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Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. Blackwell Publishing and Royal Economic Society are collaborating with JSTOR to digitize, preserve and extend access to The Economic Journal. http://www.jstor.org * We are grateful to Robyn Dawes, Paul Milgrom, John Carter, and two anonymous referees for helpful comments, and to Dan Schneidewend and Soren Hauge for expert programming and research assistance. Andreoni also thanks the National Science Foundation, grant SES 882 I 204, for financial support. Errors are the responsibility of the authors. 1 See also Kreps and Wilson (I982), and Milgrom and Roberts (I982). 2 See, e.g. Palfrey and Rosenthal (i 988), Andreoni (i 989, I 990), and Cooper et al. (I990) for a discussion of this. 3 See Camerer and Weigelt (I988) for a more complete discussion of other experiments that pertain to reputation building. [ 570 ] ' See Roth and Murnigham (I978) and Roth (I988) for reviews of prisoner's dilemma experiments a historical review of prisoner's dilemma experiments in psychology and sociology, see Rapoport Chammah (I965). See Dawes and Thaler (I988) for a recent review and discussion of cooperatic providing public goods. 5 For reviews and discussions of the psychology and sociology literatures on cooperation and altri behaviour, see Dawes (I980) and Piliavin and Charng (I990).

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We develop a model of two-party spatial elections that departs from the standard model in three respects: parties' information about voters' preferences is limited to polls; parties can be either office-seeking or ideological; and parties are not perfect optimizers, that is, they are modelled as boundedly rational adaptive actors. We employ computer search algorithms to model the adaptive behavior of parties and show that three distinct search algorithms lead to similar results. Our findings suggest that convergence in spatial voting models is robust to variations in the intelligence of parties. We also find that an adaptive party in a complex issue space may not be able to defeat a well-positioned incumbent.

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Results are presented from 500 ps molecular dynamics simulations on the native dodecamer d(CGCGAATTCGCG)2 and the lesioned dodecamer containing a cis,syn-thymine cyclobutane dimer at the TT step. The computations, performed with AMBER4.1, included explicitly represented solvent with periodic boundary conditions applied within the constant temperature and pressure algorithm. Electrostatic interactions were calculated with the particle-mesh Ewald method. Distortions to DNA structure produced by the lesion were found to be localized at the dimer site and include mainly a substantial kink in the helical axis, rolled and tilted base pairs, and weakened hydrogen bonding at the 5‘ base pair of the lesion. A slight change in orientation around the glycosyl bond for the 5‘ thymine of the lesion and highly stiffened deoxyribose rings for both thymine bases were also observed. The global curvature of DNA is increased by about 10° by dimer incorporation. Calculations of H(1‘)-H(6)(pyrimidine) and H(1‘)-H(8)(purine) interproton distances from the performed simulations agree very well with the pattern of NMR NOE signals reported in various dimer containing oligonucleotides, where an interruption of NOE connectivities is found on the 5‘ side of the lesion. Comparison of the pattern of distortions observed at the dimer site with the crystal structure of a complex between dimer-containing DNA and repair enzyme endonuclease V (Cell 1995, 83, 773−782) leads to the hypothesis that dimer recognition may involve a whole pattern of small distortion at the lesion site rather than one particular structural/dynamical feature associated with the lesion.

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