Sons of the farmers, the origins of Africans

By Razib Khan | December 17, 2010 2:40 am

553px-African_language_famiMost readers at this point are aware that I am very curious as to the origin of Europeans at the interface of hunter-gatherer populations and Neolithic farmers. What we thought we knew around the year 2000 does not seem to align very well with the conflicting results coming out of recent analyses. There is no ascendant consensus at this point. All possibilities are still in the field of play.

Part of the issue of course is that the spread of farming in Europe was a prehistoric affair, very far back in time. There have been several cultural, and possibly demographic, revolutions in Europe since the arrival of the first farmers. Pulling apart the manifold layers of the palimpsest is a task of great difficulty, and the confident results utilizing the tools of the past should make us cautious of the inferences of the present. This is why I believe focusing on case-studies such as Japan are essential. From a range of specific cases we may infer general patterns, which will then allow us to have firmer ground when making conjectures about times and places where the empirical results can not resolve conflicts of opinion. Japan is an island which made the transition to agriculture relatively late, so the fog is a bit less daunting than is the case with prehistoric Europe. Africa is perhaps even a better case: the Bantu expansion is very recent, having reached its stable frontier only within the last ~1000 years. If it is true that Phoenicians circumnavigated Africa in the ~600 BC, then they would have encountered many non-Bantu groups south of Kenya at that time. Linguists have long noted the similarities of the Bantu languages from north to south, but the genetic similarities also exist. Here’s a figure from the Bushmen paper in Nature:


bush1

Eigenvector 1 explains three times as much genetic variance as eigenvector 2, so you can see how diverse Bushmen are, as well the fact that geography does not explain genetic distance in this case. Here’s a figure from The Genetic Structure and History of Africans and African Americans:
bantu1

The Hazda, Sandawe, Pygmies, and Khoesan (Bushmen, Nama, etc.), are often considered ‘relic’ populations. Remnants of diverse groups which were marginalized or absorbed by the Bantu in their expansion south and east from their urheimat. And it is interesting that the Khoesan are on the same branch as the Mbuti Pygmies of the eastern Congo, who are a particularly distinctive group genetically. The Hadza and Sandawe are non-Bantu populations in Tanzania. They also seem to speak languages with some affinity to that of the Khoesan. The “long branch” of the Hadza suggests genetic drift through a population bottleneck. As the last hunter-gatherers of East Africa it is likely that there has been very little gene flow between themselves and the farming majority, so their effective population has been low.

This seems to be another case where farmers rapidly exploded demographically and totally marginalized hunter-gatherers. The widespread presence of Khoesan and Pygmies is obviously a function of ecology. In the cooler and dry lands of southwest Africa the Bantu crops did not flourish. Additionally, some of the Khoikhoi became herders. Similarly, the deep rainforest was not congenial to agriculture either. In the comments below Randy McDonald asks:

Razib: Might the implications of the outcompetition of the Jomon be more proof that genetic diversity among humans today has shrunk considerably from the period predating the expansion of agricultural civilizations?

We often talk about Africa’s genetic diversity. What if what we see across much of the continent is actually greatly diminished from what it once was? It was famously reported last winter that Bushmen seem to differ genetically amongst themselves more than Europeans and Asians do. These two latter groups have been separate for at least 40,000 years. Granted, Eurasians went through a bottleneck “Out of Africa,” but the great diversity of the Bushmen is possibly a last compressed snapshot of what was before the Bantu expansion.

So now we seem to have two cases where prehistory is close enough to ascertain that farmers nearly replaced hunter-gatherers. More later….

CATEGORIZED UNDER: Genetics, Genomics
MORE ABOUT: Farmers, Genetics, Genomics
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  • onur

    OK, it is very understandable that farmers probably almost always replaced or nearly replaced hunter-gatherers and fishers while expanding in their territories, as farmers had a clearly more advanced culture and economy that allowed much higher population densities than in hunter-gatherers and fishers. But what about the recent expansions of nomadic pastoralists like Arabs (there were farming or city-dwelling Arabs already before their expansion, but they were a small population compared to the nomadic pastoralist Arabs) and Turkics (Turkics coming to Iran and Byzantine were almost totally nomadic pastoralists) in the territories of advanced farming civilizations like Byzantine? What were the demographic/genetic effects of such expansions from lower cultures to higher cultures? The Slavic expansion in the Roman Balkans and the Germanic expansion in the Roman Britain are also cases of expansion from lower culture to higher culture, though Slavs and Germanics were already farming before their expansions.

