Papaya- the Sex-change King, Queen and more besides


The papaw or papaya not only has two well known names but it is said to have 31 different sexes, and presumably a highly complex social life as a result.

These 31 different sexes can be simplified as males, females and hermaphrodites. Some individual plants always remain predictably male or female or hermaphrodite. However, things are more complicated than that. Some hermaphrodite plants only ever have hermaphrodite flowers, which produce both pollen and eventually fruit from the same flower. Other hermaphrodite plants have separate male and hermaphrodite flowers. While other plants can have separate hermaphrodite and female flowers and some indeed have separate male, female and hermaphrodite flowers simultaneously all on the one plant.

Things start to get really complicated when some male and some hermaphrodite plants go through seasonal sex changes or respond to physical damage in the same manner. Thus, some male plants will produce hermaphrodite flowers and subsequently fruit at certain times of year, or if their stems are damaged by blows from a cutlass. This technique is often used by those unfortunate enough to find that their solitary papaw plant in the back garden is male and therefore unlikely to produce fruit if left to its own devices. Similarly, an hermaphrodite plant which normally only produces fully hermaphrodite flowers may sometimes be induced to produce entirely female flowers as well. Hermaphrodite plants which normally produce male and hermaphrodite flowers, may change to stop producing male flowers and produce female flowers instead etc. Confused; just imagine how complex their social life could be!

Then you could ask, how is all this sexual variety regulated? The answer is more complicated still. In fact there are several competing theories, and it would be true to say we just do not know in detail. However, basically it appears to be regulated by sex chromosomes similar to those in humans with XX female and XY male. But papaws also have an another form of the Y chromosome, such that XY2 individuals are hermaphrodites, and combinations with any two Ys are lethal. With this system if you cross a male plant with an hermaphrodite you get equal numbers of males, females and hermaphrodites in the offspring.  But if you cross a female with an hermaphrodite you only get females and hermaphrodites.

In addition to its incredible love life papaws have another amazing ability. The latex of the papaw plant contains not one but two protease enzymes. These chemicals actually digest proteins. Within the plant world this ability is usually only associated with insectivorous plants such as the Venus flytrap and pitcher plants. The papaw must have evolved this ability to discourage grazing animals. After all you are unlikely to consume a plant that is going to digest you rather than visa versa. What is more, we must ask how did the papaw manage to evolve the ability to synthesise these protease enzymes without digesting itself?

The latex is tapped from the unripe green fruits, by making a series of cuts into the fruit with a piece of broken glass. This operation is performed in early in the morning. Throughout the day the latex drips from the fruit into a coconut shell or pot. The sap is then sun dried. About 1000 fruit are required to produce enough sap to make half a kilo of dried product. Mankind has found many different uses for the protein digesting sap of the papaw plant. In addition to the obvious use as a meat tenderiser, papaw extract has been used to digest protein hazes out of cloudy beer, employed medically to dissolve unwanted growths, and to remove hair from hides before tanning. It is used widely to remove unwanted protein residues in many manufacturing processes and routinely to purify DNA extracts in modern molecular genetics. Perhaps the grossest use of papaw extract is, it’s injection into cattle before slaughtering. Under these circumstances the protein in the animal’s muscles actually start to break down while it is still alive. However, such meat understandably comes with the health warning – ‘do not eat rare!’ otherwise you too could be digested by your own dinner.

