DNA reveals how the chicken crossed the sea

Ancient Polynesians may have brought birds to the Americas.

The discovery of chicken bones with Polynesian DNA at an archaeological site in Chile has added hard, physical evidence to the controversial theory that ancient seafarers from the south Pacific visited the New World long before Columbus.

When the Spanish conquistador Francisco Pizarro first visited Peru in 1532, he noted the importance of chickens in the daily lives and religious rituals of the Incas. But how the birds got there was a mystery. Chickens were first domesticated in Asia, and their absence from archaeological sites in the Americas indicates that they were not carried by migrating peoples over a land bridge from Asia to Alaska.

One alternative theory — that Polynesians visited the Americas, bringing livestock with them and perhaps influencing cultural and technological development in the region — has long been disparaged by mainstream archaeologists, as it has largely been supported by supposition rather than evidence.

So Alice Storey of the University of Auckland, New Zealand, was not particularly enthusiastic when a colleague in Chile asked her to sequence DNA from a trove of ancient chicken bones he had excavated at El Arenal, a site occupied between 700 and 1390 AD, to see if their origins could be traced to the Pacific islands. “I thought, 'Well, we'll give it a go',” she says.

It's all relative: Chile's Araucana chicken shares its DNA with ancient birds from Polynesia. Credit: DEREK SASAKI/WWW.MYPETCHICKEN.COM

Storey and her team reconstructed a 400-base-pair fragment of mitochondrial DNA from both the Chilean bones and chicken bones excavated on five archipelagos in Polynesia. Mitochondrial DNA doesn't mutate much and so is useful for tracing evolutionary lines. The Chilean sequences were identical to those from prehistoric sites in Tonga and Samoa (A. A. Storey et al. Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0703993104; 2007). Radiocarbon analysis dated the bones to between 1304 and 1424 AD, firmly before Europeans arrived on the east coast of South America in the 1500s. The same sequences are also present in the modern-day Araucana chicken, an odd Chilean breed that has tufted 'ears', lays blue eggs and lacks a tail.

The study has left the research community cautiously optimistic that hard evidence for migration of Polynesians has been found. Jaime Gongora, a molecular geneticist at the University of Sydney, Australia, says the paper is a significant contribution to the field, but warns that the small fragments obtained from ancient DNA may tell only part of the story. The final verdict will require more extensive DNA data to make a full family tree of both modern and ancient breeds, he says.

“It's essentially unequivocal evidence.”

Archaeologist Terry Jones at California Polytechnic State University in San Luis Obispo, who has studied prehistoric Polynesian contact in the New World, is less circumspect. “It's essentially unequivocal evidence,” he says.

Evidence of contact between the communities has been put forward in the past. In 1947, Thor Heyerdahl famously filmed his journey by raft from Peru across the Pacific to try to prove that South Americans could have settled the Pacific islands; although the theory was at odds with much of the evidence.

More recently, Jones, along with Kathryn Klar at the University of California, Berkeley, has argued that the Polynesians introduced complex fish hooks and sewn plank canoes to the Chumash and Gabrielino Indians in southern California and the Mapuche Indians in Chile (K. A. Klar and T. L. Jones Am. Antiquity 70, 457–484; 2005). Others argue that Polynesians must have visited the tropical coast of South America in order to bring back the sweet potato and the bottle gourd. The voyage to South America is no more daunting than other trips Polynesians are known to have made.

Even so, one of the co-authors on the chicken study, Atholl Anderson at the Australian National University, Canberra, is wary of overestimating the extent of this cultural diffusion without further study. Although the chickens provide hard evidence of transoceanic contact, the evidence that large-scale cultural exchange occurred remains largely circumstantial, he says.

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Borrell, B. DNA reveals how the chicken crossed the sea. Nature 447, 620–621 (2007). https://doi.org/10.1038/447620b

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