There’s no doubt that selection involves causations. But what sort of causation? The account proposed in the end of the last chapter recognises that the sort of causation involved is causal connections between organisms’ traits and their respective reproductive success. Such causal connections are surely causations in a looser sense:
Traits can be causally connected or contributory to reproductive success only via the occurrences of organismal-level events/processes, and their causal contribution to reproductive success is usually cumulative and/or indirect. But there are no special metaphysical concerns against them. They are generation-long causal connections. They go well beyond causal relations between organismal-level events such as predations causing deaths. And they are subsumed under types. Such generation-long causal types are what selection consists in. Or rather, selection with respect to a trait-determinable consists in a multiple of those causal types that differ from one another in this way: The cause-types are different types of determinate under that trait-determinable, and the effect-types are different ranges of determinate degree of reproductive success. So, like all other process views of selection, the present account accepts that a proper characterisation of selection requires the recognition of the sort of causal type the cause-type of which has to do with organisms’ having certain properties and the effect-cause-type of which concerns their having certain reproductive success.
However, the sort of causal type that selection consists in does not go beyond that the instance of which is the causal connection between an individual organism’s having a certain determinate property (or having certain determinate properties) and its having a certain determinate degree of reproductive success. Specifically, selection does not consist in the sort of causal type the instance of which is the causal connection between
variation (or difference) in a certain property (determinable) amongst a population of organisms (or between a pair of organisms) and variation (or difference) in their reproductive success (with respect to that property (determinable)). This is where I part company with all other proponents of the process views of selection in the current debate. My reasons against this sort of causal connection are largely metaphysical: If the talk of variations/differences is taken at the determinable level, then either determinable variations/differences are really properties but are causally inefficacious ones due to the exclusion problem, or there are no such properties/relations such as determinable variations/differences due to the ontological consideration that it is unnecessary to accept determinables as ontologically real. Either way, there are no causal connections of the aforementioned sort. If, however, the talk of variations/differences is taken at the determinate level, then causal connections of that sort may be acceptable. Yet it is a matter of conceptual necessity that any type of those causal connections is identical to, or reducible to, a certain type of collection of multiple causal connections each between an individual organism’s having a certain determinate property (under the determinable the variation/difference in which is the variation/difference in a given case) and its having a certain determinate degree of reproductive success. The talk of such causal types is thus nothing but an abbreviated talk of the latter types of collection of multiple organismal-level generation-long causal connections. Besides, it is semantically strained and characterising selection in terms of it creates unnecessary complications. These plainly suggest that we’d be better off without it, at least in characterising selection.
By contrast, failing to recognise the sort of generation-long causal connection between an individual organism’s having certain properties and its having a certain degree of reproductive success leads Matthen and Ariew to say that selection in the ordinary sense is a mere aggregation of organismal-level events. Every case of selection
is surely a collection of organismal-level events. But selection is more than that. And its truth implies that there is indeed selection in the ordinary sense rather than the contrary.
Matthen and Ariew apparently have an overly restricted conception of causation, event and process, so that they don’t acknowledge that a suitable collection of events can itself be considered an event or process, or that an object’s having a property can be causally efficacious with respect to its being so and so long afterwards in a cumulative manner, via a series of causally related short-term events in which it is involved and with respect to some of which its having that property is causally efficacious.
Admittedly, talks of causation and process in special sciences are usually loose talks from the view of standard metaphysics. But many of them are readily compatible with it.
Some efforts in this regard have been made when we try to metaphysically accommodate the distinctively evolutionary biological talks of selection being a cause of evolution and its being itself a (causal) process. Since we can make sense of these talks in the standard metaphysical framework, and since evolutionary biologists do not apply the notion of selection to a case because it exhibits the formal pattern identified by the growth-rate theorem, there is no reason to change the subject when giving an account of the nature of selection. Even though every case of selection necessarily exhibits that formal pattern, it is just not what selection in the ordinary sense consists in.