Domestication a Fishy Tale

The story of the domestication of both plants and animals is notoriously difficult to untangle. For the most part the transition from wild population to farmed species occurred such a long time ago that the process has frequently become the stuff of myths and legends. Most domestication events occurred long before people bothered or were able to formally record such things. Around the world various oral traditions tell of crops falling from heaven as gifts from the gods. Our ancestors had no need to record their actions because at the time they would have been totally oblivious of the significance of their activities for subsequent generations.
Remarkably few people other than Jared Diamond and myself have bothered to question why so few species were ever domesticated. As a botanist until now I have restricted my thinking to crops. But Jared Diamond has argued that exactly the same principles apply to the domestication of both crop and animals. He argues that even fewer animals were capable of being domesticated than was the case in plants. Think about it for a minute, we really do routinely eat only cows, sheep, pigs and chickens as domesticated animals. That’s amazing given the diversity of life on earth.
Jared Diamond claims that domestication was a rapid process that occurred a long time ago, because all the species that could potentially be domesticated were identified in the distant past and quickly made that transition to farmed crop or livestock long ago. However, it turns out that not only are we still domesticating new crop plants the same is also occurring in the animal kingdom. So we don’t have to use flimsy fossil records or myths for prehistory to understand domestication; we can actually observe the process first hand.
So what does the animal world have to tell us about the process of domestication? In the last 50 years salmon has been transformed from being an expensive luxury item caught from the wild by aristocrats, small traditional scale netting operations, with some sea trawled fish being tinned. Today salmon is a cheap everyday farmed commodity. But has the Atlantic salmon really been domesticated? Surely a farmed salmon and a wild salmon are identical. OK farmed individuals don’t get to roam the vast oceans and fight their way up river to their natal spawning grounds but surely they could, they look just the same don’t they? Because of the considerable economic importance of both wild and farmed populations of salmon, we probably know more about the unintentional genetic changes associated with its early domestication than any other species. Although they may appear superficially similar research has shown that wild and farmed salmon are quite different. Marc Gross from the University of Toronto argues that farmed salmon should actually be considered as a new biological entity – Salmo domesticus. (
There are very real concerns that during storm events millions of farmed salmon (which now vastly out number wild populations) are able to escape into the wild. The fear is that these escapologists will interbreed with wild fish populations that are already threatened by over fishing and chemical pollution. This could be important because it is possible that hybrid fish that are half wild and half farmed salmon may not be able to find their way home to their traditional spawning grounds. Other important behavioural and ecological characteristics could also be altered as wild populations are invaded by the new domesticated types.
It appears that these concerns about the potential genetic pollution of wild salmon stocks by farmed fish may not be fully justified. Evidence suggests that just a generation or two of domestication seem to render farmed salmon ill prepared for the rigours of life in the wild. In captivity the individuals that thrive are the fish that come to the surface and actively compete for the food pellets which are liberally scattered for them. This very same trait is probably a death sentence for wild fish. In natural conditions any fish that actively swims on the surface looking for food rapidly becomes food and is eaten by a host of predators. In the wild environment it is much better to lurk in deep water out of sight off the menu. Conversely hiding away at the bottom is a stupid thing to do for a farmed fish, because they will very quickly go hungry. As a consequence of these strong and opposing selection pressures, fishermen’s attempts to restock rivers with farmed fish have proved consistently and controversially futile. Even so, it is thought that because of the almost constant flow of massive numbers of maladapted escaped farmed fish in Norway it mean that entire fjords have ‘lost’ their wild salmon populations.
Unfortunately this is probably not the most significant problem facing wild salmon stocks. Marine survival rates are insanely low at the moment (0.5-2% versus 10-20% a century ago), implicating climate change. It is going to be a tough few decades for salmon as severe natural selection favours those fish able to find their way in a changing ocean. They will manage, but abundance is likely to remain low for some time.
This fishy tale rather suggests that Jared Diamond is correct and that domestication is a rapid and dramatic process. With both plants and animals we have frequently selected for traits that make them easy to handle and more pleasant to eat. These genetic changes often mean that domesticated species are unable to survive in the wild. This is why there are few populations of farmed animals and plants that successful escape cultivation. Wild animals that are easy to handle and good to eat are not going to survive for long.
Of course life is rarely this simple. There are examples of species that have lived in association with humans for thousands of years and have not changed that dramatically from their wild ancestors. The reindeer is one of these semi-domesticated species. Since the last ice age the Sami people have depended for their survival on herding reindeers and driving them vast distances across the tundra. After all this time and many generations the deer remain mostly unaltered and are certainly able to thrive without humans in these harsh artic conditions.
So it appears that animal domestication is similar to crop domestication. For many species their association with humans began many years ago. But this does not mean that it is impossible to domesticate new species. In fact with our modern understanding of genetics this is easier than ever before. The salmon story tells us that such genetic changes can be rapid, while reindeers are an example where genetic change is slow.

