Organisms, Groups, and Memes: Vehicles or Replicators? Part 2

I have never understood Punctuated Equilibrium in the manner that Dawkins, in his chapter, spends considerable time refuting. Evolution is gradualist, as Dawkins says, in the sense that there is no such thing as half an animal. A "transitional fossil" can be a confusing concept, giving one the idea that certain animals are "transitional" as opposed to being "normal" (when in fact every living thing is "transitional"). This misunderstanding is exploited by creationists in their tiresome demand for "transitional" fossils.

P.E. is, essentially, a reinterpretation of the fossil record which turns out not to be as radical or revolutionary as Gould portrayed it to be. Dawkins likens the difference between previous interpretations and the Gould-Eldredge proposal as the difference between walking up a hillside and ascending a staircase. There are no "gaps" in the fossil record, only steps.

Dawkins explores Gould and Eldredge's equation: P.E. + Wright's Rule = Species Selection

Wright's Rule: "The proposition that a set of morphologies produced by speciation events is essentially random with respect to the direction of evolutionary trends within a clade." In other words, in an apparent analogy with mutational randomness, if a species of horse shows marked progression toward larger body size, a new species of horse would not necessarily follow this trend, if Wright's Rule is preserved. As many new species would be smaller than the clade as larger. Therefore, Wright's Rule must be tested.

However, Dawkins points out (quoting Gould): "'If Wright's Rule be valid, and new species of horses arise equally often at sizes smaller and larger than their ancestors, then the trend is powered by species selection. But if new species arise preferentially at sizes larger than their ancestors, then we don't require species selection at all, since random extinction would still yield the trend.' Gould here simultaneously sticks his neck out and hands Occam's Razor to his opponents!" Dawkins adds that he can imagine some major speciational trends of the type described by Cope's Rule,* but points out that this is quite different that the original question, that of individual sacrifice behavior or adaptations "for the good of the species." The difference is between the concept of the group as replicator versus the group as a vehicle for replicators.

Palaeontological major trends, such as the length of horses' legs, are simple, requiring only a few replicator replacements, whether we mean genes or species at this point. However, many more replicator replacements are required for the evolution of a complex adaptation such as those that allowed a land mammal to evolve into whales, for example. Even if such a complex phenomenon could be broken down into smaller evolutionary events, the adaptation involves an interrelated web of changes that group-selectionism just could not produce them without yielding, over and over again, a highly unlikely barrage of parallel beneficial trends. (Indeed, this mistaken idea of group-selectionism could be what some creationists imagine evolution to be, leading them to dismiss evolution as improbable.)

Dawkins writes:

The theory of species selection, growing out of that of punctuated equilibria, is a stimulating idea which may well explain some single dimensions of quantitative change in macroevolution. I would be very surprised if it could be used to explain the sort of complex multidimensional adaptation that I find interesting, the 'Paley watch," or 'Organs of extreme Perfection and Complication' kind of adaptation that seems to demand a shaping agent at least as powerful as a deity. Replicator selection, where the replicators are alternative allels, may well be powerful enough. If the replicators are alternative species, however, I doubt if it is powerful enough, because it is too slow. Eldredge and Cracraft (1980, p. 269) appear to agree.

Part 3: Memes

Organisms, Groups, and Memes: Vehicles or Replicators? Part 1

An active replicator is that which exerts at least some kind of influence over the likelihood of its being copied. A DNA molecule is a replicator; a piece of sheet music considered valuable enough to be xeroxed can be considered a replicator (Dawkins, p. 83); but an individual organism, sexual or asexual, cannot be considered a replicator.

Here's why.

Because we reject Lamarckism, we know that characteristics acquired during an organism's life cannot be passed down to its offspring. Even in the case of asexual reproduction in which the entire genome is passed down, any acquired features--a lost limb, developmental factors, etc.--is not replicated in the lineage, and in order for the organism as a whole to be called a replicator it must pass these on. "There is a causal arrow," writes Dawkins, "going from gene to bird, but none in the reverse direction." However, the genome of an organism that reproduces asexually could be a candidate for the term "replicator."

Can a species be considered a replicator? Again, Dawkins points out that a species, being mutable, is not comparable to a gene and its alleles. However, the gene pool of a reproductively isolated species could be a candidate.

In examining this possibility, Dawkins explores "differential lineage extinction"--for example, the statistical rates of extinction of ammonites and bivalves that have a high rate of evolving a larger size, say, than those who do not (those that more rapidly increase their size over successive generations are also more likely to die off). However, while these different rates of extinction are a form of selection, they do not drive "progressive evolutionary change" and thus these lineages are not replicators, either. They are merely, as Dawkins terms them, "survivors."

(And at this point, people, I confess I must read the chapter again.)

