Potatoes played their part in history, as empires rose and fell, and battles were lost and won. But potatoes were changing too. The nineteenth and early twentieth century saw the creation of a great range of new cultivars, as potatoes and other domesticates became subjected to intense selective breeding. While potatoes had once allowed the Spanish slave-drivers to unlock the silver from Potosi, this New World crop was finally becoming respected as a treasure in its own right. Potato breeders became fabulously wealthy. One new variety, created at the beginning of the twentieth century, was even named Eldorado. But this treasure from the Americas also brought with it a curse.
Feast and famine
Potatoes became another staple food in Europe, complementing grain, and helping to improve food security – up to a point. The problem arose when countries started to depend on the crop too heavily – and it owed much to the way that this crop is propagated. When potatoes failed, they failed badly.
If you want to plant potatoes in your garden, you can buy a bag of seed potatoes. The name is, of course, completely misleading. These are potatoes, certainly, but they are not seeds. The plants that emerge from these small potatoes are clones of their parents, which have been grown in carefully controlled conditions to keep lines pure and minimise interbreeding between separate cultivars. Potatoes are flowering plants – and quite pretty ones at that, with their five-petalled lilac flowers – and the whole point of flowers is sexual reproduction. As insects visit the blooms to take what they need, in the form of nectar, they bring pollen from other plants. Pollen is the plant equivalent of sperm: it contains a half-set of plant chromosomes – male DNA from another plant, or even the same plant. The important thing about this DNA is that it’s been mixed up a bit as the pollen is made; the same thing happens as the ovum is formed. The germ cells that give rise to the gametes – the pollen and ovum – contain pairs of chromosomes. Within each pair, the chromosomes swap genes with each other, during meiosis – the special type of cell division which forms the gametes. (This is the point at which duplications can happen – remember the multiplying amylase genes in dogs.) A gene on one chromosome may differ a little from the equivalent gene on the other chromosome. Just one of each chromosome pair passes into the pollen grain or ovum, with a selection of gene variants pulled from one or other of the original pair – so this is already something new, and different to the chromosomes of the parent.
When pollen and ovum combine, the chromosomes derived from each parent pair up – and a completely novel combination of gene variants, or alleles, is created. Sexual reproduction is all about creating novelty and variation. But potatoes also reproduce, quite naturally, by asexual reproduction. In fact, this is precisely what the tubers are for, from an evolutionary perspective. Not for human (or any other animal) consumption, but for creating new versions of themselves.
While gathering seeds from potatoes to plant next year’s crop may be possible, it’s not the most obvious way to create another generation. It’s far easier to save a few small potatoes to do just that. Using seed also introduces an element of uncertainty about next year’s plants – sexual reproduction guarantees a level of variation which is far from welcome if you’re trying to grow plants with particular characteristics. Using ‘seed’ potatoes eliminates that uncertainty – in fact, the potatoes you’re planting aren’t really a new generation at all. They are the identical twins of the plants from which you took those potatoes. This is asexual reproduction: the new crop is a clone of the old.
This may sound like a good idea – if you have a crop with particular, desirable characteristics, you surely want to hang on to those features. But eliminating variation is a dangerous game to play. The fact that so many plants and animals reproduce sexually is important – it works. Creating variation with every new generation provides the possibility of new variants which will have an advantage – especially if the environment changes. So generating variation is nature’s way of future-proofing species. The environment is more than the physical situation in which a plant or animal lives – it’s biological too: it involves all the other biological entities that may interact with that particular organism. Many of those entities pose a threat: they may be viruses, bacteria, fungi, other plants, animals. And those potential enemies are always evolving better ways to attack, better ways to avoid any defences which have evolved in the organism under threat. It’s nothing less than an arms race – and if the defender fails to keep up, its fate is clearly marked.
If you grow potatoes from seed potatoes, and keep some potatoes from that crop to plant again, and keep on doing that – you have trapped those potatoes in suspended evolution. You may be able to protect your potatoes from other, potentially damaging or competitive plants – a little weeding should sort that out. You may be able to protect your precious plants from animals which would like to chomp on leaves or tubers (though beetles can be extremely difficult to guard against). But the most sinister and pernicious threat comes from pathogens so small that they are invisible to the human naked eye: the viruses, bacteria and fungi. Make no mistake, the pathogens – the evildoers – will not be holding back. They’ll be evolving newly powerful and mischievous ways to get at your potatoes. And ultimately, they’ll win. If there’s decent variation amongst your potatoes, there’s a chance that some will be endowed with resistance, and survive the onslaught. If there’s very little variation, then the pathogen could be utterly devastating. It could wipe out a whole crop. It could wipe out a whole country’s worth of crops. And that’s precisely what happened in Ireland in the 1840s.