The case of fitness is more complicated. The current use of the term “fitness” as an evolutionary biological jargon comes principally from population genetics, where it means (standardised) expected (per capita) reproductive growth rate or simply expected reproductive success. Given this notion of fitness, saying that a trait-type is fitter than another—where the two trait-types are two different determinate-types under the same determinable(s)—in a certain type of environment is just saying that organisms of the former trait-type typically have a degree of reproductive success within a certain range
in that type of environment and those of the latter trait-type typically have a degree of reproductive success within another range, where the two ranges are significantly different. Hence, the talk of fitter-than is essentially a talk of two generalisations. Such generalisations are not in themselves causal ones. They are causal generalisations only when the traits mentioned in them are indeed causally efficacious with respect to reproductive success. A plurality of such causal generalisations which mention different trait-types under the same trait-determinable, different levels of reproductive success and the same environmental conditions then express exactly the same multiple organismal-level generation-long causal types which selection with respect to a trait consists in. So long as the notion of fitness and the talk of fitter-than are so understood, there is no problem with the commonsensical idea that selection is a matter of some organisms’ being fitter than others.
But that idea is fine only in the above understanding of the fitness-talk. Selection does not consist in the connections between different trait-types’ fitnesses taken as reproductive growth rates and their number proportions. Nor does it consist in the mathematical relations between two different mathematical functions of growth rates.
Such connections are mathematical in nature: All collections of life-histories of a population of organisms within a generation (with different trait-types having different reproductive growth rates) necessarily exhibit any of those connections, and their exhibiting each of them can all be known a priori. Identifying selection with any of them deprives all the epistemic significance of a presumably explanatory notion. And again, none of them captures the idea of what evolutionary biologists call “selection”.
Nor does selection consist in the supposed causal type the instance of which is the supposed causal connection between fitness difference and difference in reproductive success, where fitness is taken to be the property that specially grounds the
population-genetic talk of fitness, i.e. reproductive growth rate. If we have to posit such a property at all, then it has to be a second-order functional property, whether it is said to be a unary property or a binary one (i.e. a binary relation) and regardless of what it is otherwise called. Its being functionally or causally identified by reference to reproductive success as its supposed effect-type precludes it from being causally efficacious in the latter respect (the problem of metaphysically necessary dependency).
And since it is a second-order property, due to the exclusion problem it is again causally inefficacious in respect of reproductive success. Either way, there is no aforementioned causal type. Furthermore, fitness in this sense is explanatorily superfluous. For whatever is supposed to be explainable by it in conjunction with various environmental and background conditions can be fully and directly explained by traits in conjunction with the same conditions. Plus, nothing in the current evolutionary biological use of the term
“fitness” requires us to recognise that it designates a property. Therefore, the posit of the property of fitness is redundant, and we should refrain from characterising selection in terms of it.
The fact that selection consists in causal types that differ from one another in their cause-types, i.e. the different traits, not only at the determinate level but also at the determinable level indicates that selection is really an open set of distinct types of process as opposed to a single type of process. This point is also suggested by the idea that selection must be selection with respect to a particular trait (determinable) and there is simply no selection simpliciter. While selections with respect to different traits may be said to be similar to one another primarily in virtue of their all consisting in causal types the effect-types of which concern reproductive success, such a similarity is non-causal and is largely formal or linguistic. And extending the talk of selection to cover cases both within and outside the domain of biological selection, so that they are all
called “selection” because they can all be described as a process that is such that the number proportions of the different types of things within a given boundary change within a given time (and why this happens has something to do with why those things are of different types), is nothing but devising a summarily sentence scheme that mentions no types at all. There is nothing inherently wrong with this. But there is nothing significant either.
A broader implication of selection’s being an open set of distinct types of process is that evolutionary biology is not distinguished by a handful of all-inclusive laws. I don’t find this a problem. Yet it suggests that we view evolutionary biology in a more liberal way. The PNS, or something like that, is often taken as a law, or the law, that lies at the core of the theory of evolution. Now that the posit of the property of fitness has been rejected, what, then, lies at the core of the theory of evolution? More fundamentally, what does the theory of evolution consist in? One thing is for sure: It doesn’t consist in a set of mathematically necessarily true equations or theorems in population genetics.
Perhaps, we should follow many evolutionary biologists to regard evolutionary biology as an interdisciplinary or integrated study that does not have its own core of theory distinguished by a few laws but, instead, relies upon all relevant bodies of knowledge—
distinctively biological or otherwise—in order to offer explanations of differences in reproductive success and of evolution and to furnish more global hypotheses about the evolutionary history of life on the earth. This doesn’t make evolutionary biology a less well-established scientific practise than any area of physics. I see this a better way of viewing evolutionary biology than presuming that it has a few proprietary, all-encompassing laws lying at its theoretical core. At any rate, any candidate of such laws should not be sought in population genetics, in a priori and/or conceptually true general statements, or in something associated with the idea of fitness.
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