Out of all of the food eaten by all of the  humans on the entire planet, one half of those calories come from just three  staple crops: maize, wheat, and rice.

But it wasn’t always like this. People used to chow down on all sorts of things.

Some early crops are familiar,  like squashes and sunflowers. But have you ever heard of knotweed?  What about maygrass? Pitseed goosefoot?

In their heyday, these crops did a  fine job sustaining human populations, until circumstances changed,  they fell out of favor, and they were more or less  forgotten… until recently. Scientists are now rediscovering  the foods we used to eat. And these lost crops provide  new insights about our past and can teach us lessons for the future. [♪ INTRO] Lost crops are plants that were at one  point domesticated, but no longer are.

Here in North America, these  are knotweed, sumpweed, little barley, maygrass, and pitseed goosefoot. All five of these plants have living  relatives that look like weeds you might want to remove from your  garden instead of growing on purpose. While they might not look particularly appetizing, they nevertheless served as an important  food source for indigenous Americans.

Important enough that indigenous communities  even started to domesticate them. Evidence of the domestication  of these plants has been found throughout the prairie regions  of what is now the United States, including the states of Tennessee, Kentucky, Ohio, Indiana, Illinois, Missouri, Arkansas, and Iowa. Scientists know that these were at one  point domesticated because the seeds that have been found by archaeologists  and paleobotanists throughout this region look markedly different from the  seeds of their wild relatives.

The domesticated seeds are larger  and have thinner seed coats, both of which make the seeds more  nutritious and easier to eat. The presence of these traits  suggest that people had been purposefully cultivating these plants  to enhance these specific properties. Plus, these seeds have been found by  the millions in large storage pits and in human poop, so those  are some pretty surefire signs that someone had been saving  them up and eating them.

Some of these seeds were found in a cave  in Kentucky as far back as the 1930s. However, at that time, they were  dismissed as being too small to be a major food source and therefore  not worth paying attention to. There are a variety of factors that  likely went into this dismissal.

First, these seeds are quite small. For example, goosefoot is a relative  of quinoa, but has even smaller seeds. And the scientists of the 30s just  could not fathom that people would spend time growing, harvesting, and preparing something so small as a food source.

Additionally, the scientists in the  30s didn’t have the same kinds of tools that scientists have at their disposal now, like radiocarbon dating to  know how old the seeds were. And finally, it seems like  the world was just not ready to change its perception of  how agriculture came to be. See, there’s this big stereotype  when it comes to agriculture, which is that it was invented only a  few times in a few specific places.

At that point in time, the prevailing  belief was that agriculture popped up in Mesopotamia, the Yangtze  River valley, and Mesoamerica, and then spread like wildfire  throughout the world. In the Americas, the belief was that  development and spread of agriculture was tied to the spread of the use of  corn, more precisely referred to as maize. Maize originates from a grass called teosinte.

And that domestication event was absolutely a big deal that would shape the  history and culture of the Americas. But it can’t possibly have been the only big deal. But first, all science needs funding,  including us, so here’s an ad. [midroll] Samples of these lost plant seeds have  been dated back to about 3000 years ago, which predates the arrival of maize  to the North American prairie.

So some form of agriculture must have  arisen in the prairies before maize. The question then becomes: How did Indigenous peoples  cultivate and grow these foods? One of the ideas is based on  the fact that these plants were simply the most abundant  edible plants around.

Some of the living relatives of these  lost crops grow in the river deltas of the Mississippi and Missouri rivers,  which suggests that these ancestral plants would have been abundant and locally available to the Indigenous communities  that lived in these areas. It would make sense, then,  that the plants that are the most available would be the ones that got eaten. And of those abundant plants, people  would likely choose the plants with the largest seeds that  were the easiest to harvest, putting selective pressure on the plants to have certain traits without necessarily meaning to.

Eventually this could have turned into  purposeful selection and cultivation of plants with the best yields that are the easiest  to grow, and lo and behold… agriculture! Another potential early agricultural  scenario involves bison. The living relatives of these  plants can also be found in plains where there are bison, and specifically  only where there are bison.

Some of these plants are reliant  upon the bison to thrive. Only since the reintroduction of bison  to the American prairie in the past few decades has there been substantial  quantities of some of these lost plants. The prairies are a densely populated ecosystem, hard for new seedlings to get a foothold.

