Book Club: Chinua Achebe’s Things Fall Apart, pt 3/3

 

Chinua_Achebe_-_Buffalo_25Sep2008_crop
Chinua Achebe, Author and Nobel Prize winner

Welcome back to our discussion of Chinua Achebe’s Things Fall Apart. Today I wanted to take a closer look at some of the aspects of traditional Igbo society mentioned in the book.

If you are a regular reader of this blog, you know by now that just as early modern humans (Homo sapiens) mated with Neanderthals and Denisovans somewhere over in Eurasia, some sapiens mated with archaic humans in Africa.

Unfortunately, the state of knowledge about African genomes and especially archaic African genomes is very primitive. Not only does ancient DNA not preserve terribly well in many parts of Africa, but the continent is also rather poor and so people there don’t send their spit to 23 and Me very often to get DNA tested. Thus, sadly, I do not have archaic DNA percents for the Igbo.

WAfricaAdmixture
“Approximate Bayesian computation estimates for the introgressing population across four African populations (Yoruba from Ibadan (YRI), Esan in Nigeria [ESN], Gambian in Western Divisions in the Gambia [GWD], and Mende in Sierra Leone [MSL]),” from Recovering Signals of Ghost Archaic Introgression in African Populations
However, we do have data for their neighbors, the Yoruba, Esan, Mende, and Gambians.

Keep in mind that so far, Eurasians measure about 1-4% Neanderthal and Melanesians about 6% Denisovan, so 10% Ghost in west Africans is a pretty big deal (if you’re into archaic DNA.) The authors of the study estimate that the admixture occurred about 50,000 years ago, which is coincidentally about the same time as the admixture in non-Africans–suggesting that whatever triggered the Out of Africa migration may have also simultaneously triggered an Into Africa migration. 

If you’re not familiar with some of these groups (I only know a little about the Yoruba,) the Esan, Mende, Gambians, and Yoruba are all speakers of languages from the Niger-Congo family (of which the Bantu languages are a sub-set.) The Niger-Congo family is one of the world’s largest, with 1,540 languages and 700 million speakers. It spread within the past 3,000 years from a homeland somewhere in west Africa (possibly Nigeria) to dominate sub-Saharan Africa. As far as I can tell, the Igbo are quite similar genetically to the Yoruba, and the admixture event happened tens of thousands of years before these groups spread and split, so there’s a good chance that the Igbo have similarly high levels of ghost-pop admixture.

Interestingly, a population related to the Bushmen and Pygmies used to dominate central and southern Africa, before the Bantu expansion. While the Bantu expansion and the admixture event are separated by a good 40 or 50 thousand years, this still suggests the possibility of human hybrid vigor.

Edit: A new paper just came out! Whole-genome sequence analysis of a Pan African set of samples reveals archaic gene flow from an extinct basal population of modern humans into sub-Saharan populations:

Here, we examine 15 African populations covering all major continental linguistic groups, ecosystems, and lifestyles within Africa through analysis of whole-genome sequence data of 21 individuals sequenced at deep coverage. We observe a remarkable correlation among genetic diversity and geographic distance, with the hunter-gatherer groups being more genetically differentiated and having larger effective population sizes throughout most modern-human history. Admixture signals are found between neighbor populations from both hunter-gatherer and agriculturalists groups, whereas North African individuals are closely related to Eurasian populations. Regarding archaic gene flow, we test six complex demographic models that consider recent admixture as well as archaic introgression. We identify the fingerprint of an archaic introgression event in the sub-Saharan populations included in the models (~ 4.0% in Khoisan, ~ 4.3% in Mbuti Pygmies, and ~ 5.8% in Mandenka) from an early divergent and currently extinct ghost modern human lineage.

So the ghost population that shows up in the Pygmies the same ghost population as shows up in the Mende? Looks like it.

