D. Crystal, The Cambridge Encyclopedia of Language (Cambridge University Press, Cambridge, UK, 1997).

G. K. Zipf, Human Behaviour and the Principle of Least Effort. An introduction to Human Ecology, 1st ed. (Addison-Wesley, Cambridge, MA, 1949); reprinted by (Hafner, New York, 1972).

R. Kör, J. Quantitative Linguistics 6, 46 (1999).

R. Kör and G. Altmann, J. Quantitative Linguistics 7, 189 (2000).

L. HrebÃ-k, Quantitative Linguistics, edited by G. Altmann, R. Kör, and B. Rieger (Wissenschaftlicher Verlag, Trier, 1995), Vol. 56.

M. D. Hauser, N. Chomsky, and W. T. Fitch, Science 298, 1569 (2002).

T. W. Deacon, The Symbolic Species: The Co-evolution of Language and the Brain (Norton, New York, 1997).

M. Donald, Origins of the modern mind (Cambridge University Press, Cambridge, MA, 1991).

M. Donald, in Approaches to the Evolution of Language: Social and Cognitive Bases, edited by J. R. Hurford, M. Studdert-Kennedy, and C. Knight (Cambridge University Press, Cambridge, 1998), pp. 44--67.

A. E. Motter, A. P. S. de Moura, Y.-C. Lai, and P. Dasgupta, Phys. Rev. E 65, 065102 (2002).

M. Sigman and G. A. Cecchi, Proc. Natl. Acad. Sci. U.S.A. 99, 1742 (2002).

M. Steyvers and J. Tenenbaum, e-print cond-mat/0110012.

O. Kinouchi, A. S. Martinez, G. F. Lima, G. M. Lourenç and S. Risau-Gusman, Physica A 315, 665 (2002).

R. Ferrer i Cancho and R. V. SoléProc. R. Soc. London, Ser. B 268, 2261 (2001).

S. N. Dorogovtsev and J. F. F. Mendes, Proc. R. Soc. London, Ser. B 268, 2603 (2001).

R. Ferrer i Cancho (unpublished).

N. Chomsky, Syntactic Structures (Mouton, S-Gravenhage, 1957).

A.-L. Barabá and R. Albert, Rev. Mod. Phys. 74, 47 (2002).

S. N. Dorogovtsev and J. F. F. Mendes, Adv. Phys. 51, 1079 (2002).

M. E. J. Newman, SIAM Rev. 45, 167 (2003).

I. Melcuk, Dependency Syntax: Theory and Practice (SUNY, New York, 1988).

R. Hudson, Word Grammar (Blackwell, Oxford, 1984).

D. Sleator and D. Temperley, Carnegie Mellon University Technical Report No. CMU-CS-91-196, 1991 (unpublished).

I. Melcuk, in International Encyclopedia of the Social and Behavioral Sciences, edited by N. J. Smelser and P. B. Baltes (Pergamon, Oxford, 2002), pp. 8336--8344.

B. Bollobá Modern Graph Theory, Graduate Texts in Mathematics Vol. 184 (Springer, New York, 1998).

D. J. Watts and S. H. Strogatz, Nature (London) 393, 440 (1998).

A.-L. Barabá and R. Albert, Science 286, 509 (1999).

J. Uriagereka, Rhyme and Reason. An Introduction to Minimalist Syntax (MIT Press, Cambridge, MA, 1998).

L. UhlÃ-va, I. Nebeskáand J. Krák, in COLING 82, Proceedings of the Ninth International Conference on Computational Linguistics, Prague, edited by J. Horeckýth-Holland, Amsterdam, 1982), pp. 391--396.

M. TesitelováKvantitativni Charakteristiky Soucasnéestini [Quantitative Characteristics of Present-day Czech] (Academia, Praha, 1985), p. 249s.

M. E. J. Newman, J. Stat. Phys. 101, 819 (2000).

E. Ravasz, A. L. Somera, D. A. Mongru, Z. N. Oltvai, and A.-L. Barabá, Science 297, 1551 (2002).

E. Ravasz and A.-L. Barabá, Phys. Rev. E 67, 026112 (2002).

K.-I. Goh, E. Oh, H. Jeong, B. Kahng, and D. Kim, Proc. Natl. Acad. Sci. U.S.A. 99, 12583 (2002).

M. Barthémy, Phys. Rev. Lett.91, 189803 (2003).

U. Brandes, J. Math. Sociol. 25, 163 (2001).

M. E. J. Newman, Phys. Rev. Lett. 89, 208701 (2002).

M. E. J. Newman, Phys. Rev. E 67, 026126 (2003).

L. A. Adamic, Proceedings of the ECDL'99 Conference, LNCS 1696 (Springer, Berlin, 1999) pp. 443--452.

S. Valverde, R. Ferrer i Cancho, and R. V. SoléEurophys. Lett. 60, 512 (2002).

H. Jeong, S. Mason, A.-L. Barabá, and Z. N. Oltvai, Nature (London) 411, 41 (2001).

R. Ferrer i Cancho and R. V. Soléin Statistical Mechanics of Complex Networks, edited by R. Pastor-Satorras, J. M. Rubi, and A. Diaz-Guilear, Lecture Notes in Physics Vol. 625 (Springer, Berlin, 2003), pp. 114--125.

M. A. Nowak and D. C. Krakauer, Proc. Natl. Acad. Sci. U.S.A. 96, 8028 (1999).

M. A. Nowak, J. B. Plotkin, and V. A. Jansen, Nature (London) 404, 495 (2000).

M. A. Nowak, Philos. Trans. R. Soc. London, Ser. B 355, 1615 (2000).

D. Bickerton, Language and Species (Chicago University Press, 1990).

J. A. Hawkins, in Innateness and Function in Language Universals, edited by J. A. Hawkins and M. Gell-Mann (Addison-Wesley, Redwood, CA, 1992), pp. 87--120.

P. Lieberman, Uniquely Human: The Evolution of Speech, Thought and Selfless Behavior (Harvard University Press, Cambridge, MA, 1991).