Wednesday, August 1, 2007

Dawkins #6: One Goal to Rule Them All

[ This post is number 6 of a series. They will be of interest mainly to those who've read Richard Dawkins' book, The Selfish Gene. I recommend they be read in order. ]

Richard Dawkins ascribes two different goals to genes: "survival" and "increase". In previous posts, I pointed out that these produce different models, which in turn predict different results. I expanded the "goal" metaphor out into literal terms, and showed that if this "thought problem" is worked out with genes taken on a "snapshot" basis, their goal is clearly seen as survival.

In the last two posts I showed that "increase goals" will not work without a well-defined condition or "target". Pure "increase goals" had several problems, the worst of which showed up when I expanded the "goal" metaphor into literal terms. Pure increase goals require us to believe genes have an intent, not just metaphorically, but in literal fact. Unlike limited increase goals, where we can justify our statements that genes have those goals by pointing to the actual effect of the genes in the material world, pure increase goals require us to make statements about what genes "would" do if they "could". That takes us from metaphor into fantasy.

It remains to look at "increase goals" with well-defined conditions. Testable (if not necessarily realistic) examples might be "Increase the germline gene count if foraging produces more than the target level of N calories per average day, otherwise regulate the germline gene count to maintain or restore that level" or "Maintain a germline gene count which keeps the species at 9% of the epipelagic Antarctic biomass."

In one sense, these are not goals of "increase" as stated by Dawkins, but "maintenance goals". But I will give any goal based on germline gene frequency, honorary status as an "increase goal". More important than whether they track Dawkins language (Extended Phenotype, p. 84) closely is whether they make a satisfactory alternative to the survival goal. That's not a question that should be answered with a semantic quibble.

The basic problem with the limited versions of "increase goals" is best shown by their confusion in the face of outlaw genes. Assume that genes do have gene-frequency goals which, at least at points, involve maintaining a certain population level. What's to stop a new mutation that cheats? At first glance, it would seem that if the genome of a species has settled on a rule that says "stop increasing gene count at level X", any gene that ignores it will have a selection advantage over its law-abiding fellow genes.

I won't dwell on the practical side of this problem: how the law-abiding genes in a genome can "police" these outlaws. (Dawkins deals with "outlaws" in The Extended Phenotype, ch. 8.) I'm more interested in the definitional problem which the practical issues highlight.

"Population outlaws" are outlaws because they don't share the limited increase goal which is supposed to be the general goal of natural selection. But if a limited increase goal is going to be the general goal of natural selection, it needs to describe the behavior of law-abiding genes and outlaw genes alike.

The general goal of natural selection has to be a law not in the sense of the law against train robbery, but in the sense of the laws of physics. Train robbers can decide to ignore the criminal code, but they've got to shoot straight or suffer the consequences, the same as any lawman. The general goal of natural selection must impose itself on outlaw genes the way the laws of physics impose themselves on gunmen.

Ideally, in fact, the general goal of natural selection will tell us why outlaw genes do what they do. A survival goal would seem to describe "population outlaws" well: All genes try to increase their probability of survival. Population outlaws are genes that attempt to survive at the expense of the other genes in a genome by cheating on their population discipline.

The existence of "population outlaws" shows that a limited "increase goal" cannot stand in even as the law governing the genome of a single species. Limited increase goals are even worse when applied to the genes outside of a genome. Even if there were no such thing as "population outlaws", a limited increase goal would describe the behavior of, at most, a narrow range of species.

A pure "increase goal" is general enough to cover all life, but we were forced to rule it out because it was incoherent. We have to rule out impure, or limited increase goals precisely because they are limited and specific.

With the elimination of both limited and unlimited gene-frequency goals, my argument that survival is the general goal of natural selection is complete. "Increase" goals and gene-frequency targets are tactics employed by certain genes at certain times in the battle for survival. Gene-frequency targets themselves evolve and go extinct. The goal of survival will not go extinct before life itself does.

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