A big thankyou to Kyle Young for his comments on this post

The Animals Went in Two by Two

But What About the Plants?
or How to Avoid an Overdraft at the Gene Bank

How long does a plant have to be cultivated before it can be considered a crop rather than a wild species? Is the process of domestication rapid or a long drawn out affair, in which genes flow freely between wild and cultivated populations over many generation? Just as there are days when we all feel a little more ‘feral’ than others, the answer to these questions probably varies between species.
You might imagine that the process of selecting the very first individuals from the wild to cultivate occurred so far back in the mists of time that it’s irrelevant to modern farmers and growers. However, it seems likely that first steps along the domestication road may have unintentionally influenced its final destination.
Far from being ancient history, collecting seeds from wild crop relatives is an important job that gene-bankers do routinely for virtually all our modern crops. When you are tasked with finding and capturing truly undomesticated genotypes, you really start to appreciate how difficult it is pluck something from the wild, without producing a whole raft of surprising consequences. In the biblical account of the flood, Noah did something similar by collecting all the animals in pairs. Noah’s ark can be considered the world’s first gene-bank. However, small this collection, there is no mention of the subsequent effects of inbreeding, genetic bottle necks or random genetic erosion.
One of the most important factors that causes genetic change during domestication is generation upon generation of selecting preferred types. Having said that, unintentional random choice right at the start of the process may radically limit the subsequent choices available.
Many plants reproduced by both seeds and vegetatively. Some crop species are grown to harvest their seeds, others for their vegetative storage organs. Given there appears to be some biological truth behind the expression – ‘you cannot have everything in life’ here lies the rub. If our ancestors were effective at identifying the plants that were most prolific in producing root tubers, then in subsequent generations, they may struggle to produce seeds. Even more striking, similar examples include selecting for seedless grapes and citrus. These may be much easier to eat without those fiddly seeds. But what happens when you want to cross breed them for disease resistance?
In the wild, not all plants are not the same size and it’s not always easy to see where one individual stops and the next one starts. In grasslands and woods plants can grow through each other. Even those apparently separated, may in fact be the same genetic individual, where the inter-connecting sections have died. Such complexity make it really tricky if you are trying to select plants truly randomly and not over collect the few really large individuals. This is really important if you are to avoid losing genes that might be really useful in future breeding programmes.
The first few generations are also likely to be disproportionately important in introducing bias into the gene pool and slashing crop genetic diversity. I came across a great example of this on a recent visit to NIAB in Cambridge. They have been investigating why wild flower seed mixes designed to produce flowers for pollinators all summer long, were only flowering for a brief period in the middle of summer. They soon discovered that the seed mix which had been chosen to contain early, mid and later flowering species was in fact being harvested for seed on a single occasion in mid-season. Thus in one single generation of domestication, the later flowering species had been selected to flower in mid-summer. Many of the late flowering genes had been lost by accident in a single season. This can hardly be described as domestication, but it beautifully illustrates how genetic change can be rapid and unintentional as species transition from wild to cultivated forms.

I Want Yams Where I Am

Poison Arrow

No one would dream of knowingly investing their hard-earned financial resources in a bank that did not take adequate security precautions. Similarly, plants which survive the winter or arid seasons by hoarding food supplies have evolved many different mechanisms for protecting their investments from thieving herbivores. Plants which produce storage organs full of carbohydrates must have seemed attractive to our hunter-gatherer ancestors and to early farmers in search of potential crops to cultivate. However, unlike fruit, which are ‘designed’ to be eaten because they have evolved as a method of seed dispersal, storage organs tend to be unpalatable or even toxic. For example wild and green potatoes contain poisonous alkaloids and cassava tubers are full of cyanide. Such, plant chemical defences have generally been a problem to those attempting to either domesticate or exploit species containing them. On other occasions man has discovered novel ways of utilising these compounds for his own ends; for example the tubers of yams have been harvested for their toxins to poison arrows, to poison in-laws, to catch fish, and to apply to other crops as an insecticide. In more recent times, large quantities of wild yam tubers have been collected commercially for an even more unusual purpose.

Yams grow wild all around the world, scrambling through other vegetation, with some vines twisting clockwise, and others anticlockwise, depending on species.  Plants are usually single sexed, producing either all male, or all female flowers, but with both types producing large subterranean tubers. Wherever yams have occurred, they appear to have attracted the attention of man, with different species being domesticated in Asia, Africa and South America. The greater yam, the lesser yam, the Chinese yam and the bitter yam were all first cultivated in Asia; the yellow and white guinea yams and cluster yams are of African origin. The potato yam, which produces strange aerial tubers, occurs wild in both Asia and Africa, and appears to have been cultivated independently in both regions. In South America only the cush-cush yam was considered worthy of domestication but other species may have been collected from the wild. Even Britain has a native yam, called black bryony. Although it is now generally considered to be toxic, bryony tubers, measuring up to 60 cm, were eaten from prehistoric times, even to this day some French cookery books describe how to detoxify them, by prolonged soaking and boiling. The French name for the plant is herbe aux femmes battues, or literally the battered wives’ herb. Within the UK and the US the tuber most commonly called a yam is in fact the unrelated sweet potato, which is actually related to the ornamental morning glory.

