Endless Forms Most Beautiful, The New Science of Evo Devo and the Making of the Animal Kingdom by Sean B. Carroll. New York, NY: W. W. Norton, 2005. $25.95 hardcover; 350 pp; 18 page appendix; 22 pages of sources for further reading. The book is illustrated throughout with black & white photographs and drawings as well as 16 pages of color plates.
Once I had ordered Endless Forms Most Beautiful from my favorite book source its arrival was highly anticipated. The promise was revolutionary new insight into the workings of evolution with maybe enough evidence to sway staunch creationists. I was certainly not disappointed.
Carroll presents a brief history of evolutionary theory giving Darwin the lead position for the first revolution. The discovery of genetics and the Modern Synthesis in 1942 constitutes the second revolutionary event in understanding evolution. Evolutionary Development, or Evo Devo for short, in Carroll's opinion is the third revolution in evolutionary thought. Based upon the depth of the evidence presented in this book I have to agree. Evo Devo is not just an addendum to the Modern Synthesis.
Evo Devo has its roots in the work of geneticists who worked for decades with the rapidly reproducing fruit fly. Hopefully, many of my readers will have at least passing knowledge of this work from High School biology classes where we marveled at flies with legs for antenna or no wings at all - genetic monsters. What may have seemed like strange experiments with no practical use at the time has provided us with a basic understanding of how living things are constructed from genes and chemistry.
Endless Forms Most Beautiful is divided into two main sections: Part I - The Making of Animals and Part II - Fossils, Genes, and the Making of Animal Diversity.
In the chapter, "Animal Architecture" in Part I: Modern Form Ancient Design, we gain an understanding of the modularity of animal design - organization by repetition. Homology (bird wings, tetrapod forelimbs, and our arms are all homologues derived from a common ancestral form) and serial homology (forelimbs and hindlimbs are derived from repeated and differentiated structures) are among a number of important principles explained by Carroll. The key to the variety of animal forms lie in their similarities, not their differences.
As Carroll takes us through the following chapters in Part I we see further evidence of sameness. Much of what has become known about evolutionary development has come from the study of naturally mutated animal forms as well as the aforementioned fruit fly work. Gentics, DNA, RNA, and protein synthesis are explained at length in the chapter "From E. Coli to Elephants." The breakthrough discovery of Homeobox or "Hox" genes was primarily a result of the fruit fly studies. These gene clusters control the development from egg to fly. Specific Hox clusters control specific parts of the body. Mutations in these clusters produce strange forms in adult flies. Once this discovery was made, Pandora's box was opened and evolutionary biologists sought to discover Hox genes in other animals. As Carroll explains, "When the sequence of these homeoboxes were examined in detail, the similarities were astounding. Over the 60 amino acids of the homeodomain, some mice and frog proteins were identical to the fly sequences at up to 59 of 60 positions. Such sequence similarity was just stunning. The evolutionary lines that led to flies and mice diverged more than 500 million years ago . . . No biologist had even the foggiest notion that such similarities could exist between genes of different animals. These Hox genes were so important that their sequences had been preserved throughout this enormous span of animal evolution." (Endless Forms Most Beautiful, p. 65) This is a magnificent discovery and the foundation of why Evo Devo is such a powerful fundamental proof of how evolution works.
In "Making Babies: 25,000 Genes, Some Assembly Required", Carroll takes the reader through the process of fruit fly development from egg to adult in basic terms. He builds upon this with the same process in vertebrates and the role of the "tool kit" genes. In the following chapter he reveals the operating instructions that genetic switches provide to the master tool kit genes. The switches are special sequences of DNA bound by proteins that can tell a gene to turn on or turn off. The whole process is complex but ultimately fascinating and satisfying as we get to see the magician's trick revealed.
Part II of Endless Forms Most Beautiful begins to apply the principles of Evo Devo to the fossil record. As Carroll states in his introduction to Part II, "the central idea is that the animal forms evolve through changes in embryo geography." (Op. Cit. p. 134). And on page 135 Carroll states in part, "Some of this new evidence conclusively settles long-running debates in evolutionary biology, some raises entirely new ideas, while other discoveries revealed one of the 'Holy Grails' of evolutionary biology - the precise genetic changes responsible for evolution in particular species." This is truly profound.
