News: DNA reveals how the chicken crossed the sea.

Nature
Published online: 5 June 2007; | doi:10.1038/447620b
DNA reveals how the chicken crossed the sea
Ancient Polynesians may have brought birds to the Americas.

Brendan Borrell

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.

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.

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.

--
Bob.

.

Relevant Pages

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