The mystery of maize
I live in Mexico so of course I’m obsessed with corn. It’s the foundation of the cuisine and in many ways the culture, and it has been for at least 4,000 years. But there are lots of things scientists don’t know about it, including how and why people bothered domesticating it in the first place. Teosinte, maize’s wild ancestor, isn’t a plant you look at and think “yum.” It has about six kernels per finger-sized cob, each covered in a shell hard enough to break a tooth, and they fall right off the plant once they’re mature. Collecting enough to grind, as you do with corn, seems all but impossible. This week I learned you can pop teosinte kernels, which sounds better but still isn’t a tremendously appealing ratio of effort to calories. Lots of people’s current best guess is that maize née teosinte was first domesticated for its sugary stalks, which could be brewed into beer, or maybe eaten when times were really tough. But no one really knows.
Teosinte is so unappealing as a food, and so unlike maize, that it took about 100 years and the invention of genetics for scientists to accept it was corn’s wild ancestor. In particular they settled on the teosinte subspecies parviglumis, which grows in the western lowlands of Mexico where maize was first domesticated. But this week, researchers announced they’d discovered that all of today’s maize has a second wild ancestor nobody knew about: the highland teosinte mexicana. From my story:
Jeffrey Ross-Ibarra, an evolutionary biologist at the University of California, Davis, started to study the relationship of the mexicana teosinte subspecies to maize in order to understand how the lowland domesticate adapted to the chilly highlands of central Mexico. But, “We kept finding evidence of this second teosinte in other places we looked,” he says. The team examined nearly 1,000 maize genomes from traditional varieties, modern cultivars, and ancient plant remains excavated from the southwestern United States to eastern Brazil. Unexpectedly, mexicana ancestry is “absolutely everywhere,” Ross-Ibarra says. Reconstructions of the maize family tree suggest it first mixed with the highland teosinte between 6,000 and 4,000 years ago. Indeed, the only maize sample the team found without mexicana ancestry was a 5,500-year-old cob from the southern coast of Peru, thousands of kilometers away from where the hybridization was taking place.
Six thousand to 4,000 years ago—that’s an intriguing date range. It’s when people were inventing maize agriculture, which eventually spread all over the place and became the dominant way of life in much of the Americas. And apparently, unbeknownst to scientists until now, all those early farmers were using the new mexicana maize.
But weirdly, nothing stands out as all that different or special about the new maize, at least genetically. Old maize was already pretty good, and new maize was…also pretty good. And yet, it replaced every existing variety across two continents and perhaps lay at the heart of one of the biggest societal transformations in human history. Hmmm!! Ok. What?!
When people find out I’m a science journalist, I think they expect me (via the scientists) to have learned a lot of facts about how the world works. Really, doing this job means discovering just how little we know about almost everything, over and over again. There’s no answer to this maize mystery yet. But suddenly, there are lots of new questions.
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