Invasive Aliens. Dan Eatherley

the planet.

      Around the time that people first domesticated sheep and goats, cattle also joined the ranks of tamed ruminants. Cows were descended from the extinct wild ox, or aurochs. This was a spectacular beast, particularly the bull which stood nearly two metres high at the shoulder and sported fearsomely curved horns. Unlike the bezoar and mouflon, aurochs were already present in post-glacial Britain – indeed, they roamed the entire Eurasian landmass; however, domestication probably occurred in the Middle East. That’s because early cattle were much smaller than our native aurochs, and DNA studies show that modern cows, including British ones, are genetically closer to Syrian aurochs than home-grown ones. In fact, today’s entire global cattle herd – numbering some 1.5 billion cows – is believed to be descended from a founding stock of just 80 animals, likely to have originated in the Middle East. There’s a good chance, however, that hybridisation would have occurred between local British aurochs and the smaller incoming cattle. Neolithic farmers may not have been thrilled about this: their petite cows, bred for milking, may have risked serious injury when attempting to birth an outsized hybrid calf.

      Other modern domesticates with native British versions also seem to have derived from imported stock. These include the pig, whose ancestor, the wild boar, was widespread here before the advent of agriculture. Porkers are thought to have been first farmed in the eastern Anatolian region of modern-day Turkey about 10,000 years ago – along with a later independent domestication event in central China – and descendants of these Anatolian versions were subsequently brought to Britain. As with cattle, the amount of wild boar DNA in the genome of domestic pigs suggests frequent hybridisation between the two. To an extent, this may have benefited pig farmers, as crossbred versions may have been better suited to the more bracing local conditions in Britain, although too much of the ‘wild’ in a pig could make it a handful. A balance had to be struck.

      Many of our supposedly native crops may also have come from elsewhere too. For instance, Britain’s blackberries, raspberries, carrots and parsnips, as well as the perennial ryegrass, red clover and common vetch traditionally used as animal fodder, all probably derive from southern European strains.

      Whether there’s the whiff of the exotic about other domesticated species is less certain. For instance, the honeybee is thought to have originated in Asia, or maybe Africa, around 300,000 years ago, later spreading naturally across Europe, so the likely presence of this woodland insect in Britain before the most recent Ice Age would qualify it as native. Yet, the earliest known archaeological evidence for honeybee exploitation by humans in this country – as suggested by beeswax residues on seven pieces of Neolithic pottery found in southern England – dates to as recently as 4,000 years ago. That’s several millennia after sweet-toothed pioneer farmers in Turkey, and later in central Europe, began gathering honey and wax from the insects, and possibly even domesticating them. So, we’re left to wonder if Britain’s first apiarists collected honey from wild bees or perhaps were using a tamer, introduced, variety that had been bred on the continent. In a sense, this discussion is somewhat academic, since pretty much all of our honeybees are today derived from southern European stock after parasitic mites devastated Britain’s existing honeybee population in the early twentieth century.

      So, how did the ‘Neolithic package’ – although this term for an apparent commonality of elements, including domesticated crops and livestock, along with other characteristic artefacts, is increasingly criticised as over-simplistic – reach our shores? Did Fertile Crescent farmers themselves migrate north and west, or was it just their agricultural practices that travelled, along with the wheat, barley, sheep, goats and other domesticated species upon which they were reliant? The question has been debated for well over a century, although recent research is beginning to support the former hypothesis. For instance, a genetic study published in 2018 found strong affinities between Mesolithic British and western European hunter-gatherers over a period spanning Britain’s separation from the continent. The authors of this paper believe that British Neolithic people derived much of their ancestry from Anatolian farmers who followed the Mediterranean route of dispersal and entered Britain from northwestern mainland Europe. One thing is certain: when times were good, farming guaranteed a steady food supply and supported a burgeoning human population. In Britain, its practitioners rubbed along with nomadic hunter-gatherers for hundreds if not thousands of years, but the agricultural way of life, and the settled civilisation it supported, proved irresistible. So too, would the invasive species that profited from both.

      The omens were there from the start. For millions of years, a spectrum of fast-growing, fast-spreading pioneer plants, both annuals and perennials, evolved to benefit from landscape impacts very similar to those that humans would one day cause. Many were adept at exploiting forest clearings opened up by fallen trees or recolonising habitats scraped clean by fires, glaciers, floods, landslips, volcanic activity and other natural disturbances. So, when the first farmers razed woodland and stripped soil bare in readiness for crops, they were teeing things up for a plethora of undesirable species. Commonly known as ‘weeds’, they have plagued us ever since.

      Most troublesome of all were the weeds that resembled crops. These included darnel, a toxic grass which happened to be a dead ringer for wheat, and which infested the Middle East’s earliest agricultural sites. Pastoralism only worsened the situation, as grazing and browsing livestock suppressed tree regrowth, maintaining the sort of open conditions favoured by weeds. What’s more, just like crops, many weeds were adapted to thrive on the elevated levels of soil fertility resulting from all that extra animal dung.

      British farmers, like their continental antecedents, set about annihilating the wildwood with their crops and livestock. Shifting agriculture was probably practised at first, with the felling of a few trees and controlled burning of understorey, followed by successive plantings of cereals. After a few seasons, the plot’s soil nutrients were exhausted, forcing people to move on and repeat the destructive pattern. Anthropogenic deforestation was hardly a new thing – as we’ve seen, hunter-gatherers were keen on woodland openings – but its scale from the Neolithic onwards was unparalleled.

      Trees were removed for reasons beyond the need for cropland: their timber was a source of both fuel and building material, while the clearances themselves may have held a symbolic value. Britain’s vanishing woodland is reflected in changes in the incidence of particular pollen species in the archaeological record. As the representation of oak, elm, lime and ash dwindled, grasses, shrubs and wildflowers came to the fore. Invertebrate communities also changed, with a decline in specialist forest insects, including those associated with old or decaying timber, their place taken by varieties adapted to open and disturbed ground; dung beetles flourished thanks to livestock. Every so often a prolonged spell of climatic deterioration – as occurred between 5,000 and 3,500 years ago – would lead to a temporary abandonment of arable farming in Britain. Forests then had a chance to recover, although pastoral farming would still have been practised.

      Of course, Britain’s Neolithic farmers had their work cut out dealing with the weeds that prospered in the denuded landscape. Many unwanted plants already lurked as seeds in our soil, just waiting for their moment in the sun; others were conveyed from further afield as contaminants of grain imports. The field, or corn, poppy, well-known to early Middle Eastern civilisations, is among the more familiar of the non-natives to have debuted in Britain around this time. The ancient Egyptians were taken by the striking blood-red blooms which infested their wheat and barley fields at harvest. The poppy’s reappearance each year was a metaphor for rebirth and regeneration. The flower was woven into funerary bouquets and depicted on tombs.

      Another arrival in Britain was charlock, or wild mustard, which was once described as the most troublesome annual weed of arable land. Indeed, an assortment of familiar crops including artichokes, flax, garden peas, leeks, lentils, lettuces and radishes may have started out as invaders of arable fields. Given that these are all fast-growing, short-lived species thriving on bare soil, their weedy heritage seems to fit. Even einkorn – one of the first types of wheat to be cultivated on a large scale – may have started life as a contaminant of emmer wheat crops. Furthermore, bread wheat, today’s single most important variety, thanks to its easier threshing and greater grain yield, arose in the Fertile Crescent at least 8,500 years ago as a result of hybridisation between emmer and another weed, wild goat grass.

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