Re: New Methodology on Analysis of Language Change


Joe Murphy wrote:

>> I tried to figure out exactly what they were doing but failed. The quest
>> took me to the "Science" website and I have to pay $10.00 for a day pass to
>> read the bigger article.

And On Wed, 11 Jan 2006 23:49:57 GMT, Peter T. Daniels wrote:

> I hope you didn't do so ... Your central public library, and even the
> bigger branches, should ahve *Science*; if it's current, you can buy it
> at Borders (or B&N).

And Joe Murphy now writes:

Eureka! Now "Science" is showing what looks like the entire article.
That wasn't the case a few days ago when I first looked at it.

It's here:

Structural Phylogenetics and the Reconstruction of Ancient Language History

Michael Dunn,1* Angela Terrill,1,2 Ger Reesink,1,2 Robert A. Foley,3
Stephen C. Levinson1,2

The contribution of language history to the study of the early dispersals
of modern humans throughout the Old World has been limited by the shallow
time depth (about 8000 ± 2000 years) of current linguistic methods. Here it
is shown that the application of biological cladistic methods, not to
vocabulary (as has been previously tried) but to language structure (sound
systems and grammar), may extend the time depths at which language data can
be used. The method was tested against well-understood families of Oceanic
Austronesian languages, then applied to the Papuan languages of Island
Melanesia, a group of hitherto unrelatable isolates. Papuan languages show
an archipelago-based phylogenetic signal that is consistent with the
current geographical distribution of languages. The most plausible
hypothesis to explain this result is the divergence of the Papuan languages
from a common ancestral stock, as part of late Pleistocene dispersals.

1 Max Planck Institute for Psycholinguistics, Post Office Box 310, 6500 AH
Nijmegen, Netherlands.
2 Center for Language Studies, Radboud University, Post Office Box 9102,
6500 HC Nijmegen, Netherlands.
3 Leverhulme Centre for Human Evolutionary Studies, University of
Cambridge, Downing Street, Cambridge CB2 3DZ, UK.
* To whom correspondence should be addressed. E-mail: michael.dunn@xxxxxx

The linguistic comparative method used to construct language family trees
relies on recognizing "cognate sets": words in different languages that are
related in meaning and form because they can be shown to have the same
ultimate source in an ancestor language. The comparative method has helped
define the major linguistic family groups that are recognized today.
Unfortunately, because of the continual process of linguistic change, the
method is limited to a time depth of approximately 8000 ± 2000 years (1).
However, it is probable that a considerable portion of linguistic
diversification occurred at earlier dates, associated with later
Pleistocene human dispersals. Alternative attempts to reach further back
and link the world's 300 language families (2) into larger taxonomic units
are controversial (3–5).

One example of this older diversification may be found in Island Melanesia.
Radiocarbon dating for Island Melanesia has demonstrated Pleistocene
occupation more than 35,000 years ago (6, 7) (Fig. 1). Evidence suggests
high levels of inter- and intrapopulational genetic variation (8, 9), with
no simple relationship with linguistic patterns. The languages spoken in
the area are of two groups: (i) over 100 languages belonging to four groups
of the well-established Austronesian family, which probably originated in
the area close to Taiwan and spread to this region about 4000 years ago
(10); and (ii) 23 "Papuan" languages, which are not known to have any
phylogenetic relation to one another and are of much greater antiquity in
the region

