Say Hello to the Scientist Harvesting Clues About Ancient Gourds and Maize

Archaeologist Logan Kistler explains how he studies the roots of plant domestication

A pile of gourds spilling out of a tipped over container onto a brick floor with a bale of straw in the background.
Modern gourds like pumpkins typically taste sweet, while their wild relatives are incredibly bitter. At the Smithsonian’s National Museum of Natural History, archaeobotanist Logan Kistler studies how cultivated gourds gained their flavor. Bunches and Bits {Karina}, CC BY-NC-ND 2.0

There's always that friend who goes gourd-crazy in the fall. But for some, this seasonal obsession is a lifelong profession.

At the Smithsonian’s National Museum of Natural History, one scientist has made a career of studying ancient gourds and other crops to understand more about the roots of plant domestication.

In this “Meet a SI-entist,” archaeobotanist Logan Kistler shares how he became interested in plant and human relationships and the knowledge he’s harvested along the way.

What started you down the path to researching ancient plants and their genomes?

I grew up in Kentucky near Mammoth Cave, which is an important geologic and cultural site. I did some archaeological research there as part of my college coursework. I also worked there as a park ranger for a couple summers. It started to show me how we can learn about people who lived in the past from the material remains they left behind.

Later, I became intrigued by the crops that feed the world. Almost everybody relies on them. Plant domestication has been such an important process in humanity worldwide. It enabled the social changes that inspired technological development for ancient humans. So, combining archaeology and plant science came naturally to me as I worked on understanding the past.

Logan Kistler conducts research on gourd evolution across South America. One of his sites is based in Brazil. Mato Grosso

You are an archaeologist who studies ancient plants, or an archaeobotanist. But you also look at ancient plant DNA. How do these three fields — archaeology, botany and genomics — overlap?

Archaeology is using material remnants of past societies to learn more about people in different times and places. Archaeobotany is examining all the little pieces of plants people have used in the past, like traces of seeds at archaeological digs, to study past diets. It involves thinking about how patterns in plant use reflect changes over time. And archaeogenomics is using those same plant tissues preserved in archaeological sites and extracting their genetic material to see how they evolved.

So, archaeobotany tracks plants’ changes through their physical characteristics and archaeogenomics looks to the genome to understand what happened to plants in terms of natural selection and evolution.

All of these can tell us more about human-environment interactions and how non-human species have evolved alongside people.

One common example of a human-environment interaction is plant domestication. But that process hasn’t been quick or easy historically. What does it involve?

Overall, plant domestication is a process where humans first change a landscape. Then, plants move into that landscape and evolve to be more fit in the human environment. It’s a mutualistic evolution of plants in a human environment — or a symbiotic relationship. Humans get a stable food supply and plants are reliably planted, ensuring their species exists for another generation.

You’ve done a lot of research on the modern gourds we eat today and their non-cultivated counterparts. How did crops like pumpkins, butternut squash and spaghetti squash evolve through this type of mutualistic interaction?

Ancient megafauna like mastodons ate wild gourds. Through their dung, they spread gourd seeds around the Americas. Regina Hart, no changes made, CC BY 2.0

A few years ago, we were looking into the domestication of squashes and pumpkins, which come from all over the Americas and show up pretty early in the archaeological record, about 10 thousand years ago. If you look at gourds in the wild, they’re about the size of baseballs and are hard as a rock. They’re extremely bitter and moderately toxic. But from these horrible things, you get today’s squashes, gourds and zucchini.

To understand gourd domestication, our team ran several analyses. The findings suggested the natural history of the plant was that it was dispersed by large megafauna herbivores, like mastodons, through their dung. But when megafauna went extinct, the gourds were left without an ecological partner to eat them and distribute their seeds across the landscape. Onto the scene came humans, creating disturbed habitats and developing a new niche for these wild gourds. This arrival offered an opportunity for the gourds to adapt. So, the plants evolved to be palatable for humans to ensure they’d continue to be planted and survive.

Crop survival is a hot topic now because of the climate crisis. Where does your work on past plant domestication and biodiversity fit into the ongoing conversation about agriculture challenges in our rapidly warming world?

While research we do on the past will not solve the climate crisis, it does highlight how traditional Indigenous farmers have maintained biodiversity, prioritized ecological management and created sustainable food systems in part by using biodiversity.

From our research, we can see that the knowledge and activities of traditional farmers led to a situation where most domesticated plants we now cultivate have as much diversity as they originally did in the wild. There was very little loss of diversity during this process. It’s more of a re-shaping of populations.

Analyzing ancient DNA from maize has allowed Logan Kistler and his colleagues to understand more about how the plant species was domesticated. Thomas Harper, The Pennsylvania State University

Take domesticated maize, which evolved in landscapes over millennia, and has significant genetic diversity. Compare that to the corn grown in the Midwest. That corn is hugely important worldwide, but has low genetic diversity, which makes it vulnerable. It’s the same principle as what happened with the potato famine in Ireland. When you grow from a very small genetic subset of a crop, you have no natural resistance to threats sometimes.

Basically, there is resilience in genetic diversity. That’s one of the most important lessons that we should be thinking about today. We should be looking to Indigenous knowledge and expertise in this space, because folks have been managing sustainable food systems while maintaining ecological biodiversity for millennia. Biodiversity is not the only solution to food security as our climate crisis intensifies, but it’s an important piece of the puzzle.

This interview has been edited for length and clarity.

Meet a SI-entist: The Smithsonian is so much more than its world-renowned exhibits and artifacts. It is a hub of scientific exploration for hundreds of researchers from around the world. Once a month, we’ll introduce you to a Smithsonian Institution scientist (or SI-entist) and the fascinating work they do behind the scenes at the National Museum of Natural History.

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