But when the bison trample  and eat the tall grasses, these lost crop species will  grow in the newly tilled soil. This tendency is very noticeable  with the lost crop sumpweed, which turns a slight purple color in the fall. That causes the stands of sumpweed  growing together to stick out a bit more, and they tend to overlap with known  bison trails and grazing areas.

In this scenario, the development of  agriculture could have gone something like this: Indigenous Americans  tracked the bison as a food source. They used the well-trodden trails the  giant bison made through the tall grasses to get around, and they would find sumpweed  and other plants along their route. Then they could use these abundant  plants and select for specific traits to make them more palatable and easier to grow.

Together, these ideas paint a new picture  of the development of agriculture, as something more gradual that arose  wherever plants and humans co-existed… rather than a single Big Bang-type  event that then spread far and wide. And while this has been a story  about agriculture in the Americas, similar findings have been made around the world, supporting the idea that agriculture  developed gradually and diffusely. The discovery of these lost crops  not only changes our perception of agriculture’s past, but also may  provide insights for agriculture’s future.

We can learn from these plants  about what makes a good crop. Varieties of these plants can still  be found in the United States, and by using their current forms,  the archaeological remains, and gardening experiments,  researchers can identify what traits and genetic backgrounds might  make a plant more “tame”. Similar to how wolves that were  more tame were permitted closer to human groups, setting the  stage for wolves to become dogs as we know them today, plants  with more “human-friendly” traits were also more likely to be domesticated.

For example, many wild plants  have germination requirements that help tell the seeds  when to grow and when not to. In colder climates, these  germination requirements can include prolonged exposure to cold temperatures, which helps to signal to the plants that winter has come and gone before they  waste precious energy to grow. This sort of germination requirement  is useful for a wild plant, but if humans are collecting seeds and  trying to grow new crops every year, it is much easier to just be able to stick  a seed in the ground and have it grow, without worrying too much about  exposing it to different temperatures.

So if you could artificially select  out that temperature requirement, you’d have a version of the  plant that was easier to grow. In a paper published in Plos ONE in 2023, a team of researchers were able to  show that within a single experimental growing season, the wild version of knotweed  lost these germination requirements. This capability would make it  much easier to grow as a crop.

Along those same lines, plants with  increased flexibility in response to changes in the environment make  for better domesticated crops. Think about two species of plants. With one, it produces the same number  of seeds no matter how you grow it.

You weed around it, you space  it far apart or close together, and it's always the same number of seeds. For the other, when you change  up the way it’s growing, it changes up its shape, size, or  the number of seeds it produces. The second plant would make your life much easier if you were trying to grow it for food.

Instead of waiting for generations  for selection to act on the plants, you could change up the way you’re growing the plant and see how best to get more seeds. And there is evidence that at least  knotweed is capable of doing just that. Knotweed typically grows  along the banks of rivers, where it competes for light  with other weedy plants.

When they are spaced out,  they grow many more branches to take advantage of the new light availability. The seeds are found on these branches, meaning they produce many  more seeds when spaced out. It’s likely that people trying to grow  these plants realized this through some trial and error and were able to  use this flexibility to their advantage.

Given the fact that these plants are  pretty well suited to domestication, it’s not totally clear why they  fell out of agricultural fashion. However, there are some ideas. First, these plants pre-dated  maize in this area of the Americas, which means that eventually maize did turn up.

There is a reason why maize is one  of the most abundant and common foods on the planet - it is easy to grow, it  can be grown in a wide range of climates, and it is extremely versatile. While Indigenous communities  around the Ozarks made significant strides in  domesticating these lost crops, it makes sense that when maize came  around, people made the switch. Additionally, these foods also predated  the appearance of European settlers.

As the Europeans arrived and  expanded throughout the continent, they brought a whole host of diseases and disturbances to the Indigenous  people of the Americas. This disruption to life could have caused  communities to adopt different ways of living in order to survive, and abandon  other ways that were then lost or forgotten. Even though these plants did not persist  as domesticated crops to this day, that doesn’t mean they couldn’t be reinstated.

As the climate changes and puts more  and more pressure on our ability to produce food, these lost crops can not  only inform researchers about what traits make a good crop, they could also serve  as potential new food crops themselves. For example, goosefoot, the quinoa  relative, has a higher yield per acre of edible seed than quinoa  when grown with similar methods. Who knows, maybe goosefoot grain  bowls will be the next big thing. [♪ OUTRO]