The Consistently Incorrect Mapping of Language Differentiation in Bouckaert et al.

As mentioned in previous GeoCurrents posts, the animated map that accompanies the Science article of Bouckaert et al. depicts their model in action, showing the expansion and differentiation of the Indo-European languages in time and space. Earlier posts criticized the map’s contour shadings, which indicate high probabilities of IE languages being spoken in given areas at given times. Today’s post takes on a related issue, that of the branching lines that spread across the map as the presentation unfolds, indicating both linguistic relationship and the general directions of language-group expansion. Here we can clearly see that the model generates a nearly continuous stream of misleading information and outright error.

Analyzing the ramifying lines on animated map is challenging. Nothing is labeled, colors are often hard to differentiate, and no key is provided. The companion website does promise a “legend for movie S1,” but provides only a brief caption: “Movie showing the expansion of the Indo-European languages through time. Contours on the map represent the 95% highest posterior density distribution of the range of Indo-European.” One must thus infer what the lines represent based on the supplementary text and on the manner in which different segments lengthen and divide in particular places as time proceeds.

Each line represents a branch of the Indo-European language family. Those that appear early in the animation indicate the deepest divisions, while those that emerge later represent the shallower splits of linguistic “sub-sub-families” and so on. In some cases, minor instances of linguistic differentiation are marked, extending down to the dialectal level. The North Germanic line, for example, begins to bifurcate on the Sweden-Norway border in the late 1700s, showing the divergence of Norwegian and Swedish, and then splits again in central Sweden in the mid 1800s, indicating differentiation that, according to the authors, produced three separate Swedish languages (see the maps below). Over most of the map, however, splits at the level of individual languages, let alone that of dialects, are not noted: if they were, the map would be so cluttered by the end as to be undecipherable. Yet again, consistency does not seem to be a priority.

The lines are not of uniform appearance. Older language stems are clearly depicted in a darker shade than more recent branches. As elsewhere, differentiating the hues employed is difficult, especially after the background color used to denote IE languages in general abruptly changes from yellowish-greens to shades of blue-green. (As a result of this problem, in some of the maps that follow I have changed the green lines under investigation to shades of red.) Interpreting differences in line shape and thickness is another challenge. Almost all lines are equally thick and even, extending uninterrupted across the map. In some instances, however, thin, irregularly shaped spurs emerge from the main stems, some of which eventually thicken and spread into new areas. Certain lines are interrupted, with unexplained gaps appearing on the map. Some of these gaps seem to indicate language divergence without diffusion, but other remain mysterious, as is the case with the differently shaped and colored line fragments that appear in what is now western Germany (see map detail to the left). By the end of the animation, Italy is covered by a jumble of oddly uneven and discontinuous lines that are almost impossible to parse out, as can also be seen on the map posted here.

The spatial extension of the lines over time seemingly indicates the pace of expansion of the various IE subgroups into new territories, while the shaded contours depict the expansion of Indo-European as a whole. The two methods of showing expansion, however, do not always correspond. While the 95 percent probability contour for IE as a whole never reaches Russia (except for a tiny zone in near Pskov), the East Slavic line pushes well into what is now western Russia, although it does not do so until the early 1600s. Such a depiction is of course absurd on face value, as East Slavic languages had been spoken in this area and well beyond it for many hundreds of years; it must be recalled, however, that the animated map is designed to show only the latest possible time of expansion, not the actual period in which it occurred.

The major significance of the lines, however, is not their depiction of language group expansion but rather of linguistic divergence. The authors emphasize repeatedly that their animated map depicts the locations at which linguistic differentiation occurred, which in turn generated the branching patterns of the Indo-European tree. Although they formally model such divergence as occurring at precise points, they admit that it cannot be pinpointed in such a manner:

Our phylogeographic model allows us to infer the location of ancestral langauge (sic) divergence events corresponding to the root and internal nodes of the Indo-European family tree. Since we model internal node locations as points in space, our posterior estimate for the location of divergence events can be interpreted as a composite of the range over which the ancestral language was spoken and stochastic uncertainty inherent in the model.