  • bob sykes

    I stumbled across a comment recently, somewhere (I’ll look), that steppe pastoralists actually enjoyed high population densities, because the exploitation of the horse for milk as well as meat provided very high calories per unit area, comparable to grain-based agriculture.

    High population densities would place steppe pastoralists on a numerical par with sedentary farmers, and the pastoralists generally better health and larger size and agressiveness would tip the balance in any conflict.

  • AG

    Living in USA, I hardly seeing any black deer hunter. Most African Americans are into fishing. Most large game hunters are white, plus a very small number of East Asians. I am an enthusiastic deer and large game hunter. Big game hunting needs a lot of planing, time and patience (strong future orientation). My instinct to hunt might has a lot to do with northern hans mixing with mongolian or manchurians. So most likely, west Africans are descendants of gatherers/tropical farmers.

  • dave chamberlin

    Fascinating stuff. Being a long time reader of your blog I would like to make the very general comment that it appears what we can scientifically deduce from our pre history is rapidly accelerating. I would guess your readership (number of blog hits)is rapidly increasing as well.

  • Rimon

    Razib, you can delete my comment for not adding to the conversation (though please don’t ban me), but I just want to say that I have never seen a comment as stupid as AG’s in all the years I’ve been reading this blog.

  • Nick Patterson

    I’m a geneticist with interests well aligned with the interests of this blog, which
    has indeed commented on a fair proportion of my work. I’m currently working on
    the prehistory of Europe, and a co-author of the Bushmen paper.

    I want to comment on Africa’s genetic diversity. There is a great deal of genetic
    diversity within many African populations. For instance more diversity within Yoruba
    than within Europe. But many African populations are quite similar. For instance divergence
    between Kikuyu (Kenya) and Yoruba (Nigeria) is just a little more than (Spain, Holland).
    This is of course caused by the Bantu expansion as Razib explained.

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

    Razib, you can delete my comment for not adding to the conversation (though please don’t ban me), but I just want to say that I have never seen a comment as stupid as AG’s in all the years I’ve been reading this blog.

    you haven’t been reading since the beginning, have you? i agree that AG’s comment was not up to snuff. bring your game up AG.

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

    bob, please dig up the cite if you have time! i’m skeptical on the assertion a priori because of basic ecological principles. the step of converting energy into meat & milk is more ‘wasteful’ than farming (though in some situations farming is not productive at all, ergo, nomadism).

  • AG

    @Razib

    Thank you for suggestion. I should think more before posting. It well could be SES factor that limit African Americans chance to hunt big game since it can be very costly to hunt. Simple insult is cheap way for some people who hate to use their brains.

    Nomadism is often result of bad land (unproductive farmland) if you observe where most US ranches located. Same pattern can be observed in Peru or China.

  • http://washparkprophet.blogspot.com ohwilleke

    A remarkable part of the figure is that the Fulani are linguistically part of the Niger-Kordofanian language family, and yet are genetically much closer to the speakers of Afro-Asiatic languages (Chadic and Cushitic) and speakers of Nilo-Saharan languages.

    A subset of Fulani and Chadic language speakers, particularly in Northern Cameroon, are of particular interest when trying to reconstruct Africa’s pre-history because those populations are genetic outliers with much more affinity to West Eurasians than any other African population without a historically documented history of admixture with West Eurasian populations.

    In the Fulani case in particular, the autosomal data in the chart supports prior mtDNA and Y-DNA evidence that the outlier populations were probably immigrants to the region from somewhere to the North (e.g. via the Nile Basin) who probably converted en masse to a Niger-Kordofanian language at some point lost to history. (There is admixture with East Eurasians in Madagascar, and historic era admixture with West Eurasians in Ethiopia, Egypt and South Africa to name a few, but we know from historical records or very convincing circumstantial evidence what happened and when it happened in those cases).

    In Southern Africa, where we have a very good idea what two of the source populations (the Bantu and white Europeans) looks like, a bar chart admixture figure might be more interesting than the PCA. My intuition is that the great diversity in the Southern African cluster reflects a great diversity in the substrate pre-Bantu Bushmen population translated in roughly the same amounts to a different part of the PCA chart by eigenvalues attributable to a Bantu component.

    But, that might be wrong. It could be that there was more than one substrate clusters, one akin to the Bushmen, and another with no extant pure popuplation remaining. The genetic distance of the Sandawe and Hadza cluster from the Khoisan-Pygmy cluster, the Niger-Kordofanian speakers, the Afro-Asiatic speakers, and the Nilo-Saharan speakers, is suggestive of the idea that they might be the closests representatives of a “lost people” of Africa that is distinct from the Bushmen.

