by Steve Jones
The advocates of avocado are still in a minority. Many of their fellow Americans or Europeans have meals almost as dull as those of the first peasants, without the privilege of growing the raw materials themselves. Just as at the dawn of agriculture, their choices are narrower than were those of their parents and grandparents. Cheeseburgers, chips and sweet drinks are full of cheap energy and the poor have seized upon them. Nowadays, the British obtain twice as many calories from fats as did their immediate forebears and on average the intake of sodium has gone up by ten times and that of calcium down by half compared with earlier times.
The junk food revolution tells the tale of artificial Darwinism in all its details. The taming of the hamburger also shows how man, the most domestic creature of all, has paid a high price as he tests the biological limits set by his own evolution.
The first farmers, like the modern poor, became less healthy as their dietary options shrank. The symptoms were different from those of today, but the causes - an abundant but inadequate cuisine - were the same. Their bones show signs of deficiency disease and the average height of adults dropped by fifteen centimetres as the new way of life spread. The loss was not regained for several thousand years. In North America, where maize became the basis of almost every meal and where it was worshipped as a god, another problem was a shortage of iron, for maize lacks the mineral and also interferes with the ability to absorb it from meat. Many people became anaemic. No doubt they were tired, weak and depressed as they pursued their wretched lives as tillers of the soil. Deficiency and its diseases - lassitude, infirmity and sadness included - have returned, but disguised as excess.
Thirty thousand premature deaths a year in the United Kingdom are due to an expanded waistline and ten times that number in the United States, where, in 2005, obesity overtook smoking as the main preventable cause of mortality. It is more than a coincidence that as America’s spending on food as a proportion of national income went down by almost half, that on health care was multiplied by three times. In Central and Eastern Europe, even more healthy years of life are lost per head than in Britain. The present generation of men and women - those who grew up before the new age of edible trash - may be the longest-lived in history.
The problem for their children is fat. Medicine has long known how dangerous the blight can be; in Hippocrates’ words: ‘Corpulence is not only a disease itself, but the harbinger of others.’ Thousands have died before their time of heart disease, stroke, cancer and diabetes, the four horsemen of the obese. Many others suffer from gout, arthritis, bladder problems, reduced fertility and the other conditions that affect the fat far more than the thin. The most dangerous effect of gluttony is to grow to resemble an apple rather than a pear, for extra inches on the waist are much more harmful than the same on the backside - and the apples are taking over from the pears even among women, who used to put more on the bottom than the belly as their weight went up. The apple brigade store fat around their livers, where it is readier to spring into action and to release fat itself, hormones and agents of inflammation into the bloodstream.
In the modern United States, as in the New World at the dawn of agriculture, Native Americans have paid a particularly high price for the change in diet. A century ago, many kept to their traditional cuisine. The Pima Indians of Arizona - the Corn People as they called themselves - were thin as they ate their hearty meals of tortillas or porridge, based on maize. Now, they gorge on burgers, chicken and sweet drinks instead. In some ways, however, their food input has not changed for the Pima eat just as much maize as did their grandparents. The difference is that today it has been through a cow, a chicken or a soft-drinks factory first.
Cheap corn gave birth to fast food. One American meal in five is eaten in the car and the maize needed to feed its four passengers with a cheeseburger each would more than fill its tank. A Chicken McNugget has thirty-eight ingredients - and thirteen come from maize. The fizzy beverage that washes it down is based on corn syrup and the raw material of the post-prandial milkshake comes from a cow fed in a yard, on maize, rather than in a field, on grass. The ‘natural strawberry flavour’ that adds its dubious tang is natural only because it is made from corn and not synthesised from chemicals. A quarter of the food items in American supermarkets now contain maize, and their rows of cheap packaged products - and thousands are introduced each year - bear witness to the second agricultural revolution that has taken place in the lifetime of most readers of these pages.
Seed crops - maize most of all - transform sunshine into food. Even better, they are easy to store and to move. Cows evolved to eat grass in fields, but now it makes more economic sense to feed them on grain on giant lots. More than half the maize and soy grown in the world is eaten by animals. As a result, global meat production has gone up four times since the 1960s, and the amount of flesh available per head has doubled.
Scientific farmers have done in a few decades what took peasants centuries to achieve with no science at all, but the early farmers’ approach was, in its essence, identical to that of modern technologists. They understood little of what they were up to and may not even have made the tie between sex and reproduction. By the Middle Ages, the idea that attributes ran in families was accepted; as the 1566 book The Fower Cheifyst Offices Belongyng to Horsemanshippe put it: ‘it is naturally geven to every beast for the moste parte to engender hys lyke’. Soon artificial selection, conscious breeding from the best, was under way (even if the horse-racing and dog-fancying fraternities clung to the odd idea that qualities were passed only down the male line). In the eighteenth century, English improvers became aware of the need to mate animals of equal ‘beauty’ and agricultural science was born. Robert Bakewell, chief among the breeders, was frank about his motives. He called his barrel-chested New Leicester sheep ‘machines for turning herbage … into money’ and hired out his rams for stud at £1000 a season - a huge sum for those days.
