Out of Africa, into Asia

This thread is about the complexity of Asian migrations.Here’s an image of the great human family tree.Here's an image of the Out of Africa migrations:And here's one I modified slightly, just in case you find that looking at a world without Greenwhich at the centre of it makes everything look as though it were from the pre-Cambrian era:According to these images, there were two separate great migrations to Eastern Asia and Oceania, separated by a difference of several thousand years. The first migration yielded such races as South Chinese, Native Australians and Polynesians. Before the second migration occurred however, two more closely related populations diverged, and one of these populations migrated to Eastern Asia and the Americas and yielded such races as Japanese, Native Americans and Koreans, whereas the other population migrated to Europe and the Middle East, and yielded such races as Indians, Europeans and Iranians.This has made me think about convergent evolution. You’ll notice that the first migration into Asia yielded, among others, South Chinese and Native Australians. There are obvious superficial differences between these two races, perhaps the most striking being the epicanthal folds of Chinese people. Despite being more closely related, one would say that Chinese are more closely related to Japanese than to Native Australians.There are two explanations that I can think of for this, one being convergent evolution, and one being interbreeding between first wave Asians and second wave Asians. Both of these happenings are the resultant effects of spending time in Eastern Asia.First, convergent evolution. What’s so special about Eastern Asia that makes epicanthal folds so useful to have? Is it high winds? High altitude? There must’ve be some very strong pressure on selecting for epicanthal folds in this part of the world.If it’s not convergent evolution, then is it interbreeding between races? Did the second wave of Asians have sex with the first wave of Asians as they made their way through Asia to the further Eastern reaches and to the Americas? If so, then surely it’s not so easy to draw a family tree like the one I’ve posted above, and it’s absurd to suggest that there's such a thing as pure races occupying their own hefty stub on the great human family tree.So my questions are:There were several migrations through Asia. What is it about Asia that produces such powerful evolutionary effect as the pronounced similarities between Chinese and Japanese? And just how complex were the Asian and American migrations? Was there interbreeding between first wave and second wave Asians?Edited by Zawinul, : more appropriate titleEdited by Zawinul, : No reason given.Edited by Zawinul, : No reason given.

Thread moved here from the Proposed New Topics forum.

I think your latter explanation is more feasible. I doubt that we can really trust crude cladograms wholeheartedly that chiefly draw upon their anthropological inferences by looking at cranial (dis)similarities. What I mean is that convergence is not always so nice, neat, or orderly.As for the diversity amongst sino-asians, I too have wondered what selective pressures prompted the development of such a pronounced epicanthal. I thought of high, cold winds too as a possible variable, but it got me thinking about caucasoids who also have inhabited regions of very cold climate for thousands of years. Surely they could stand to have developed such a feature as well. But they didn't.And as for the slight anatomical differences between the Chinese and Japanese, we shouldn't discount long periods of isolation. Afterall, all humans share the progenitor. Therefore, its concievable that the first humans looked alot alike. It wasn't until they dispersed and became isolated for so long that these new features, already stored with the genetic code, began to come out-- perhaps some recessive traits winning over the dominant ones on occasion.After a considerable period of stasis, interbreeding began to occur because of commerce. Some new and unique features began to emerge until you have the melting pot we have today. [qs]There were several migrations through Asia. What is it about Asia that produces such powerful evolutionary effect?Its probably because the East was separated for so long for geological reasons like mountain ranges. If you look at western china and Mongolia, and Tibet, there are not too many smooth pathways. There are the Himalayas, the Gobi desert, and thousands upon thousands of miles of lush, dense forest in between them.Other than that, I can think of no other reason why they are as diverse as they are,

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One theory I heard about the epicanthal eye-folds is that they reduce the amount of light going into the eye, a useful trait if the ancestoral populations of the East Asians were mostly in the very far north. Natural snow goggles, if you will.Of course, another possibility is mundane genetic drift. The trait rose in some individual, the trait had no significant effects on the reproductive fitness of the individuals, and then, just through chance, it became established in the population, and the non-folded allele disappeared.As a non-anthropologist who knows nothing about East Asians, I would guess that interbreeding between populations would be the best answer for the existence of this trait in the two different populations. I mean, if you have two different populations coexisting on more or less the same geographical area, how would you prevent interbreeding?At any rate, if the levels of interbreeding were small enough, you could preserve the overall genetic integrity of each of the populations. Population A would get an influx of alleles of from population B; if the amount of interbreeding were small enough (or fairly recent), then the Hardy-Weinberg principle would seem to indicate that most of these alleles would be present in a fairly small percentage of the entire population. However, the Hardy-Weinberg principle is basically a statistical phenomenon -- we would expect that once in a while an allele from B would not only become established in population A but eventually become the dominant variant.-

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If so, then surely it’s not so easy to draw a family tree like the one I’ve posted above, and it’s absurd to suggest that there's such a thing as pure races occupying their own hefty stub on the great human family tree.

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Indeed. It is absurd to suggest that there is such a thing as pure races. And it isn't so easy to draw these kinds of family trees. These trees are the result of years and years of painstaking, careful research trying to find genes whose alleles more or less remained tied to the specific breeding populations comprising the migrations. But inter-breeding tends to blur these lines. This type of research is only possible because before modern technology made travel so much easier, people tended to breed mainly with their more or less close neighbors, who would obviously be more likely to be of the same ethnicity. Interethnic breeding would mainly occur among the relative smaller number of people on the boundaries of the territories occupied by different ethnic groups.

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Great diagrams - it's good to see the world from a different angle!

ps poor old Greenland and Iceland!

Nice.This also conforms to the Dmanisi findhttp://www.dmanisi.org.ge/index.html

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The Oldest Hominid Site Found in Eurasia to Date

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Paleontological, archaeological, geochronological, and paleomagnetic data from Dmanisi

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all indicate an earliest Pleistocene age of about 1.8 MA

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The Dmanisi hominid remains are the first hominids discovered outside of Africa to show clear affinities to African H. ergaster rather than to more typical Asian H. erectus or to any European hominid.

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We also have that issue left over from Neanderthal Genes???

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Lahn's team found a brain gene that appears to have entered the human lineage about 1.1 million years ago, and that has a modern form, or allele, that appeared about 37,000 years ago -- right before Neanderthals became extinct.

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"The gene microcephalin (MCPH1) regulates brain size during development and has experienced positive selection in the lineage leading to Homo sapiens," the researchers wrote.

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Positive selection means the gene conferred some sort of advantage, so that people who had it were more likely to have descendants than people who did not. Lahn's team estimated that 70 percent of all living humans have this type D variant of the gene.

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Wonder how that 70% living humans fit that cladogram eh?Thanks.

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