Russell D. Gray

Language-tree divergence times support the Anatolian theory of Indo-European origin

Languages, like genes, provide vital clues about human history. The origin of the Indo-European language family is “the most intensively studied, yet still most recalcitrant, problem of historical linguistics”. Numerous genetic studies of Indo-European origins have also produced inconclusive results. Here we analyse linguistic data using computational methods derived from evolutionary biology. We test two theories of Indo-European origin: the ‘Kurgan expansion’ and the ‘Anatolian farming’ hypotheses. The Kurgan theory centres on possible archaeological evidence for an expansion into Europe and the Near East by Kurgan horsemen beginning in the sixth millennium BP. In contrast, the Anatolian theory claims that Indo-European languages expanded with the spread of agriculture from Anatolia around 8,000–9,500 years bp. In striking agreement with the Anatolian hypothesis, our analysis of a matrix of 87 languages with 2,449 lexical items produced an estimated age range for the initial Indo-European divergence of between 7,800 and 9,800 years bp. These results were robust to changes in coding procedures, calibration points, rooting of the trees and priors in the bayesian analysis.

Language phylogenies reveal expansion pulses and pauses in Pacific settlement

Debates about human prehistory often center on the role that population expansions play in shaping biological and cultural diversity. Hypotheses on the origin of the Austronesian settlers of the Pacific are divided between a recent “pulse-pause” expansion from Taiwan and an older “slow-boat” diffusion from Wallacea. We used lexical data and Bayesian phylogenetic methods to construct a phylogeny of 400 languages. In agreement with the pulse-pause scenario, the language trees place the Austronesian origin in Taiwan approximately 5230 years ago and reveal a series of settlement pauses and expansion pulses linked to technological and social innovations. These results are robust to assumptions about the rooting and calibration of the trees and demonstrate the combined power of linguistic scholarship, database technologies, and computational phylogenetic methods for resolving questions about human prehistory.

Can ecological theory predict the distribution of foraging animals? : a critical analysis of experiments on the ideal free distribution

Opinions differ on the empirical success of the Ideal Free Distribution. The Ideal Free model predicts that the distribution of organisms between resource sites should match the distribution of resources. Many studies report support for this prediction. We review tests of this model utilising a method of analysis derived from the psychological principle called the matching law. Our reanalysis revealed that the distribution of organisms is consistently less extreme than the distribution of resources. This systematic deviation from the Ideal Free Distribution means organisms underuse richer sites and overuse poorer sites. We examine how deviations from the Ideal Free Distribution may arise as a consequence of discrimination constraints, competitive interactions, competitive asymmetries and travel between sites, and recommend ways in which the design of future tests of the Ideal Free Distribution may be improved.

Language trees support the express-train sequence of Austronesian expansion

Languages, like molecules, document evolutionary history. Darwin observed that evolutionary change in languages greatly resembled the processes of biological evolution: inheritance from a common ancestor and convergent evolution operate in both. Despite many suggestions, few attempts have been made to apply the phylogenetic methods used in biology to linguistic data. Here we report a parsimony analysis of a large language data set. We use this analysis to test competing hypotheses—the “express-train” and the “entangled-bank” models—for the colonization of the Pacific by Austronesian-speaking peoples. The parsimony analysis of a matrix of 77 Austronesian languages with 5,185 lexical items produced a single most-parsimonious tree. The express-train model was converted into an ordered geographical character and mapped onto the language tree. We found that the topology of the language tree was highly compatible with the express-train model.

Mapping the Origins and Expansion of the Indo-European Language Family

A Family of Languages English is part of the large Indo-European language family, which includes Celtic, Germanic, Italic, Balto-Slavic, and Indo-Iranian languages. The origin of this family is hotly debated: one hypothesis places the origin north of the Caspian Sea in the Pontic steppes, from where it was disseminated by Kurgan semi-nomadic pastoralists; a second suggests that Anatolia, in modern-day Turkey, is the source, and the language radiated with the spread of agriculture. Bouckaert et al. (p. 957) used phylogenetic methods and modeling to assess the geographical spread of the Indo-European language group. The findings support the suggestion that the origin of the language family was indeed Anatolia 7 to 10 thousand years ago—contemporaneous with the spread of agriculture. Spatial models of language lineage evolution support an Anatolian homeland for Indo-European languages. There are two competing hypotheses for the origin of the Indo-European language family. The conventional view places the homeland in the Pontic steppes about 6000 years ago. An alternative hypothesis claims that the languages spread from Anatolia with the expansion of farming 8000 to 9500 years ago. We used Bayesian phylogeographic approaches, together with basic vocabulary data from 103 ancient and contemporary Indo-European languages, to explicitly model the expansion of the family and test these hypotheses. We found decisive support for an Anatolian origin over a steppe origin. Both the inferred timing and root location of the Indo-European language trees fit with an agricultural expansion from Anatolia beginning 8000 to 9500 years ago. These results highlight the critical role that phylogeographic inference can play in resolving debates about human prehistory.

Evolved structure of language shows lineage-specific trends in word-order universals

Languages vary widely but not without limit. The central goal of linguistics is to describe the diversity of human languages and explain the constraints on that diversity. Generative linguists following Chomsky have claimed that linguistic diversity must be constrained by innate parameters that are set as a child learns a language. In contrast, other linguists following Greenberg have claimed that there are statistical tendencies for co-occurrence of traits reflecting universal systems biases, rather than absolute constraints or parametric variation. Here we use computational phylogenetic methods to address the nature of constraints on linguistic diversity in an evolutionary framework. First, contrary to the generative account of parameter setting, we show that the evolution of only a few word-order features of languages are strongly correlated. Second, contrary to the Greenbergian generalizations, we show that most observed functional dependencies between traits are lineage-specific rather than universal tendencies. These findings support the view that—at least with respect to word order—cultural evolution is the primary factor that determines linguistic structure, with the current state of a linguistic system shaping and constraining future states.

Diversification and cumulative evolution in New Caledonian crow tool manufacture.

Many animals use tools but only humans are generally considered to have the cognitive sophistication required for cumulative technological evolution. Three important characteristics of cumulative technological evolution are: (i) the diversification of tool design; (ii) cumulative change; and (iii) high–fidelity social transmission. We present evidence that crows have diversified and cumulatively changed the design of their pandanus tools. In 2000 we carried out an intensive survey in New Caledonia to establish the geographical variation in the manufacture of these tools. We documented the shapes of 5550 tools from 21 sites throughout the range of pandanus tool manufacture. We found three distinct pandanus tool designs: wide tools, narrow tools and stepped tools. The lack of ecological correlates of the three tool designs and their different, continuous and overlapping geographical distributions make it unlikely that they evolved independently. The similarities in the manufacture method of each design further suggest that pandanus tools have gone through a process of cumulative change from a common historical origin. We propose a plausible scenario for this rudimentary cumulative evolution.

The crafting of hook tools by wild New Caledonian crows.

The ‘crafting’ of tools involves (i) selection of appropriate raw material, (ii) preparatory trimming and (iii) fine, three–dimensional sculpting. Its evolution is technologically important because it allows the open–ended development of tools. New Caledonian crows manufacture an impressive range of stick and leaf tools. We previously reported that their toolkit included hooked implements made from leafy twigs, although their manufacture had never been closely observed. We describe the manufacture of 10 hooked–twig tools by an adult crow and its dependent juvenile. To make all 10 tools, the crows carried out a relatively invariant three–step sequence of complex manipulations that involved (i) the selection of raw material, (ii) trimming and (iii) a lengthy sculpting of the hook. Hooked–twig manufacture contrasts with the lack of sculpting in the making of wooden tools by other non–humans such as chimpanzees and woodpecker finches. This fine, three–stage crafting process removes another alleged difference between humans and other animals.

Rise and fall of political complexity in island South-East Asia and the Pacific

There is disagreement about whether human political evolution has proceeded through a sequence of incremental increases in complexity, or whether larger, non-sequential increases have occurred. The extent to which societies have decreased in complexity is also unclear. These debates have continued largely in the absence of rigorous, quantitative tests. We evaluated six competing models of political evolution in Austronesian-speaking societies using phylogenetic methods. Here we show that in the best-fitting model political complexity rises and falls in a sequence of small steps. This is closely followed by another model in which increases are sequential but decreases can be either sequential or in bigger drops. The results indicate that large, non-sequential jumps in political complexity have not occurred during the evolutionary history of these societies. This suggests that, despite the numerous contingent pathways of human history, there are regularities in cultural evolution that can be detected using computational phylogenetic methods.

Spontaneous metatool use by New Caledonian Crows.

A crucial stage in hominin evolution was the development of metatool use -- the ability to use one tool on another [1, 2]. Although the great apes can solve metatool tasks [3, 4], monkeys have been less successful [5-7]. Here we provide experimental evidence that New Caledonian crows can spontaneously solve a demanding metatool task in which a short tool is used to extract a longer tool that can then be used to obtain meat. Six out of the seven crows initially attempted to extract the long tool with the short tool. Four successfully obtained meat on the first trial. The experiments revealed that the crows did not solve the metatool task by trial-and-error learning during the task or through a previously learned rule. The sophisticated physical cognition shown appears to have been based on analogical reasoning. The ability to reason analogically may explain the exceptional tool-manufacturing skills of New Caledonian crows.