Carroll emphasizes that the genetic tool kits are ancient with some enduring since the Cambrian. Seemingly unrelated forms appear with shifts in the location of Hox genes within the genome and the timing of gene expression. One of the examples used is neck length differences between a mouse, chicken, goose and snake. Two of these have relatively short necks, one is long and the snake has no neck at all. Position of the Hoxc6 gene has been shown to control this phenomenon.
One of the favorite bits of anti-evolution rhetoric is that evolutionary intermediates would possess useless half structures like partial legs or non-functional eyes. Carroll dismisses this by first reminding us that even Darwin's thoughts on this were on-track. Darwin thought that it was possible for an animal to possess two organs contributing to a particular body function so that over time one could shift its function to something new without harm to the organism. Evo Devo provides the proof and Carroll use the development from a lobopod limb such as those on the Cambrian Opabinia to the jointed limb of an arthropod. Another fascinating example is invertebrate wing development from gill-like appendages. Both of these examples show the power of the Hox genes and genetic switches. In fact, both are supported by fossil evidence. With numerous other examples, Carroll reminds us that despite what may appear to us as novel new structures appearing through animal evolution, all are merely variations using existing genetic material.
In his chapter "Paint it Black", Carroll explains the evolutionary genetics of black, white, stripes, spots and redheads. In rock pocket mice for example, dark color has evolved in distant isolated populations using different genetic pathways proving that there is more than one way to achieve the same end. Selection of advantageous genetic mutations as the driver for evolution is a basic Darwinian tenet. How big of a change is needed and how long does it take? This can actually be determined mathematically using a formula provided on page 245. The astonishing answer is that a very small advantageous mutation can spread through a population fairly quickly. In one of the examples given, a 1% advantage can spread through a population of 10,000 individuals in about 2,000 years. A .1% advantage can take 20,000 years. These are insignificant time frames in relation to geologic time.
Endless Forms Most Beautiful discusses human evolution in the chapter "A Beautiful Mind". Among other important points Carroll discusses the pattern of human evolution showing that the fossil record supports a mosaic pattern - not the old "Chain of Being" missing link approach that has lingered in paleoanthropology for over 100 years. He also shows that the pattern of human evolution occurred in the same fashion and timing as in other mammals.
In Carroll's' summary chapter "Endless Forms Most Beautiful" he offers that Evo Devo has provided the most compelling proof of one off Darwin's central ideas - that all life forms on Earth have evolved from one or only a few common ancestors. Also important to note is that evolution has been shown to work by modification of existing structures and not by designing new ones - "The invention of wings never occurred from scratch, but by modifying a gill branch (insects) or forelimbs (three times [pterosaurs, bats, birds])." (Op. Cit. p. 289)
The inexcusable state of evolution education in the United States is noted in this last chapter as well. Carroll notes a National Science Board survey from 1996 that showed 52% of Americans either believed that or were not sure whether the earliest humans lived alongside the dinosaurs. His comment is priceless: "Score that fact as two points for The Flintstones, zero for Darwin, Huxley, and the educational system of the world's most wealthy, powerful, and technologically driven nation." (Op. Cit. p. 293) Evolution is not just a component of biology hidden in the back of text books. It is the real foundation of the science. Carroll suggests ways in which evolution should be taught as an integral part of biology. Fossils are an important part of his proposal: "Dinosaurs and trilobites are the poster children of evolution, and they inspire the vast majority of those who touch them. By placing these wonders of the ancient past in continuum from the Cambrian to the present, life's history is made much more tangible. It would indeed be a wonderful world if every student had guided, repeated classroom contact with some fossils." (Op. Cit. p. 295) Carroll quotes Goethe, "Nothing is worse than active ignorance" (Op. Cit. p. 297) and offers that the "gaps" in scientific knowledge so loved by creationists as reason not to believe are rapidly disappearing. This third revolution in evolutionary theory, Evo Devo, has brought tremendous insight to the biological sciences in just the last 20 years or so and since science builds upon earlier work, the next twenty years should bring even more.
Readability - General readers High School and up with biological background.
On the Upside - Well written, easy to read account of the latest and best proofs of evolution to date. Evo Devo is the link between biology and paleontology.
On the Downside - Part I is a bit more technical but not so much as to make the book difficult to understand. Technical terms are defined.
Overall Rating - I can highly recommend Endless Forms Most Beautiful to not only biology specialists but also to those interested in understanding paleontology and those beautiful yet strange fossils. If you are going to read only one book in the next year concerning biology and evolution then this should be the one.