Discussion:
  1. Mohan Matthen & André Ariew (2009). Selection and Causation. Philosophy of Science 76 (2):201-224.
    We have argued elsewhere that: (A) Natural selection is not a cause of evolution. (B) A resolution-of-forces (or vector addition) model does not provide us with a proper understanding of how natural selection combines with other evolutionary influences. These propositions have come in for criticism recently, and here we clarify and defend them. We do so within the broad framework of our own “hierarchical realization model” of how evolutionary influences combine.
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2009-10-21
Comment
Notwithstanding the arguments of Matthen&Ariew, there is still a simple and banal sense in which "natural selection is a cause of evolution". I presume Matthen & Ariew would not dispute that complex adaptations arise as the cumulative effect of the selection of genes. So the selection of genes causes the evolution of complex adaptations. 

As far as I can see, this claim is compatible with seeing the "selection" here as a statistical trend (or "outcome") rather than a causal process (or "force"). Of course, if by "evolution", one merely means "change in gene frequencies", it would be questionable to call selection a cause of evolution for all the reasons Matthen & Ariew give. But if one means "evolution of complex adaptations", selection most certainly is a cause, however one conceives of selection.

2009-10-21
Comment
Isn't the evolution of complex adaptations identical to a particular change in gene frequencies? If so, then if selection isn't a cause of changes in gene frequencies, then neither is it a cause of the evolution of complex adaptations.


2009-10-24
Comment
Reply to Kris Rhodes
Thanks Kris. The difference I'm getting at here is that the evolution of complex adaptations involves the cumulative selection of genes as they appear in the population by mutation. Maybe I should try and make this clearer. Karen Neander's 1995 and 1995 are helpful on this. I will sketch the basic idea.

Suppose that for a population of haploid organisms there is a possible complex adaptation that would require the presence of two genes at two loci. Let's represent this possible situation as AB. Unfortunately, at time t every member of the population has a different pair of genes at these loci. Let's represent their actual genes at t as ab

Now suppose that the probability of AB arising in one big mutation is vanishingly small, but that the probability of Ab or aB appearing by means of a mutation at one locus is much greater. Ab is adaptive, AB is even more adaptive, but aB is maladaptive, and will not last long if it appears.

Now imagine Ab appears by mutation, is selected and goes to fixation. At t', every member of the population has Ab. It will now only take a single mutation at a single locus in any member of the population to introduce AB. The key point is that the probability of AB appearing in the population has been raised by the selection of Ab. 

This is the sense in which natural selection is a cause of the evolution of complex adaptation. My claim is that this causal relationship is unaffected by whether one conceives of the "selection" of Ab as a causal process or a statistical outcome.





2009-11-10
Comment
I agree that the appearance and increase of Ab is some sort of cause of the fixation of AB.  I even agree that the increase of Ab is an instance of natural selection.  But does it follow that natural selection is a cause of the fixation of AB?  In the sense that interests me, only if you reify natural selection and make it a cause of the appearance and increase of Ab.

In Matthen and Ariew 2009, we contrast two cases.  (a) If mass 1 affects mass 2, there is an intervening variable, gravitational force -- a tertium quid over and above the two masses.  (b) When type Ab has a greater reproduction rate than ab and so the proportion of A increases, there is no intervening variable, natural selection -- no tertium quid over and above the causes of the births and deaths of Ab and ab

I won't repeat the argument here, but it involves the use of the manipulability test.

2009-11-12
Comment
Thanks Mohan, and thanks for an interesting paper. I like the arguments you make. I just don't think they can establish the strong conclusion you want to draw, viz. the falsity of the claim that "natural selection causes evolutionary change". This is because, even once the myth of selection as a reified "force" is busted, there remains an ontologically innocuous sense in which the selection of traits causes the evolution of adaptive complexity.

In your post, you settle for the weaker claim that natural selection is not a cause of evolution "in the sense that interests me". From this I gather that your paper is really aimed at Elliott Sober's 1984 ontologically-heavy conception of selection as a force. My worry, however, is that any biologist reading the paper would take you to be challenging the causal role they ascribe to natural selection in explaining adaptive complexity, and I do not think your argument actually raises such a challenge. 

I think you can see this as a plus point of your general approach to natural selection. One might worry that a statisticalist, non-reifying approach robs natural selection of causal-explanatory import when it comes to explaining adaptive complexity. And one might see this as a reason to reject this approach in favour of something ontologically heavier. But on closer inspection, it turns out we can maintain that selection of traits causes the evolution of adaptive complexity without invoking a spooky tertium quid.

As regards the example I gave, it looks like we agree on these claims:

1. The increase in frequency of Ab is a cause of AB appearing.
2. The increase in frequency of Ab is an instance of natural selection.

From this it follows that:

3. An instance of natural selection is a cause of AB appearing.

I would add another claim:

4. An instance of natural selection in which Ab increases in frequency can be legitimately described as "natural selection of Ab".

Yielding:

5. Natural selection of Ab is a cause of AB appearing.

Importantly, I don't think such a claim reifies natural selection in any spooky way. Its explanatory role here is not as a tertium quid, but rather as a label for a causally relevant frequency increase. Hence, if a biologist were to remark, "natural selection of successive earlier structures caused the evolution of the eye", I would not take her to be saying anything controversial. A statisticalist picture of natural selection is not in conflict with the causal role biologists ascribe to natural selection in making claims such as this.



2009-11-12
Comment
Thanks Jonathan.  This is an interesting suggestion.  I have a question, though, about your labels.  Suppose I agree with your:

5. Natural selection of Ab is a cause of AB appearing.

Suppose analogously I hold that:

6.  Natural selection of camouflage colours is a cause of most moths in population P being camouflaged.

One could ask: is there something ("natural selection") that is a cause both of AB appearing and of most moths in population P being camouflaged?

This conclusion would follow if "natural selection" were an independent term in 5 and 6.  But as I understand your suggestion, it is not.  "Natural selection" occurs as a non-detachable part of a larger term in the two sentences.  (This larger term consists of all the words before 'is' in each statement.)

Do you think that the biologists you allude to in the last sentence of your post would accept this conclusion?  If so, I am completely on board.

2009-12-08
Comment
Reply to Mohan Matthen
Thanks Mohan.

What I have in mind is something like this: suppose "natural selection" just means "frequency increase in accordance with predictive fitness values". On such a view, there can be no "natural selection" independent of particular frequency increases. If this view is right, then, just as any frequency increase is a frequency increase of some trait(s), so all natural selection is natural selection of some trait(s), though mention of the traits may be elided.

This seems to grant everything to the statisticalist and nothing to the causalist in the interpretation of evolutionary theory, and as such will look to many like an implausible construal of what biologists are really talking about when they talk about "natural selection". But I'm not sure it is so implausible. Crucially, the view I have sketched preserves the key causal role biologists attribute to natural selection. On this view, it still makes perfect sense to say that, in general, "natural selection [of monogenic traits] causes the evolution of [polygenic] complex traits".

In short, we can take the causation out of selection without denying selection a causal role in long-term adaptive evolution. This looks like having our cake and eating it; but it isn't, because they are two different cakes.