes – three sets of pairs: a hexaploid plant. This hybridisation is estimated to have happened some time around 10,000 years ago – and it produced Triticum aestivum: common wheat or bread wheat.

  A doubling-up of chromosomes seems greedy enough. Most organisms can get along perfectly well with two sets of chromosomes. Four sets seems unnecessary. Six sets seems extraordinarily profligate. But many plants exhibit polyploidy – possessing multiple sets of chromosomes – and it doesn’t seem to do them any harm. In fact, it can create significant advantages. The presence of extra genes means that, if one gene has been damaged by a mutation, there’s another one available to take its place, and fulfil its function. The mutated gene might even end up doing a new and interesting job in the genome. Bringing together genetic material from different sources – as happened when emmer hybridised with goatgrass – can also lead to hybrid vigour, as novel combinations of genes start to work together, even without new mutations. In addition, polyploidy tends to be associated with an increase in cell size in plants, and it can result in larger seeds and better yields too. It’s not all rosy, though – being polyploid can be problematic. Reproduction gets a little trickier, with all those sets of chromosomes to sort out. And embryonic development can get confused, sometimes in a lethal way. But, in bread wheat at least, the evolution of hexaploidy certainly seems to have been – on balance – a good thing.

  In particular, the productivity of bread wheat was enhanced by a specific genetic mutation which led to an unusual shape of ear. The wild ancestors of this wheat possess flat ears, with spikelets arranged, in a staggered fashion, on each side of the central spine or rachis. But in bread wheat, a single, favoured mutation produced something quite different: a square ear, with densely packed spikelets – the classic shape of an ear of wheat that makes it look so distinct compared with other grasses. It seems likely that the emmer-goatgrass hybrid that we know as bread wheat, Triticum aestivum, may have immediately been a productive cereal that the early farmers would have recognised and cultivated.

  And so wheats partnered up with humans, forming a bond which would last for millennia and only get stronger over time. But where did it all start? Prec
isely where in that grand sweep of the Fertile Crescent did each of these wheat crops – einkorn, emmer and bread wheat – originate?

  The Middle East has been a Mecca for archaeologists for two centuries, and the geographic origin of the Neolithic founder crops has been at least one of the holy grails being sought. But even with the new discipline of archaeobotany, with its precise approach to individual species – that Vavilov would surely have approved of – the origins have proved somewhat elusive and obscure – until very recently.

  Here, there or everywhere

  The Fertile Crescent is a vast area which takes in parts of modern-day Israel, Jordan, Lebanon, Syria, Turkey, Iran and Iraq. As we’ve seen, the seeds of cereals – first wild forms, later replaced by domestic varieties – are found in archaeological sites across this region. It’s also a place where the distributions of separate species of wild wheats, barley and rye also overlap. But it’s a huge area. Vavilov focused in on each species, carefully recording and sampling varieties of domestic and wild species, and using his data to suggest a homeland for each. For a while, it seemed as though genetics and archaeology were in step.

  The great Australian archaeologist Gordon Childe, a leading light at the Institute of Archaeology in London, saw the invention of agriculture as a momentous step-change in human history. In 1923, he coined the term ‘Neolithic Revolution’. The transition from hunter-gathering to farming was like a regime change. The old order was overthrown. The New Wave surged across Mesopotamia and the Levant, sweeping all in its path. It all came together beautifully – ideas would ripple out from a centre of creativity; new species would spill out from their centres of domestication. The archaeologists’ ‘Neolithic Package’, including all the founder crops, mapped neatly on to Vavilov’s ‘Centres of Origin’. The northern arc of the Fertile Crescent seemed to be the focus for the revolution that would change the world. An elite group of proto-farmers in the Near East was brave enough to tame nature – then their burgeoning population spread, taking their new idea with them.

  Geneticists moved on from looking at numbers of chromosomes – as Vavilov had done – to decoding the DNA within them. By the 1990s, the technology had advanced to a point where geneticists could look at several equivalent sections of DNA in different plants, and compare their sequences. It was a more powerful technique than just looking at one small area of the genome. And so they looked at wild and cultivated varieties of einkorn and found that the domesticates formed a neat family tree with a single origin. Einkorn seemed to have evolved from one, discrete population. The DNA of domesticated einkorn was closest to that of wild varieties growing in the foothills of the Karacadag Mountains of south-eastern Turkey. Wheat with two sets of chromosomes – including emmer – looked very similar under such analyses. It, too, bore the marks of a single origin – and once again, that seemed likely to have been in Karacadag. Barley also looked like it had come from a single origin, this time in the Jordan Valley. The new, molecular science of genetics had waded into the debate about the origin of domesticated crops – and settled it. The results emanating from these studies which dealt in molecules not middens, which somehow delivered certainty in a way that archaeology never could, and which were revered enough to be published in the most widely read scientific journals, appeared to be decisive.

  So it seemed that Vavilov and Childe were right: cereal crops had been domesticated, rapidly, in discrete centres – before spreading out as the craze for farming took hold. The old idea of the Neolithic Revolution was vindicated. There really were core areas, and a single origin, for each domesticated species. It even seemed that a select cultural group in south-eastern Turkey might have come up with an amazing idea which would propel them towards an elite status and allow their population to swell and spread.

