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Phylogenetic models and MCMC methods for the reconstruction of language history Robin J. Ryder CEREMADE  Paris Dauphine / CREST  INSEE Joint work with Geoff K. Nicholls at the Department of Statistics, University of Oxford www.slideshare.net/robinryder
Carles li reis, nostre emper[er]e magnes Set anz tuz pleins ad estet en Espaigne : Tresquen la mer cunquist la tere altaigne. Ni ad castel ki devant lui remaigne ; Mur ne citet ni est remes a fraindre, Fors Sarraguce, ki est en une muntaigne. Chanson de Roland , 1r (11 th  century)
La plus commune fa巽on d'amollir les coeurs de ceux qu'on a offensez, lors qu'ayant la vengeance en main, ils nous tiennent  leur mercy, c'est de les esmouvoir par submission  commiseration et  piti辿. Montaigne,  Essais , I, 1 (1580)
Tes yeux sont si profonds qu'en me penchant pour boire J'ai vu tous les soleils y venir se mirer S'y jeter  mourir tous les d辿sesp辿r辿s Tes yeux sont si profonds que j'y perds la m辿moire Aragon,  Les Yeux d'Elsa  (1942)
Et la piaule swingue au son du ghetto, on tape  la porte Chill c'est trop fort ! baisse le son merde ! j'connais A chaque fois c'est pareil tant pis il faut qu'巽a p竪te Et profite en tra樽tre des nouveaux albums qu'Rod m'ach竪te Akh辿naton,  Juste une pression  (2005)
What to expect Description of the data
Model of language diversification
MCMC for phylogenetic trees
Synthetic studies
Analysis of two data sets
Indo-European languages
Indo-European languages
Language diversification Languages change in a way comparable to biological species Similarities between languages indicate that they may be cousins. Most common model : phylogenetic tree
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Questions Topology
Internal ages
Age of the root: 6000-6500 BP or 8000-9500 BP?
(BP=Before Present)
Core vocabulary 100 or 200 meanings, present in almost all languages :  bird, hand, to eat, red...
Borrowing is possible (non-tree-like change), but:
 Easy to detect
Uncommon
Does not introduce systematic bias
Data coding Old English:  stierf綻 Old High German:  stirbit ,  touwit Avestan:  miriiete Old Church Slavonic:  um牒ret鏑 Latin:  moritur Oscan: ? Cognacy classes: 1.  {stierf綻, stirbit} 2.  {touwit} 3.  {miriiete, um牒ret鏑, moritur}
Constraints Constraints on parts of the topology
Constraints on some internal ages
We use these constraints to infer rates and other ages
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Description of the model (1) Traits are born at rate  了
Trait instances die at rate 亮
了 and 亮 are constants
Description of the model (2) Catastrophes occur at rate
At a catastrophe, each trait dies with probability 虜 and Poiss(僚) traits are born.
了/亮=僚/虜: the number of traits is constant on average.
Description of the model (3) Observation model: each data point (0s and 1s) is missing with probability 両
Some traits are not observed and are therefore deleted from the data
Registration process
Registration process
Registration process
Registration process
Posterior distribution
Likelihood calculations
Prior distribution on trees Our main focus is on the root age
We would like the marginal prior on the root age to be (approximately) uniform over (say) 5000-15000BP
MCMC moves Random walk on the parameters
Various moves on the tree (Drummond et al., 2002)
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Checking mixing and convergence Auto-correlations
Need statistics on the tree
Length of the tree
Root age
Presence/Absence of a few subtrees

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Phylogenetic models and MCMC methods for the reconstruction of language history