Regardless of the uncertainty that the model encompasses, language divergence cannot realistically be modeled as occurring through discrete events that happen in restricted places. The differentiation of languages is rather a process that often occurs over an extended period through an expansive area of related dialects (see the earlier GeoCurrents post on the “wave model”). Leaving such objections aside, however, it must still be asked whether the model of Bouckaert et al. accurately depicts the generalized locations and timings of the divergence “events” that gave rise to the different branches of the Indo-European family, allowing that they did not occur at the precise points indicated on the map, but rather merely in the general vicinity of those places. Here the answer is—yet again—an emphatic “no.” As it turns out, virtually every depiction of linguistic differentiation that can be traced by historical sources is incorrect. Considering as well the erroneous mapping of linguistic expansion given by both the extending lines and the spreading contours, the animated map can only be regarded as a vast compendium of error. It is not that it fails to get everything right, but rather that it gets virtually nothing right.

To illustrate the level of error generated by the model, I will examine in detail the depictions of the expansion and differentiation of several branches of the Indo-European family. One could do the same for all IE sub-families, but such an exercise would be unnecessarily tedious. Before beginning the exercise, a few stipulations are necessary. To begin with, the following analysis is based strictly on the animated map, ignoring material found elsewhere in the article or website, which often runs against the cartographic depiction. While the authors note in their textual supplements, for example, that West Germanic speakers arrived in Britain around 400 CE, the map delays the event for several hundred years. Yet as we have previously seen, what such a cartographic portrayal actually means is that the diffusion of Germanic languages to Britain could have occurred no later than the date indicated by the map, within the general parameters of uncertainty allowed. My point, however, is that we know from historical sources that Germanic languages definitely arrived in Britain at a much earlier period, as the authors themselves acknowledge. If the cartographic depiction of the linguistic “Germanification” of Britain is thus not simply “wrong,” it is both misleading and exceptionally trite.

The Greek and Albanian subfamilies make good starting point, as their cartographic depiction is particularly telling. Bouckaert et al. idiosyncratically regard Greek and Albanian as together constituting a distinct IE sub-family. (Most linguists regard Albanian as an IE isolate that shares certain affinities with Balto-Slavic, Germanic, and Greek; the Science authors classify it with Greek most likely on the basis of borrowed words, as the two languages have been in intimate contact for millennia). Their animated map depicts the ancestral Albano-Hellenic group as arriving on the eastern shores of the Greek Peninsula circa 3000 BCE, and then differentiating into the Greek and Albanian branches around 1500 BCE. Greek then pushes southward into Attica (the Athens area), while Albanian moves to the west into Thessaly in what is now central-eastern Greece. Subsequently, virtual stasis ensues for a few thousand years, with no significant movement of either branch and no further linguistic differentiation. Motion finally kicks in during the thirteenth century CE, when Albanian experiences a “divergence event” in central Greece and begins expanding to the west and north. By the 1500s, the northern Albanian branch finally reaches what is now Albania. At about the same time, the southern Albanian line begins a several-hundred-year maritime phase during which it diffuses across the waters of the Adriatic, finally reaching southern Italy in the 1800s.

The actual geo-histories of the Greek and Albanian languages are completely unlike the fantasy version advanced by the model. As it would again be wearisome to recount all of the many errors involved, I will focus instead on explaining why their depiction is so spectacularly wrong. As is generally true, the erroneous portrayals of these two language groups was predetermined by the error-pocked initial map of language distribution, ancient and modern, that informs the mathematic model. As was discussed in earlier posts, Illyrian, the likely progenitor of Albanian, is ignored, Ancient Greek is absurdly shown as limited to Attica, Albanian is unreasonably divided into four languages, and the areas occupied by Albanian-speaking communities in southern Greece are grotesquely exaggerated while those of Albania itself are absurdly reduced. As garbage is fed into the equations, garbage not surprisingly comes out.