Now animal breeding has become a massive business. Champion bulls and stallions can sire thousands of offspring, and new statistical methods allow their young to be compared over hundreds of farms to see which have done best. Often, the actual genes that lie behind their talents are not known. Milk yield in cows has doubled since the 1940s, but the sections of DNA that did the job stayed hidden for sixty years. Molecular biology is beginning to change that, with the DNA sequence of most domestic animals now complete, together with maps of hidden diversity that can track down where the most productive variants might be. The annual gain in meat or milk production brought by genetics is, in the developed world, around 1.5 per cent a year, well over a billion pounds’ worth in Europe alone. Artificial aids - mechanical cows into which bulls can ejaculate and have their semen smeared across the globe, cloned sheep, engineered crops and more - promise wondrous things. Even so, with the consumption of meat expected to double in the next decade that will not keep up with demand. Plant technology has been even more successful and many genes for high yield or disease resistance have been tracked down, with many brought in from the wild relatives of our domestic species. Agriculture now works with foresight, a talent quite unknown to evolution but used, at least subconsciously, by the first farmers of all.
What did it take to become domestic? The basic demand is for a creature able to coexist with man. Men can choose, often without much thought, the most favoured individuals to found the next generation. For both plants and animals, improvement becomes inevitable.
Darwin knew little about the origin of fruits, grains and vegetables: ‘Botanists have generally neglected cultivated varieties, as beneath their notice. In several cases the wild prototype is unknown or doubtfully known; … Not a few botanists believe that several of our anciently cultivated plants have become so profoundly modified that it is not possible now to recognise their aboriginal parent-forms.’ Now the aboriginals have been found, hidden in their descendants’ DNA.
All crops have a lot in common. From tomatoes to barley and from chickpeas to plums, the domestics
are less diverse than their wild predecessors, grow taller and less branched and have fewer but larger fruits or grains that taste less bitter than before. They flower at different times of year and their seeds spring into life at once when planted rather than (as do those of many of their wild fellows) demanding a long rest.
The tale of all those changes is hidden in the DNA. The story of maize - the raw material of junk food - shows how biology can reveal the past. Maize descends from a wild plant moulded not long ago into a dietary staple so different in appearance from its ancestor that for many years its origin was unknown.
Darwin himself knew that maize was ancient, for on the Beagle voyage he found cobs embedded in a beach raised by slow upheaval many metres above the sea. Its story began in southern Mexico around eight thousand years ago when people began to harvest, and then to grow, a wild grass called teosinte, the ‘grain of the gods’. The tale of maize is that of the New World. Teosinte is still abundant over large parts of South America, even if several of its dozen or so species are under threat. Male and female organs are held in different places on the same individual, with a ‘tassel’ that bears pollen, and a number of small spikes that carry the female parts.
At first sight, the wild version looks quite unlike the familiar corn on the cob of today and was once assumed to be a relative of rice instead. A teosinte cob - a family of seeds held together on the same structure - is little more than twenty-five millimetres long, compared with thirty centimetres or more for its cultivated equivalent. When mature, the teosinte seeds, each within its own hard coat, form an ‘ear’ with half a dozen or so separate segments. The coat protects them from the digestive juices of the animals and birds that eat the cob. Each seed breaks off when ripe and, with luck, passes through the gut, falls on fertile ground and germinates to form the next generation.
The maize cob, in contrast, has five hundred or more kernels. The seeds are larger than before, come in a variety of colours and contain far more starch. They do not fall off without help and lack a protective outer sheath. They are, as a result, digested, rather then excreted, should they be eaten. If, at the end of the season, the whole cob is not harvested but falls to the ground, it bears so many seeds that almost none survive the intense competition for light and food. Maize is, as a result, entirely dependent on its human masters for reproduction. The plant has changed to such a degree that it looks quite unlike its ancestor.
Even so, the kinship of maize and teosinte is still close enough to allow certain wild strains to hybridise with their tamed descendants (farmers hate the idea for it degrades their crop, but scientists use it to rescue valuable genes before the natives disappear). The DNA of the modern crop is closest to that of the teosinte that grows in the hills around the Balsas river basin in south-west Mexico. There, McDonald’s finds its roots. The oldest known cobs, six thousand three hundred years old, come from a cave in the valley of Oaxaca, four hundred kilometres away. At about that time, the people of South America began to thrive on their tamed grass. They soon learned to treat it with lime to release its essential vitamins - a talent forgotten until the mid-twentieth century, when the deficiency disease pellagra was tracked down to a diet of untreated maize.
At least a thousand genes in modern maize differ from those of teosinte. Fossil DNA from seeds four and a half thousand years old shows that, even by then, the farmers had already selected genes to improve grain quality and size. Just five genes, or groups of genes, were responsible for most of the shift towards the domestic. Many more play a smaller part. The move from grass to food involved mutations that change the slim side-branches of the grass into stout maize ears, others that remove the hard case around each seed, while yet others ensure that the grains stick to the cob and do not shatter when touched. Long stretches of DNA on either side of those points scarcely vary at all, as a hint that large blocks of inherited material were dragged through the population by breeders as soon as the new attribute was noticed.
