Some of our most important crops were never intentionally domesticated. They were weeds that evolved to impersonate wheat so well that ancient farmers could not tell them apart. Rye started as an annoying weed in wheat fields but fooled farmers for thousands of years until agriculture spread to colder climates where the weed outperformed the real crop. The Soviet botanist who figured this out, Nikolai Vavilov, was arrested in a field while collecting seeds and died of starvation in prison under Stalin.
Chiswick Chap, CC BY-SA 4.0
The farmer's shadow
Around 10,000 BCE in the Fertile Crescent of the Middle East, the first farmers began cultivating wild grasses. This act of deliberate planting created a new, human-made environment and triggered an evolutionary arms race. The farmers selected for desirable traits in their crops, like wheat (Triticum) and barley (Hordeum vulgare), but they also applied an accidental, or "unconscious," selection pressure on the weeds growing in their fields. This process of a weed evolving to resemble a crop is now called Vavilovian mimicry.
Two weeds in particular became master impersonators: wild rye (Secale) and wild oats (Avena). Early farmers would weed their fields by hand and save seeds for the next season. Any weed that looked too different from the crop was pulled. Any weed seed that was a different size or weight from the crop seed was separated during winnowing. Over many generations, this relentless, albeit unintentional, selection favored individual rye and oat plants that most closely mimicked the wheat and barley. They evolved larger seeds, a more upright growth habit, and a synchronous ripening time. They also evolved a non-shattering rachis—the tough stem that holds the seeds to the plant, a trait of all domesticated grains. This prevented their seeds from scattering before the harvest, ensuring they would be gathered, stored, and replanted right along with the intended crop.
From pest to protagonist
The mimicry was so successful that rye and oats became permanent, unavoidable contaminants in wheat and barley fields. The farmers were duped, accidentally cultivating their own pests. But the story took a turn as agriculture spread from the temperate Fertile Crescent north into the harsher climates of Europe. The pampered wheat and barley crops often struggled in the colder temperatures and poorer soils. The mimic, however, thrived. Rye and oats, being inherently hardier, often produced a better yield than the crop they were impersonating. Farmers in these new regions began to favor the weeds, and these "secondary crops" were born. Archaeological evidence shows rye being cultivated as a crop in its own right by the Bronze Age, around 4,000 years ago.
The botanist who identified this phenomenon was Nikolai Ivanovich Vavilov (1887-1943). He developed the theory of "centers of origin," identifying the geographic areas where domesticated plants first arose and showed the highest genetic diversity. His work it put him in direct opposition to the politically powerful Trofim Lysenko, whose anti-Mendelian ideas were favored by Joseph Stalin. In August 1940, Vavilov was arrested on false charges of spying while on a seed-collecting expedition in Ukraine. He was sentenced to death, a sentence later commuted to 20 years' imprisonment. On January 26, 1943, the man who devoted his life to ending famine died of starvation in a Soviet prison.
💡Fun Facts
Another example of a Vavilovian mimic is gold-of-pleasure (*Camelina sativa*), a weed that evolved seeds of a similar size and density to flax seeds to avoid being sorted out.
Nikolai Vavilov established one of the world's first major seed banks in Leningrad (now St. Petersburg). During the brutal 28-month Siege of Leningrad in World War II, a dozen of his colleagues starved to death while protecting the massive, edible seed collection.
The wild ancestor of cultivated rye, *Secale cereale* subsp. *vavilovii*, is named in his honor.
Barnyard grass (*Echinochloa crus-galli*) is a modern example of Vavilovian mimicry; it has evolved to closely resemble rice seedlings and is now considered one of the world's most problematic agricultural weeds.