While other north-west European countries were slow to adopt potato farming, Ireland broke the mould. When English immigrants introduced the crop to Ireland in 1640, potatoes were enthusiastically embraced. The Irish farmers found in the potato something that they could cultivate for themselves – on the poorest plots, while their more fertile fields were dedicated to growing grain for absentee landowners in England. The potatoes introduced to Ireland in the mid seventeenth century were probably still essentially Andean varieties. It may seem odd that they settled in so easily, in such a northerly latitude. But the Irish climate was so mild – with September just as warm as June – that potatoes could be grown well into autumn. A potato whose ancestors had grown used to short days, near the equator, would tuberise just as happily, close to the equinox, in temperate Ireland.
By the nineteenth century, Irish farmers were still exporting the vast majority of their grain to England, while they and their families depended on potatoes – almost to the exclusion of anything else. But in this verdant, well-watered isle, the farmers had no way of storing their harvest. They grew them, and ate them, and grew them again. And the genetic diversity amongst the crops was astonishingly narrow. Farmers grew just one type of potato, the Lumper. It was a nationwide experiment in clonal monoculture – and it was doomed.
In the summer of 1845, a fungus called Phytophthora infestans reached Irish shores. Its spores may have arrived on a ship from the Americas. The Irish potato crops had no resistance to this novel pathogen. The spectre spread through them with astonishing speed, its spores carried on the wind from field to field; leaves and stems blackened, and underground the tubers turned to pulpy mush; the air was full of the stench of putrefaction. The blight struck again in 1846, and again in 1848. It tore through potato crops right across Europe, but it was in Ireland that the effects were most apocalyptic.
With astonishing, brutal disregard for the plight of the farmers, grain was still shipped out to England. Social injustice compounded the biological tragedy. The Irish farmers and their families had no other staple crops to rely on, and starvation, typhus and cholera stalked the land. The tragedy set in train by the blight became known as An Gorta Mór, the Great Hunger – or the Irish Potato Famine. People left Ireland in droves; the famine prompted a huge exodus of Irish refugees, heading west across the Atlantic. Those who made it to North America were the lucky ones. Back in Ireland, in just three years, a m
illion people died. The population of Ireland today is still smaller than it was before the famine and the mass emigration – around 5 million people compared with over 8 million back in the 1840s.
The terrible tragedy holds important lessons for us today. Controlling the characteristics of the plants we grow and the animals we keep for food seems so desirable. It allows us to manage supply and demand, to plan ahead. But it comes at a price – a potentially devastating price – if it means that we prevent domesticated species from evolving, especially where pathogens are concerned.
It seems paradoxical that we’ve managed to create such great vulnerability when the entire development of agriculture might be viewed as an exercise in managing risk. The lifestyle of the hunter-gatherer seems so precarious compared to that of the farmer: one relies on nature providing, the other controls the harvest and stores any food left over as insurance, ready for hard times – but can also translate any surplus into wealth and power. But it seems as though our control of nature may be less complete – and even much more illusory – than we’d like to think. We’ve ended up trying to pin biology down, to stop it changing, when the fundamental way of nature is to change. By limiting evolution in domesticated species, we can make them exquisitely vulnerable.
And surely hunter-gatherers have something to teach us about flexibility. They may use tubers as fallback foods, but they try very hard not to rely on just a few sources of sustenance. I’m not suggesting we all adopt hunting and gathering. The global population is far too large for that to be an option. Agriculture has supported a huge expansion in the human population, but at the same time, in some ways, we’ve become trapped by this cultural development. This seems like a paradox too. With a whole world of plants and animals to choose from, we’ve narrowed our options right down. On the face of it, the Columbian Exchange created new diversity on both sides of the Atlantic – but globally, we’ve come to rely on a relatively small range of plants and animals. And within those domesticated species, diversity can be precipitously, dangerously low. The genetic diversity among domesticated potatoes far away from their Andean homeland is paltry today.
A single Andean farmer may grow more than a dozen distinct varieties of potato. These varieties are very diverse in appearance, from the colours and shapes of the tubers and flowers, to their growth patterns. Each cultivar evolves to be suited to a subtly different ecological niche up in the mountains, where the conditions vary dramatically over short distances. In contrast, the thrust of industrialised agriculture is to focus on fewer and fewer varieties, committing huge areas to monoculture. Not just monoculture – but clonal monoculture. We’re breeding organisms that are inherently fragile.
Michael Pollan, who occupies his own ecological niche somewhere between nature writing and environmental philosophy, wrote that ‘to Western eyes, the [Andean] farms look patchy and chaotic … offering none of the familiar Apollonian satisfactions of an explicitly ordered landscape.’ And yet, these farms, where the various types of cultivated potatoes can breed fairly freely with wild neighbours, and where variety acts as insurance against pests and droughts, increasing the chances that at least some cultivars will survive, seem to provide a more robust solution than industrial monoculture. However knowingly they’ve done it, the Andean farmers have been successful in cultivating and preserving genetic diversity in their crops.
Farmers have recognised the problems of inbreeding for centuries, possibly even millennia. Producing a population of animals or plants with very little variation may satisfy cultural mores and supermarket requirements, but leaves those organisms dangerously susceptible to disease. Rare breeds and cultivars represent a precious library of much wider genetic diversity, making it incredibly important to preserve those varieties – at the very least, in the case of plants, to collect and store their seeds. Maintaining large, diverse genetic libraries – out in the landscape as well as archives like seed banks – may be our best chance of future-proofing our domesticates. Somewhere in that library is the potential for resistance against diseases which may not even have emerged as a threat yet, as well as the capacity for creating other new, desirable traits.
