Saturday, January 20, 2007

The Selfish Gene (Richard Dawkins)

Although he’s recently become more well known for his opposition to religion and supernaturalism in works like The God Delusion (see review), Richard Dawkins is, first and foremost, a biologist and animal behaviorist. The Selfish Gene, his first book, concerns itself with a basic question of evolution: Where does natural selection act?

The common understanding of the process is that it takes place at the level of the individual organism: for example, a zebra that has slightly better leg muscles than other zebras, and can therefore run faster, is less likely to be run down by a lion looking for dinner. It is also therefore more likely to reproduce and pass its slightly better leg muscles down to the next generation, and eventually most zebras have those slightly better leg muscles.

This is all well and good, but it also quickly runs into difficulties in the real world. For example, how can this explain a bird that, upon spotting a predator, makes loud warning cries to the rest of its flock? This is good for the flock, obviously, but it also draws the predator’s attention to the bird making the warning cries—seemingly the opposite of a better leg muscle, and something that on the face of it shouldn’t be favored by natural selection. Similarly, the real crux of evolution is in reproduction, with survival important mainly because it allows reproduction to occur. So what to make of nonreproductive drones and workers in insect populations, most of whom never pass on any genes at all?

A conventional answer when Dawkins wrote The Selfish Gene was that natural selection takes place at both the level of the organism and the level of the group or species. The bird’s warning cry is bad for the organism, but good for a particular flock—flocks that used warning cries were more likely to survive than flocks that did not. Similarly, although sterile workers are little good to themselves as far as reproduction goes, their ability to concentrate on finding food and other tasks, without having to expend energy on reproduction, benefits their group.

Dawkins’s argument runs counter to this thinking, not in its effect (apparent individual altruism for the benefit of the group), but in its cause. Rather than moving up to the level of the group or species, we have to move down to the level of the gene. The question to ask is not whether or how a particular trait is good for an organism, or good for a species, but whether it’s good for the gene that influences the trait. When we say that a fast zebra is able to pass its slightly better leg muscles on to the next generation more effectively than other zebras, what we are really saying is that the DNA structures that produced those muscles have become more common in the population. From the gene’s point of view, the muscles are incidental. In this model, the organism, and the species it belongs to, are “survival machines” or “vehicles” that have, through the slow incremental processes of natural selection, been built by DNA replicators because those replicators that had good vehicles were better at surviving and reproducing than those who did not build such vehicles. It perhaps started with elements as simple as a cell wall, or two strands entwining to produce something better than each could on its own, and the argument in The Selfish Gene is that all of the complexity of life today is a difference of scale, not of principle.

This leads to all sorts of interesting and counterintuitive consequences. A central idea of the book (not original to Dawkins, although he expands on it) is the idea of kin selection. In local populations, there’s a good chance that a gene in any particular animal is also in other nearby animals, simply because they’ve been reproducing with one another. So although the bird warning others of a predator might be less likely to reproduce on its own, the warning is likely to benefit the same gene sitting in other members of the flock. We would also expect, for example, that animals would be more likely to show this altruism toward members of their family—who are, after all, the ones most likely to share the same gene. And not only that, but they should presumably be most likely to be altruistic toward those closely related to them, and less likely the further away you get: parents share 50 percent of their genes with their children and 25 percent with their grandchildren, so you would expect them to go more out of their way to help their children than their grandchildren. Siblings (who also have a 50 percent chance of sharing any given gene) should be more likely to help each other than they are to help cousins (who have only a 12.5 percent chance of sharing a gene).

This helps explain the nonreproductive insect workers mentioned earlier. A number of insect species are haplodiploid, which just means that rather than a chromosome determining gender (as in humans), eggs that have been fertilized by a male become females, and eggs that have not been fertilized become males. In these species, males have half the number of genes of females, which in terms of kin selection means that males share 100 percent of their genes with their mother. From the gene’s point of view, helping the mother to propagate children is just as good as if the individual male itself were able to reproduce.

These are just two basic examples, and simplified accounts of them at that; much of the pleasure of the book is in Dawkins’s fuller explication of these and many others. Ideas from game theory like the prisoner’s dilemma and the evolutionarily stable strategy turn out to be remarkably relevant to the gene’s “desire” to propagate itself at the expense of rival genes, and Dawkins has a talent for explaining these complicated ideas nonmathematically in vivid, lucid language.

He also moves beyond pure biological evolution to a more general theory—that natural selection and evolution are not specific to plants and animals, nor even to DNA. The only elements required are:

  • Stable replicators capable of making copies of themselves with a high degree of accuracy, but not perfect accuracy
  • Competition among these replicators such that the differences between them make some more likely to replicate and spread than others
In other words, reproduction, variation, and competition—these three things must lead, in principle, to natural selection and evolution. Dawkins speculates that life anywhere in the universe, regardless of how different it might be from life here, will have arisen from this process, and he also notes that it need not even apply solely to living things. This was the book that introduced the now widespread term meme, a cultural analogue to the gene that propagates itself through human minds and also possesses the three requisite elements for evolution. A meme reproduces when one person passes it to another, varies when the person it passes to doesn’t remember it or understand it exactly as the first person did, and competes with other memes for prominence in individual minds and in the culture at large.

The 30th anniversary edition of the book was released last year, and is worth reading almost as much for the endnotes as the text itself. Although he has mostly refrained from revision, and says that he still holds substantially the same views now as he did when he originally wrote the book, he also notes places where he turned out to be wrong, or he has changed his mind, or further evidence has come to light, or others have expanded on his ideas or raised interesting counterarguments.*

He does also display some of the weaknesses later evident in books like The God Delusion. In the endnotes, he admits at several different points that he went overboard with his rhetoric—for example, when he predicts that we will eventually see the idea of the evolutionarily stable strategy as “one of the most important advances in evolutionary theory since Darwin,” and says in the endnotes that this was “a bit over the top. I was probably over-reacting to the then prevalent neglect of the ESS idea in the contemporary biological literature.” You wonder whether the same type of overreaction might have resulted in some of the angrier-sounding passages of The God Delusion. He also seems unable to refrain from taking potshots about his pet peeves, which you wish his editor had been able to convince him to cut. (In The God Delusion, I’d imagine that those who agree with him would term them “witty asides”; those who don’t, perhaps “snide barbs.”) Toward the end of The Selfish Gene, for example, he devotes a couple parenthetical sentences in the middle of a paragraph to explaining the correct pronunciation of the word algae. Perhaps correct (at least at the time), but also pedantic and irrelevant.

Those aside, The Selfish Gene is a terrifically engaging book—it won’t topple The Blind Watchmaker from atop my list of favorites, but it’s well worth reading. Although since Dawkins mentions more than once in the endnotes that The Extended Phenotype is the book he’s personally most proud of, that one will be getting a shot soon.

* Sometimes in funny ways. In a section discussing the division of labor in social insects that leads to some individuals devoting themselves to bearing offspring and others to caring for those offspring, he notes, “Although it is theoretically possible for evolution to proceed in this direction, it seems to be only in the social insects that it has actually happened.” The endnote to this sentence begins, “That is what we all thought. We had reckoned without naked mole rats.” Hehe.

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