Against Positive Selection
My usual complaint: it's too far past bedtime to write sufficiently about this topic. It's true, but it's also true that I think the topic is much bigger than I can adequately attend to at this bleary-eyed hour. Nevertheless, I'll sleep better if I jot down a few sentences. (I've alluded to this idea before, here and here.)
In short, I've long wondered whether many hard-core Darwinists have made a slight error in perception that has led to possibly major errors in application and deduction. I want to examine the idea more fully, partly because I don't want to be misunderstood, and I certainly don't want to be immediately labelled as a crank (or worse: a fringe scientist!). In fact, in these troubled times of "faith-base pseudo-science", I've undoubtedly gone from Darwinist to staunch Darwinist: scientific extremism in response to adaptive pressures.
It all has to do with the manner of operation of natural selection. I believe that the summarizing phrase "survival of the fittest" has inadvertantly come to mean, in most people's mind, that natural selection operates as a positive force on evolution, a force that somehow selects for certain characteristics: those that confer survival advantage (to the individual or to the species, depending on point of view). I also believe that most of the error is linguistic, at least originally, but that the error has persisted and (dare I say) evolved into a trope that leads to misadventure when it comes to understanding adaptation and the causes of specific adaptations.
My slightly revised gloss on "survival of the fittest" goes like this: natural selection, as a mechanism of evolution, selects against undesirable characteristics. The key difference between the two (since I reject the "law of the excluded middle" in this context) is that natural selection is, therefore, benign or neutral when it comes to the question of neutral, non-negative characteristics. By "non-negative characteristics" I mean those characteristics that are neutral to survival — annoying and useless, perhaps, but not a selective detriment.
Said differently: natural selection does not select for positive characteristics, is selects against negative characteristics. This seeming quibble over syntax ("isn't it just a kind of double negative?") has serious implications for the consideration of benign characteristics if their existence doesn't require a positive explanation.
As an example, if the human appendix is not causing a problem, then natural selection is indifferent and the appendix remains as a vestigial organ, possibly available for some other use on the road to evolving some other function. Pointedly, I do not see the reason to spend a lot of wasted effort on trying to imagine unnecessary reasons that would explain why the appendix is still there (i.e., what it is "good for"), as though it must be needed for something simply because natural selection has not disposed of it.
Now, I've already included a few entries earlier in the blog that I claim support my contention that people mistakenly think of natural selection as a positive force, but I've harbored anxieties that some of the evolutionists that I'd read may not have thought so, even though I thought I remembered many who did. I need to review a lot of literature, starting with Henri Bergson's Creative Evolution, since that seems to be the source towards which these lines converge. That's one more reason why I've been circumspect about saying anything too provoking. Oops — too late!
So it was with some surprise that I read this very bald statement by Richard Dawkins, one of the important Darwinian voices, that professes the positive viewpoint about natural selection:
“Anting” is the odd habit of birds such as jays of “bathing” in an ants’ nest and apparently inciting the ants to invade their feathers. Nobody knows for sure what the benefit of anting is: perhaps some kind of hygiene, cleansing the feathers of parasites. My point is that uncertainty as to the purpose doesn’t—nor should it—stop Darwinians from believing, with great confidence, that anting must be good for something.
[Richard Dawkins, "What Use is Religion?"]
In: All, Hermeneutics, It's Only Rocket Science
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on Wednesday, 6 April 2005 at 13.27
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[…] I was siezed with an undeniable fever to write some notes on my notions concerning "Negative Selection" about how Evolutionary Biologists had gotten it all wrong (c'mon, I know better […]
on Wednesday, 6 April 2005 at 13.52
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There is a difference between positive and negative selection. Assume we start with a newly arisen mutation and describe how natural selection acts on that mutation. If that new mutation is benificial then natural selection is said to drive the mutation to fixation (positive selection). Conversely, if the new mutation is deleterious, then natural selection purges the mutation from the population (purifying/negative selection). This the accepted terminology in the Molecular Evolution literature; I'm not making this stuff up on the spot.
Fitness depends on environment and the other alleles present in the population. For instance, if a new allele for "no appendix" appeared in the population, it may be driven to fixation by natural selection if it confers some fitness benefit. The "appendix allele" is only deleterious when the "no appendix allele" is also present in the population. (It may also go to fixation due to neutral processes.) Also, if the environment changed such that we need an appendix to perform some function, then there would be strong purifying selection against those mutations that cause loss-of-appendix. Now the "no appendix allele" is deleterious.
Positive/negative selection depends on how you define your fitness parameters (eg h, s, and w in population genetics theory). Therefore, it all comes down to relativity.
on Tuesday, 15 August 2006 at 13.53
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I am afraid your (1 RPM) idea of positive and negative is a bit off. Look from the point of view of mutation. Negative selection perse is deleterious. Example: a certain molecular change results in a offspring phenotype "No mouth". The offspring cannot eat hence dies. Deleterious=resulting in deletion. Positive selection on the other hand means that a certain offspring has an advantage over another offspring. This will result in purging and the population is purified from less fit individuals! The confusion arises from the idea that purifying is the same as negative. True, but here it all depends on the point of view: with positive selection a mutation results in the purging of the old genotype. With negative selection a mutation results in the purging of the offspring.