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In his important recent discussion on natural selection and associated evolutionary processes, already presented in Chapter 1, Godfrey-Smith (2009b) drawing on a long tradition of summaries for ENS, defines a Darwinian population, that is, a population that has the capacity to undergo ENS, in the minimal sense as:

[A] collection of causally connected entity things in which there is variation in character, which leads to differences in reproductive output (differences in how much or how quickly entities reproduce), and which is inherited to some extent. Inheritance is understood as similarity between parent and offspring, due to the causal role of the parents. [...] Any Darwinian population will have these properties plus others. (p. 39)

This set-up for ENS expresses Godfrey-Smith’s particular views on a number of philosophical issues in evolutionary theory. For example, differences in fitness are ultimately regarded as differences in reproductive output. Although, I criticised this standard view it in the previous chapter, I will accept it initially (sections 2.2 and 2.3) in this chapter for expository purposes. One could also question the necessity for entities, to be causally connected. I will also accept this for now but will question it in Chapter 6.

Another striking feature of Godfrey-Smith’s setup of a minimal Darwinian population, but in line with his evolutionary nominalism, is that perfect inheritance between parents and offspring is seen as unnecessary. This choice seems at first natural since in any real population perfect or quasi-perfect inheritance of most traits seems to be the exception rather than the rule. Following Godfrey-Smith’s definition, a population in which there is perfect inheritance between parents and offspring should thus be regarded as a special case of minimal Darwinian population. In fact, with perfect inheritance not only do parents cause their offspring to resemble them as

required by the setup, but the resemblance is perfect. Perfect inheritance seems thus to be a very special case of minimal ENS.

Godfrey-Smith’s general strategy with his Darwinian space is to use a ‘prototype and similarity’ approach to ENS. The minimal Darwinian population is a sort of benchmark against which populations are compared. Although useful in many respects, this approach, which from now I will refer to as the population perspective on ENS, has some limits. One of them, relevant for my purpose, is that if ENS should be expected in a minimal Darwinian populations, it might well be the case that other evolutionary forces are partly responsible, in concert with natural selection and in a substantial way, for the production of the total evolutionary change observed (if there is any). This is in fact what happens in a number of cases reviewed by Godfrey-Smith (2007, 2009) in which there is heritable variation in fitness, but no evolutionary change is observed. In those cases, at least one other force ‘pushes’ in the opposite direction to natural selection. The minimal set-up and more generally the population perspective on ENS, seem unable, on their own, to account for those cases unless one recognises that different evolutionary processes are taking place at the same time. We will examine some of those cases in more detail in Section 2.6.

Another limitation of Godfrey-Smith’s approach is visible when he explicitly criticises the replicator view of ENS (2009, 31-36). As I noted earlier, the replicator framework presupposes a (quasi-)perfect transmission of types across generations. Although Godfrey-Smith’s criticism is targeted towards the idea that ENS does not require perfect transmission, Godfrey-Smith ends up claiming that perfect inheritance is not necessary for Darwinian explanations (2009, 36) in general. While I agree with the claim that Darwinian explanations in general do not require the faithful transmission of traits across generations, this does not demonstrate that the part of the explanation due solely to natural selection does not require the faithful transmission of some trait

at some level. Indeed, the fact that there is imperfect inheritance might be entirely causally explained by evolutionary forces distinct from the process of natural selection.

To determine whether ENS requires perfect transmission across generations, I propose that one must use a complementary approach to that of Godfrey-Smith, one that will allow us to evaluate in the first instance the concept of ENS from what I call a process perspective. The goal of the process perspective is to delimit what the minimal requirements for a population to exhibit nothing but natural selection (what I will call pure ENS) are. Thus, the goal here is to assess whether the evolutionary change observed in a population with imperfect transmission of traits across generations is compatible with pure ENS. One way to carry out this evaluation is to consider a population (albeit a highly idealised one) of entities in which all the evolutionary forces except natural selection have been stripped down: that is, one without mutation, migration and/or drift. In such a case, any remaining evolutionary change in this population will be ENS in its pure form. I call this class of populations, which is a subclass of minimal Darwinian populations, pure Darwinian populations.

Table 2.1. The difference between the population and process perspective on ENS.

Population perspective Process perspective Corresponding

Darwinian population Minimal Darwinian population Pure Darwinian population Evolutionary cause(s)

present in the population exhibiting ENS

Natural selection and possibly other

evolutionary forces

Nothing but natural selection

Targeted explanation What the minimal properties of a population to exhibit

some ENS (minimal

ENS) are

What ENS is/What the minimal proprieties of a population for it to exhibit nothing but ENS (pure ENS) are