Paul Minnis of the University of Oklahoma in Norman is obsessed with a chile seed. He found it buried last summer, two meters below ground, in a pile of trash left behind a millennium ago by indigenous people in northwestern Chihuahua, Mexico. "The chile seed came from a trash deposit under the floor of a room, suggesting it was deposited before the room was built," says Minnis. For this researcher, it offered a keyhole-sized peek at a mysterious past.
Minnis is a professor of archaeology and paleoethnobotany, a field that got its first big boost in the 1960s when archaeologists realized that not all plant remains rot. "Once we started looking for plant remains, we found them," Minnis says. He and his colleague, Michael Whalen...
They sort through the debris they find using a technique called flotation, in which they flood dirt removed from a cooking site or a trash heap—known in archaeology-speak as 'midden'—with water. Plant remains, being lighter than water, float, while the dirt sinks. The researchers use a screen to skim off the floating plant remains, and dry them. "We typically use a bridal veil-type material purchased at a fabric store" as a screen, says Minnis. They then take a close look at the debris, consisting mostly of seeds and charcoal. "I love sorting little, ugly, invisible remains under the microscope."
Using this technique, they have found what these early pueblo dwellers ate, what woods were used as fuel, whether the wood was locally gathered or "imported" from other locations, a metric for settlement. (As a group settles into an area, the people range further and further afield to search for wood.) Seeds are particularly important, as they can reveal whether food was cultivated, imported, or gathered wild. Cultivation shows a certain sophistication, involving both a developing agriculture and a possible transportation network. It's a lot to learn from old trash.
"We don't know specifically how chiles were used at Casas Grandes," Minnis says in an email. "We only have a single cultivated chile seed (and two other seeds that might be chile)." He concludes it belongs to the genus Capsicum on the basis of two anatomical features: a beaked shape where the seed once attached to its plant (hilum) and parallel cells on the seed coat. It was likely cultivated, he reasons, because wild seeds are generally smaller.
"It is interesting because chile became such an important food post-Spanish contact but seems not to have been used prehistorically in the Southwest (except for our single chile seed found last summer)," says Minnis. "The change from pre-contact to post-contact cuisine is especially interesting because of the Mesoamerican crops that could have been grown in the Southwest, all but the chile and tomato arrived in prehistoric times."
Just how old is this seed? Luckily, the trash contained styles of pottery that have been dated before, and Minnis and his team are still performing a radiocarbon date run on the organic material in the trash. (Most of these long ago peoples don't have specific tribal or local names. Distinctive names occur when they become associated with a specific location, like the Mimbres and their pottery.)
It isn't just food the scientists are after. "We found a piece of charred cloth which tells us they cultivated cotton." Minnis adds. The early people of southwestern North America had cultivated cotton and wove it into cloth, implying a society developed past simple agriculture for food. "There are four species of cotton that are cultivatable, two from the old world, two from the new, isn't that neat?"