There’s a lot of interesting stuff in this paper, but I’d just like to highlight this one graph:

Populationsize

I don’t really understand how they compute these things, much less if this is accurate (though their present estimate for the size of the Han looks pretty good,) but assuming it is, we can say a few things: One, before 100,000 years ago, all of the groups–except the Laal of Chad–tracked closely together in size because they were one group. Most of the groups then got smaller simply because they split up. But there seems to have been some kind of really big population bottleneck a bit over a million years ago.

The other really interesting thing is the absolute Pygmy dominance of the mid-10,000-100,000 year range. The authors note:

It is noteworthy that we observed by PSMC a sudden Ne increase in Baka Pygmy around 30 kya. A similar increase was observed in another study that analyzed several Baka and Biaka samples [25]. In addition, this individual presents the highest average genome-wide heterozygosity compared to the rest of samples (Fig. 1b). Nevertheless, such abrupt Ne increase can be attributed to either a population expansion or episodes of separation and admixture [60]. Further analyses at population level are needed to distinguish between these two scenarios.

Until we get more information on the possible Pygmy-cide, let’s get back to Things Fall Apart, for the Igbo of 1890 aren’t their ancestors of 50,000 BC nor the conquerors of central Africa. Here’s an interesting page with information about some of the rituals Achebe wrote about, like the Feast of the New Yams and the Egwugwu ceremony:

 The egwugwu ceremony takes place in order to dispute the guilty side of a crime taken place, similar to our court trials… Nine egwugwu represented a village of the clan, their leader known as Evil Forest; exit the huts with their masks on.

Short page; fast read.

The egwugwu ceremony I found particularly interesting. Of course everyone knows the guys in masks are just guys in masks (well, I assume everyone knows that. It seems obvious,) yet in taking on the masks, they adopt a kind of veil of anonymity. In real life, they are people, with all of the biases of ordinary people; under the mask, they take on the identity of a spirit, free from the biases of ordinary people. It is similar to the official garb worn by judges in other countries, which often look quite silly (wigs on English barristers, for example,) but effectively demarcate a line between normal life and official pronouncements. By putting on the costume of the office, the judge becomes more than an individual.

I have long been fascinated by masks, masquerades, and the power of anonymity. Many famous writers, from Benjamin Franklin to Samuel Clemens, published under pseudonyms. The mask implies falseness–on Halloween, we dress up as things that we are not–but it also allows honesty by freeing us from the threat of retribution.

It is interesting that a small, tightly-knit society where everyone knows everyone and social relations are of paramount importance, like the Igbo, developed a norm of anonymizing judges in order to remove judicial decisions from normal social relations and obligations (as much as possible, anyway). Since most Igbo villages did not have kings or other aristocrats to dictate laws, rule was conducted by notable community members who had effectively purchased or earned noble titles. These nobles got to wear the masks and costumes of the egwgwu.

Ok, so it’s getting late and I need to wrap this up. This moment comes in every post.

I know I haven’t said much about the book itself. The plot, narrative, pacing, structure, writing style, etc. To be honest, that’s because I didn’t enjoy it very much. It was interesting for its content, along with a sense of “I’ve been trying to tell people this and I could have saved myself a lot of time by just pointing them to the book. And if this is a book taught in schools (we didn’t read it in my highschool, but I have heard that many people did,) then why aren’t people more aware of the contents?

What was tribal life like before the Europeans got there? Well, women got beaten a lot. Children were murdered to avenge tribal conflicts. Infant mortality was high. In other words, many things were pretty unpleasant.

And yet, interestingly, much of what we think was unpleasant about them was, in its own way, keeping the peace. As Will (Evolving Moloch) quotes from The Social Structure of Right and Wrong on Twitter:

“Much of the conduct described by anthropologists as conflict management, social control, or even law in tribal and other traditional societies is regarded as crime in modern [nation state] societies.” This is especially clear in the case of violent modes of redress such as assassination, feuding, fighting, maiming, and beating, but it also applies to the confiscation and destruction of property and to other forms of deprivation and humiliation. Such actions typically express a grievance by one person or group against another.

