On a hot summer day around 10,000 years ago, in the Fertile Crescent of what’s now the Middle East, a farmer tended their wheat.

This crop was a recent human invention, part of a dramatic agricultural revolution that was sweeping through this part of the ancient world.

But as the farmer went about the tedious routine of weeding their field, and collecting seeds to sow in future seasons, they failed to notice an imposter.

It was a mutant weed that had begun to look a little like wheat, adapting to exploit the efforts of the farmer by disguising itself as a crop.

And the trick worked perfectly.

Not only did the weed blend in well enough to avoid removal, its seeds were also mistakenly collected, meaning its offspring would be grown alongside wheat in future fields, too.

This dupe would have massive long-term consequences for both the weed and the weeder.

It was an entirely new form of mimicry an accidental, human-induced twist on a classic evolutionary process.

Ancient weeds began mimicking early crops again and again over the course of the agricultural revolution, as ancient farmers made similar mistakes in different places at different times.

And it turns out, some of our closest plant friends today actually started out as uninvited guests that hid their true identity From a certain evolutionary point of view, these plants tricked us into domesticating them.

But this mimicry came with a dark side along with some accidental plant friends emerged an accidental plant enemy, too.

The concept of crop mimicry is also known as Vavilovian mimicry, after the Soviet botanist Nikolai Vavilov who first proposed it in the early 20th century.

Vavilov was one of the leading plant scientists of the time, but his story was also one of the most tragic.

His work focused on figuring out where and when our modern crops were first domesticated, as well as how they might be improved in the future.

He traveled to 64 countries on 5 continents to study diverse crops and their wild relatives, collecting local seeds and local knowledge as he went.

He wanted to use these resources in plant-breeding projects that could help feed the world by selecting desired traits from a huge seedbank of biodiversity.

And it was during this work that he first conceived of crop mimicry - the idea that ancient weeds in prehistoric fields may have accidentally been selected by humans to increasingly resemble crops over time.

One plant that he eyed with particular suspicion was domesticated rye.

Rye has been widely grown as a key crop in some parts of the world, but Vavilov noted on his travels that, in others, rye was just an annoying weed that infested wheat and barley fields.

Some of these weedy rye varieties were almost impossible to spot by eye and fully remove.

They often resembled wheat at certain stages of growth, and their seeds were sometimes too similar to tell apart.

Vavilov realized that, as ancient farmers tried to weed out wild rye from their fields generation after generation, they had unintentionally selected for the evolution of ryes that could fool them.

And he proposed that many modern cultivated plants might have begun this same way - as crop mimics whose disguises got too good.

As they were pressured to be more and more crop-like, they eventually just became well, straight-up crops.

In the case of rye, Vavilov thought that intentional cultivation probably began when agriculture spread into more difficult conditions Like colder environments with worse soil, where wheat and barley failed, but the hardier rye weed survived.

This unwanted hitchhiker would have actually turned out to be a lifesaver for the ancient farmers, ending up as a crop in its own right.

Vavilov described domestic plants that started out this way as secondary crops.’ Now, Vavilov’s ideas came from his views on how genetics and inheritance worked topics that were becoming intensely political at the time.

And it might seem strange, but eventually, this botanist found himself facing the personal wrath of Josef Stalin.

See, Vavilov was committed to the basic principles of Darwinian selection and Mendelian inheritance.

Random variation naturally exists in a population, and variations of traits that offer survival and reproductive advantages are favored or selected.’ Either the challenges of the environment are doing the selecting - aka natural selection - or we humans are doing it intentionally - aka artificial selection.

Heritable traits favored by selection are more likely to be passed down genetically to future generations and spread throughout the population, resulting in change over time.

This simple process is enough to turn weeds into crop-mimics, and wolves into chihuahuas.

But in the 1930s, the Soviet Union largely rejected the concepts of genes and selection, replacing them with a new pseudoscience that became the official state ideology of biology.

The idea was that new heritable traits could be acquired in an individual’s lifetime - and that what really brought about change was an individual’s experiences and material conditions, not their genetics.

Like, if you expose seeds to cold conditions, they become educated’ to grow better in the cold, and pass those acquired traits on to the next generation.

Vavilov was an influential figure, so his open dissent from this state-sponsored pseudoscience led to his arrest in a field in Ukraine while out collecting seeds in 1940.