Part II: Punctuated Equilibrium and Memes

The Active Germ-Line Replicator

What is a "gene"? Dawkins admits to using the term loosely. In this chapter he tries to nail down the term more precisely, in order to give a clearer, "gene's eye-view" of the replicator as the unit of selection.

In 1957 S. Benzer split the gene into three units: the muton (minimum unit of mutational change); the recon (minimum unit of recombination); and the cistron (roughly equivalent to the unit need for one polypeptide synthesization). Dawkins proposes the optimon (and Ernst Mayr the selectron) as the unit of natural selection.

Dawkins briefly describes Gould's objection to his proposal, and critiques Gould't characterization of the selfish gene replicator as located "below" the level of the individual (which for Gould was the unit of selection), as the species group-unit is located "above" the level of the individual. Dawkins points out that this "single-dimensional ladder" analogy is not apt in that genes are replicators, whereas vehicles (individuals and species) are not. Individual vehicles are selected, but they are not replicators (more on this later). Likewise, replicators are selected by proxy as individuals (vehicles) are selected.

The issue of species versus individual selection is a question of what is to be properly considered a vehicle; the issue of individual/species versus gene selection is a question of what is to be considered a replicator.

"I define a replicator as anything in the universe of which copies are made," says Dawkins. These may be active (displaying some ability to influence their being copied) or passive, "germ-line" (such as gametes), or "dead-end" (somatic). It is the active, germ-line replicator that Dawkins names as his optimon.

Because chromosomes, and the genes within them, are subject to splitting due to crossing-over in sexual reproduction, replicators may consist of various codon lengths, but, depending upon their length and the strength of the particular selective pressure on them, various replicators will have different "half-lives," and the most successful replicators will, by exerting their phenotypic effects, have the longest half-lives with respect to their alleles.

It now becomes obvious why no individual, nor even an individual's genome, can be considered a replicator.

In the next chapter, Dawkins explains what individuals and species are, and why species also cannot be defined as replicators.

Arms Races and Manipulation, Part 2

If evolution can be viewed as a sort of “arms race,” one often assumes that if an animal manipulates another, the victim will, via random mutation and natural selection, develop counterstrategies to escalate the arms race rather than capitulate. However, Dawkins shows several examples of how this is not necessarily so.

For example, the foster parents of the cuckoo continue to feed their changeling “child” despite the obvious absurdity of a tiny Garden Warbler straining to feed a cuckoo several times its size. Why doesn’t the Warbler recognize this incongruity, when apparently some host parents of cuckoos can indeed recognize flaws in the cuckoo’s egg mimicry? Why does the host parent recognize the parasitic egg but not the more obvious parasitic changeling fledgling bird?

Dawkins’s answer is that natural selection does not act uniformly at all times in any animal’s life. Selective pressure may be stronger at some points in the life cycle than others, or natural selection may have no effect on evolution even if a beneficial mutation were to arise. As an example of the first case, Dawkins points out that recognition of a cuckoo egg in one’s nest gives the host parent the chance to gain an entire breeding cycle, whereas recognition of the incongruous fledgling would buy at most a few days, and that probably too late for the host parent to breed again. Moreover, the actions of the cuckoo, its exaggeratedly gaping mouth, its size, could indeed act as a “drug” on the foster parent, no less than the song of a male nightingale acts as a drug on the female reproductive cycle (and, incidentally, upon the poet’s imagination).

However, a fascinating example of how an animal’s victimhood can be perpetuated is exemplified by slave-making ants. Some species of ants spend a great deal of their time raiding the nests of others and carrying off the larvae and pupae, which subsequently hatch in the new nest and begin to labor for their “masters.” This is a disturbing and puzzling development. Why don’t the enslaved worker ant colonies develop a resistance to the strange environment, filled with others not their genetic sisters—for example, by evolving a genetic disposition to cease work (to go on “strike”) when in a strange queen’s lair?

Remember that worker ants do not reproduce. Therefore, any beneficial mutation that arose in the enslaved ants would not be passed on to the rest of their home nest. At any rate, the raids do not happen often enough to destroy the victims utterly, who are under little selective pressure to evolve complex adaptive countermeasures against slave-making behavior on the part of others that, while aggressive, does not threaten the existence of the nest. An uneven battle ensues, in which the slave-making ants can be said to win the war.

Dawkins indicates that this situation is not unlike the phenomenon of a certain species of hybrid frog, which has one set of chromosomes that is jettisoned in meiosis and one set that is passed on to its offspring. The set of chromosomes (dead-end replicators) that is jettisoned in the hybrid frog is perpetuated in the pure bred species that carries two sets of these chromosomes (which become germ-line, not dead-end, replicators in this species). Thus, any beneficial mutation in the dead-end replicator line will be passed on in the pure bred species that contains two sets of these chromosomes (because in this species these sets of chromosomes are not dead-end replicators), but will not be passed on in the hybrid species. The situation of the enslaved ants is like that of the hybrid species of frog: their genes have phenotypic effects and can even be selected, but they will not be transmitted in the hybrid species, and thus are irrelevant to that particular species' evolution.