But there is another way of injecting novel, protective – or otherwise useful – genetic traits into a domestic strain. Selective breeding works, but it’s slow and doesn’t always produce the desired result. For centuries, it’s all we’ve had, and it has of course produced impressive changes in domestic plants and livestock. But our ability to change organisms to suit our needs has been transformed by new technology – where we alter the genes themselves. Genetically modified plants can be designed to be resistant to a particular pathogen. In the mid 1990s, farmers in North America were experimenting with growing potatoes called ‘New Leaf’, which had been genetically engineered to produce their own toxin, to fend off Colorado beetle infestation. These potatoes were ‘transgenic’: a gene from another organism – in this case, a bacterium – had been introduced into the plant’s genome.
Genetic modification may prove to be a useful weapon in our armoury – but it certainly doesn’t replace the need to preserve genetic diversity. It will never end the arms race between crops and pathogens – evolution will not stand still. It’s also – still – a controversial technology. It can introduce novelty into the genetic code with perhaps unpredictable effects. But it can also involve transferring genetic information from one species to another, transgressing that species boundary. And it breaks another ‘biological rule’. With selective breeding, the farmer effectively chooses between available genetic variants. He or she does not create the variant to start with. As Darwin wrote in On the Origin of Species, ‘Man does not actually produce variability.’ But with genetic engineering – that’s precisely what we are doing. Concerns have been raised about the potential – though unknown – long-term effects of breaking the species boundary. There are worries about the escape of novel genes into wild plants. And then there are suspicions about the motivations of the large corporations that have been pushing this technology through.
In the end, New Leaf potatoes never really took off. These GM potatoes were expensive, they required complicated crop rotations to lessen the likelihood of resistance developing amongst the beetles, and then a new, effective pesticide appeared on the market. It was market forces rather than ethical objections that put an end to this particular experiment, after less than ten years.
But perhaps we shouldn’t be turning our backs on GM just yet. There’s another way of employing genetic technology to produce some of the specific attributes we want to feature in our domesticates – and that’s by looking for desirable versions of a particular gene which already exist in that species’ genetic repertoire, and spreading that gene through the breeding population. This time it’s not about moving a gene across species boundaries, but instead short-circuiting the traditional practice of selective breeding. I wanted to understand how this ‘gene editing’ worked in practice, so I made an appointment to visit the Roslin Institute in Edinburgh – to meet the geneticists there, and their flock.
6
CHICKENS
Gallus gallus domesticus
A hen is only an egg’s way of making another egg.
Samuel Butler
The chicken of tomorrow
Today, chickens outnumber humans on the planet by at least three to one at any time. They are the most common birds on earth, and around 60 billion of them are raised and slaughtered each year to feed our hunger for their flesh. Chickens have become the most important agricultural animal on the planet. But it wasn’t always this way. In fact, the chicken’s rise to global domination happened very recently, and very fast. And it all started with an American competition launched in 1945 – to find the chicken of the future.
The idea behind the competition was to refocus chicken breeders on meat, not just eggs, and to find the plumpest chicken in the United States of America. The sponsors of the competition, leading poultry retailers, A&P Foodstores, made a film abo
ut it in 1948, ingeniously entitled Chicken-of-Tomorrow.
The film starts with a close-up on a crate of fluffy chicks, while an oboe plays a plaintive air. Then the music fades, and the picture changes so that now we see two women in white shirts, fondling the cute little cheeping chicks and throwing them from one crate into another. ‘Did you know that poultry is the nation’s third largest agricultural crop, a 3-billion-dollar business?’ intones the American infomercial-style voiceover. The informative script is read by no less than the film-maker and broadcaster Lowell Thomas – the voice of 20th Century Fox’s newsreels until 1952.
Then we’re looking at more women, this time transferring eggs into a rack. ‘Breeders have achieved great results in boosting the egg output of the average hen. Today’s hen averages 154 eggs per year. Some birds produce over 300 annually.’ This sounds good, but it’s not good enough. ‘But with this emphasis on egg production, poultry meat has been more or less a by-product of the industry,’ continues the voiceover. Now we see two men in white coats, inspecting very skinny, dead chickens and then hanging them back up by their feet on hooks. The poultry industry got a boost in wartime, we’re told, filling a gap in the market produced by a shortage and rationing of red meat. Poultry leaders were worried about maintaining the demand after the war, so A&P Foodstores – originally the Great Atlantic & Pacific Tea Company – stepped into the breach, sponsoring a national competition. They were quite clear about what they wanted from farmers and breeders: ‘A broad-breasted bird with bigger drumsticks, plumper thighs and layers of white meat.’ They’d even made a wax model of what they wanted the future chicken to look like. Essentially, they wanted a chicken that looked more like a turkey.
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