Maize improvement has become an industry. The plant is the most widely cultivated crop in the world, with three hundred million tons grown each year in the United States alone. It has been mutated, selected and hybridised to give hundreds of distinct strains. Some are tall - seven metres high - and some short, some large, coarse and used as cattle fodder, with others selected to have tiny ears, the size of those of teosinte itself, and just right for a cocktail snack. Sweet-corn is full of sugar. The starch itself, in some kinds, bursts apart when heated, to give popcorn. The plant now flourishes from the far north to the tropics and is far more productive than its ancestors of even fifty years ago. The science of maize has changed the global economy as much, or more, than has nuclear power.
The maize genome has a bizarre and unexpected structure. It contains almost as much DNA as our own and can boast of twice as many genes. Most consists of bits of mobile DNA that invaded long ago. Some of those molecular parasites can no longer copy themselves and sit sullenly in place, while others wake up now and again and move to a new site. They can cause mutations as they go or capture a functional gene, altering its effects as they do. Many of the mutations involved in the improvement of maize emerged from this constant flux. Maize DNA still changes fast. Some inbred lines descend from a shared ancestor that lived just a few decades ago, but are already as distinct from each other as are humans and chimpanzees. The mobile elements have been so active that, when two inbred lines are compared, on average a fifth of all genes differ in where they sit on the chromosome. Maize, plain food as it is, has a complicated biology.
Other crops have a less chequered history. Apples are easy. Fifty years ago, Almaty, in Kazakhstan, was - like Norwich in Tudor times - ‘either a city in an orchard or an orchard in a city’. Its name means ‘father of apples’, but the place is now more notable for its Porsche and Mercedes dealerships. The city and its surrounds were the site of a vast domestication. The genes of the chloroplast - the green structure found in leaves - show that the apples we eat today are almost all the descendants of just two ancient Kazakh trees. Those mothers of all the world’s apples grew not far from Almaty. Wild trees, some as big as an oak, are still scattered through the Tien Shan Mountains nearby. They are part of what was once a vast fruit forest, the home of the snow leopard, filled with walnuts, grapes and apricots as well as apples. Today’s varieties, from the insipid Golden Delicious to rare strains such as Zuccalmaglio, have emerged through mutations and selective breeding in the lines that trace their ancestry from those two progenitors. They are maintained with grafts and cuttings.
Unlike the small and bitter crabs borne by most wild apples, the fruits of the Tien Shan are large and sweet. They became luscious when the trees changed their reproductive partners. The seeds of most wild apples are moved by birds that peck at the fruit, but in the Tien Shan, the Mountains of Heaven, bears do the job instead. Both animals eat fruit and both scatter seeds in their excrement. A bird is happy with a small reward but a hefty mammal demands a more substantial bait. The trees grew sweet apples to oblige. Eight thousand years ago, people and their horses moved into the fruit forest and developed a taste for the ursine delicacy. Kazakh apple seeds travelled in horse and human guts down the silk roads that skirt the mountains. Now, their descendants fill supermarkets across the globe. The peach also traces its origin to a wild mountain landscape in western China and reached Europe only in Greek times. It has diverged, like many other fruits with stones, into a variety of forms since then.
The potato has a more restricted history. It finds its home in a small patch of land, in Peru, north of Lake Titicaca. It has been cultivated for five thousand years and has diverged into a large variety of forms (to underline its importance, the United Nations Food and Agriculture Organisation defined 2008 as the International Year of the Potato). Lentils and chickpeas, too, each descend from just a single wild ancestor, as do peas. The various strains of rice, in contrast, emerged from two or three distinct species of wild grass cultivated in China. Wheat is different agai
n, for the modern crop emerged as a result of crosses between several species of grass, some still around today, which came together to generate a plant with many more chromosomes than before.
Not long after wheat, chickpeas and the rest appeared on the plate, wild beasts were invited into the household. No more than a few accepted the offer and most of them had done so before the time of Christ. Quite soon society was transformed. Cows, pigs, horses and sheep became every farmer’s treasured possessions, and a lot of effort was devoted to keeping them happy. As soon as they abandoned the wild, the animals began to change, and all in more or less the same way.
Farm animals, of whatever kind, tend - like their botanical equivalents - to follow some general rules. They are smaller and more lightly built than their unbroken counterparts, with shorter faces and smaller jaws. Often, they vary more in colour and shape than before, and many develop spotted coats. They are fatter, with longer intestines, breed through the year and make more milk. Most show less of a difference between males and females than in the wild. In many of their ancestors - wild cattle, horses and pigs - a large part of the force of natural selection involves differences in sexual success. Battles among males lead to the evolution of expensive horns or tusks, with days spent locked in combat. Once sex is under human control that wasteful effort can be directed to the production of milk, meat or wool instead, which is why domestic bulls or rams are less infuriated by their rivals than are their untamed relatives. In their lazy lives they tend towards promiscuity rather than the faithful bonds some of their ancestors preferred - which is useful for farmers when they wish to choose particular animals as parents.
One species in particular was quick to abandon its ancestral habits. It was the first to accept servitude and has used its own personality to manipulate mankind. It reveals, more than any other, quite what it takes to become tame.
