Evolution in Four Dimensions

The Book Elves have been at work again, and my mailbox was recently graced with Evolution in Four Dimensions, by Eva Jablonka and Marion Lamb. This book presents an interesting and slightly bold argument for why we should change the way we view evolution. Jablonka and Lamb (J&L) argue that mutations are not as random as we have traditionally assumed, and that several different mechanisms of change allow both genetic mutations and other forms of adaptation to be passed to future generations. They present their case in a unique way: there is a section at the end of each chapter that is a mock dialog with a fictional "devil's advocate." This could have been hokey or contrived if it was done poorly, but they pull it off it very well and use the feature to reinforce the main message of each chapter and clarify any possible points of confusion.

What are the four dimensions, you ask? J&L outline four systems involved in evolutionary change: genetic, epigenetic, behavioral, and social learning (focusing on the use of symbolism in communication). Each of the systems is given its own chapter, but the last chapters focus on demonstrating how the different systems interact.

J & L are very upfront about claiming their acceptance of Lamarckism, the inheritance of acquired characteristics. Lamarckism, you exclaim! Isn't that the guy that thought giraffes have long necks because their forefathers were good at stretching? He was what one up-and-coming author has called "official whipping boy of evolutionary science." Haven't we shown that guy was pretty backwards? Actually, Lamarck never used the giraffe example himself, and although his ideas about mechanisms of inheritance have been shown to be misguided, he did not "invent" the idea of inheritance of acquired characteristics. Darwin himself discussed the effects that use/disuse could have on transmission of various traits. Lamarck is frequently ridiculed, but it is important to recognize him as an influential early proponent of evolution, even if his views on the mechanisms didn't pan out. Or did they? J&L argue that we can in fact inherit acquired traits from our ancestors, and they present both molecular and behavioral evidence for this mechanism of evolution. They are not advocating some early views, such as that amputating body parts would cause deformities in offspring, but they use modern research to present a more refined, updated approach.

The key here is to keep in mind that J&L assert that their approach is neo-Lamarckian, just as many others have used a neo-Darwinian approach for decades now. Over the years, both schools of thought have evolved and enriched the original eighteenth-century theory that they were derived from. The concept of Lamarckism that J & L subscribe to is simply that not all inherited traits are the result of random mutations and classic natural selection. In their view, organisms have mechanisms designed to make "best guesses" about the most favorable responses when they are exposed to stressful conditions. It is widely acknowledged that certain areas of the genome are mutational "hotspots," and J&L cite this as evidence that mutations are not always random, but are targeted in areas likely to produce adaptive changes. Many organisms have been shown to increase their mutation rates when exposed to a challenging environment, almost as if they are scrambling around to mutate as fast as possible to increase their chances of hitting on a more favorable phenotype.

Plasticity is key here, and J & L emphasize that DNA can change in response to environmental cues. I think one of the major strong points of this book is the coverage of different epigenetic mechanisms. The many diagrams that are extremely cartoony, but they do an excellent job of getting the point across. J&L use epigenetics as an example of how phenotypes can change within the ontogeny of a single individual. They explain how these changes may be inherited via various mechanisms, including genomic imprinting, RNA interference (gene silencing), self-sustaining loops, and structural inheritance. This can result in genetic assimilation, the transmission of acquired mutations/adaptations to future generations, which is at the heart of Lamarckism, although the modern version is definitely an updated version of his original ideas that takes into account many advanced biochemical and genetic studies.

Behavioral and social learning interactions are a natural progression in any discussion of inherited characteristics. Can offspring inherit a behavior or tradition from their parents? J&L discuss how "cultural changes in animals can be cumulative...one habit can stabilize other habits, so eventually there is a network of habits that together construct a new lifestyle" (p 179). This should remind you of the Baldwin Effect, in which phenotypic plasticity (which includes behavior as well as morphology) allows adaptation that is later stabilized by genetics. J&L don't advocate extreme behavioral inheritance, however and they caution that "most assimilation processes will not end up with a completely internalized, instinctive response...some learning will still be needed, but it will have become much more rapid and efficient" (p 290).

J&L don't claim to have all the answers. In the dialog sections, they frequently admit that not enough is known about a specific topic, and call for further research. I think that their arguments lack support in some areas but are very convincing in others. Even if you do not buy all the points they make (if you buy all the points ANYONE tries to make you probably need to be careful of sandbox salesmen while you're on spring break at the beach...) their ideas are fascinating and they present many issues that need to be accounted for, whether they are ultimately accepted or rejected, as we move towards revisions of the Modern Synthesis.

One complaint I have about the book is a technical issue: the endnotes are not indicated in the text. I am not a fan of endnotes period, I much prefer footnotes, but I have never understood why some authors don't mark the endnotes in the text. The notes are very helpful and interesting, but they are easily overlooked because they are not referenced within the chapters.

J&L sometimes slightly exaggerate the degree to which "mainstream" view of evolution is adherent to a strictly reductionist views that attribute all evolution to purely random genetic mutations. They are promoting a new viewpoint, so it is in their interest to emphasize the ways it differs from the predominate mode of thought, but lay readers that are not very familiar with current views on evolution might get the wrong idea about how modern scientists view evolutionary mechanisms.

Overall this is a fascinating book, it is a must-read for anyone interested in staying up to date about current views on both biological and cultural mechanisms of evolution.