Meet The South American ‘Superfood’ Responsible For 1 Million Deaths In The 1800s — A Biologist Tells The Story

What happened in Europe from about 1845 to 1852 should serve as a strong warning against becoming overly reliant on any single nutrient source.

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When the Spanish conquistadors first encountered the potato (Solanum tuberosum) in the Andean highlands of South America, they couldn’t have imagined how profoundly it would shape global history. This is the plant that sustained the Inca Empire, given its ability to grow at altitudes and in soils where few other crops could. It’s also the plant that would eventually feed entire continents.

It was a botanical marvel: calorie-rich, easy to cultivate and astonishingly adaptable. But just three centuries later, this very same superfood would also become the trigger of one of the most devastating famines in modern human history. From approximately 1845 to 1852, Ireland suffered a catastrophe of unimaginable scale. The Great Famine (known in Irish as An Gorta Mór) is estimated to have killed around one million people, and forced even more to emigrate.

It’s believed that a single organism was the proximate cause of the famine: a microscopic plant pathogen that exposed the region’s dependence on a single crop.

A Crop Of Promise

As classical research from Science explains, the potato was domesticated about 8,000 years ago in the Andes, in what’s now southern Peru and northwestern Bolivia. Indigenous farmers cultivated thousands of varieties; each was adapted to specific microclimates, from chilly mountain terraces to warmer valleys. But for the Inca, the potato was a cultural cornerstone that they preserved as chuño (a freeze-dried form). This is what they used to feed their armies and communities through lean years.

As further 2019 research from Nature Ecology & Evolution explains, the potato was slow to gain acceptance when Spanish colonizers eventually returned to Europe with it in the 16th century. Europeans were initially suspicious of its strange appearance and its relation to the deadly nightshade family. But over time, practicality overcame prejudice. Planting started in the seventeenth century and then gained true momentum in the eighteenth. By the nineteenth, the potato had become one of Europe’s main staple crops.

It thrived in poor soils and cold climates, it required less labor than cereal grains, and it yielded more calories per acre than any other crop known to Europeans at the time. These are the factors that, for the Irish in particular, made the potato synonymous with survival.

The Irish Connection

Ireland’s mild, damp climate is ideal for potato cultivation; in fact, the same applies to much of Europe and Asia. As the abovementioned Nature Ecology & Evolution study notes, 82% of the potatoes on the planet are grown in Eurasia.

By the early 1800s, roughly half of the Irish population depended almost entirely on the crop, primarily poorer families in rural areas. Many families subsisted on a few acres of potatoes and little else. Nutritionally, this reliance was not entirely irrational. The potato is remarkably dense in nutrients: it provides carbohydrates for energy, vitamin C and potassium. And when eaten in sufficient quantities, and when combined with milk, it also provides enough protein to sustain human health.

For decades, it appeared to be the single most perfect crop for Ireland’s growing population. But therein lay the danger: the entire system depended on only one singular genetic lineage.

The Pathogen Arrives

In 1845, a new plant disease inexplicably appeared in Ireland. Farmers noticed that their healthy-looking potato leaves were suddenly developing dark spots, which turned them black and withered. Upon digging up the tubers, they noticed that all of them were becoming soft, brown and foul-smelling. Devastatingly, it only took a few weeks for entire fields of potatoes to be ruined completely.

As 2013 research from eLife explains, the culprit was Phytophthora infestans. This is a type of oomycete, or a water mold; it’s not a true fungus, but rather a fungus-like organism. It’s since been established to have originated from the highlands of central Mexico, where wild potato species have long since co-evolved resistance to it. This is most likely where it spread from to Europe, via infected tubers shipped from the Americas through to either Belgium or England.

Ironically, the cool, wet conditions of Ireland’s climate — that were once ideal for the potatoes — are where P. infestans found a perfect environment. The blight then spread rapidly via microscopic spores, which travel mostly through the air and rain. Once they landed on a susceptible potato leaf, P. infestans subsequently germinated, penetrated the plant tissue and consumed it from within.

The Biological Devastation

What made P. infestans so particularly devastating in Ireland was the crop’s genetic uniformity. Essentially every single potato plant was equally vulnerable, which is what ultimately allowed the pathogen to spread unchecked. By late 1846, nearly the entire Irish potato harvest had failed.

The impact of this microscopic organism went far beyond botany. With neither food reserves nor help from the British colonial government, the blight swept across Ireland. In turn, Ireland’s population fell from about 8 million to less than 6 million in less than a decade.

Biologically, the famine revealed how vulnerabilities arise when an ecosystem, or even a society as a whole, becomes dependent on a single species for survival. And in evolutionary terms, this monoculture was an invitation to disaster. As efficient as this population of genetically identical organisms was, it had little to no buffer against disease. It only takes one mutation in a pathogen or one shift in climate for an entire system to collapse in on itself.

In Ireland’s case, the potato’s uniformity meant that P. infestans faced no resistance whatsoever. The second it was introduced, the pathogen was able to complete its life cycle until there were no potatoes left. Spores from one infected plant could infect thousands more in a matter of days. The very traits that made the potato a “superfood” — its high yield and reliability — is what became its Achilles’ heel.

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