A genetic map of the world

The above map is from a new preprint on the patterns of genetic variation as a function of geography for humans, Genetic landscapes reveal how human genetic diversity aligns with geography. The authors assemble an incredibly large dataset to generate these figures. The orange zones are “troughs” of gene flow. Basically barriers to gene flow.  It is no great surprise that so many of the barriers correlate with rivers, mountains, and deserts. But the aim of this sort of work seems to be to make precise and quantitative intuitions which are normally expressed verbally.

To me, it is curious how the borders of the Peoples’ Republic of China is evident on this map (an artifact of sampling?). Additionally, one can see Weber’s line in Indonesia. There are the usual important caveats of sampling, and caution about interpreting present variation and dynamics back to the past. But I believe that these sorts of models and visualizations are important nulls against which we can judge perturbations.

As I said, these methods can confirm rigorously what is already clear intuitively. For example:

Several large-scale corridors are inferred that represent long-range genetic similarity, for example: India is connected by two corridors to Europe (a southern one through Anatolia and Persia ‘SC’, and
a northern one through the Eurasian Steppe ‘NC’)

We still don’t have enough ancient DNA to be totally sure, but it’s hard to ignore the likelihood that “Ancestral North Indians” (AN) actually represent two different migrations.

India also illustrates contingency of these barriers. Before the ANI migration, driven by the rise in agricultural lifestyles, there would likely have been a major trough of gene flow on India’s western border. In fact a deeper one than the one on the eastern border. And if the high genetic structure statistics from ancient DNA are further confirmed then the rate of gene flow was possibly much lower between demes in the past. Perhaps that would simply re-standardize equally so that the map itself would not be changed, but I suspect that we’d see many more “troughs” during the Pleistocene and early Holocene.

Because there are so many geographically distributed samples for humans, and frankly some of the best methods developers work with human data (thank you NIH), it is no surprise that our species would be mapped first. But I think some of the biggest insights may be with understanding the dynamics of gene flow of non-human species, and perhaps the nature and origin of speciation as it relates to isolation (or lack thereof).

12 thoughts on “A genetic map of the world

  1. Razib, is there a book/series of books of world history who conforms to the at least the archaeological findings if not the genetic findings of the last couple decades?
    I homeschool and every history book is very weak in the “people” regard, focusing more on societies and without linking relationships.

  2. Look at all those mini barriers in Europe!

    I’ve always (not very originally) hypothesized that Europe eventually experienced a lot of innovation (after a critical mass), because its geography aided transmission of technology and knowledge, but retarded invasions and centralization, which in turn meant many little hyper-competitive nations and peoples, constantly angling for advantages (that, in turn, led to quick technology adoption and innovation).

  3. Hi Twinkie, I going to hazard a guess that we are seeing the effects of sampling bias there. When the rest of the world is sampled to Euro level it might all look like that.

  4. Razib: how the borders of the Peoples’ Republic of China is evident on this map (an artifact of sampling?)

    It would be very cool for Chiang to add an EEMS run into his paper pre-publication: https://www.biorxiv.org/content/early/2017/07/13/162982. Would probably see a barrier between Guangxi and other regions, and lots more east-west spreadzones.

    (Something like patterns from “770,000 genomes” – https://www.nature.com/articles/ncomms14238, though actually deeper at a genotype level. “Go West, young Han” relatively new, as agricultural societies tend to hug coastlines? Europe has deeper east-west structure as more coasts? I believe Sichuan also repopulated from east after Ming Dynasty, following mass death, which would seem less to happen if there wasn’t a big empire ruling over both, and instead would just see a population rebound.).

    Esp. with broader East Asian samples (Vietnam, Korea, Japan, Ryukyu, Atayal).

    One thing I do have difficulty with when it comes EEMS is how to interpret how positions and barriers provide distance. That is, is the real distance between two population pairs the euclidean distance (“as the crow flies”), or is it distance across the path of least resistance?

    Like, if you take Fig2a and want to estimate the distance between the NW Iberian sample and the central French sample, then do you go via the direct euclidean distance between the samples, even though that takes you through the barrier / low migration Basque region, or do you zip along the path of least resistance across the Bay of Biscay?

  5. What is the orange zone btw/ the Black and Caspian Sea? It looks like the center of the Pontic–Caspian steppe, which I thought was an important migration corridor.

  6. That makes sense – do you know, roughly, what the sampling density difference is between Western Europe and East Asia on the map?

  7. That makes sense – do you know, roughly, what the sampling density difference is between Western Europe and East Asia on the map?

    it’s on the order of magnitude i assume. POPRES and other databases have a decent national-scale database. i don’t know if chinese province level stuff is nearly as thorough in the public domain.

  8. Thanks. I still think that Europe will turn out to have more barriers than much of East Asia. The terrain of the former is much more diverse than the latter.

  9. sort of. southern half of china has a lot of ruggedness. OTOH i have read that much of sichuan was repopulated from hunan relatively recently in time. the political unity that facilitated gene flow may be key….

  10. Yes, but northern China is plains, and once it was united, it became too formidable/centralized/mobilized for others around to resist.

    Europe has so many more rivers and mountains… every valley cries out for isolation, to be a bit cheeky.

    Korea and Japan, on the other hand, are quite mountainous.

  11. I suppose it’s too obvious to point out that these areas coincide pretty strongly with the common sense notion of races?

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