[1] Albert R and Barabasi A -L 2002 Rev. Mod. Phys.
74 47

[2]Watts D J and Strogatz S H 1998 Nature 393 440

[3]Barrat A and Weigt M 2000 Eur. Phys. J. B 13
547

[4]Barabasi A-L and Albert R 1999 Science 286
509

[5]Barabasi A-L and Oltvai Z N 2004 Nature 5
101

[6]Ravasz E, Somera A L, Mongru D A, Oltvai Z N and
Barabasi A-L 2002 Science 297 1551

[7]Xuan Q, Li Y J and Wu T J 2006 Phys. Rev. E 73
036105

[8]Strogatz S H 2001 Nature 410 268

[9]Colman A M 1982 ooperation and Competition in Humans
and Animals (Wokingham: Van Nostrand Reinhold)

[10]Nowak M A, Sasaki A, Taylor C and Fudenberg D 2004
Nature 428 646

[11]Hauert C and Doebeli M 2004 Nature 428 643

[12]Roberts G and Sherratt T N 1998 Nature 394 175

[13]Taylor P D and Day T 2004 Nature 428 611

[14]McNamara J M, Barta Z and Houston A I 2004 Nature
428 745

[15]Ackermann M and Chao L 2004 Curr. Biol. 14
R73

[16]Rainey P B and Rainey K 2003 Nature 425 72

[17]Vellcer G J and Yu Y -T N 2003 Nature 425 75

[18]M-Gibbons M and Adams E S 2002 Science 298
2146

[19]Palameta B and Brown W M 1999 Animal Behavior
57 F1

[20]West S A, Pen I and Griffin A S 2002 Science
296 72

[21]C-Brock T 2002 Science 296 69

[22]Brandt H, Hauert C and Sigmund K 2006 Proceedings
of the National Academy of Sciences 103 495

[23]Roughgarden J, Oishi M and Akcay E 2006 Science
311 965

[24]Nowak M A and Sigmund K 2005 Nature 437 1291

[25]Fehr E and Fischbacher U 2003 Nature 425 785

[26]Fowler J H 2005 PNAS 102 7047

[27]Nowak M A and Sigmund K 2002 Nature 418 138

[28]Anghel M, Toroczkai Z, Bassler K E and Korniss G 2004
Phys. Rev. Lett. 92 058701

[29]Santos F C and Pacheco J M 2005 Phys. Rev. Lett.
95 098104

[30]Zimmermann M G, Eguiluz V M and Miguel M S 2004
Phys. Rev. E 69 065102(R)

[31]Holme P, Trusina A, Kim B J and Minnhagen P 2003
Phys. Rev. E 68 030901(R)

[32]Gintis H, Smith E A and Bowles S 2001 J. Theor. Biol.
213 103