The majority of the world’s yams are grown and consumed in the ‘yam belt’ of West and Central Africa, in the region east from Ivory Coast through Ghana, Togo, Benin and Nigeria to Cameroon. In spite of yam cultivation being labour intensive and yields being low, yams have been particularly valuable in the tropics, because they are easy to handle and store well for several months. Their keeping properties made them ideally suited for ships’ stores in the days of sail, in this manner yams were transported from Africa to the Americas as provisions onboard slave ships and similarly Asian yams were dispersed across the Indian and Pacific Oceans in the pre-European period.

Within the last one hundred years wild yams have been harvested for a new and unexpected purpose. The story dates from 1933 when the Eastman Kodak Company first isolated the human hormone progesterone. Huge quantities of cattle brains were required to produce a few grams of the desired compound. It was quickly realised that progesterone had great potential as a contraceptive, as it was found to halt ovulation in laboratory rabbits. The discovery that the hormone could be synthesised from various naturally occurring plant compounds stimulated a search, which was described by an American pharmacology newsletter as a ‘story warranting a Hollywood movie, full of intrigue, deception, scandal, corporate envy and trickery, bribery even violent harassment and murder’. Although 250, plants containing progesterone like compounds were identified, including: red clover, liquorice, fennel and soybeans, the first commercial synthesis of progesterone for use as an oral contraceptive was from diosgenin, derived from wild Mexican yams. This simple fact appears to have generated a plethora of stories and claims about the medicinal properties of wild yams.

Lotions and potions containing wild yam extracts or ‘natural progesterone’ are marketed as alternative medicines as a form of hormone replacement therapy, or to ease the discomforts of pre-menstrual tension, and even as contraceptives. Stories are told of South American Indians, who for centuries were able to regulate their own fertility by chewing on yams. The truth behind all these tales is that the compounds found within yam tubers are grazing deterrents and not active human hormones. Although yams have been used in the synthesis of the Pill, there are several complex chemical changes involved in the conversion of the naturally occurring diosgenin to progesterone and these are chemical changes that the human body is unable to perform for itself. If you were considering eating yams as a form of birth control, you may just as well have a box of liquorice all-sorts or rely on a lucky four leafed clover.

Fifty Shades of Green

This piece was published recenrly in Prom – The Aberystwyth University Alumni magazine

It gives you a flavour of

Now please get online and order the book 😉

It is frequently but apocryphally claimed that Eskimos have 50 words to describe snow. Closer to reality, but almost never quoted is the observation that there are 45 words for shades of green in the Icelandic language. In fact in most languages there are many more words to differentiate shades of green than there are for any other colour. This is because we live on a planet dominated by the colour green, where the forces of natural selection have equipped our species with eyes that are particularly sensitive to light in the green sector of the spectrum. When offered photographs of landscapes, people prefer the more intensely green images. There are good biological reasons behind this bias and this biology is reflected in our electronic gadgets that capture or present coloured images. To be able to represent the world in a way that humans recognise televisions, cameras etc. need to include more green receptors or colour cells, than those for other shades.

You might not think so, but humans have evolved as botanists with acute abilities to differentiate plants species. The ability to differentiate between subtly different shades of green and thus different species of plant is a talent, which greatly enhances your ability to survive in the wild. If you eat the wrong plant then you are poisoned. Conversely brighter shades of green tend to indicate elevated nutritional values. It is therefore no surprise that our crop plants tend to be particularly bright green, and agricultural fields are a brighter green than the wider countryside. It is not a coincidence that many of the wild relatives of our crops are found along coasts and in floodplains. These habitats are naturally highly fertile, as they are regularly supplied with nutrients courtesy of defecating seabirds or inundation by rich sediments. Wild cabbages, carrots, wild-beets, asparagus, peas, kale and various members of the spinach family all have maritime distributions, while many cereals are at home in fertile river valleys.

