Natural Science Forum / Biology / Paleontology / June 2004

Rat DNA clues to sea migration

Scientists have used DNA from rats to trace migration patterns of the
ancestors of today's Polynesians.
People are thought to have arrived in Polynesia, comprising the Pacific
islands of Fiji, Tonga and Samoa, by boat some 3,000 years ago.

Rat data suggests the journey was more complex than the popular "Express
Train" theory, which proposes a rapid dispersal of people from South Asia.

Details appear in Proceedings of the National Academy of Sciences.

Elizabeth Matisoo-Smith and Judith Robins from the University of Auckland,
New Zealand, analysed variation in the DNA of the Pacific rat (Rattus
exulans).

The genetic material was extracted from cell structures called mitochondria
rather than the nucleus.

Mitochondrial DNA (mtDNA) changes at a steady rate over time, so the
scientists were also able to use it to track changes in the rat population
over time.

Rats on a ship

They found clear geographic patterns of rat DNA across Oceania. Rats appear
in a region known as Near Oceania, which comprises the island of New Guinea,
the Solomon Islands and Bougainville, after 3,500 years ago.

They apparently hitched a ride on boats used by ancient seafarers known as
the Lapita, a people regarded by many researchers as ancestors of modern-day
Polynesians.

The rat mtDNA types fell into three haplogroups, or types: I, II and III.
Haplogroup I is found primarily in South-East Asia. Haplogroup II was found
in South-East Asia and a region known as Near Oceania.

Haplogroup III is only found in an area known as remote Oceania, comprising
the islands of Vanuatu, Fiji and Samoa.

The researchers claim this result allows them to reject two well-known
theories for the colonisation of Polynesia, including the Express Train To
Polynesia (ETP) theory and the Bismarck Archipelago Indigenous Inhabitants
(BAII) theory.

These two theories are at opposite ends of the spectrum. The ETP theory
focuses on a rapid dispersal from Taiwan to Polynesia. The BAII proposes
that there was no migration into Near Oceania, and that the Lapita culture
arose from indigenous people in the area.

Matisoo-Smith and Robins argue that the truth was somewhere in-between.

The absence of Haplogroup III rats from Near Oceania seems to preclude a
progressive expansion from that area into Remote Oceania where Haplogroup
III rats are common.

Instead, the researchers claim, the seafarers who brought Haplogroup III
rats to Remote Oceania did not come from nearby New Guinea or the Solomon
Islands but from close to the Asian mainland, completely by-passing Near
Oceania.

From BBC
http://news.bbc.co.uk/2/hi/science/nature/3784759.stm