The lexical evidence for relationships between Papuan languages is minimal.
Apart from shared Austronesian loans, there are few plausible cognate
candidates found in comparisons of pairs of words from Papuan vocabularies
(Fig. 2) [see, however, (11)]. Assuming that the rate of vocabulary loss in
the Papuan languages is similar to rates observed elsewhere, these
languages are either unrelated or have been separated at least since the
early Holocene or late Pleistocene. These languages do, however, show a
high degree of structural similarity, distinguishing them as a group from
their Austronesian neighbors, which has led scholars to propose
genealogical (or near-genealogical) groupings (12, 13). In the absence of
identifiable lexical cognates, we have used computational cladistic
analysis of these features of linguistic structure to test whether a
phylogenetic signal can be identified beyond the resolution of lexical
form-based methods [for other cladistic methods using lexicons, see
(14–21)]. The structural features of a language, like the lexicon, are
subject to processes of decay over time and can also be borrowed or
exchanged across languages. However, such exchange usually only occurs
under special conditions of prolonged and intensive contact, and it is at
least plausible that where the lexical signal has been lost, a faint
structural signal might still be discernible. Linguistic structure—that is,
grammar rather than vocabulary—has previously been used in historical
linguistics to show statistical evidence for ancient links between
languages from different parts of the world (1, 2, 22, 23) but not directly
to reconstruct phylogenetic relationships.

A questionnaire-based database was constructed, in which linguistic
structural features were coded for their presence or absence in each of the
target languages. These characters were abstract (coded without respect to
their formal expression) and were selected to provide broad typological
coverage, reflecting the known linguistic variation of the region (24), as
well as to be features that would typically be described in a published
sketch grammar. Traits invariant in the region (either entirely absent,
such as polysynthesis or proximate/obviative case distinctions; or present
in all the languages, such as the existence of a word class of verbs) were
not coded. Characters that show strong implicational correlations were
excluded, although characters with weaker tendencies to covariance were not
excluded where the current state of linguistic typological knowledge does
not allow us to systematically distinguish functionally motivated
covariance from phylogenetic or areal patterns. The completed data matrix
contained 125 binary features coded for 15 Papuan and 16 Austronesian
languages spoken in an overlapping region. The Papuan database was mostly
compiled by linguists with field experience in the language and was
supplemented from published and unpublished sources where available. The
Austronesian database was constructed from published sources (25). All sets
of data were checked by a second coder to ensure consistency.

The binary-coded linguistic features allowed us to treat these as character
traits distributed among taxonomic units (languages) and thus to apply
cladistic algorithms (maximum parsimony or NeighborNet) to determine
potential phylogenetic relationships among them (26).

The hypothesis that grammatical structure retained a phylogenetic signature
was first tested among 16 languages belonging to the Meso-Melanesian,
Papuan Tip, and North New Guinea linkages, three sister clades within the
Western Oceanic subgroup of Austronesian, the relationship of which has
been established by the comparative method (10, 27) {although not
completely unambiguously, because there is lexical evidence in particular
that the Papuan Tip and the North New Guinea linkages had a period of
shared history after their separation from Meso-Melanesian [(10), p. 101]}.
We carried out a parsimony analysis on the structural data from these
languages, from which we obtained a consensus tree [tree length, 224 steps;
consistency index (CI) = 0.42; rescaled consistency index (RC) = 0.19;
retention index (RI) = 0.46]. When this tree (Fig. 3, right) is compared
with the classification based on the comparative method (Fig. 3, left),
there is a close match. In the consensus tree, the Meso-Melanesian group
forms a major branch. Papuan Tip and North New Guinea together form a
clade, with the North New Guinea linkage nested as a subclade within it.
This is consistent with uncertainties in the linguistic reconstruction. The
internal structure of the Meso-Melanesian group is quite flat, but all
except one of the clades posited by the comparative method are congruently
represented in the consensus tree. These results show that cladistically
analyzed grammatical structure can preserve a signal that is consistent
with a known phylogeny derived by traditional lexical techniques.

On the basis of this result, we applied the same method to a set of
languages in which lexical similarities are not present. Taking 15 Papuan
languages for which we have full structural data and applying the same
methods, we obtained a consensus tree of the most parsimonious cladograms
for the bootstrapped data set (Fig. 4). This tree has a tree length of 349
steps, CI = 0.35, RC = 0.14, and RI = 0.39. The results show a remarkably
geographically consistent pattern: The major clades represent archipelagos,
and within each archipelago nearest neighbors tend to form sister clades,
despite a nearly complete absence of lexical relatedness.

