Evolutionary Party Loyalty
Kristin Kanthak
335 Social Sciences Building
Department of Political Science
Tucson, Arizona 85721
kanthak@u.arizona.edu
January 2, 2004
Abstract
If rational legislators consider the rules of their legislature when deciding whether or not to leave the
body, those decisions will affect the composition of the legislature, as those who the rules most favor stay,
and their less-favored colleagues go. The current paper explores this phenomenon using an evolutionary
game theoretic model to show that rules that favor legislators who are more ideologically proximate to
their parties will result in a legislature with more loyal legislators. I test the theoretical model using
a competing risks duration model to show that, as the evolutionary model predicts, legislators who
represent districts that are more ideologically proximate to their parties and who vote more like their
party are most likely to receive committee chairs, while those whose districts are further from the party
are more likely to leave the House to run for a higher office.
Prepared for presentation at the 2004 meeting of the Southern Political Science Association. Earlier versions
of this paper were presented at the 2002 meeting of the Southern Political Science Association and the
2001 meeting of the American Political Science Association. Thanks to Jeff Williams for excellent research
assistance and John Aldrich, Keith Poole, Brian Humes and participants of the Micro Incentives Research
Colloquium at Duke University for comments on previous drafts.
1
Party control of the nomination process tends to create more cohesive parties within legislatures. Legisla-
tors toe the party line because failure to do so will likely result in the loss of one’s job. But even legislatures
in which parties have little electoral control generally have some set of rewards (for example, plum committee
assignments in the U.S. House or Senate, or cash in many Latin American legislatures) the party assigns
to those legislators it values most. These per