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Will DNA Swabs Launch CSI: Cargo Scene Investigation?
13 October 2011 1:11 pm
Ceramic jugs known as amphorae were the cardboard boxes of ancient Greece. Produced in the millions, they contained goods that were shipped across the Mediterranean and beyond. But what was in them? In a new study that uses a DNA-based method inspired by crime-scene protocols, scientists say they've uncovered a cornucopia of cargoes, but other researchers are skeptical of the technique.
Shipwrecks and other sites have yielded plenty of intact amphorae. Maddeningly, nearly all are empty, devoid of obvious clues to what they once held. Researchers have scraped bits of ceramic from the vessel's interior to look for leftover genetic material. In the new study, however, they also turned to a less destructive method straight from television's CSI: swiping the amphorae with a swab. The idea came from the Massachusetts State Police, whom the investigators called for leads.
A team led by maritime archaeologist Brendan Foley of the Woods Hole Oceanographic Institution tested the new protocol on nine 5th to 3rd century B.C.E. amphorae that had been languishing in a government storage room in Athens for more than a decade. All had been hauled up in fishermen's nets before being handed over to the Greek government in the 1990s.
To reveal what the vessels once held, the researchers collected DNA from the amphorae and mixed it with snippets of DNA from a selection of plants. When amphora DNA stuck to one of these genetic probes, the investigators knew they'd found a match. The scientists also sequenced amphora DNA, then searched a DNA database for the same sequences.
The results, published online last week by the Journal of Archaeological Science, suggest that swabbing works better than shaving the ceramic. And the data seem to show something less surprising as well: The ancient Greeks really liked olive oil. The team found that olive oil, olives, or some combination of the two were even more common in the amphorae than grape products such as wine. Many of the amphorae also had traces of DNA from oregano, thyme, or mint, which may have been used to flavor and preserve foods. Most common of all was DNA from the juniper bush, "not something you typically think of in the ancient Greek diet," Foley says. "Maybe a whole lot of juniper berries were added to food and drink in the ancient world."
Eight of the nine amphorae bore DNA from a complex mixture of foods, leading Foley to support the argument made by some scholars that amphorae were reused for maritime trade rather than being discarded after one voyage. He also argues that the findings show that rather than shipping single commodities, Greek merchants were trading in "value added" items, the ancient Greek version of the prepared-food aisle in the supermarket. The findings "open up a whole series of questions about the way the first economies, the first markets actually worked," he says.
Although Foley's team took careful steps to avoid contamination, one scientist is dubious that the technique worked as advertised. It is "remarkable" that the amphora "should release endogenous DNA by simply swabbing the surface," Oliver Craig of the University of York in the United Kingdom said via e-mail. Craig, who specializes in recovering DNA and other molecules from ancient artifacts, would need to see more control tests to be convinced.
But if the technique is validated, it would be a valuable tool, say archaeologists not connected with the study. "If that [analysis] can be done on just any old jar lying around a store room for a long time, that's great," says Mark Lawall, an amphora specialist at the University of Manitoba in Canada. It could allow researchers to pin down the contents of amphorae found on a specific shipwreck, for instance, and then calculate the value of the ship's cargo-offering deeper insight into ancient economies.