Rachel Laudan

Why Do Some Plants Become Food Crops and Others Not? And What Does That Tell Us?


Sunflower, Sunflower Seeds, Sunflower Oil. Wikimedia CCL. www.torange.us


Out of thousands of plant species, only a few are important food crops

Globally important food crops in the early twenty-first century include wheat, rice, sugarcane, maize, soya bean, potatoes, barley, oil palm, beans, tomatoes, bananas and plantains, and sugar beet, according to a recent paper by Colin K. Khoury et al in the Proceedings of the Royal Society entitled “Origins of food crops connect countries worldwide.” They expand their analysis in Increasing homogeneity in global food supplies and implications for food security,” in the Proceedings of the National Academy of Sciences.

All these crops are grown far from their places of origin wherever conditions permit. The resulting commodities–sugar and oil, for example–are traded around the world.*

Both papers have been much discussed. I’d like to add a historian’s perspective.

The list of important food crops has a history

  • Wheat, rice, maize, and beans (and perhaps plantains and you could argue soya beans) have been important food crops for many thousand years, spreading way beyond their places of origin.
  • Sugar cane began its ascent to an important food crop around 200 B.C., moving west from southeast Asia to South Asia /ca 700 A.D.), then to China and West Asia, to the Mediterranean, to the Canaries and the Azores (ca. 1550 A.D.), to Brazil, Mexico and the Caribbean (ca. 1600), to the American south, to Hawaii, Australia, and tropical islands.
  • ca. 1600-1900 A.D. Maize, wheat and rice spread again.
  • ca. 1800  Potatoes become a widely-important food crop.
  • ca. 1850 Oil palm and sugar beets join the list.
  • ca. 1900 Eating bananas and tomatoes become important.
  • ca. 1930  Soya beans and maize spread again.

Although the general trend has been to increasing globalization of food crops, some food crops have declined in importance, like barley and the various millets and sorghum that spread across Eurasia at the same time as wheat and rice, or cassava that spread with maize in the early modern period.  Others have stayed on the list because their uses have changed: maize and soya beans, for example. once spread across Eurasia.


Why did these plants become food crops?

So why these?  In large measure because we can turn these plants into human food.


Consider the sunflower, not on the top of the list, but now very important in eastern Europe and Russia as a source of cooking oil. For most of human history, sunflowers (one of the few North American plant species that is now a major food crop) were a very minor food

I passed this stand of wild sunflowers this morning.  It would have been inconceivable that Native Americans in Texas, where I live, would say to themselves “Let’s make some cooking oil from the seeds of that flower.” Even today, in a society accustomed to glug-glugging oiI from a bottle into a frying pan, I would not have a clue how to get oil out of sunflower seeds in sufficient quantity to make the labor worthwhile.

Only when humans know how to process a given plant into food does it become an important crop. Or, in other words, when a plant becomes an important food crop this is due as much to food technology (processing) as to the nature of the plant. 

Of course this is too simple. It’s also important that the plant is reasonably easy to grow and harvest, can be successfully bred to yield more than the wild variety, can be transported, can be packaged, can be stored so its use is not limited to a single season, and so on. Even so, unless you can process the plant into food it’s a non-starter as an important food crop.

  • Wheat, rice, and maize depended on pestles and mortars for de-husking, stones for grinding, granaries for storing, pots and ovens for cooking and fermenting. These technologies have been improved again and again.
  • Sugar cane required heavy crushing equipment and sophisticated boiling, purifying and condensing apparatus.
  • Potatoes were relatively easy, depending more on breeding and transport
  • Vegetable oils, like palm and sunflower and corn, depended on mills and solvents, purifying and deodorizing
  • Beets needed diffusers, chemicals to precipitate impurities, condensers, centrifuges, and other highly sophisticated equipment, that was then used for cane as well
  • Tomatoes needed canning to become more than a seasonal luxury
  • Bananas needed refrigerated transport to become more than a tropical fruit

Food processing is one of the most sophisticated of technologies requiring huge capital investment, complicated machinery, and the ability to handle large quantities of liquids. An amazing achievement.

New food crops may emerge with new ways of processing

There is no reason to think that, like sugar beet or sunflower, formerly unimportant plants will not become important with new processing methods.

Nor is there any reason to think that a given food crop will not become the source for a new food commodity.

What does the rise and fall of food crops say about preserving genetic diversity?

I am completely in agreement that the pair of articles that prompted this post offer reasons for “considering the underlying genetic diversity of important food crops an important public good,”

I am, though, a bit confused about why we fasten on today’s food crops.  Given our accelerating abilities to change plants into food, we simply don’t know what other crops will become important food crops with new methods of processing, with new forms of transport, and with new packaging.

Or am I missing something?


*For quick summaries, try Jeremy Cherfas on The Salt, NPR’s food site or Jayson Lusk conclusion:

what we think of as “our” cultural foods are probably relatively recent historical constructs.  Second, one of the reasons people eat more similarly to each other across the world is that we are now all eating each other’s foodstuffs.  We’ve taken the best from each country and culture and exported it everywhere, and as a result have more diverse diets.  Finally, this trade has forestalled the doom-and-gloom Malthusian concern, as there has been a near universal increase in calorie availability worldwide.





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