Interpretation is problematic, because there are no generally accepted
independent linguistic criteria for assessing the Papuan trees. One
possibility is that these trees reflect contact with local Austronesian
neighbors, providing an areal rather than phylogenetic signal. In
experiments, combined Austronesian-Papuan consensus trees were in some
cases intermeshed, but the result was statistically weak (28). Because
Papuan and Austronesian are very unlikely to be genuine sister clades, a
high degree of homoplasy can be the result of either contact or chance
convergence, and combined trees of very remotely related families are
likely to be less robust than those where there are good grounds for
assuming monophyly. A second possibility is the null hypothesis of no
relatedness between the Papuan languages. In that case, we would not expect
the orderly and geographically consistent phylogenetic signal that does
emerge from the data. This signal is consistent with migration followed by
divergence through local isolation. A further possibility is that the
geographically consistent tree reflects recent areal contact among Papuan
speakers, but most of these languages are not currently spoken in
contiguous regions. Because these languages may have been contiguous in the
past, regional diffusion also may account for the phylogenetic signal
observed, a possibility that we cannot test without more detailed
archaeological information.

We therefore suggest that this method reveals evidence of large-scale
genealogical clustering of the Island Melanesian languages; the lack of
putative lexical cognates dates these relationships considerably before the
Austronesian arrival, in line with the radiocarbon dates from the later
Pleistocene, when humans entered Island Melanesia from mainland Papua New
Guinea.

There remain important issues to resolve. The first is methodological;
bootstrap values, especially in the deeper branches, are low by comparison
with biological systems, and further work is required to determine whether
this reflects rates of convergence, trait covariation, or processes other
than phylogenesis alone. Second, the branching sequence does not fit the
generally expected dispersal path. A priori, Island Melanesian Papuan
languages should show a general west-to-east pattern of diversification,
with the center of diversity in the west. The results of our data are more
complex. In particular, the position of the Solomons languages is
anomalous, located in the tree between the Bismarcks clade and the
Bougainville clade, in violation of geographic expectation [because
Bougainville is the natural way-station on the route from mainland New
Guinea to the Solomons (Fig. 1)]. During the late Pleistocene, Bougainville
and the Solomons were united into a single island, from which the Bismarcks
were always separate. A plausible interpretation of the Papuan language
tree is thus that the two language groups now located on the Solomons and
Bougainville separated from a common ancestor. This could have happened
while they could still freely migrate on a common landmass, a time depth
(10,000 years) in accord with that required to erode traces of common
vocabulary. This population history hypothesis will require further testing
with both linguistic and genetic data.

If grammatical structures can retain a phylogenetic signal beyond the
current temporal ceiling on the reconstruction of language history, then
the possibility is opened up of finding relationships between others of the
world's 300 or so existing language families and isolates.