See, for example, when the village burned down Okonkwo’s house for accidentally killing a villager, when they burned down the church for “killing” a deity, or when they took a little girl and killed a little boy in revenge for someone in another village killing one of their women. To the villagers, these were all legal punishments, and the logic of burning down a person’s house if they have killed someone is rather similar to the logic of charging someone a fine for committing manslaughter. Even though Okonkwo didn’t mean to kill anyone, he should have been more careful with his gun, which he knew was dangerous and could kill someone.

Unlike penalties imposed by the state, however, private executions of this kind often result in revenge or even a feud—Moreover, the person killed in retaliation may not be himself or herself a killer, for in these societies violent conflicts between nonkin are virtually always handled in a framework of collective responsibility–or more precisely, collective liability–whereby all members of a social category (such as a family or lineage) are held accountable for the conduct of their fellows.

And, of course, penalties so meted out can be incredibly violent, arbitrary, and selfish, but ignoring that, there’s clearly a conflict when traditional, tribal ways of dealing with problems clash with state-based ways of dealing with problems. Even if everyone eventually agrees that the state-based system is more effective (and I don’t expect everyone to agree) the transition is liable to be difficult for some people, especially if, as in the book, they are punished by the state for enforcing punishments prescribed by their own traditional laws. The state is effectively punishing them for punishing law-breakers, creating what must seem to them a state of anarcho-tyranny.

As for polygamy, Achebe seems to gloss over some of its downsides. From Christakis’s Blueprint: The Origins of a Good Society (h/t Rob Henderson), we have:

Co-wife conflict is ubiquitous in polygynous households… Because the Turkana often choose wives from different families in order to broaden their safety net, they typically do not practice sororal [sister-wives] polygyny… When co-wives are relatives, they can more easily share a household and cooperate… But while sororal polygyny is especially common in cultures in the Americas, general polygyny tends to be the usual pattern in Africa. An examination of ethnographic data from 69 nonsororal polygynous cultures fails to turn up a single society where co-wife relations could be described as harmonious. Detailed ethnographic studies highlight the stresses and fears present in polygynous families, including, for example, wives’ concern that other wives might try to poison their children so that their own children might inherit land or property.

Anyway, let’s wrap this up with a little article on human pacification:

There is a well-entrenched schism on the frequency (how often), intensity (deaths per 100,000/year), and evolutionary significance of warfare among hunter-gatherers compared with large-scale societies. To simplify, Rousseauians argue that warfare among prehistoric and contemporary hunter-gatherers was nearly absent and, if present, was a late cultural invention. In contrast, so-called Hobbesians argue that violence was relatively common but variable among hunter-gatherers. … Furthermore, Hobbesians with empirical data have already established that the frequency and intensity of hunter-gatherer warfare is greater compared with large-scale societies even though horticultural societies engage in warfare more intensively than hunter-gatherers. In the end I argue that although war is a primitive trait we may share with chimpanzees and/or our last common ancestor, the ability of hunter-gatherer bands to live peaceably with their neighbors, even though war may occur, is a derived trait that fundamentally distinguishes us socially and politically from chimpanzee societies. It is a point often lost in these debates.

I think we should read Legal Systems Very Different from Ours for our next book. Any other ideas?

Cracks in the Out of Africa Theory?

The most exciting finding of the past two decades in biological anthropology has been, without a doubt, evidence for interbreeding between Homo sapiens, Neanderthals, Denisovans, etc. and the sheer multiplicity of new hominin species being uncovered.