The fact that crop plants tend to be bright green and highly nutritious have not been the only factors in determining which species of plants our ancestors chose to domesticate. There are approximately 400,000 species of plant on earth. However, we regularly only eat about 200 of them, which equates to less than 1% of what is possible. So what makes our crop plants so special? The answer to the question why do we eat the plants we do appears to be related to their sex-lives rather than the more obvious – we avoid the poisonous ones. In fact many important crops contain toxic chemicals, classic examples being; potatoes, tomatoes, cassava, even wheat if you are gluten intolerant. The Jamaican national dish of akees, regularly results in lethal poisons of its citizens.

The most compelling evidence that a plant’s sex-life limits its ability to be domesticated is provided by the orchids. There are 20,000 species of orchid. They are the most species rich of all plant families and yet we cultivate just one of them for food. The fact that we don’t exploit orchids for food is perhaps a little surprising given that many of them have starch filled root tubers. Historically wild orchid tubers were boiled to make a starchy drink called salep, which was a common street food in London and is still drunk Turkey. Salep was thought to have aphrodisiac powers, this belief was linked to the fact that orchid tubers typically grow in pairs, which in turn is linked to the derivation of the word – orchid from the Greek for testicles.

The reason we don’t cultivate orchids as food crops is linked to their bizarre sex lives. Orchid flowers are highly complex and typically specialised for pollination by a single species of insect. Both orchid and insect species are interdependent on each other for their survival. If you try and cultivate an orchid away from its specially adapted pollinator, it will fail to set seeds and ultimately fail as a crop. The one species of orchid that is grown commercial therefore relies on hand pollination. This species is the vanilla orchid and it remains viable as a crop because natural vanilla pods command a price high enough to cover the cost incurred by hand pollination.

If crops are going to be successfully grown over wide geographic ranges, then they need to have generalist pollination mechanisms that rely on either the wind or on the services of common insects such as bees. The ten most important crops on earth are: maize, wheat, rice, potatoes, cassava, soybeans, sweet potatoes, sorghum, yams and plantains. Of that list most are wind-pollinated cereals, or root crops that don’t require insect pollinations. Plantains (bananas eaten as a vegetable) are fruits that don’t contain seeds. From this list only soybean produces a seed crop that is not depended on wind. However, soybeans tend to self-pollinate without the need for insects.
If the world’s most important food crops are not depended on insect pollination, why then does the UN claim, “seventy out of the top 100 human food crops, which supply about 90 percent of the world’s nutrition, are pollinated by bees”?

Although the majority of our staple crops are wind pollinated, it is striking that many other crops are insect pollinated, including virtually all temperate fruit trees. This is particularly strange since the majority of these trees originally evolved in deciduous woodlands that are dominated by large wind pollinated species such as oak, ash, beech etc. In their natural habitats, the ancestors of apples, pears, cherries, almonds, peaches etc are never as abundant or as tall as the wind-pollinated species. There is a simple biological explanation responsible for this fact. Wind pollination is an effective mechanism to ensure fertilisation if you are abundant. But smaller, less common species cannot reply on such a random delivery method and have to utilise the more precise pollen delivery service operated by insects.
This observation begs the question -why are so many fruit crops derived from smaller, less abundant, insect pollinated species rather than the larger, more abundant, wind pollinated trees such as oaks, ash and beech? For example why have we domesticated the almond rather than an acorn? Even without domestication both of these species produce large nutritious nuts and as it happens both are naturally poisonous. Wild almonds are full of cyanide and acorns are full bitter tannins. The answer is simple, if our ancestors had been lucky enough to find a tannin free oak tree and tried to establish an edible acorn farm, then this new palatable variant would have quickly become swamped by pollen from the local oak forests and the next generation of oaks would revert to the bitter wild type. In contrast, if you stumble across a cyanide free almond tree, it’s a relatively easy task to prevent it crossing with its poisonous wild relatives, as in the wild these are much more uncommon than are oak trees. If you establish an almond orchard the chances of any of your trees crossing with a wild toxic almond is fairly remote.
It appears therefore that many of our fruit crops tend to have sex-live that are less exotic than those of orchids but are less promiscuous than oak trees that throw caution to the wind. Unfortunately there is a very pressing reason behind this botanical voyeurism. Populations of many of the world’s pollinating insects appear to be declining and this could have important implication for our food security. As we have seen our most important food crops are not depended on insect pollination. So the good news is that we are unlikely to starve if bees become extinct. However, many of our fruit crops do require insect pollination. In the wild, these species tend to occur, as scattered trees within the forest, so are the focus of much insect activity. In contrast today, many of these crops are grown on an industrial scale in monocultures often outside the range of their native pollinators. Thus, even without the problems resulting from chemical pesticides, disease and climate change, insects are always going to struggle to pollinate all flowers we need to maintain a well-balanced and interesting diet.