The depiction of the Balto-Slavic languages is risible as well. This language sub-family is portrayed as branching off the main western IE stem circa 3000 BCE in the northern Danubian basin, and then as heading northward over the Carpathian Mountains into what is now central Poland. A small gap emerges on this line circa 950 BCE roughly along the Carpathian crest, which might indicate the Slavic languages differentiating from the Baltic ones. The Baltic line then continues to move northward, although it does not reach Lithuania until the fifth century of the Common Era. A Slavic spur, meanwhile, clearly emerges at roughly 300 BCE, again in the Carpathian Mountains, and begins to slowly creep southward in the early centuries of the Common Era. Diffusing back across the Danubian Basin, it reaches what is now Croatia in the 600s CE. By 900, it has extended as far south as Macedonia, at which point it breaks into several segments. East Slavic emerges out of the same Carpathian hub in the mid 900s CE, and then heads in a northeasterly direction; a hundred years later, West Slavic makes its appearance, branching off from roughly the same location. By the early 1600s, West Slavic has moved westward along the modern Czech-Poland border, approaching what is now eastern Germany. Over a hundred years later, it finally reaches the area now occupied by the Lusatian (Sorbian) speakers. Meanwhile, the East Slavic branch generates three smaller branches circa 1600 in the area where modern Poland, Ukraine, and Belarus converge; these twigs presumably represent Ukrainian, Polish, and Belarusian, which Bouckaert et al.—and no one else—regard as forming a minor Slavic sub-family.

Everything that we know about the historical evolution and distribution of the Slavic languages directly contradicts the mapping of Bouckaert et al., as we should now come to expect. As it would again be tiresome to specify all of these errors, I will note only a few of the more glaring examples. First, it has long been established that the Slavic languages had expanded westward all the way to the Elbe River in what is now central northern Germany in the immediate post-Roman period, entering the lands that had been essentially abandoned by the Germanic tribes that invaded the dying Western Roman Empire. It is also understood that the process of Drang nach Osten in the high medieval period resulted in the re-Germanization of the far western Slavic lands, extending as far east as Silesia and Pomerania. The Lusatian-speaking areas, however, resisted this tide, and thus long remained as Slavic enclaves in a Germanic sea. Silesia and Pomerania, however, were in turn “re-Slavicized” after the post-WWII expulsions of German-speakers. The modeled spread of the South Slavic languages is equally off base. It is also well known that Slavic languages pushed southward into Greece beginning in the 500s and especially during the chaotic aftermath of the Byzantine coup of 602, reaching the central Peloponnesus by the end of the century. As Byzantine power collapsed though most of the peninsula, the Greek language retreated to coastal enclaves. The re-Hellenization of the Greek Peninsula did not begin until the reign of the Empress Irene in the late 700s, and was never fully completed. In regard to the East Slavic branch, numerous absurdities have been discussed in previous posts, and hence will not be recounted here.

Perhaps the most amusing depictions concern the expansion of Insular North Germanic, a minor branch that today includes only Icelandic and Faroese. Recall that Bouckaert et al. model the spread of languages over water the same way that they model it over land, only at a much slower pace (with the exception of their “sailor [sub-] model,” which postulates equal rates of expansion over water and land.) But they always take expansion over any surface as a gradual, diffusional process; recall that instances of “rapid” expansion are purposively ignored, although the pace required for such a designation is never specified. The expansion of North Germanic languages to the islands of the North Atlantic is thus modeled as an example conventional diffusion across isotropic space. The animated map thus show the language group spreading out of northern Denmark in the 700s and heading into the North Sea. Some two hundred years later, these languages are portrayed as reaching the Faroe Islands, and by the mid 1000s they are shown as having finally landed on Iceland.

