Pav and Frequency Dependence: Once Again UD Fails to Understand the Issues

Over at UD Pav has discovered the fruit fly research I blogged about. In writing about it he betrays a vast amount of ignorance when it comes to natural selection and population genetics. As I pointed out in my post on the subject, the research concerned negative frequency dependent selection. What does Pav make of it?

I know there are population geneticists out there, so, if you can, how would you explain NS being able to virtually decide that it is “best” to conserve both forms, rather than to single out one of the two forms? Or, does this mean that there really is no such thing as “fixation” and “extinction”, thus rendering neo-Darwinism null and void?

A commenter (Bob O’h) tries to set him straight:

PaV – I’m afraid your questions show that you haven’t understood evolution. It’s basic that evolution isn’t teleological, so it doesn’t “decide” that it is best to conserve diversity. It’s just that, in this case, the population will evolve to a state with more than one phenotype. So your question is moot.
What’s being described is called frequency dependent selection, and is well known in population genetics. It’s also not universal: there are some traits that are under frequency dependent selection (the sex ratio is one), but not all traits (and probably only a minority). Hence, your second question is also moot.

Pav responds:

You’ve given this phenomena a name, and in the article they call it “negative frequency-dependent selection”. But giving something a name doesn’t mean you’ve explained the phenomena; nor does it mean that the phenomena fits into standard population genetics [emphasis mine – afarensis]. Again, I would appreciate some attempt at explaining why we find this phenomena in nature. Can you supply it?

Let’s start with the part I bolded. Pav claims frequency dependent selection does not fit into standard population genetic theory. Let’s look. I pulled five books off my shelf and looked up frequency dependent selection.
Evolutionary Biology by Douglas Futuyma. Granted this is not specifically about population genetics, but let’s hear what the evolutionary biologists have to say first. On page 166 Futuyama starts his discussion. He points out that in models discussed earlier the fitness of each genotype was constant within a given environment. There are other cases, he says, in which fitness varies. After , briefly, giving some of the mathematical underpinnings he goes on to give the example of aposematic coloration. Then he says:

Indeed, it is likely that there is a frequency-dependent component in virtually all selction that operates in natural populations [emphasis mine – afarensis] for interactions among members of a population affect the selective advantage of almost all traits, and such interactions usually give rise to frequency-dependent effects.

A Primer of Population Biology by Edward Wilson and William Bossert. Wilson and Bossert discuss frequency-dependent selection under the heading of balanced polymorphism.
Principles of Population Genetics (2nd Ed) by Daniel Hartl and Andrew Clark. The discussion starts on page 184:

In reality, a genotype may have different fitnesses depending on many aspects of the environment, including food or light availability, population density and the relative frequencies of other genotypes (frequency-dependent selection).

They then go on to show the math behind frequency-dependent selection and give a few examples.
Introduction to Quantitative Genetics by D. S. Falconer (3rd Ed). Falconer discusses frequency-dependent selection on page 45:

Having a phenotype that is rare may itself be an advantage, irrespective of what the phenotype is. The direction of selection is then dependent on the gene frequency: an allele at low frequency produces the rare phenotype and is favored, but the same allele at high frequency is selected against. This leads to a stable equilibrium gene frequency and so to a balanced polymorphism

Falconer mentions several examples and concludes:

In general, the development of special methods of attack and of defence in the relationships between predator and prey and between pathogen and host, seem likely to result in frequency-dependent selection.

Population and Evolutionary Genetics: A Primer by Francisco Ayala. Ayala begins his discussion on page 114 and he, too, discusses frequency-dependent selection in terms of balanced polymorphism. Selection is frequency-dependent when:

…the genotypic fitnesses vary with their frequency. In the examples of selection discussed so far, it was assumed that the fitnesses were constant, no matter what the frequencies of the genotypes. This simplifies the mathematical treatment of selection but is often unrealistic.