    The palimpsest is also harder to parse in some places than others. In East Africa, we know from historical records when and how the Ethio-Semitic language speakers came to adopt their languages and have measured genetically with some precision how much of that transition was cultural and how much it involved population replacement. We can also fairly infer from history, language and genetics that the immediate predecessors of the Ethio-Semites were probably quite similar to the Oromo language speakers of today (an Afro-Asiatic language that is not Semitic).

    But, the relationship of the various Afro-Asiatic languages to each other is not a consensus matter. Some argue that this language family pre-dates farming and herding and may even be the indigenous language family of much of the region where it was found when historical records began, while others argue that it expanded with farming and herding. Some argue that it originated in the Levant and spread with the expansion of Fertile Crescent domesticates, while others argue for an African origin, perhaps connected to Ethiopian domesticates.

    If Afro-Asiatic languages are not the indigeneous language family of most of North and East Africa, and might not even be indigenous to Africa at all, the natural next question is “what did the pre-Afro-Asiatic linguistic layer look like?”

    The question is more profound that it would be when asked any place else in the world, because the evidence seems to most strongly support supports the argument that East Africa (somewhere from Ethiopia through the Rift Valley) is the birthplace of humanity, more poetically, that it is Eden. To ask what people spoke in East Africa before they spoke Afro-Asiatic is to ask “what was the original language of man?”

    Knowing the original language of man may not help you find your way to the bathroom in a busy airport or read the instruction manual for your kids new toys, but it certainly carries some bragging rights. The fact that all of Africa’s major language families have populations in or near East Africa also makes a simple geographically based answer to this language non-obvious. Given the fact that we have several historical examples (Arabic in North Africa, Ethiosemitic in parts of Ethiopia, and Bantu in Southern Africa) of total language replacement in large swaths of African territory, we can’t even safely assume that languages spoken in a place now were spoken there at any great time depth earlier in history.

    Genetic evidence is starting to make it possible to assign tentative dates to the population expansions associated with major African language families, and to pin point multiple instances of probably language transition by whole peoples. Some of those dates, for example, for Nilo-Saharan languages, are remarkably young.

    The genetic gap between West African Bantus and Southern African Bantus caused by admixture with and assimilation of pre-existing populations, with Bushmen as a control group, also potentially serves as a nice natural experiment comparing the importance of cultural v. genetic roots in evolution. To the extent that culturally Bantu people in Southern Africa are quite genetically distinct from West African Bantus, but live similar lives, genetics starts to look more like a surname – something that can identify you ancestry but may have played a secondary role in human evolution.

  • Gav

    Slightly off-thread but just to remark that given the existence of some large population centres the conditions that might favour pastoralism (as distinct from hunter-gathering) over farming at a particular location could be economic too – von Thünen and all that.

  • Sandgroper

    AG’s second comment is no more cerebral than his first.

    Ted Nugent must be a genius.

  • AG

    @ Sandgroper

    Hunting is privilage for both Chinese and European noble class in hitory. Does that help?

  • Sandgroper

    But historically not in Africa or America.

  • Insightful

    It was famously reported last winter that Bushmen seem to differ genetically amongst themselves more than Europeans and Asians do. These two latter groups have been separate for at least 40,000 years.

    At least? Razib, you are way off on the separation time of Europeans and East Asians. I think it’s much closer to 30,000 years at most. There is growing evidence that ancestral Europeans and ancestral East Asians were one and the same people until 22,500 years ago.

    Present-day Europeans and East Asians descend largely from a small nomadic population that once roamed Eurasia’s northern tier—a belt of steppe-tundra that stretched from southwestern France to Beringia during the last ice age. This population then split in two around the time of the glacial maximum (Rogers, 1986; Crawford et al, 1997). Chronologically, this barrier to east-west gene flow matches the dating by Laval et al. (2010) of the split between ancestral Europeans and ancestral East Asians.

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

    Razib, you are way off on the separation time of Europeans and East Asians.

    dude, don’t assert something that is debated, OK? i know about the lower bound results. i’m not a retard. for various reasons i do not believe them, but could be convinced otherwise. chill with the attitude. also, there’s not a consensus for the model your proposing of the north siberian origin. so don’t offer it as if there is.

    (and watch your HTML, had to close your italics)

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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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