Hunting for the ancient lost farms of North America


Losing a crop

Pe005b 300x355A beautiful sample of wild erect knotweed, found in Kentucky along the Red River.

Perhaps the strangest part of this story is the fact that people simply stopped cultivating so many crops that were central to their diets. Imagine what would happen if we decided to abandon wheat to the wilderness. Suddenly, there would be no more baguettes and pastas—not to mention cakes. Sure, we could make delicious breads from corn and tasty noodles from rice or beans. But for many of us, it would feel like an incredible loss of a comforting staple. No doubt, that’s how the loss of knotweed felt to aboriginal Americans, too.

It’s likely that the Eastern Agricultural Complex (EAC)—a catch-all term for the lost crops of North America—faded away slowly. Though we can't be sure what triggered its decline, Mueller thinks it may have suffered its first blow from one of the most popular crops in the Americas: maize, which came north from Mexico about a millennium ago.

Maize is an amazing crop,” Mueller said. “All over the world, when it arrives, people give up their old crops and start growing it. It’s productive and has lots of sugar so it gives you quick energy.” By the time Cahokia was at its height in the 1000s, maize was already edging out crops like erect knotweed.

But the death knell for erect knotweed probably came from Europe. Archaeologists find no more examples of domesticated erect knotweed after colonists began to settle the Americas in the 1400s, destroying local civilizations as they went. “There was so much displacement, disease, and warfare over the next couple hundred years that a lot of knowledge was lost,” Mueller explained.

Still, a lot can be learned from America’s lost crops, and it’s not just about finding the next quinoa for health-food nerds. Mueller has been working with Smithsonian Institute anthropologist Logan Kistler to sequence the genomes of lost domesticates. He’s fascinated by how many of these crops went through an entire cycle of domestication and re-wilding in the past few thousand years. Most plants that we eat, from wheat and barley to dates and beans, were domesticated more than 10,000 years ago and never went back. The EAC offers an unprecedented glimpse at what happens to plants when we turn them into food crops. And these domestication events are recent enough that we can get good genomic material from samples.

We have a fairly good sense of how domestication affects animal species over time. Domesticated pigs, horses, dogs, and even humans have all undergone physical changes, often described as “paedomorphosis,” which means retaining infantile body features (softer faces, smaller bodies) throughout life. But we’re just starting to understand plant domestication. “These crops have a good archaeological record that's well preserved,” Kistler said. “It gives us a chance to study domestication in real time, with a good record of what comes in between wild and domestic varieties.”

The EAC is also exciting for Kistler because it represents a diverse group of plants. Until recently, archaeo-botanists looked mostly at domestic plants emerging in the Fertile Crescent over 10,000 years ago during the Neolithic—but these are just grasses and legumes. In the Americas, Kistler explained, “We’ve got five good domesticated species. They’re taxonomically extremely diverse and yet grown in same fields and harvested at the same time. It builds in a little bit of control for looking at multiple species.”

Once he’s been able to sequence these crops, we may begin to see common domestication patterns across plant species. Likely they’ll be things like fast germination and larger fruit size, but we may find some surprises, too.

For Mueller, the search for erect knotweed isn’t just about understanding the mechanisms of domestication. It’s also about coming to terms with everything we’ve lost.

I want to identify as many populations of these species as possible before they go extinct, because they are all threatened,” she said. She’s learned about how ancient people encountered these plants and how they incorporated them into their lives. But she’s also learned about how much the American landscape is still changing.

I was out from October to November, driving around looking for populations of these plants. Partly it’s based on records from botanists going back at least 100 years.” Sometimes plants are still growing where they were a century ago, she said, but sometimes they aren’t.

You realize how much the land has changed even in 100 years,” Mueller reflected. “There are so few places for native species to grow.”