The only way to make sense out of such mapping is to imagine the speakers of these languages as living at sea on boats that remained relatively stationary over the course of many years, gradually diffusing to the north as the decades passed. The authors, I am almost certain, would object to this characterization, noting that their mapping of Insular North Germanic expansion is not actually meant to depict what it actually does depict (“the language could have arrived any time earlier than the date at which our model shows it as arriving”).  The fact remains, however, that the ancestral language of Icelandic—Old Norse—arrived in Iceland by way of a few voyages that lasted weeks, not month or years, let alone centuries.  This relatively well-attested process was intentional, can be dated relatively precisely to the late 800s, and is known to have been initiated largely by men from what is now Norway, although most of their wives/female-slaves were Irish (see, e.g., Bryan Sykes’ Saxons, Vikings, and Celts: The Genetic Roots of Britain and Ireland). By the explicit criteria specified by the authors, such a “rapid expansion of a single language” should have been ignored. But regardless of how such particular instances are handled, it is clear that if one insists on modeling the spread of languages to distant islands by a process of diffusion, nonsense necessarily results.

Finally, the portrayal of the Romance languages is equally ludicrous. This history of this group is particularly well known, as the spread and differentiation of the various Romance languages, all descended from Latin, occurred in relatively recent times and have been thoroughly documented in written sources, many of which Bouckaert et al. reference in their supplementary materials. Latin spread rapidly with the armies and administrative hierarchies of the Roman Empire, and is hence discounted by the model. As Latin expanded, it began to differentiate, a process that began well before the establishment of the Empire; as noted in a previous GeoCurrents post, a non-IE substrate on Sardinia evidently resulted in significant divergences from standard Latin on the island during the Republican period. Elsewhere, various vernacular forms of speech began to diverge under Roman rule, a process that accelerated after the fall of the Western Empire in the fifth century. The result was the establishment of a widespread Romance dialect continuum that eventually gave way, although never completely, to the standardized national languages of the modern era.

Now consider the manner in which Bouckaert et al. model the spread of the Romance languages. As they do no consider the initial expansion of Latin, they keep the Romance branch confined to central Italy until the fall of the Western Empire. As the empire weakens in the third century, new branches seem to emerge and begin to diffuse in this Italian heartland, although the color scheme leaves some doubt about this process (see the map call-outs). Romance languages clearly emerge in the following century, and by the early 600s one branch finally makes its way to what is now southern France, whereas another has extended to the middle of the Adriatic Sea. Three hundred years later, the western branch reaches the Pyrenees. In the twelfth century, another “divergence event” produces the group that encompasses French and Walloon; beginning along the Mediterranean coast, this division does not reach central France until the 1600s. The Iberian branch, however, is even more delayed, not reaching Portugal until the late 1800s. At about the same time, another Romance sub-family finally makes its landfall in Sardinia.

I anticipate that if the authors were to respond to such criticisms, they would charge me with engaging in a naively literal reading of their animated map. Language divergence “events” along a branching patterns of linguistic differentiation, they might insist, have to be mapped as if they took place at a single location, when in actuality the model supposes only that they took place somewhere within the much larger areas in which the given parent languages were spoken. Such an objection would be fair enough, but it still does not hold water if the actual differentiation processes took place hundreds of miles away from the areas indicated on their maps. In actuality, French emerged out of the Germanic-influenced “Vulgar” Latin dialect(s) of the Paris Basin, and subsequently spread outward, due in large part to the power and prestige of Paris and the French state. Significantly, it did not diffuse outward in an even manner, but rather spread to cities and town well before it penetrated the countryside. French also expanded more slowly where it encountered markedly different dialects/languages, and where other Romance dialects had already established their own prestige registers. Yet again, the issue is not that Bouckaert et al. make few mistakes and that we are unwilling to tolerate error, as has been charged. The issue is rather that their model gets just about everything wrong, often spectacularly so.



Sykes, Bryan (2007) Saxons, Vikings, and Celts: The Genetic Roots of Britain and Ireland. W. W. Norton & Company.