The Indonesian cline

By Razib Khan | March 11, 2012 2:34 pm

Dienekes has touched upon it in detail, so I don’t have much to add. Except for two points:

1) The ancestry cline here is not due to isolation-by-distance, but the expansion of the Austronesian population rather precipitously ~4,000 years ago. As Dienekes observed this was rather clear by non-genetic means; this is just icing on the cake.

2) There is evidence of an Austro-Asiatic substrate across maritime Southeast Asia. For whatever reason it seems that Austro-Asiatic speaking agriculturalists ceased their push east at the Wallace Line.

MORE ABOUT: Southeast Asia
  • http://www.eurasian-sensation.blogspot.com Eurasian Sensation

    I guess the question this raises for me is: What happened to all the Papuans/Negritos in Western Indonesia? Clearly there must have been some there at some point.

    A clue might be in the Austro-Asiatic substrate. Having preceded the Austronesians into Western Indonesia, the Austro-Asiatic farmers probably either absorbed, out-competed or killed off those “Papuans”.
    Prior to Mongoloid expansions out of the mainland, I doubt that Papuans were particularly more numerous in Eastern Indonesia than Western. But those east of the Wallace Line only had to deal with one wave of invading agriculturalists (Austronesian) and thus their genes are still around in force; whereas those west of the Wallace Line had to cope with both the Austro-Asiatics and then later the Austronesians. By the time the Austronesians arrived in Western Indonesia, the Papuan population had probably taken a significant hit already.

  • Karl Zimmerman

    1 –

    The indigenous population of Indonesia might not have been “Papuan” at all. Some Papuan languages are spoken as isolates in Eastern Indonesia, and I’ve linked to earlier studies on here which suggested the Papuan genetic contribution in the Lesser Sundas was mainly of recent origin from New Guinea, not ancient. Perhaps the New Guinea highlander’s remote descendents did actually begin expanding through Eastern Indonesia and developing to moderately high densities. The Austronesian expansion later however swamped them and erased most linguistic evidence besides a handful of languages on Timor and a few other islands.

  • http://www.eurasian-sensation.blogspot.com Eurasian Sensation

    # 2:
    Karl, perhaps I should have been clearer… when I say “Papuan”, I was really just talking about a vaguely Australoid or Negritoid physical type. Given that there are pockets of them all over SE Asia (Andamans, Malaysia, Philippines), you’d expect that they would have been in Indonesia as well. Unless they didn’t survive the Toba eruption, which I guess is a possibility.

    But yes, if Papuans moved westward and colonized Eastern Indonesia, that is an easy explanation for the cline. I wonder if the Austro-Asiatics and Papuans were simultaneously moving towards the Wallace Line from different directions.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #1, see papers at this link:

    http://blogs.discovermagazine.com/gnxp/2011/09/out-of-africa-onward-to-wallacea/

    long story short, the pre-mongoloid populations in western maritime indonesia may have been substantially different in character from the melanesians. also note that the ‘negritos’ of malaysia and southern thailand, possibly the only ‘pure’ relics of this element, speak austro-asiatic languages (probably due to picking it up from their agriculturalist neighbors).

  • http://www.isteve.blogspot Steve Sailer

    Is the Wallace Line particularly hard to cross due to prevailing winds or currents?

  • dave chamberlin

    @5 The Wallace line that runs between Bali and Lombok is seperated by water that is both deep and fast. Animals or people on primitive rafts trying to make that crossing would have been pushed out into the ocean, making their seperation far larger than it would appear.

  • http://www.isteve.blogspot Steve Sailer

    Thanks. Most informative.

    As I’ve mentioned before, the isolation-by-distance clinal model works great, except where it doesn’t. In this case of the Wallace Line, unique local oceanographic conditions that aren’t noticeable from a globe conspire to cause a significant genetic difference over what looks like it ought to be as easy to traverse as, say, Indonesia to the Philippines.

  • http://www.eurasian-sensation.blogspot.com Eurasian Sensation

    I think the significance of Wallace’s Line is also that the islands to the west were part of a single land mass during the Ice Age. It would have been possible for early man to walk from Malaysia to Bali, but going further would require a water crossing. Obviously Homo erectus and the ancestors of Papuans and Australian Aborigines both made that crossing at different times, but it still would have limited gene flow between east and west.

  • Sandgroper

    #5 – An Austrian (sic, not Australian) guy and some locals made the Bali-Lombok crossing fairly recently on a primitive paddled raft – it was not easy, but it was doable, after several very determined attempts. Pretty hairy, though. The key problem is the strength of the current, as alluded to by dave at #5. So it was a barrier, but a porous one, as in what ES said at #8.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #8, the sahul vs. sundaland distinction is probably what separates the ‘melanesians’ from the ‘western negritos,’ of whom the malaysian negritos and andaman islanders seem the only ‘pure’ representatives.

  • BDoyle

    Oh, yay! Finally something I can comment on as a geologist. The main ecological feature of the Wallace Line is that it is always under water, even at glacial maximum. How deep the channel is right now is not really that important. I really envy you people studying human genetics right now, everything is happening SO FAST. The only thing I can compare it to in my experience is the discovery of plate tectonics, and I was about 5 years too late for that one.

  • Sandgroper

    “How deep the channel is right now is not really that important.”

    Right, but the point is that it was a deep, fast flowing channel during the Pleistocene as well, up to and including the last glacial maximum, and it still is now. The Austrian guy’s test was a reasonable test of what was achievable in the past (unlike Thor Heyerdahl, who proved nothing).

    I think the really significant point in what he demonstrated was that a successful crossing was unlikely to have been accidental.

  • AG

    No new post for several days. Is every thing ok with Razib?

  • Sandgroper

    Probably just busy.

  • Karl Zimmerman

    Yeah, is the new father of an infant, after all. I’m surprised he has as much time to blog as he does.

  • Nathan

    Has it been established that Austro Asiatic originated in South East Asia? Heres a 2010 entry from Dienekes where he mentions the above theory and the rival theory of AA originating in the SubContinent.

    http://dienekes.blogspot.com/2010/10/origin-of-indian-austroasiatic-speakers.html

  • dave chamberlin

    Our fearless leader is probably just seriously sleep deprived. If the wallace line is a fast flowing channel now imagine what it was like during the hieght of the ice age when all that water was forced through just one small passage. We can’t be certain but it is quite feasible that crossing it back then would have been much harder than it is now.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    i’m ok. to be frank i have more things going on in my life than even my daughter ;-) but it’s all positive, so no worries.

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This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com

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