Monday 13 July 2020

Thor woz right

One of the formative books of my sub-teen life, along with Triffids, was Thor Heyerdahl's Kon-Tiki: Across the Pacific in a Raft [Kon-Tiki ekspedisjonen]. The common theme is a self-sufficiency adventure involving a small group of people leaving the civilised masses behind. They made a film of the book a few years ago which was a fair telling of the story; and which we got to see.  I saw a 1:1 replica of Kon-Tiki [the original being destroyed in the climactic crash-landing] when I was teaching in Oslo in the late 90s.

Heyerdahl's theory was that South Americans had travelled across the Pacific to land on RapaNui  hundreds of years before Europeans had arrived to impose their name Easter Island. This outsider's theory was met with harrrmphing immediate dismissal by the anthropological inner circle, including my hero Wade Davis. Why, everyone knew that Polynesians had island-hopped their way from Asia to people pretty much every speck of dry-land in the vast wet stormy expanses of the Pacific Ocean.  Eee, they were quite cross. But distant drums of evidence have been accumulating that at least part of Heyerdahl's thesis is probably true. Chickens went East, sweet-potato Ipomoea went West. Some hold that Ipomoea made it without human help, like floating coconuts, but only Gary Larson could imagine Polynesian chickens in canoes [he hasn't yet].

One of the themes on The Blob is the rolling triumph of DNA evidence in shining light on the history of the world. There is a quiet sense of vindication for me because I spent 10 years of my early scientific life using [present day] genetics to trace the history of colonial migration in the 16thC and 17thC. Sequence analysis has shown that whales are streamlined hippos; there is more than one giraffe;  ditto elephant. The last 25 years has seen really careful lab work coupled with really nifty big-byte software develop a shining signal from really old, really degraded, really noisy, DNA samples. One of the drivers of the rise and focus of spotlight DNA is Dan Bradley at my Alma Mater Genetics TCD; most recently the bus has been in the capable hands of Lara Cassidy who has been revealing where Irish people are buried. At the end of June they were documenting incest and trisomy 23 in the ruling classes of Neolithic Ireland 5,000 years ago. The incest was revealed by showing longer chunks of similar DNA sequence than you'd expect if Mammy and Dad were unrelated.
Now, on the other side of the World, analysis of DNA extracted from present day inhabitants of Europe, South America and Polynesia is firming up the foundations [N&V] for Westwards travel in the Pacific. Title says it all: Native South Americans were early inhabitants of Polynesia. Heyerdahl's expedition was in the spirit of Elon Musk's SpaceX project: all ya gotta do is get there; getting back is a another day's work. It's looking a lot like there was traffic back and forth across the featureless ocean between the Marquesas, Rapa Nui and Colombia. The first author of the Nature paper Alexander G. Ioannidis is from Stanford; I can't easily establish if he's related to John Ioannidis [bloboprev] of the same institution.

The methods used by Ioannidis, A. and Andres Moreno for Pacific peopling are very similar to those of Cassidy and Bradley for Neolithic Ireland. These analyses are a bit above my simple-mind pay-grade but it looks like the granularity of the genomic chunks is key to determining how long ago they were "admixed".  For Ireland the sequence of brother and sister appear in long contiguous stretches across the chromosomes: that says 20 years of separation. In the Pacific they can date the timing of the arrival >!KaPooof!< of the first South American in the Marquesas to 800 years ago from the size of characteristic S.American DNA chunks. Intriguingly that's the best estimate of the time that Polynesians extended their range to Rapa Nui 3,000km south-by-east. These dates can be calibrated by the presence of larger lumps of European DNA in the plain people of Rapa Nui today. That cannot have happened before 1722. And in Rapa Nui, which was annexed by Chile in 1888, the genetic waters are further muddied by Native South American genes arriving with Chilean army conscripts.

Needless to say, there will be push-back from those who have a vested interest in tracing history by artefact, or language, or what they learned in graduate school 40 years ago. But, at least as part of an integrated platform involving trad archaeology,
DNA is The Future of The Past

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