The Japan Times, January 25, 1999
By SARA ABDULLA
Nature News Service
Hitchhiking lizard's guide to the Pacific
A small lizard (Lipinia noctua) may have provided the solution to the long-running controversy of how humans colonized the islands of the central and eastern Pacific - a question that could also contain important clues to how other human cultures evolved.
The lizard can be found all over the Pacific region, an area larger than all the continents put together. So the betting is that it has humans to thank for its staggeringly broad distribution. Unless they were prodigious swimmers, L. noctua's forbears were probably stowaways in the first settlers' canoes.
With this in mind, Christopher Austin of the Institute of Statistical Mathematics, Tokyo, Japan, and the South Australian Museum, Adelaide, Australia, has carried out a genetic analysis of 29 L. noctua lizards from 15 different island populations. He reported in the Jan. 14 issue of Nature that, on the evidence of the short DNA sections he compared, the lizard populations seem very closely related.
Broadly speaking, archaeology, linguistics and genetics have come up with two main theories on how Oceania was colonized. The "express train" hypothesis, first proposed a decade ago (in Nature) by Jared Diamond of the University of California, Los Angeles, argues that people moved from Taiwan to the Bismarck archipelago between about 3500 B.C. and 1600 B.C., after which it is thought they spread out to Fiji, Samoa and Tonga within only a few hundred years. In evolutionary terms, both these migration phases were so rapid that they allowed little time for genetic exchange with any populations that the colonialists passed along the way.
The "entangled bank" theory, on the other hand, is the argument that movement of humans into the Pacific islands (the last parts of the world to be colonized) was far more gradual and drew on more diverse populations.
Austin's discovery indicates that the express-train colonization hypothesis, rather than the entangled bank hypothesis, best describes how this area became inhabited.
The striking genetic similarity of the lizards studied (all the animals differed by two or less units, or base pairs, of genetic code) suggests that, like the humans they hitched rides with, the modern lizards' vagrant ancestors had little time for genetic mingling during their passage. Moreover, lizards in the geographically distinct region of Kapingamari in Micronesia, where people are ethnically Polynesian rather than Micronesian, are also closely related to those elsewhere in the Pacific, whereas lizards in other parts of Micronesia show considerable genetic diversity.
This, Austin believes, "strengthens the association between L. noctua and human colonization."
Austin speculates that by DNA-typing lizards from the areas assumed to be possible starting points of the express train, genetic sleuthing could soon settle another contentious question of human migration: where the express train started its journey.