Press Archive
More from the Carroll laboratory
INTERVIEW
Sean Carroll: Charmed by snakes: Nature
Thomas Hayden
6/19/03
Life changes: To understand how organisms evolve, biologists start at the beginning: The San Diego Union-Tribune
Leigh Fenly
5/18/05
REVIEWS
Dances with fruit flies: US News and World Report
3/28/05
Evo Devo is the new buzzword for the 200 year old search for links between embryos and evolution: Scientific American
Brian K. Hall
April/2005
Where do they all come from? A new theory traces animal forms to an 'ancient tool kit': Christian Science Monitor
Lori Valigra
4/05/05
Evolution Revolution: Toronto Globe and Daily Mail
Michael Ruse
4/16/05
Evolution today is highly controversial, particularly in the United States, where there are ongoing battles about whether it should be taught in schools. Yet, when Charles Darwin published his Origin of Species in 1859, very many people in Britain, in Europe and even on this side of the Atlantic at once agreed that all living organisms, including us humans, are the end results of a long, slow process of natural development, from very simple forms, perhaps even originally from inorganic substances. A major reason why Darwin was so effective was that he showed that the idea of evolution explains so many different things: paleontology, geographical distributions, anatomy and more.
One area covered by Darwin was embryology, the development of the individual organism from conception to adulthood. Organisms are basically alike in their earliest stages and then diverge along different pathways. Darwin was always very proud that he could show that this is all a matter of evolution, especially evolution by his own mechanism of natural selection, where only the fittest survive and pass on their features to subsequent generations. Darwin's point was that the earliest stages of development show shared origins, and adult diversity occurs -- and only occurs -- because natural selection works on organisms to fit them for different adult conditions and environments and lifestyles.
After Darwin, embryology almost took over evolutionary studies, but not in the way he intended. Drawing on ideas dating back to the poet and polymath Goethe, biologists ignored natural selection and used embryology to work out individual histories. German scientist Ernst Haeckel argued that the history of the individual reveals the history of the race -- "Ontogeny recapitulates phylogeny" -- and in the subsequent spinning of stories of origins, Darwin's own contribution to embryology was quite forgotten. More unfortunate was the fact that the foundations of the new evolutionary embryology were desperately insecure, for too often the history of the race is not revealed by the history of the individual.
Hence, it is not surprising that when, in the 1930s, evolutionists rediscovered natural selection, combining it with the new theory of heredity -- then Mendelian genetics, later molecular genetics -- almost to a person they rejected or ignored embryology. The great theorists of the day -- Ronald Fisher in England and Sewall Wright in the United States -- treated organisms as black boxes. They were interested in the genes; they were interested in the fully fledged organisms; and they were not interested in much in between. One has a gene for brown eyes, one has a Guernsey cow, and no one cared too much about the processes taking life from the one level to the other.
Of course, there had to be something wrong or incomplete here. The great evolutionist Ernst Mayr, who died earlier this year at the magnificent age of 100, used to speak contemptuously of "beanbag genetics." He implied that simply treating the units of heredity as isolated entities separate from the whole living being had to be wrong. Darwin was right. Any adequate theory of evolution simply has to consider the whole organism, especially the developing whole organism.
About 25 years ago, there was a veritable revolution, and embryology came rushing back into the evolutionary story. By then, the molecular biologists had done their easy bits -- working out the double helix, the genetic code and those sorts of things -- and were now ready to tackle the really hard jobs. These included development, and overnight one had the beginning and growth of a whole new sub-discipline, looking at embryology and then trying to relate it to the evolution of organisms: evolutionary development, or as it is more popularly known, "evo devo."
As explained in Endless Forms Most Beautiful, by U.S. geneticist Sean Carroll, one of the leaders of this new field, immediately there were very exciting discoveries. Darwin himself had always argued that the way of evolution is rarely to build the entirely new, but to take the already existing and modify and reuse. The forelimb of vertebrates is a classic example. Don't build a whole new structure for flying. Take what you have -- something used for walking and grasping -- and shape it accordingly.
What no one realized is the extent to which this would be going on at the genetic level. Who would dream that there could be something significantly in common between humans and the little fruit fly, Drosophila? But it turns out that there is. Basically, what we now know is that organisms are built on a modular fashion. It is not a question of everything being done at once. Rather, bits and pieces are built, and if you want something more, then you repeat one of the pieces that you have and then modify it. Or you drop one piece and add another kind of piece and so forth. Snakes are obviously built this way -- think of all of those vertebrae -- but the same is true of other organisms. Start with a pair of legs, double them, turn one set into wings -- good idea -- get another set, and turn those into wings as well. And so it goes.
But how does it go? It turns out that the answer is at the level of the genes, but not just any genes. Some genes produce substances (proteins) that do not make things, but control the making of things by other genes. They turn on (or off) the DNA. This is the secret to repeating things -- double your DNA and your switches -- and to transforming things -- alter the order of switches or their operating, and you have your desired end product. It is these controlling genes -- what Carroll calls the "genetic toolkit" -- that are the secret to building an organism or of transforming one organism into another kind of organism.