Less than three years later, the man who wanted to feed the world died of starvation in prison.

But Vavilov was right about the mechanisms of selection and inheritance.

And his suspicions that rye might be an accidental result of them turned out to be correct, as well.

Today, both archeological and genetic evidence point to domestic rye having started out as a weed and evolved in the three phases that Vavilov predicted.

First, around 10,000 years ago, its wild ancestor found itself in and around new wheat and barley fields as early agricultural systems developed in the Fertile Crescent.

Within just two thousand years, archeological evidence from what’s now Turkey shows that it had become a weedy mimic: small quantities of rye grains show up mixed in with domestic wheat, and look a lot like it, too.

Compared to its wild ancestor, the weedy rye evolved larger seeds that were more firmly attached to the plant and at some point even switched when it produced seeds to match the life cycle of wheat and barley.

And in this region, around 5,000 years ago, we see evidence of the final stage that Vavilov predicted.

Rye grains began showing up in large amounts as agriculture expanded into Europe - signaling more intentional cultivation as the weed proved its value in harsher, colder climates.

There, rye became an official secondary domesticate - a plant that began as an annoyance, morphed into an imposter, but eventually grew on us.

And rye wasn’t alone.

Vavilov also correctly proposed that oats - an even more widely-grown modern crop - emerged from this process, too.

Evidence suggests that the common oat transitioned from a weedy mimic to a crop later in the agricultural revolution, around 3000 years ago in Europe, under similar tough conditions.

Both plants ended up becoming vital for some farmers in some places, favored even over the crops that they had evolved to mimic!

But not all of these mimics ended up on such good terms with us humans.

And even more recently than rye and oats, just 1000 years ago in the rice paddies of China, this process helped create a monster.

Its scientific name is Echinochloa crus-galli, also known as barnyard grass, and today it’s considered to be one of the world’s worst weeds.

It’s native to tropical Asia, where it formed an unhealthy attachment to domesticated rice that has now carried it across the globe.

It infests paddies, contaminates their seeds with its own, and hogs key soil nutrients, often reducing rice yields by more than 35%.

Seeing as we rely on rice to feed literally billions of people, barnyard grass is a huge problem in modern agriculture.

Now, it comes in both mimic and non-mimic forms.

The wild plant seedlings have drooping leaves and crooked stems tinged red or purple.

But the mimics grow straighter and more compact, with upright leaves and green stems - giving them a strong resemblance to rice seedlings.

And in 2019, researchers in China published a paper that revealed the origin story of barnyard grass in more detail than for any previous case of crop-mimicry.

They compared the genomes of hundreds of individuals - both mimics and non-mimics - from across the Yangtze River basin region of China.

This is where rice was first domesticated and has been grown for thousands of years.

And they found that the region’s barnyard grass-mimics all descend from a single origin around 1000 years ago.

This is well-within recorded history, unlike the other, more ancient cases of crop-mimicry.

So the researchers were even able to match this evolutionary shift with a known historical trigger - a cultural shift that forever changed the DNA of the local plants See, according to Chinese historical records, this was also a time of massive societal change.

The Yangtze River basin became the economic center of the ruling Song Dynasty right around this time.

This spurred rapid population growth in the region that, in turn, massively increased rice cultivation.

So perhaps it’s not surprising that this was also when the region’s rice-mimics emerged.

The intensification of rice production would have led to more intense selection pressure on the local weeds that were constantly being detected and removed, encouraging the evolution of rice-mimicry.

And once a mimic emerged that was good enough to fool the farmers, its descendants spread through the entire region.

The researchers identified 87 genes related to shape and structure that seem to have undergone significant changes in the mimics since they arose a millennium ago.

These included a gene called Lazy1, which is important for determining the angle at which a plant’s side shoots develop from the main stem.

The researchers found a strong signal of past human selection on this gene, favoring variants that gave the weed a more upright, compact, rice-like look.

And today, 1000 years later, rice farmers are still regularly fooled by this disguise.

At its core, Vavilovian mimicry is a simple process that comes almost inevitably from the interplay of variation, selection, and generations of human mistakes.

Despite all of our planning and intention, we reap what we sow whether that’s crops, weeds, or something in between.