Arms Races and Manipulation, Part 1

Dawkins' purpose in his book The Extended Phenotype is to dash the concept that the individual is the unit of selection, that is, the idea that, among other things, individuals act in a manner as to increase copies of itself. (Ann Coulter, for example, in her crap book Godless asks why, if evolution is true, she doesn't want to have children. Once again, she has mistaken evolutionary theory for a naive "for the good of the species" caricature of evolution. I should think that organisms (i.e., Dembski) manipulating other organisms (i.e., Coulter) into believing in creationism would be a prime example of said manipulation.)

Organisms may consistently work against their own interests (inclusive fitness) through being manipulated by another organism. Examples of manipulators are angler fish and cuckoos.

Although it's easy to assume that one animal manipulating another is only a temporary phenomenon until the other animal evolves some method of fighting back (that is, that the manipulation is a "time-lag" phenomenon--see my post on constraints on perfection), in reality the manipulator can in fact succeed continuously under certain conditions. An example of this is intraspecific manipulation (manipulation within the species, particularly kin-manipulation). Examples are parents manipulating their offspring, and offspring manipulating their parents.

Altruism is defined here, in a biological sense, as a behavior that favors other individuals (their inclusive fitness) at the expense of the actor.

Dawkins believes that parents who manipulate their children have an advantage over parents who do not, but states that parents do not have any built-in advantage over their children by the mere fact of their being parents.

The Extended Phenotype - Constraints on "Perfection"

One of the flaws in Ann Coulter's arguments in Godless is the fact that she believes that mutations arise already labeled neutral, beneficial, or non-beneficial, as if God had willed it so. Mutations do not arise in a vacuum, however, and any mutation is potentially any of these. When one says that a mutation (or adaptation) is beneficial, this must be taken in context with the vehicle's (organism's) genetic structure, environment, the existence of predators and competitors, the potential costs of this benefit as opposed to other benefits that could have evolved instead, etc. That a mutation carries an advantage in its particular context does not mean that the resulting adaptation is perfect, or that "things came together in perfect harmony" (as I often hear people say), or that the adaptation would even be considered adequate given fewer external constraints!

"It is simply meaningless to speak of an absolute, context-free, phenotypic effect of a given gene."--Dawkins

6 Constraints on "Perfection," or 6 Objections to Naive Adaptationism

-Time lags--the animal observed is "out of date," built under the influence of genes selected in an earlier era under different conditions. (The "lag load")

-Historic constraints--natural selection, having no foresight, modifies existing structures for new uses, leading in many cases to an obviously suboptimal formation, which nevertheless carries an advantage over no such formation at all.

Two species can respond to the "same selective forces in slightly different ways." --Lewontin

-Available genetic variation--"No matter how strong a potential selection pressure may be, no evolution will result unless there is genetic variation for it to work on."

-Constraints of Costs and Materials--adaptive organization is a "tangle of compromises."-Imperfections at one level due to selection at another--again, natural selection has no foresight.

-Mistakes due to environmental unpredictability or "malevolence"--adaptation to conditions is statistical in terms of success; moment-by-moment changes in an environment can trip up even the most successful animal. Moreover, manipulation of one animal by another can exploit the victims abilities, which in this context become disadvantages. The "loser" of this arms race may develop the ability to resist such manipulation; may find the manipulation beneficial to itself as well or may shape it to be such; or may actually go extinct, which does not necessarily benefit the aggressor.

The Extended Phenotype - Introductory Summary

-There is survival value in the "packaging of life into discrete units" called "vehicles" or organisms.

-We can speak of "adaptations as being 'for the benefit of' something, but that something is best not seen as the individual organism" but the "active, germ-line replicator" which are not selected directly, but by proxy.

-A behavior pattern "can be treated like an anatomical organ."

-A species or "group" is not the unit of selection, and gene selectionism is not genetic determinism.

Regarding the defining of what constitutes an adaptation, Dawkins first takes on the concept of extreme adapationism and identifies three proposed constrants on "perfection" (or optimal function) that he finds less persuasive:

-Neutral mutations, which are changes in polypeptide structure having no effect on enzymatic activity of the protein, and thus having no phenotypic effect at all.

(Biochemical controversy: Do all gene substitutions have phenotypic effects?)
(Adaptationist controversy: Is this phenothypic effect the result of natural selection?)
Though it is possible to a phenotypic effect to be selectively neutral, beware human subjectivity in these judgements. Genetic drift plus natural selection may result in more optimal function than just the effects of natural selection alone.

-Allometry, which is the disproportionate growth of a characteristic (such as a large head in small humans and in large ants).

-Pleiotropy, which is the possession by one gene of more than one phenotypic effect.