Here we go again…

Share on FacebookShare on Google+Email this to someoneTweet about this on Twitter

I’m not going to spend too much time on this, but Larry Moran has responded to my post. He, of course, makes it sound as if he’s being perfectly reasonable. But consider what he wrote in July:

[E]volutionary biologists like Dawkins and the other adaptationists should have known about random genetic drift. Isn’t it amazing that they don’t?

And compare with his new line:

There are many adaptationists who recognize that random genetic drift exists. They will, when pressed, admit that neutral alleles can be fixed in a population.

He goes on to dispute that his quotation from Dawkins was misleading. I obviously disagree, because I was misled! When Dawkins writes “If a whole-organism biologist sees a genetically determined difference among phenotypes, he already knows he cannot be dealing with neutrality in the sense of the modern controversy among biochemical geneticists”, I assumed (as most readers likely did) that Dawkins was dogmatically asserting that absolutely no phenotypic change can be neutral. He wasn’t, of course.

In any case, if Moran wants to define an “adaptationist” as someone who hypothesizes an adaptative force driving most phenotypic changes, then sure, Dawkins is probably an adaptationist, as am I and many reasonable biologists. Hypotheses have to be confirmed, of course, and “adaptationism” (tempered with knowledge of demographic forces) is a powerful hypothesis-generating machine. Keep in mind that one of Moran’s “textbook examples” of neutral phenotypes is eye color. OCA2 (the major locus controlling eye color in humans) of course shows one of the strongest signals for selection in the human genome. I have hypotheses about why this is (could be an example of pleiotropy), but if you can just assert that eye color is a neutral character, why even bother?

UPDATE: Larry Moran claims the first of his quotes above was both ironic and sarcastic. Judge for yourself (in his favor, the claim is obviously wrong. in his disfavor, if you weren’t familiar with Dawkins’s writing, it wouldn’t seem obviously wrong). Maybe he means ironic in the Canadian sense.

6 Comments

  1. I wonder about what sort of mental model people like Larry have. It just seems brutally obvious to me that a phenotypic difference having *zero* probabilistic effect on reproductive success is like a coin landing on its edge — this will happen if you flip it enough times (i.e. look at enough traits) but the frequency of it is an engineering zero. Whether the functional significance of a given phenotypic difference is immediately obvious to us or not is simply not material, because selection sees myriad things that we don’t. There are certainly demographic situations where noise can swamp signal and these certainly can be evolutionarily important when they happen, but the circumstances required are so relatively unusual that invoking drift to explain phenotypic change should require some special motivation. Hitchhiking & pleiotropy are more ubiquitous, so if you’re trying to tell a non-adaptive story about something these would be the more a priori probable places to start — but of course Larry won’t like that either because stories about hitchhiking and pleiotropy are still intimately tied up with functional stories about other traits.

  2. Hitchhiking & pleiotropy  
     
    it’s an interesting question about pleiotropy and the extent with which the G-matrix constrains directional selection on one trait. far more interesting than: 
    ADAPTATIONIST!!!! 
     
    NO I’M NOT!!!! 
     
    ADAPTATIONIST!!!! 
     
    NO I’M NOT!!!! 
     
    ADAPTATIONIST!!!! 
     
    NO I’M NOT!!!! 
     
    ADAPTATIONIST!!!! 
     
    NO I’M NOT!!!! 
     
    ADAPTATIONIST!!!! 
     
    NO I’M NOT!!!! 
     
    …at least for most people ;-) the important point is that questions like these seem ill-served by one sentence expositions of one’s position. and of course, verbal expositions always leave a way out by allowing one to say “i didn’t mean that, you misunderstood me.”

  3. Well, you can imagine there being some kind of frequency dependent selection where the advantage of having the same phenotype as everyone else is large but which particular phenotype becomes ubiquitous for the species doesn’t really matter much. I’m thinking pheromones and such.

  4. at least for most people ;-) 
     
    heh. yeah, more interesting for me too, I just get sucked in…

  5. heh. yeah, more interesting for me too, I just get sucked in… 
     
    …like moth to the flame…. ;-)

  6. George brings up a good example. There are a lot of aspects of organisms that are evolutionary “don’t cares” in the sense that something has to fill that functional slot but there are a wide range of possible solutions that will serve the purpose equally well. Hormones would be another one — there has to be some kind of molecule that can carry a particular chemical signal around the body via circulation, but there might be a bunch of different ones that would do the trick and which one becomes the “standard” is mostly a matter of path-dependent historical accident. Though even in that case there’s still functional constraint: the molecule can’t be too big or too small, etc, or else it doesn’t suit the purpose. 
     
    But even cases like this are not always easy to prejudge, so it’s not a mistake to ask the question “why is it like this rather than some other way?”, even if it turns out that there’s no functional reason, because at least then you’re likely to learn something about the trait you’re examining. Throwing up your hands prematurely and saying it’s just a Damned Thing that got that way because it got that way is not going to lead you to many fruitful investigations.  
     
    Razib — Agreed. When confronted with weird axe-grinding like this, nowadays I usually just try to deflect the challenge to a higher level of abstraction. Though I “adaptationist” is a label I wouldn’t really care about — to me it’s like calling someone a “rationalist” in debates about methodological assumptions in economics. Sure, people don’t always behave “rationally” (however you want to define that operationally), but you get a lot more mileage out of that assumption than any other because modelling non-rational actors is often hard and always involves a lot of ad hockery.

a