Models of Mechanisms: The Case of the Replicator Dynamics - Mechanism and Causality in Biology and Economics - page 80

biological and economic models, too wide for the respective mechanisms to share a
common abstract causal structure that could be represented by the general RD
model.
The chapter is structured as follows. Section 2 introduces the needed distinctions
between mechanism sketches, abstract models and complete models on the one
hand and particular mechanisms and abstract mechanisms on the other. Section 3
surveys the formal RD model and its derivation from evolutionary game theory.
Section 4 discusses its use by population biologists, who intended it as a represen-
tation of biological mechanisms. In Sect. 5 , I discuss economists' use of the same
RD equation to represent social mechanisms and argue that these social
mechanisms are distinct from the biological ones. Section 6 contains the main
argument, showing that the biological and economic models are separated by an
'idealisation gap' too wide for the respective mechanisms to share a common
abstract causal structure that could be represented by the general RD model.
Section 7 concludes.
2 Models and Mechanisms
The notion of mechanism has had significant impacts on the way philosophers of
science account for the use of models in the sciences, in particular in biology,
economics and the neurosciences. According to these accounts, models explain
because they represent the mechanism that produces the phenomenon to be
explained (Craver 2006 , p. 367). Models help in controlling the real world, because
their mechanism representations enable modellers to answer counterfactual
questions (Woodward 2002 , p. S371). Finally, we can make true claims with
models, because they correctly represent an isolated mechanism, even when they
idealise the influence of many background condition (M¨ki 2009 , p. 30).
In each of these functions, models represent mechanisms. Whatever the specific
definition of mechanism is (I will remain noncommittal here, as different incom-
patible definitions are extant and the detail of these does not matter for my purposes
here), it is clear that mechanism is considered a part of the real world, characterised,
for example, as 'material structures' (Craver and Kaiser 2013 , p. 130) or a 'portion
of the causal structure of the world' (Craver and Kaiser 2013 , p. 141).
A mechanistic model may be designed to represent more or less details of a
mechanism. Here authors have distinguished between mechanisms sketches, sche-
mata and complete mechanistic models. A sketch is an 'incomplete model of a
mechanism' (Craver 2006 , p. 360). While characterising some parts, activities and
features of the mechanism's organisation, it leaves blanks. These blanks are not
necessarily visible, as they may be camouflaged by 'filler terms': terms like
'activate', 'inhibit' or 'produce' that indicate activity in a mechanism without
detailing how the activity is carried out. Thus, there is more to the represented
mechanism than a representing model sketch says.