Sisters Three; Corn, Beans and Squash


Iroquois FlagThe environmental wisdom of the Native Americans is often quoted with the strap-line, that it should be emulated today. This wisdom of the ancients encompasses such ideals as ‘living in balance with nature’ and ‘farming as nature intended’. At first glance these phrases have a ring of good-old fashioned common sense, but after further thought one is left asking; what is the balance of nature or what sort of farming does nature intend?

In North America, backyard gardeners are encouraged to embrace the environmental knowledge of the Iroquois tribe by planting a “three sisters” plot of corn, beans and squash. The entire project is frequently surrounded in mythology, muck and magic. The Iroquois are said to have believed in the three spirits of corn, beans and squash, and that these three spirits love each other dearly and can only thrive together. Each of these sister spirits or De-o-ha-ko were considered precious gifts from the Great Spirit given to sustain both us and each other. Or in horticultural terms; maize provides the structure for the beans to climb up, removing the need for poles. The beans fix nitrogen in the soil to the benefit of the squash and the corn. While the squash spreads along the ground acting as a living mulch keeping the soil moist and free from competitive weeds.

It is rather fortuitous that these three American sisters get along so well because they are the product of a rather dysfunctional family. Squash is probably the oldest sibling and may be as much as 10,000 years old. There are many wild species of squash, pumpkins and gourds in Mexico and Guatemala. Although these are bitter tasting, they all contain edible seeds and were probably first cultivated for making bowls and spoons. The middle sister is probably maize, ‘born’ about 6000 years ago again at the hands of the indigenous peoples of Mexico. Beans are the baby of the family and like squash are in fact many different species that have been cultivated for thousands of years in both Central and South America.  The sisters’ life together as one happy family is much more recent than this. The Iroquois have been cultivating the three crops together for about 700 years and the term ‘three sisters’ only dates from the 19th century.

Similar multi-cropping systems or companion planting methods are widespread around the small garden agricultural systems of the world. They make good ecological sense as the different crops are complementary, exploiting both the soil and sunlight in different ways, utilizing their different root and stems architectures and growth periods. Mixed plantings also reduce the likelihood of a pest or disease sweeping through a monoculture field and provide an insurance against environmental extremes. The down side of companion planting is that it is labour intensive. In the case of the three sisters, there are very complex growing instructions about ground preparation, inter-planting distances and different planting times for the different crops. For example, the corn needs planting before the beans so they have something to grow up. Then of course they require manual harvesting at different times so as not to damage the later maturing crops. This is all very well in a back-yard plot, but not very practical on the industrial scale of modern agriculture.

So what do the Iroquois sister spirits of corn, beans and squash tell us about environmental harmony? The three sisters do indeed live in harmony in the confines of a backyard plot if we are prepared to tend to their individual needs. But one suspects that sibling rivalries will emerge if we force the sisters to grow together in the scales required to feed a global human population of seven billion.  Restoring the balance of nature is no longer a matter of resolving a squabble between sisters, but realizing that there are more gardeners than garden.


Learning from the Potato

Potato Famine

Historians tell us that the reason for studying the past is to prevent us from repeating the mistakes of our ancestors. The rest of us know that its true purpose is to allow us to smile smugly at the follies of forebears. Proof of this, if proof were needed is the potato, which more than any other crop has attracted the attentions of historians. So what have we learnt from the potato induced disasters of the past?

Potatoes were first domesticated about 7000 years ago in the Peruvian high Andes around Lake Titicaca. In this region wild species of potato can still be found. They include highly variable sexually promiscuous species and less variable inbreeding species. Occasionally tubers are still harvested from the wild, but they are extremely bitter and rendered virtually inedible by toxic compounds called alkaloids. These same chemicals are also responsible for the poisonous nature of the potatoes relative the deadly nightshade. The first step in the domestication process must therefore have been the selection of less bitter, less toxic varieties. This was achieved with some success, but it is frequently said that if the potato were to be invented to day, it would be banded because of the toxic residues it contains. The next stage of domestication involved a doubling of the number of chromosomes. Potato scientists cannot agree if this occurred automatically or following the hybridisation of two different species. But this matters little to the story.