References and Notes


1. J. Nichols, Linguistic Diversity in Space and Time (Univ. of Chicago
Press, Chicago, 1992).
2. J. Nichols, in The Handbook of Historical Linguistics, B. D. Joseph, R.
D. Janda, Eds. (Blackwell, Oxford, 2003), pp. 283–310.
3. J. H. Greenberg, Language in the Americas (Stanford Univ. Press,
Stanford, CA, 1987).
4. L. L. Cavalli-Sforza, P. Menozzi, A. Piazza, The History and Geography
of Human Genes (Princeton Univ. Press, Princeton, NJ, 1994).
5. D. Bolnick, B. Shook, L. Campbell, I. Goddard, Am. J. Hum. Genet. 75,
519 (2004). [CrossRef] [ISI] [Medline]
6. P. Kirch, The Lapita Peoples (Blackwell, London, 1997).
7. M. Spriggs, The Island Melanesians (Blackwell, London, 1997).
8. D. A. Merriwether et al., in Genomic Diversity: Applications in Human
Population Genetics, S. S. Papiha, R. Deka, R. Chakraborty, Eds. (Kluwer
Academic/Plenum, New York, 1999), p. 153.
9. M. Kayser et al., Am. J. Hum. Genet. 72, 281 (2003). [CrossRef] [ISI]
[Medline]
10. J. Lynch, M. Ross, T. Crowley, The Oceanic Languages (Curzon Press,
Richmond, UK, 2002).
11. M. Ross, in The Boy from Bundaberg: Studies in Melanesian Linguistics
in Honour of Tom Dutton, A. Pawley, M. Ross, D. Tryon, Eds. (Pacific
Linguistics, Canberra, Australia, 2001), pp. 301–321.
12. S. A. Wurm, Papuan Languages of Oceania (Gunter Narr Verlag, Tübingen,
Germany, 1982).
13. J. H. Greenberg, in Current Trends in Linguistics, vol. 8, Linguistics
in Oceania, T. A. Sebeok, Ed. (Mouton and Co., the Hague, 1971), pp.
807–871.
14. D. Ringe, T. Warnow, A. Taylor, Trans. Philol. Soc. 100, 59 (2002).
[CrossRef] [ISI]
15. P. Forster, A. Toth, Proc. Natl. Acad. Sci. U.S.A. 100, 9079
(2003).[Abstract/Free Full Text]
16. R. D. Gray, Q. D. Atkinson, Nature 426, 435 (2003). [CrossRef] [ISI]
[Medline]
17. R. D. Gray, F. M. Jordan, Nature 405, 1052 (2000). [CrossRef] [ISI]
[Medline]
18. C. J. Holden, R. Mace, Proc. R. Soc. London Ser. B 270, 2425 (2003).
[CrossRef] [ISI]
19. C. J. Holden, Proc. R. Soc. London Ser. B 269, 793 (2001). [ISI]
20. K. Rexová, D. Frynta, D. J. Zrzav, Cladistics 19, 120 (2003).
[CrossRef] [ISI]
21. A. McMahon, R. McMahon, Trans. Philol. Soc. 101, 7 (2003). [CrossRef]
[ISI]
22. J. Nichols, in Historical Linguistics 1993. Papers from the Eleventh
International Conference on Historical Linguistics, H. Andersen, Ed. (John
Benjamins, Amsterdam, 1995), pp. 337–356.
23. J. Nichols, in The Origin and Diversification of Language, N.
Jablonski, L. C. Aiello, Eds. (California Academy of Sciences, San
Francisco, 1998), pp. 127–170.
24. M. Dunn, G. Reesink, A. Terrill, Ocean. Linguist. 41, 28 (2002). [ISI]
25. See sources of language data in the supporting online material.
26. Materials and methods and a description of linguistic characters are
available as supporting material on Science Online.
27. M. Ross, Proto Oceanic and the Austronesian Languages of Western
Melanesia (Pacific Linguistics C-98, Canberra, Australia, 1988).
28. This intermeshing of trees does reflect long-term contact in New
Britain (26).
29. D. Tryon, B. Hackman, Solomon Island Languages: An Internal
Classification (Pacific Linguistics C-72, Canberra, Australia, 1983).
30. This work, as part of the European Science Foundation EUROCORES
Programme OMLL, was supported by funds from the Nederlandse Organisatie
voor Wetenschappelijk Onderzoek (NWO); the Arts and Humanities Research
Council, UK; and the EC Sixth Framework Programme under contract no.
ERAS-CT-2003-980409. Additional fieldwork data used in this study were
provided by E. Lindström, S. Robinson, T. Stebbins, W. Thurston, and C.
Wegener; assistance with coding from published sources was provided by S.
Nordhoff and V. Rodrigues. We thank M. Mirazon-Lahr, E. Lindström, and G.
Senft for discussion.

There are some illustrations (graphs and tree charts) that are in the
article that I didn't try to reproduce. Also there is a "content" page in
PDF format that can be read online here:

<http://www.sciencemag.org/cgi/content/full/309/5743/2072/DC1>

Joe Murphy
Boy Linguist
.

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