He goes on to say that:

In heterogeneous environments, a genotype may have a high fitness when it is rare, because the subenvironments in which it is favored are relatively abundant. But when the genotype is common, its fitness may be low because its favorable environments are saturated.

And later:

Frequency-dependent selection in favor of rare genotypes is a mechanism contributing to the maintenance of genetic polymorphisms, since the fitness of a genotype increases as it becomes rarer…Frequency-dependent sexual selection may be particularly important in cases of migration. (e.g. the rare mate effect – afarensis)

So, to wrap things up, frequency-dependent selection is part and parcel of population genetic theory and evolutionary biology. It is used to explain a wide variety of phenomena such as balanced polymorphism, rare mate advantage, aspects of predator/prey and pathogen/host relationships, and coloration.
So, why was Pav so wildly off base? I can think of at least one reason. A lack of familiarity with even the basic literature has lead Pav to some wrong ideas about what selection is. For creationists such as Pav, there is only one type of selection and it leads only to “fixation or extinction” and they try to force everything into their own limited and ill informed notions of what evolution is.

5 Responses

  1. This is just another example of how the creationist mind can’t digest the idea of seemingly intelligent emergent properties from evolutionary processes. To them it has to be completely direct (ie stupid), or guided by some consciousness. No doubt he’d ask the same question about this robotic experiment with EAs where one subgroup of robots developed a blink-at-the-food strategy and another group developed an opposite blink-at-the-poison strategy. How did the program “decide” to do this? It didn’t. That’s just the way it worked out.
    Of course, that assumes he’d deal honestly with the implications of EAs, but he’d probably hide behind the “front-loaded intelligence” of the programmers canard.

  2. A lack of familiarity with even the basic literature has lead Pav to some wrong ideas about what selection is.For creationists such as Pav, there is only one type of selection and it leads only to “fixation or extinction” and they try to force everything into their own limited and ill informed notions of what evolution is.

    This is much too kind. Pav doesn’t even know the very basics of biology and he exposed his ingnorance more than once. E.g.: He doesn’t understand the difference between mutation rate and allele frequencies.
    Funny that DaveScot claimed copyright for all the bullshit posted on UD.

  3. Haha, part of my research is on frequency-dependent selection. I even mentioned a paper of mine a while back on my blog about it.

  4. An example of frequency-dependent selection is seen in the white clover of Port Meadow in Oxford (I am writing this from memory but I think I have the details correct). White clover spreads vegetatively by means of runners. Each plant has its own distinctive leaf markings so in a field it is possible to identify members of the same clone. Port Meadow has had the same grazing management for at least 600 years (except for 2 years when Cromwell cut it for hay) so it is reasonable to expect the best-adapted clone to occupy most of the meadow. However, when G.R. Sagar and J.L. Harper examined it in the 1960s they discovered many clones present even in a small area. What they found was happening was that the sheep, which prefer white clover to other plants, selectively graze the most common leaf-type until it is rare, then switch to the next most common leaf type (this is the most efficient way of searching). This means the most common plant is continuously being selected against.

  5. Pav is doing the oft-seen “I don’t understand what scientists do all day” dance. We’ve seen it many times before. I think it’s projection (which is endemic on the right, as we’ve seen over the past 8 years). They work on any given subject X amount, and they think that’s a lot, and it’s inconceivable to them that anyone would actually work more than that; they learn about any given subject X amount, and they think that’s a lot, and it’s inconceivable to them that anyone would actually learn more than that.
    Here’s how to think like them: Opening a book to actually study the subject is madness, since that only indoctrinates you into the temple of the ivory tower and shuts you off from the amazing insights one can only get by being ignorant of your subject and imagining that people who spend their entire careers working on that subject are as ignorant as you. So when someone points out to you that the subject is so well understood that it has a formal name and attendant writings, assume that all the scientists did was put a name on it, because that is what you would do, as in changing “creationism” to “ID” in Pandas.

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