Exactly where the lines between species lie is a bit of a matter of semantic debate–where exactly did our ancestors end and Homo sapiens begin? Should we classify Neanderthals and Sapiens as one species if we interbred? etc–but if we accept the current classifications as decent approximations, we have:

Capture
Source: Wikipedia

Sorry, I realized it would be much more efficient if I just grabbed the family tree off Wikipedia instead of copying it over bit by bit. The top part of the tree got cut off, so I’ll note that Homini (6.3 million years ago) includes us + chimps, while Hominina (5.7 million years ago) has no chimps, but includes australopithecines. Gorillas are way back in Homininae, with an e. Homo, our genus, includes all of the “human” species, but usually doesn’t include australopithecines.

There is further debate on exactly who descended from whom. We’re finding new fossils all the time, which is quite exciting, but our current record is not nearly as complete as we’d like it to be. So sometimes branches get moved around or re-categorized as more data comes to light.

The most recent notable additions to our genus are the Denisovans, Homo floresiensis, Homo luzonensis, Homo Naledi, Homo doesn’t have a name yet, and more Denisovans.

You have probably heard of the “hobbit,” Homo floresiensis. The remains we have uncovered of this diminutive hominin are remarkably good, including a skull in great condition (despite some damage caused after excavation.) They lived on the island of Flores from about 200,000 to 50,000 years ago (though their arrival may get pushed back considerably because there are stone tools on Flores that are much older–700,000 years old–we just don’t know yet who used them.)

The hobbits are remarkable in multiple ways. First, they lived in an area that was not connected to the mainland by any landbridges–that is, they had to swim, boat, or otherwise be carried to their island. I am skeptical of the idea of anyone surviving a tsunami as a means of populating an island, but they arrived in an era when, as far as we know, humans had yet to build boats. So perhaps their ancestors were among the first humans to build boats, and we just haven’t found the remains of their crafts (wood being a material that degenerates very quickly.)

Second, the Hobbits are most likely descended from Homo erectus, who lived nearby on mainland Indonesia (at the time, connected to the rest of Asia via a landbridge), but are morphologically very different. They are tiny–shorter than pygmies, Homo erectus, or even australopithecines.

There is much debate about whether they are descended directly from erectus, or part of a sister-clade to erectus that descended from a common ancestor. It was previously believed that erectus was the first hominin to leave Africa, but if Floresiensis is not descended from erectus, Flores could be the first.

Now a similarly diminutive hominin has turned up in the Philippines, also past a significant water barrier that would require some effort to cross. It has been dubbed Homo luzonensis. Not much is known, yet, about luzonensis, (we haven’t found as many of its bones), but what we do know is tantalizing:

It was soon apparent to Détroit that the remains featured a puzzling mosaic of traits both modern and ancient. “Each of the features [of Homo luzonensis] corresponds to some hominin or another,” he says. “But the combination makes for something really unique. There’s no known species with this same suite of features.”

They’re small, possibly even smaller than the Hobbits. Their feet resemble australopithecines, but australopithecines supposedly died out a couple million years before Luzonensis arrived on the scene. And their teeth were “remarkably uniform,” which probably sounds boring to anyone who isn’t a dentist, but provides strong evidence of them being a different species.

Two island dwelling species in the same area supports the idea that their ancestors either developed boats or were remarkably skilled at surviving tsunamis, and that southeast Asia was a remarkable hotspot of hominin diversity.

And then there are the Denisovans!

Denisovans are mysterious because we have so few of their bones–a chunk of skull was recently uncovered, but we have no jaws, no faces, no ribs, etc–so we don’t have a good idea of what they looked like. What we do have are Denisovan DNA (extracted from those fragments of skeletons) and traces of Denisovan DNA in modern humans.

Oddly, those Denisovan bones turned up in Siberia (a good place for preserving old bones, but not such a great place for humans adapted to warm climates) while the humans with Denisovan DNA live in modern Papua New Guinea and nearby areas.

The obvious answer to this puzzle is that both the Denisovans had a much broader range than one cave in Siberia and the ancestors of modern folks from PNG used to live in different areas than they do now.