Many historians and comedians have spun wondrous and apocryphal yarns about the introduction of the potato into Europe. Sir Frances Drake is said to have discovered them in the Caribbean whist return from evacuating a failed British settlement in Virginia. Considering them too good for Queen Elizabeth, on his return Drake passed his potatoes to Sir Walter Raleigh who had them planted on his estate in southern Ireland. By 1590 they were ready to harvest, unfortunately Sir Walter tried to eat the toxic potato fruit. Disgusted by the experience Sir Walter ordered the plants distorted, and only then when his gardener took a spade to the plants were the potato tubers finally found. Of the details included in this version of the story, only the date is anything like accurate.

The Spanish were the first to introduce the potato into Europe in around 1570. Twenty or so years later they were independently introduced into Britain, both introductions were from the South American Andes. In spite of the fact that the British frequently referred to the crop as the potato of Virginia, it was not known in North America or the West Indies until being introduced via Europe in 1621. Another inaccuracy in the tale of Drake and Raleigh is the production potato tubers at all. The first plants brought into Europe, being from the Andes were not adapted to the long summer days of the temperate North. Andean potatoes are stimulated to form tubers by the short days of more tropical clines. It was to take almost 200 years of selection before the new arrival became adapted to European long summer days. This factor and a reluctance to eat a plant, which so closely resembled the poisonous nightshades, combined to prevent the widespread planting of the crop in Britain until about 1800.

Partly because it thrives in mild wet conditions and also because their English landlords kept much of the best land capable of growing cereals for themselves, the Irish took to potato cultivation in a big way in the early eighteenth century. The crop was grown in long strips of ground about two metres wide, along which manure, seaweed or rotted turf had been heaped, on top of this earth taken from between the strips was piled. The potatoes were planted with a dibber or placed on top of the manure layer during construction. Either way ensured that they were above ground level and so protected from water logging. The method was so effective that with a few other basic supplies a strip of land just 700 metres was all that was required to support a family. The beauty of the system was that because it kept the potatoes frost-free it also worked as a store. Once planted it required no further attention until the day came to lift them for consumption. For this reason, the Irish strip method of growing potatoes became known as ‘lazy beds’. The success of the crop enabled the population of the Ireland to increase dramatically, with estimates claiming a 900 percent rise from one million to nine million in the hundred years from 1740.

However, history records in a series of grim statistics that potato cultivation in Ireland was to end in disaster and in the process change the world. Although the Irish potato famine is associated with the years 1845 and 1846, the previous one hundred years had seen a procession of nearly thirty different famines. Each one was caused by the destruction of the potato harvest due to a fungal, bacterial or viral diseases. Probably as many as half a million or one third of the population died around 1740. During the blight years of 1845 and 46 one million people died and a further million and a half emigrate. This set a trend, which resulted in more than five million leaving the country before the first decade of the twentieth century. Potato cultivation played a similar role in the Highland clearances of Scotland and the mass emigrations or ethnic cleansing that followed.

With hindsight, historians and agriculturists have both retrospectively been able to predict the catastrophe.  Such heavy reliance upon a single crop with only low levels of genetic diversity in a mild damp climate is a recipe for disaster. The structure of the potato’s lush dense foliage seems to invite attach from fungal diseases. As an agricultural system it could have been designed to propagate pathogens.

So have we learnt the lessons of the potato?  Global production of the crop is steadily increasing, and is still based on a very narrow genetic base. It is the only non-cereal in the top eight crops, which dominate world food supply. On top of which can be added the uncertainties of climate change. Predictions vary but generally forecasts include increases in both temperature and precipitation i.e. the climate looks like becoming more favourable for plant diseases. It would strike you as perhaps a good time to be storing away food reserves just in case one of the eight major staple food crops was to suffer attach from a new ‘blight’. Just the reverse has occurred, set-aside policies and the pressures of free trade have seen the depletion of the Food Mountains of the 1980’s.

On the positive side plant breeders now better appreciate the value of genetic resources, and great efforts are made to collect and conserve the genes of all the world’s major crops. For both historical and political reasons the Centro Internacional de la Papa (the international potato centre and world potato gene-bank) is located in Peru. For years the research centre has been regarded as a legitimate target by terrorists. So next time you eat a plate of chips, spare a little thought to the group of international potato scientists, who live their lives behind two sets of barbed wire and armed security guards to ensure that it is not chips for the future of the potato.