Subtitled The New Science of Evo Devo and the Making of the Animal Kingdom, this book by Sean B. Carroll claims to be the popular vanguard of the the third revolution in evolutionary biology: Evo Devo, or Evolutionary Development Biology. Calling it a "new science" seems like an over-the-top claim, but Carroll, one of the leading researchers and speakers in this area, builds a compelling case to support the idea that current developments in evolutionary biology are already overturning decades of established wisdom and/or misconceptions, and that the whole science of biology is on the brink of a radical re-structuring. In his preface, entitled "Revolution #3", Carroll has this to say:
The physicist and Nobel laureate Jean Perrin once stated that the key to any scientific advance is to be able "to explain the complex visible by some simple invisible." The two greatest revolutions in biology, those in evolution and genetics, where driven by such insights. Darwin explained the parade of species in the fossil record and the diversity of living organisms as products of natural selection over eons of time. Molecular biology explained how the basis of heredity in all species is encoded in molecules of DNA made of just four basic constituents. As powerful as these insights were, {...} they were incomplete. Neither natural selection nor DNA directly explains how individual forms are made or how they evolved.
The key to understanding form is development, the process through which a single-celled egg gives rise to a complex, multi-billion-celled animal. This amazing spectacle stood as one of the great unsolved mysteries of biology for nearly two centuries.
The premise of the book, and of the science of Evo Devo, is that so far, evolutionary biology has been incomplete, and that the inclusion of embryology, the study of the development of living things from egg to emergence, allows scientists to understand how the raw information provided by genetics acts to produce a living being from an amino acid code, and how the forces of natural selection change this developmental process over time.
The "bombshell" that precipitated the new revoloution in biology came in two parts. The groundwork was done by embryologists working on the development of fruit flies, who managed to establish a consistent scheme by which the genes controlling the development of a fruit fly embryo could be isolated. The truly amazing revelation that came soon afterwards — which, Carroll emphasizes, was "contrary to the expectations of any biologist" — was that almost all of the genes governing fruit fly development had exact counterparts performing the same function in most other animals. In other words, the development of body parts such as eyes, limbs and major organs — parts which are vastly different in form between animals, and which were thought to have evolved in completely different ways — were governed in different animals by exactly the same genes. The same gene that tells an insect to build a limb tells a human to build a leg. The discovery of this "Tool Kit" of master genes controlling the development of almost all animals is the key to Evo Devo.
The first important point is that the vast apparent differences between animal forms working with this same genetic toolkit are explained by the sequence with which genetic "switches" are turned on and off in order to precipitate specific changes. The second is that the attention of biologists is now turning to a different part of the genome. The DNA sequences for coding proteins have been known and extensively studied for quite a long time, but only comprise approximately 1.5% of the genome. Another 3% is what is called regulatory DNA, which is organized into "devices" that control the expression of proteins at very specific times and places in the development of an embryo. Examining this regulatory DNA, how it forms "devices" and how these devices work to control development, is the major part of Carroll's work in Endless Forms Most Beautiful, and takes up the first half of his book. The second half is devoted to illustrating how this new knowledge can lead us to new insights about animal diversity and evolution in action. Carroll states that the intention of the book is to answer four questions:
- What are some of the major "rules" for generating animal form?
- How is the species-specific information for building a particular animal encoded?
- How does diversity evolve?
- What explains large-scale trends in evolution, such as the change in number and function of repeated parts?
Carroll mentions almost in passing that when these new discoveries are fully understood and have permeated into the mainstream, they will sweep away the last remaining grey areas in the scientific understanding of evolutionary biology, and in so doing, will remove any scope for advocates of creationism or "Intelligent Design" to exploit doubts about such things as intermediate forms or the development of complex structures. Evo Devo, he claims, is the missing link that biologists have been waiting for.
The book's evocative title is taken from the closing sentence of Origin of Species, and this brings to mind that one of the reasons for Darwin's success in establishing himself as the household name for the science of evolution, besides his staggeringly thorough research, was the power of his writing style. Other extremely popular writers on evolution, such as Stephen Jay Gould, have built their reputation as much on the powerful and persuasive nature of their writing as on their achievements as scientists. Where Sean Carroll may fail as the spokesperson of Evo Devo is in this regard: he is far more of a scientist than a writer. Although Endless Forms Most Beautiful is well-written and often entertaining with its familiar and casual tone, it lacks the grandeur and visual imagery that distinguishes the best popular scientific writing. One gets the sense that Carroll is writing for fellow scientists more than for the average lay reader; for people more interested in diagrams, gene sequences and chains of evidence than imagination-stirring tales and leaps of intuition.
To his credit, however, Carroll does a very good job of simplifying the often highly complex evidence and arguments that are the subject of his book, and there are plenty of pictures and diagrams and illustrative stories to spark the visual imagination. He tells stories about cyclopean sheep, polydactylous baseball pitchers, mimicking butterflies and whether zebras are white-on-black or black-on-white. If you don't mind a fair bit of "hard" science, and you want to know what's happening in evolutionary biology, this is a great book to start with. One of the problems he has to deal with is the difficulty of his subject matter, which takes as its starting point the discoveries of genetics and the Modern Synthesis, and moves from there into a world of genetic toolkits and switches, and many concepts that will often be more familiar to programmers and information theorists than biologists. This is a book that brings together a great deal of experimental evidence in support of its argument, and it rewards a close and critical reading.
Finally, Carroll finishes up his book with an impassioned plea for the education system in the United States and elsewhere to catch up with the discoveries he discusses in his book. He wants education to move from a system of what he calls, after Rudyard Kipling, "Just So" stories, in which children are told that moth populations darknened because of pollution, giraffes evolved longer necks in order to reach high leaves, etc, to a system in which the true mechanics of incremental small changes in populations over large amounts of time are explained and illustrated visually. He also comes out strongly against the attacks on evolutionary theory by the religious right. Any area of ignorance or lack of evidence in the theory of evolution has, so far, been targeted by religious interest groups as a "weak point" that they can use to sow doubt in the minds of uneducated people, and the science of Evo Devo has taken a number of these weak points and supplied both experimental evidence and a powerful explanation to fill in the gaps. Carroll makes no bones about his opinions in this area, and there is no attempt to sympathize with those who ignore scientific evidence in the service of religion. He makes a call to politicians and educators to resist pressure from these interest groups and understand how important the true facts of evolution are to the future of, not only humanity, but all life on this planet.
"Nature's forms are not endless, nor are the most beautiful being spared. I am not so naive to believe that science can solve all of the world's problems, but ignorance of science, or denial of its facts, is courting doom."
— Sean B. Carroll