Natural Selection and Causal Productivity - Mechanism and Causality in Biology and Economics - page 142

1 Introduction

In the recent philosophical literature, two questions have arisen concerning the
status of natural selection: is natural selection a causal process or is it a purely
statistical aggregation? And second, is natural selection at the population level or at
the level of individual organisms? In an earlier work, I argue that natural selection
should be understood as a population-level causal process, rather than a purely
statistical population-level summation of lower-level processes or as an organism-
level causal process (Millstein 2006 ). 1
In reply, Stuart Glennan ( 2009 ) argues that (1) natural selection is produced by
causal processes operating at the level of individual organisms but that there is no
causal productivity at the population level and (2) there are many population-level
properties that are causally relevant to the dynamics of evolutionary processes. In
making these replies, Glennan relies on a claim that there are “two types of
causes,” 2 causal productivity and causal relevance.
I agree with Glennan's second claim concerning the causal relevance of natural
selection at the population level, but I disagree with his first claim concerning the
lack of causal productivity of population-level selection processes. Thus, my focus
in this chapter will be on the first claim; I will argue that natural selection is
produced by causal processes operating at the population level.
In what follows, I will first review Glennan's distinction between causal produc-
tion and causal relevance, followed by an exegesis of his arguments for the claim
that there is no causal production at the population level of natural selection. I then
respond to each of his arguments. Finally, I offer positive reasons for thinking that
there is casual production at the population level of natural selection processes.

1 In this earlier work (Millstein 2006 ), I referred to an “individual-level” causal process instead of
an “organism-level” causal process. This was a somewhat unfortunate choice of terminology on
my part, since, as I will discuss below, populations are themselves individuals. On the other hand,
the advantage of that terminology was that it was agnostic with respect to the units of selection; the
individuals in question could be genes, cells, organisms, etc. So, to be clear - in this chapter, for the
sake of simplicity - I discuss only populations of organisms , with the understanding that selection
can occur in populations of other entities. The more general question, then, which I will not be
discussing here, is whether natural selection consists of causes that act on the individuals of any
sort that constitute a population (including a population of populations) or whether natural
selection consists of causes that act on the population as a whole. Also, in this chapter I will be
discussing Salmon's sense of the term “causal process”; what I call a “causal process” in my 2006
paper would probably be, in Salmon's terms, part of a “causal nexus.” I will return to this point
briefly at the end of this chapter.
2 Others have also argued for causal pluralism , for example, Cartwright ( 2004 ) and Hall ( 2004 ).