Models of Mechanisms: The Case of the Replicator Dynamics - Mechanism and Causality in Biology and Economics - page 79

Chapter 5
Models of Mechanisms: The Case
of the Replicator Dynamics

Till Gr ¨ne-Yanoff

Abstract The general replicator dynamics (RD) is a formal equation that is used in
biology to represent biological mechanisms and in the social sciences to represent
social mechanisms. For either of these purposes, I show that substantial ideali-
sations have to be made - idealisations that differ for the respective disciplines.
These create a considerable idealisation gap between the biologically interpreted
RD and the learning interpretations of the RD. I therefore argue that these
interpretations represent different mechanisms, even though they are interpretations
of the same formal RD equation. Furthermore, I argue that this idealisation gap
between the biological and economic models is too wide for the respective
mechanisms to share a common abstract causal structure that could be represented
by the general RD model.

1 Introduction

It has become fashionable in recent philosophy of science to explicate the use of
scientific models by claiming that they represent mechanisms. In this chapter, I
discuss the replicator dynamics (RD), an important model in biology and econom-
ics, and argue that it does not represent a mechanism. The argument proceeds in two
steps. First, I show that even though the same RD model is employed in biology and
economics, the different interpretations in these disciplines make it represent
different mechanisms. Second, I argue that these different mechanisms do not
instantiate a common, more abstract, mechanism. Rather, different kinds of
idealisations are imposed on the RD model, depending on whether it is interpreted
in economics or in biology. This opens an 'idealisation gap' between the different

T. Gr¨ne-Yanoff ( * )
Avdelningen f¨r Filosofi, Royal Institute of Technology (KTH),
Teknikringen 78 B, 100 44 Stockholm, Sweden
e-mail: [e-mail]