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Probing ancient shipwrecks with DNA

Oct. 15, 2007
Special to World Science  

Stud­y­ing an an­cient Greek ship­wreck, sci­en­tists say, they’ve found they can de­code an­cient DNA to learn about the orig­i­nal con­tents of jars sunk­en for over 2,000 years.

It’s a feat “no one thought was even pos­si­ble,” wrote Ma­ria Hans­son of Lund Uni­vers­ity in Swe­den, one of the re­search­ers, in an e­mail. The disco­very “o­pens up a whole new field of mo­lec­u­lar ar­chae­o­lo­gy,” she added, as sci­en­tists could could use the tech­nique to gain in­sights in­to an­cient ag­ri­cul­ture and trad­ing net­works.

An­cient am­pho­rae, or stor­age jars, at the Chi­os ship­wreck site. (Cour­te­sy Chi­os 2005 Ship­wreck Sur­vey - WHOI, Hel­len­ic Min­is­try of Cul­ture: Eph­or­ate of Un­der­wa­ter An­tiq­ui­ties, Hel­len­ic Cen­ter for Ma­rine Re­search)

An­cient Med­i­ter­ra­nean civ­il­iz­a­tions, some of the world’s ear­li­est, of­ten used ce­ram­ic jars called am­pho­rae as ship­ping con­tain­ers. In­vented by the Ca­naan­ites of the Near East in the 16th cen­tu­ry B.C., am­pho­rae took on var­ied styles in dif­fer­ent re­gions and time pe­ri­ods, wrote Hans­son and a col­league in a pa­per re­port­ing their work.

Piles of am­pho­rae of­ten re­main as lone, mute wit­nesses to an­cient ship­wrecks where the boats them­selves have been long since eat­en away. 

But re­search­ers try­ing to learn the jars’ orig­i­nal con­tents usu­ally come up dry, ac­cord­ing to Hans­son and col­league Bren­dan Fo­ley of the Woods Hole Oce­a­no­gra­phic In­sti­tu­tion in Mas­sa­chu­setts. That’s be­cause the am­pho­rae only in­fre­quent­ly con­tain vis­i­ble clues, such as ol­ive pits.

An­cient DNA molecules, though de­grad­ed with time, could supply some of the needed ev­i­dence, wrote the pair, whose find­ings ap­pear in the ad­vance on­line edi­tion of The Jour­nal of Ar­chae­o­log­i­cal Sci­ence.

The re­search­ers scraped ce­ram­ic from in­side two am­pho­rae from a 4th-cen­tu­ry B.C. ship­wreck found near the Greek is­land of Chi­os in 2004. The wreck, about 60 me­ters (200 feet) un­der­wa­ter, has drawn head­lines be­fore be­cause—being to deep to ex­plore by con­ven­tion­al diving—in­vest­i­ga­t­ors have mapped it using robotic de­vices.

Mod­el of a 4th-century B.C. Greek mer­chant ship based on the Ky­re­nia, a wreck sal­vaged in 1967.

Adding an­oth­er new tech­nol­o­gy to the proj­ect, Hans­son and Fo­ley an­a­lyzed small DNA frag­ments found trapped in the pot­tery. 

They de­ter­mined that one ves­sel probably con­tained ol­ive oil fla­vored with oreg­a­no, a sur­prise be­cause his­to­ri­ans have be­lieved that am­pho­rae of that style from Chi­os usu­ally car­ried wine, they wrote. Chi­os was known for “fine and dis­tinc­tive vin­tages,” they not­ed, but the find sug­gests Chi­an ag­ri­cul­tur­al ex­ports might have been more di­verse than gen­er­ally as­sumed.

The oth­er jar, they wrote, con­tained DNA of mas­tic—a shrub cul­ti­vat­ed on Chi­os—or of pis­ta­chio, a re­lat­ed plant. Schol­ars have hy­poth­e­sized that an­cient Chi­ans used mas­tic res­in as a wine pre­serv­a­tive and fla­vor­ing, Hans­son and Fo­ley wrote. 

Some an­cient foods, they added, are more likely than oth­ers to leave ge­net­ic call­ing cards be­hind. For in­stance, be­cause the sec­ond jar was thought to have likely con­tained wine, they checked for grape DNA, but found none. It may have washed away be­cause wine dis­solves in wa­ter bet­ter than oil or res­in, Hans­son and Fo­ley ob­served. But overall, they wrote, the find­ings “con­tribute de­fi­nite ev­i­dence for Clas­si­cal Greek com­mod­ity ex­change and open new vis­tas for mo­lec­u­lar archeolog­i­cal anal­y­ses.”

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Studying an ancient Greek shipwreck, scientists say, they’ve found they can decode ancient DNA to learn about the original contents of jars left underwater for over 2,000 years. It’s a feat “no one thought was even possible,” wrote Maria Hansson of Lund University in Sweden, one of the researchers, in an email. The discovery “opens up a whole new field of molecular archaeology,” she added, as scientists could could use the technique to gain insights into ancient agriculture and trading networks. Ancient Mediterranean civilizations, some of the world’s earliest, often used ceramic jars called amphorae as shipping containers. Invented by the Canaanites of the Near East in the 16th century B.C., amphorae took on varied styles in different regions and time periods, wrote Hansson and a colleague in a paper reporting their work. Piles of amphorae often remain as the sole, mute witnesses to ancient shipwrecks, the boats themselves having been long since eaten away. But researchers trying to learn the jars’ original contents usually come up dry, wrote Hansson and colleage Brendan Foley of Woods Hole Oceanographic Institution in Massachusetts. That’s because the amphorae only occasionally contain visible clues, such as olive pits. Ancient DNA molecules, though degraded with time, could supply some of the needed evidence, wrote the pair, whose findings appear in the advance online edition of The Journal of Archaeological Science. The researchers scraped ceramic from inside two amphorae from a 4th-century B.C. shipwreck found near the Greek island of Chios in 2004. The wreck, about 60 meters (200 feet) underwater, has already drawn headlines because—being to deep to explore by conventional diving—researchers have mapped it with unusual robotic probes. Adding another new technology to the project, Hansson and Foley analyzed small DNA fragments found trapped in the pottery. They determined that one vessel probably contained olive oil flavored with oregano, a surprise because historians have believed that amphorae of that style from Chios usually carried wine, they wrote. Chios was known for its “fine and distinctive vintages,” they noted, but the find suggests Chian agricultural exports might have been more diverse than generally assumed. The other jar, they wrote, contained DNA of mastic—a shrub cultivated on Chios—or of a related plant, such as pistachio. Scholars have hypothesized that ancient Chians used mastic resin as a wine preservative and flavoring, Hansson and Foley noted. Some ancient foods, they added, are more likely than others to leave genetic calling cards behind. For instance, because the second jar was presumed to have contained wine, they checked for grape DNA, but found none. It may have washed away because wine dissolves in water better than oil or resin, Hansson and Foley observed. But overall, they wrote, the findings “contribute definite evidence for Classical Greek commodity exchange and open new vistas for molecular archeological analyses.”