What was totally unexpected and incredibly exciting is that these switch genes are the same in animal after animal. Humans and fruit flies share virtually identical genes doing exactly the same things. Some of the best studied are so called "Hox genes." These order development in the fruit fly, and explain why one part comes before another and why one part (say a wing) comes in the wing position and not in the position of another part (say a leg). There are almost exactly the same genes doing almost exactly the same things in humans.
The revolution is not yet over. Carroll and his fellow workers are committed Darwinians. They think that the Darwinian mechanism of natural selection is the ultimate force -- the sculptor of form -- but there is not yet a full picture of how selection works to preserve and multiply and order the switch genes. In Endless Forms Most Beautiful -- a phrase, incidentally, taken from the closing paragraph of the Origin -- the major emphasis is on following the developments of individual organisms: butterflies getting spots, zebras getting stripes and humans getting brains. There is no linking vision, like that of the Origin, bringing in paleontology, biogeography, anatomy and everything else. Building this big picture lies in the future.
Sean Carroll is a scientist who loves his work and who wants to share his joy of discovery. His very existence is a major reason why creationism is so wrong, so sterile. Science like this is the proof that, although we may be modified monkeys, the Christians were not entirely wrong when they argued that our intelligence and our imagination is the proof that we are made in the image of God.
Michael Ruse daily thanks his maker that he is a philosopher and not as other men. However, this book almost makes him wish that he had started his academic career as a biologist, around 1980.
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Library Journal:
Carroll (genetics, Univ. of Wisconsin, Madison) has written the first book for general readers on the emerging field of evolutionary developmental biology, a.k.a. "evo devo," the study of how the shapes and forms of animals and humans have developed and evolved. Besides being an important researcher at his institution, where he works on butterfly eyespot development, Carroll is also a gifted writer. In a breathtakingly effortless manner, he builds on complex concepts, e.g., that a few primitive genes gave rise to the formation of essential organs and appendages in all animals. His topic is crucial, involving the recent and profound contributions of embryology and development to our understanding of the evolution of life's diversity. These are key components of evolutionary theory that advance the conceptual "Modern Synthesis" of population genetics and paleontology of the 1930s and 1940s. In light of this new understanding, the objections to evolutionary theory based on transitional gaps and irreducible complexity become more obtuse than ever. More accessible than Rudolf A. Raff's fine pioneering work, The Shape of Life, this book belongs in all libraries. [See the Q&A with Carroll on p. 107; see also Prepub Alert, LJ 12/04.-Ed.]-Walter L. Cressler, West Chester Univ. Lib., PA Copyright 2005 Reed Business Information.
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Kirkus Reviews:
The key to understanding diversity in nature is what happens in the embryo, says Carroll (Genetics/Univ. of Wisconsin-Madison), and he provides compelling proof. One of the great revelations of comparative genome studies over the past 20 years has been the discovery that animals share certain sets of master genes and switches that determine the ultimate shape of the animal, from flies and centipedes to mice and men. The fruit fly, for example, has a set of "Hox" genes on a single chromosome ordered in such a way that when expressed, they shape the fly's body from head to end. Mind-bogglingly, these same Hox genes, or multiples of them on different chromosomes, are found in vertebrates, mammals and humans-where they play the same roles. Such "tool-kit" genes, as Carroll calls them, and the all-important genetic switches that orchestrate where and when the tool-kit proteins are turned on, not only determine animal forms but more nuanced details. These discoveries, along with the realization that embryonic development builds on repeated modular forms (think of the multiple segments of the human spine) are also clues to complexity: Further tinkering in gene expression and timing can lead to new, specialized appendages like arms and legs or wings and webbed feet. Admittedly, taking in all the details of these discoveries in the early chapters can be heavy going, but if the reader persists, there are delights to come. In the latter half, Carroll neatly describes the development of eyespots on butterfly wings, stripes in zebras, circles on fruit flies and red hair on redheads. His final chapters tackle human evolution, providing an up-to-date reprise of current fossil finds and speculation onhow unique human traits may have developed. All this is further fallout from the new field of "evo devo" (evolutionary developmental biology) and provides more fuel to fight the creationist/intelligent-design folks. Deserves to find its way into schoolrooms across the nation.
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From Booklist
*Starred Review* Evo Devo is short for evolutionary developmental biology, a new science that explores the biological processes that give rise to both the shared traits and the wild diversity of animal anatomies. Carroll is at the vanguard of this promising field, and he is also a lucent and lively popular science writer deeply inspired by the order, ingenuity, and beauty of the molecular choreography he brings to light. Evo Devo has not only proven that human beings have a surprising number of genes in common with other animals, including the humble fruit fly, it has also revealed the startling fact that every animal species on earth is derived from the same small set of "tool-kit genes." In explicating these unexpected discoveries, Carroll describes in stunning detail the geography of a growing embryo, how genes mark out a diagram of the body to come, and how exactly, thanks to "genetic switches," the "hotspots of evolution," one group of genes can produce such variations on a theme as butterflies, birds, leopards, and whales. Carroll's highly detailed and well-illustrated technical discussions are enriched by his appreciation for the philosophical, aesthetic, and ethical implications of the biological wonders he decodes, adding up to a vital and enjoyable introduction to a field with profound implications. Donna Seaman
Book Review: Endless Forms Most Beautiful: Discover
June 2005
Karl Giberson