• March 2011
    M T W T F S S
    « Feb   Apr »
  • This work is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License.

  • Advertisements

Top articles Febuary 2011: Wilmshurst et al., High-precision radiocarbon dating shows recent and rapid initial human colonization of East Polynesia

A German version can be found here.

I wish journal editors would insist on short titles for articles *sigh*. But anyway, my second article in the top 3 list is a publication on the colonization of Eastern Polynesia. Four top-class scientist came together to re-examine and evaluate radiocarbon data to get a better picture of the colonization of Eastern Polynesia: Janet Wilmshurst from the government owned Landcare Research, an environmental and research organisation in New Zealand; Wilmshurst is probably best known for her work on Pacific rats but has a wide field of interests, Terry Hunt from the Anthropology Department at University of Hawaii, who is engaged in ongoing research on Rapa Nui, Carl Lipo from the Department of Anthropology in Long Beach and co-founder of the IIRMES institute whose  interest in development of theoretical models to study patterns of change clearly showed in this article, and last not least Atholl Anderson from the ANU college of Asia & the Pacific, who is currently directing a major program on Initial Colonization in the Indo-Pacific Region.

There has been a long debate about how and in which time frame Polynesia has been settled with various partially contradicting theories. To address the conflicting chronologies Wilmshurst et al. reverted to a simple yet as it showed, extremely effective method. They sighted the available radiocarbon dates and sorted them into reliability classes. The most reliable data (which the authors named “class 1”) from short lived plants and terrestrial bird eggshells with marginal errors (to circumvent the substantial wiggle in the calibration curve) were then contrasted to less reliable radiocarbon dates, partially taken from samples without any connection materials or commensals like the Pacific rat.

This was the general view of colonization dates for Polynesia (photo from a poster display at the Bishop museum, Honolulu):

 Presuming a starting point in Samoa and Tonga from which the settlement of the Eastern islands started around 800 BC (Wilmshurst et al. 2011, 1818) Wilmshurst et al. could demonstrate that class 1 data had a very short chronology of settlement for all islands including far off ones like Rapa Nui and New Zealand. In short, the authors could establish two migrational phases: a first one to the Society Islands and possibly as far as Gambier at around AD 1025 to 1121 (orange shading on the map) and a second one to every other island in East Polynesia at AD 1200 to 1290.

Wilmshurst et al. 2011, fig.1

Their findings will have an immense impact on studies of settlement patterns in Polynesia. Some chronologies could be confirmed (e.g. New Zealand and Rapa Nui) other colonizing chronologies were shortened and pushed back in date by several hundred years (e.g. the Marquesas, Hawaiian archipelago). The most astonishing result from their study is the uniform timing of the expansion to even the remotest islands like Auckland Island, Hawaii, or Rapa Nui.

The authors then offer different cultural based explanations for the new settlement chronology like population growth, purposeful explorations with the help of technical innovations but also environmental factors or disasters; they here mention the peak El Niño in the 13th century but one can also think of volcanic eruptions although the source eruption for the AD 1259 eruption is still unknown and the Kaharoa, New Zealand eruption dates to the early 14th century and is therefore too late to be taken into consideration.

In a final point they address problems that need urgent reconsideration in respect of the new data set, as there are:

  • introduction of sweet potatoes
  • linguistics
  • artefact similarities
  • human impact on island ecosystems (deforestation, plant and animal extinctions)

Their list could be expanded to genetics (cp. Brewis et al. 1995, Asia Pacific J Clin Nutr 4, 361-5), appearance and stylistic of monumental architecture, dating of rock art to name but a few. There is hope,  that this will be a stimulus to new research into these problems in order to re-analyse present conceptions.

Overall an excellent article that showed how you can make a big step forward in a stagnating topic just by reviewing radiocarbon dates. I was very surprised to find that five islands completely lacked class 1 data and apart from New Zealand reliable radiocarbon dates are the exception instead of the rule. It also reminds us to question the reliability of C14 dates anew when trying to establish cultural development over time.

Only two minor points of critique are left on my side. One is the idea of el Niño events as driving force behind the direction of colonization. Already in the first phase migrations spread considerably to the east, while only very mild el Niño effects have been described for this period (Crowley 2000, Science 289, 2707; Mann et al. 2003, Eos 84, 256-8); The second phase is marked by a spread not only towards the east, but also towards the north and southwest. Since colonization happened within a very short period of time as the authors have demonstrated, it is unlikely that increased westerly and/or easterly winds could be responsible alone.

The second is the attribution of the island of Rapa Nui to the second phase of colonization. In fig . 3 of the article they compare the radiocarbon dates and Rapa Nui has nearly as early dates as Gambier and the Society islands. In my view they could also qualify for the early phase. Besides, if we are considering the normal oceanic circulation

 (see picture), then the equatorial counter current would have brought a maritime sailor right to the border of the American continent and hence also possibly to Rapa Nui.

 I want to conclude with a citation by the authors:

“…previously supported implications that there was a long period of relatively benign interaction among humans, rats, dogs, pigs, and indigenous vertebrates now need revision, as our refined model of colonization chronology suggests that impacts had to have been immediate, severe, and continuous.”

Maybe we can learn something for our future, because this is exactly what human impact always seems to be: immediate, severe, and continuous.

Full citation of article: J M Wilmshurst, T L Hunt, C P Lipo, and A J Anderson, High-precision radiocarbon dating shows recent and rapid initial human colonization of East Polynesia, PNAS 108 (5), 2011, 1815-20.

This article is available online through the PNAS open access option.

Leave a comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: