How old is the Indo-European language family? A biological solution to a
linguistic problem. 

Quentin D. Atkinson & Russell D. Gray

Department of Psychology, University of Auckland, Private Bag 92019,
Auckland 1020, NEW ZEALAND

E-mail: - qatk001@ec.auckland.ac.nz
 
Languages, like genes, provide vital clues about human history (Gray &
Jordan, 2000).  The origin of the Indo-European language family is 'the
most intensively studied, yet still most recalcitrant, problem of
historical linguistics' (Diamond & Bellwood, 2003).  Due to slow rates
of genetic change, admixture, and the relatively recent timescales
involved, genetic analyses have not conclusively resolved debates about
time-depth in Indo-European.  Languages, however, change much faster
than genes and so contain more historical information at shallower
time-depths.  Despite this, traditional means of linguistic analysis
have also been unable to provide convincing evidence of Indo-European
origins.  This is primarily due to problems associated with variable
rates of language evolution and an inability to quantify the degree of
statistical uncertainty in estimated ages.  Here, we explore the
application of new phylogenetic date estimation techniques to linguistic
data.  These methods are able to estimate divergence times and the
uncertainty associated with each estimate, even under conditions of rate
heterogeneity.  We combine maximum-likelihood models of language
evolution, Bayesian inference of phylogeny and rate smoothing algorithms
to test between two theories of Indo-European origin - the 'Kurgan
expansion' and 'Anatolian farming' hypotheses.  The Kurgan hypothesis
centres on possible archaeological evidence for an expansion into Europe
and the near-East by Kurgan horsemen beginning in the sixth millennium
BP (Gimbutas, 1973).  The Anatolian hypothesis claims that Indo-European
languages expanded with the spread of agriculture from Anatolia around
8,000 to 9,500BP (Renfrew, 1987).  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 7,800BP and 9,800BP (Gray &
Atkinson, In press).  The results were robust to changes in coding
procedures, calibration points, rooting of the trees and priors in the
Bayesian analysis. 


Diamond, J.  & Bellwood, P.  Farmers and Their Languages: The First
Expansions.  Science 300, 597 (2003). 

Gimbutas, M.  The beginning of the Bronze Age in Europe and the
Indo-Europeans 3500-2500 B.C.  Journal of Indo-European Studies 1,
163-214 (1973). 

Gray, R.  D.  & Atkinson, Q.  D.  Language-tree divergence times support
the Anatolian theory of Indo-European origin.  Nature (In press). 

Gray, R.D.  & Jordan, F.M.  Language trees support the express-train
sequence of Austronesian expansion.  Nature 405, 1052-1055 (2000). 

Renfrew, C.  Archaeology and Language: the Puzzle of Indo-European
origins.  London: Jonathan Cape (1987).