Cultivated plants and human food

Three ears side by side: teosinte, a hybrid and an ear of maize. — Teosinte, a maize–teosinte hybrid, and maize, side by side (photograph by John Doebley). John Doebley, CC BY 3.0, source

What we eat comes from at least eleven places in the world, where communities domesticated plants entirely independently.

The foods now seen as the most “typical” of a regional cuisine very often come from another continent, and sometimes arrived far more recently than one might imagine.

What a domesticated plant is

None of the plants we eat exists in the wild in this form. Maize, wheat, the banana and the cabbage are manufactured products — not in a laboratory, but by thousands of generations of farmers who, every year, kept for sowing the seeds of the plants that suited them best.

That is what domestication is: repeated selection, carried on long enough to transform the species. It always targets the same traits, because these are the ones that get in the way of a harvest.

The seeds must no longer fall of their own accord. A wild cereal scatters its grains as soon as they are ripe — that is how it reproduces. A domesticated cereal keeps them on the ear until someone comes to harvest them. This single trait makes it incapable of surviving without us.

We now know what controls it. In einkorn, one of the first cereals to be domesticated, the shift from the brittle ear to the solid ear is explained by the change of a single amino acid in a single protein. In rice, another gene plays the same role. A tiny mutation, spotted and then preserved by farmers who knew nothing of it, was enough to tip a wild plant over into cultivation.¹

The seeds must all germinate at the same time. A wild plant spreads its germination over several years, as a precaution. A field demands the opposite.
The part that is eaten must grow larger. The ear, the fruit, the root, the tuber — depending on what is sought.
Bitterness and toxins must decrease. Almost all wild plants defend themselves chemically; to cultivate them is also to disarm them.²

The cabbage illustrates the process better than any other. Head cabbage, cauliflower, broccoli, Brussels sprouts, kohlrabi and kale are all the same species, Brassica oleracea. One and the same wild plant, selected sometimes for its buds, sometimes for its flowers, sometimes for its stem. They are not cousins, but variants.³

On a global scale, most of what humanity eats rests on a very small number of species. Cereals, above all rice, wheat and maize, on their own provide more than half of the calories consumed on the planet. The rest is shared among a few dozen other plants, even though thousands of edible species are known.⁴

Eleven centres, at least

The domestication of plants did not take place once, in a single place, and then spread across the planet.

It happened at least eleven times, on several continents, without any contact between these initial centres. Populations separated by oceans had the same idea, each with the plants it had to hand.⁵

The bones reveal an unexpected fact: in Central Europe, for example, the skeletons of the first farmers are smaller and lighter than those of the hunter-gatherers who preceded them.⁶

Agriculture is therefore not the great step forward it is often described as. Nor is it the tragic mistake one sometimes reads about. It is a complicated path, taken under pressure from the climate and from the number of mouths to feed.⁷

What travels

Two examples are enough to gauge the speed of these journeys:

The chilli pepper left the Americas after 1492. It only reached inland China from the late seventeenth century onwards (in Hunan around 1684, in Sichuan around 1749). A culinary tradition perceived as thousands of years old is in fact less than three centuries old.
The tomato, which arrived in Europe in the sixteenth century, remained mostly a curiosity there for more than a century — grown for study and for ornament, thought harmful by some, eaten only by a rare few, before reaching people’s plates.⁸

What is taken for an immemorial heritage is almost always recent.

The case of the Siege of Leningrad

This episode shows how far some people went to keep seeds.

During the Siege of Leningrad (1941-1944), more than twenty scientists and specialists of the Institute of Plant Industry — the largest seed collection in the world at the time, assembled by Nikolai Vavilov — starved to death while protecting the stocks of edible seeds. Vavilov himself, arrested in 1940, starved to death in prison in January 1943.⁹

The city was starving, and they had rice, potatoes and wheat to hand. They did not touch them. These seeds preserved unique lines, which were used to rebuild crops after the war and which are still in today’s seed banks.

The 75% figure: anatomy of a statistical myth

It is commonly claimed that 75% of the diversity of cultivated plants was lost during the twentieth century. This figure is frequently quoted to raise the alarm about genetic erosion.

A figure without an original citation

A critical analysis published by some fifteen researchers traced this claim back to its origins. They devote an entire box to it, whose title says it all: “The mysterious origins of the 75% narrative”.¹⁰

Their finding can be summed up in one phrase: the estimate is attributed to a major international organisation, “invariably without original citation”.¹¹

It has been circulating since the 1990s. The number seems to come from efforts to gather scattered observations and anecdotes, as part of international work on genetic resources.¹²

And the sentence does indeed exist. It can be read, without a reference, in an atlas published in 1995 by that organisation: “Since 1900, however, about 75 percent of the genetic diversity of agricultural crops has been lost.” A clear-cut claim, without a source, in an official document.¹³

The authors of the analysis say it bluntly: how the jump was made from local findings to a global estimate remains a mystery.¹⁴

What one finds when one really looks

This is the most interesting result, because it is neither “it’s true” nor “it’s false”.

The authors reviewed the data available in four different settings: farmers’ varieties in the fields, modern varieties in agriculture, the wild relatives of cultivated plants in nature, and the collections held in seed banks.¹⁵

The result: marked losses are observed everywhere — but also stable situations, and even increases in diversity.¹⁶

The extent depends on the species, on the scale at which one looks, on the region — and on the method of analysis chosen.¹⁷

This last point deserves attention. It does not merely say that the answer varies from place to place. It says that it also varies according to the method of measurement. Two honest teams, in the same setting, can reach different conclusions.

So a single figure for the whole world could not exist. It is not that it has not been found yet: it is that the question, put this way, has no single answer.

What the factual data show

No major cultivated species has disappeared worldwide over the last fifty years of agricultural data.
The paradox of diets: at the national level, the variety of foods available has increased overall for individuals; but at the global level, diversity between countries has shrunk, leading to a homogenisation of food baskets across the planet.¹⁸

An essential distinction between two separate statistics

Two claims that are often merged in public debate should not be confused:

“75% of genetic diversity lost” — a statistical claim whose accuracy and methodology are scientifically disputed.
“12 plants and 5 animal species provide 75% of the world’s food” — a documented fact concerning the concentration of contemporary agricultural production (notably on wheat, rice and maize).¹⁹

Note 1

Re-sequencing of the Btr1 and Btr2 in a collection of 53 lines showed that a single non-synonymous amino acid substitution (alanine to threonine) at position 119 at btr1, is responsible for the non-brittle rachis trait in domesticated einkorn.

Pourkheirandish, Mohammad et al., “On the Origin of the Non-brittle Rachis Trait of Domesticated Einkorn Wheat”, Frontiers in Plant Science, vol. 8, 2031, 2018