I just finished reading The Extended Phenotype by Richard Dawkins, which admittedly was one of the only books of his I had not read. Part of this delay was due to its similarity in content to his most famous book The Selfish Gene, which I read several years ago. The Extended Phenotype was written with scientists as the intended audience, and it takes some of the ideas in The Selfish Gene to their logical conclusion. The central thesis of the book is that genes generate phenotypes that are not isolated to influencing only the traits within the organism itself. Genes code for all kind of behaviors, sometimes appearing altruistic or wasteful, that help complex organisms increase the probability of propagating their genes to the next generation. Some examples that come up are bowerbirds that build nests as a mere fitness advertisement (the nests are not actually used for egg rearing), and beavers’ dam building behavior that even demonstrates some cooperation among individuals. The point is that the phenotype “extends” out into influencing how the organism interacts with the environment and other organisms. The level at which we choose to observe a phenotype (e.g., during development, adulthood, or behavioral interactions) is an arbitrary one, and Dawkins argues that we need to view evolution as genes acting on multiple phenotypic levels. The line is drawn, however, at behaviors or impacts of behavior (e.g. shape of footprints) that have no value for propagating genes to the next generation.
Particularly powerful examples involve animals whose life cycles depend on other species. In these cases, genes in a parasite, for example, are influencing the behavior of the host, so we can consider the genes as temporarily high jacking the machinery of another species to influence its behavior and get the genes within the parasite to the next generation. These kinds of complex interactions are only explicable with a “gene-centered” view of evolution. By considering the organism as the unit of selection, many behaviors and life cycle strategies can appear counterproductive, and Dawkins makes a pretty convincing case for the power of a “gene-centered” view to explain a variety of phenomena in nature.
The variety of interesting terrestrial examples throughout the book reveals a problem (in my view): there are few marine examples because we simply do not understand marine systems in the same amount of detail. Many of the ideas presented in the book could apply to interactions among different zooplankton groups (e.g., fish larvae and juveniles aggregating near larger gelatinous plankton), many of which have probably not even been described. Are there genes within the early life stages of fishes or other zooplankton that can highjack the machinery of larger animals, allowing them to improve their probability of survival? Or could larvae manipulate a predator’s sensory systems to avoid being eaten? These ideas would be extremely difficult to test, but with improving (and cheaper) sequencing techniques, it is only a matter of time before we discover the genetic components of behavior, and perhaps discover genes that code for traits to locate and utilize other species.
My favorite chapters were the ones about arms races, which I think are particularly applicable to plankton communities, and the last several chapters. There are so many diverse strategies to planktonic existence that there must be intense arms races are difficult to observe (see Smetacek 2001 Nature paper). The last chapters contained the most thought-provoking material. Overall, the book was a rewarding read, and I will probably be re-reading some of the chapters and using some of these examples for course material, should I be teaching ecology or evolution in the future.