A more detailed analysis of PNG DNA was recently released, which reveals three separate, significant groups of Denisovans who interbred with sapiens:

… modern Papuans carry hundreds of gene variants from two deeply divergent Denisovan lineages that separated [from each other] over 350 thousand years ago. Spatial and temporal structure among these lineages suggest that introgression from one of these Denisovan groups predominantly took place east of the Wallace line and continued until near the end of the Pleistocene. A third Denisovan lineage occurs in modern East Asians. This regional mosaic suggests considerable complexity in archaic contact, with modern humans interbreeding with multiple Denisovan groups that were geographically isolated from each other over deep evolutionary time.

The Wallace line is a place that’s too deep for a landbridge, and thus the area to the east was an island even during the Ice Age. In other words, it looks like Denisovans could use boats. (Or survive tsunamis, pfft.)

Next, we sought to retrieve dates of divergence between D1, D2, and the Altai Denisovan genome … to encompass two deeply divergent Denisovan-related components, our best fitting model indicates that D1 and D2 split from the Altai Denisovan approximately 283 kya … respectively (Figure 4B). While clearly branching off the Denisovan line, D2 diverged so closely to the Neanderthal-Denisovan split that it is perhaps better considered as a third sister group… For context, even the youngest of these divergence times is similar to the evolutionary age of anatomically modern humans … Our model implies substantial reproductive separation of multiple Denisovan-like populations over a period of hundreds of thousands of years. … 

The genetic diversity within the Denisovan clade is consistent with their deep divergence and separation into at least three geographically disparate branches, with one contributing an introgression signal in Oceania and to a lesser extent across Asia (D2), another apparently restricted to New Guinea and nearby islands (D1), and a third in East Asia and Siberia (D0). This suggests that Denisovans were capable of crossing major geographical barriers, including the persistent sea lanes that separated Asia from Wallacea and New Guinea. They therefore spanned an incredible diversity of environments, from temperate continental steppes to tropical equatorial islands.

(We will probably reclassify some of the older fossils from Asia as Denisovans once we figure out what they looked like.)

Then we have Homo naledi, from South Africa. Naledi lived around 250,000 years ago, about the same time as Homo sapiens were differentiating from their ancestors. We have a wonderful array of Homo naledi fossils, preserved in the bottom of a cave pit. If they were placed here intentionally, this was pretty advanced behavior, though I wonder if perhaps they just got lost in the cave from time to time and then died in the pit.

At about 5 ft tall, (male height) naledi was short, but not nearly as short as Floresiensis, and taller than some groups of sapiens. Its skull was significantly smaller than a modern skull, however, and I find it odd that, out of the thousands of bones and fragments discovered, we have not yet recovered much of the front of their faces. Perhaps their faces were shattered when they fell into the cave?

Naledi, like Floresiensis and Luzonensis, shares some more modern traits with other members of the homo genus, and some traits with the older australopithecines. Unlike them, we have yet to uncover evidence that Naledi used tools.

The we have a couple of unnamed hominins

These so-called “ghost populations” are known entirely from their presence in the DNA of modern humans. We don’t have any fossils from them, either because they lived in areas where the weather didn’t favor preservation, or the modern political climate makes searching for fossils difficult.

The pygmies and Bushmen derive about 2% of their DNA from an archaic population or two that we estimate split off from the rest of us about 700,000 years ago. They met and mated with these other hominins around 35,000 years ago.

More interesting is another ghost population that shows up in the genomes of west African groups like the Mende. Now, the average non-African has about 1-4% Neanderthal DNA, and Melanesians have about 4-6% Denisovan, but some tribes in west Africa, such as the Yoruba, Mende, Gambians, and Esan, may derive about 10% of their DNA from an otherwise unknown ghost population that split off before the Neanderthals! (Razib’s very nice article summarizing the paper.)

 

Oh, jeeze, it’s three am, let me finish this in the next post…