  It makes for such a great story. If only it were true. But by the early twenty-first century, cracks had begun to appear. Both archaeologists and archaeobotanists were arguing that domestication was likely to have been a protracted and complicated process. Archaeobotanical evidence from the Euphrates Valley suggested, for example, that it took a thousand years for domesticated einkorn to develop the tough rachis – the backbone of the ear of wheat – that would prevent its spikelets shattering off the ear before threshing. This could only be squared with the genetic data if the early domesticates were kept rigidly separate from their wild counterparts, eliminating any possibility of hybridisation, right from the start. But that seemed desperately unlikely.

  Archaeologists searching for the roots of agriculture had at various times suggested specific areas within the Fertile Crescent as the likely birthplace of the Neolithic Revolution. Kathleen Kenyon’s work at Jericho in the 1950s, digging down into the Neolithic layers there, led to the proposition that agriculture began in the Southern Levant. Other archaeologists favoured the northern and eastern edges of the Fertile Crescent – the hilly flanks of the Taurus and Zagros Mountains. And then the ‘Golden Triangle’, between the Tigris and Euphrates Rivers and the Taurus Mountains – where wild forms of many of the ‘founder crops’ overlap with each other – looked like the core area. But as the archaeological evidence accumulated, it seemed to be increasingly pointing to a networked domestication of crops across a much larger region. It also seemed that the early history of agriculture was littered with false starts and dead ends. There was no clear progression. In the Middle East, the Neolithic got going in patchy and sporadic fashion, across a wide area and spanning millennia.

  Two lines of evidence, then – the archaeological and the genetic – providing contrasting views of the process of domestication.

  Computer simulations suggested that the genetic results might be untrustworthy – the techniques probably couldn’t reliably tell apart a crop that had come from a single origin versus one with multiple origins and plenty of interbreeding. But still the idea of a fast, local origin for a great range of domesticates held sway – until dissent began to appear within the genetic camp too. As geneticists spread their sequencing net wider, they also started to uncover more complexity.

  The first clue that the single-origin, core area, paradigm might be an artefact of the method, rather than a real, reliable finding, came from more in-depth analyses of barley. Plants have extra packets of DNA – separate from that in chromosomes – inside their chloroplasts (the miniature factories in plant cells that ‘do’ photosynthesis). Sequencing of particular sections of the chloroplast DNA of barley suggested that this cereal came from at least two separate homelands. The region of the barley chromosome involved specifically with the mutation that produces non-shattering ears bore the same message. More research led to the conclusion that barley had been domesticated, not only in the Jordan Valley, but also in the foothills of the Zagros Mountains. The more detail the geneticists looked for, the more they uncovered. The most recent, genome-wide analyses of barley have revealed that various strains of domesticated barley show genetic connections with nearby strains of wild barley. There seemed to be not just one wild ancestor – but many. One review seems to suggest a wonderfully lyrical source for these new insights: ‘Poets and colleagues have recently demonstrated a pattern of genetic diversity in barley that runs entirely counter to the view of a centric origin.’

  But it turns out that Ana Poets is a geneticist (although – who knows – she may be a poet as well; after all, it’s rare to find a scientist who has no artistic side), and the lead author on a recent paper about shared mutations in domesticated and wild strains of barley. She and her colleagues showed that domesticated barley, far from having a single origin, had a mosaic ancestry – it had been drawn from a wide range of wild strains, each leaving their marks scattered across modern genomes. Apparent connections with wild strains could, of course, be due to much more recent interbreeding – but the team ruled this out. The genetic mosaic of the barley crop had much more ancient roots.

  When geneticists looked at emmer wheat more closely, it also turned out to have a more complicated ancestry
than initially thought. Domesticated emmer wheat remains had been found from various sites across the Fertile Crescent dating to more than 10,000 years ago. But the earliest genetic analyses showed that the entire domestic species was closest to a discrete population of wild emmer growing in south-eastern Turkey. This seemed to suggest that agriculture emerged in a tiny, core area of the Fertile Crescent, probably around 11,000 years ago. But then the story changed – later studies showed that emmer wheat was mosaic, closely affiliated with many different wild strains, across a large swathe of the Middle Eastern landscape.

  A similar story emerged for einkorn. The original genetic enquiry into its origin suggested a single, discrete focus of domestication. But by 2007, more detailed analyses had started to produce clues to a more complex birth of the domesticated crop: there was no reduction in genetic diversity – no domestication ‘bottleneck’. Instead the genetic variation in the crop was drawn from a very wide sample of its wild progenitors, right across the northern arc of the Fertile Crescent.

  With the story of barley, emmer and then einkorn evolving in the same way, it seems that multiple, parallel centres of domestication may be the rule rather than the exception for cereal crops. A small ‘core area’ for domestication, in south-eastern Turkey, simply isn’t borne out by the evidence today. Genetics has now converged with archaeology: there were numerous, connected ‘centres’ of domestication in the Fertile Crescent. This diffuse origin of crops may have been extremely important to the success of domesticated strains, ensuring that adaptations to local habitats passed from wild into domesticated forms. This makes so much sense – local wild species would already be adapted to local conditions. Any farmer taking the seeds of a cereal domesticated in the cool, moist foothills of the Karacadag Mountains, and trying to grow them in the hot, arid plains of Southern Levant, would be unlikely to meet with success.