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Author | Sean B. Carroll |
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Country | USA |
Subject | Evolutionary developmental biology (evo-devo) |
Genre | Popular science |
Publisher | W. W. Norton |
Publication date | 2005 |
Pages | 331 |
Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom is a 2005 book by the molecular biologist Sean B. Carroll. It presents a summary of the emerging field of evolutionary developmental biology and the role of toolkit genes. It has won numerous awards for science communication.
The book's somewhat controversial [1] argument is that evolution in animals (though no doubt similar processes occur in other organisms) proceeds mostly by modifying the way that regulatory genes, which do not code for structural proteins (such as enzymes), control embryonic development. In turn, these regulatory genes turn out to be based on a very old set of highly conserved genes which Carroll nicknames the toolkit. Almost identical sequences can be found across the animal kingdom, meaning that toolkit genes such as Hox must have evolved before the Cambrian radiation which created most of the animal body plans that exist today. These genes are used and reused, occasionally by duplication but far more often by being applied unchanged to new functions. Thus the same signal may be given at a different time in development, in a different part of the embryo, creating a different effect on the adult body. In Carroll's view, this explains how so many body forms are created with so few structural genes.
The book has been praised by critics, and called the most important popular science book since Richard Dawkins's The Blind Watchmaker . [2]
Sean B. Carroll is a professor of molecular biology and genetics at the University of Wisconsin–Madison. [3] He studies the evolution of cis-regulatory elements (pieces of non-coding DNA) which help to regulate gene expression in developing embryos, using the fruit fly Drosophila as the model organism. [4] [5] He has won the Shaw Scientist Award [6] and the Stephen Jay Gould Prize [7] for his work.
The book's title quotes from the last sentence of Charles Darwin's 1859 The Origin of Species , in which he described the evolution of all living organisms from a common ancestor: "endless forms most beautiful and most wonderful have been, and are being, evolved." [8] Darwin, however, was unable to explain how those body forms actually came into being. The early 20th-century modern synthesis of evolution and genetics, too, largely ignored embryonic development to explain the form of organisms, since population genetics appeared to be an adequate explanation of how forms evolved. That task was finally undertaken at the end of the 20th century with the arrival of recombinant DNA technology, when biologists were able to start to explore how development was actually controlled. [9]
The book is illustrated with photographs, such as of developing fruit fly embryos dyed to show the effects of toolkit genes, and with line drawings by Jamie W. Carroll, Josh P. Klaiss and Leanne M. Olds.
The evolutionary biologist Lewis Wolpert, writing in American Scientist , called Endless Forms Most Beautiful "a beautiful and very important book." He summarized the message of the book with the words "As Darwin's theory made clear, these multitudinous forms developed as a result of small changes in offspring and natural selection of those that were better adapted to their environment. Such variation is brought about by alterations in genes that control how cells in the developing embryo behave. Thus one cannot understand evolution without understanding its fundamental relation to development of the embryo." Wolpert noted that Carroll intended to explain evo-devo, and "has brilliantly achieved what he set out to do." [12]
The evolutionary biologist Jerry Coyne, writing in Nature , described the book as for the interested lay reader, and called it "a paean to recent advances in developmental genetics, and what they may tell us about the evolutionary process." [1] For him, the centrepiece was "the unexpected discovery that the genes that control the body plans of all bilateral animals, including worms, insects, frogs and humans, are largely identical. These are the 'homeobox' (Hox) genes". [1] He called Carroll a leader in the field and an "adept communicator", but admits to "feeling uncomfortable" [1] when Carroll sets out his personal vision of the field "without admitting that large parts of that vision remain controversial." [1] Coyne pointed out that the idea that the "'regulatory gene' is the locus of evolution" [1] dates back to Roy Britten and colleagues around 1970, but was still weakly supported by observation or experiment. He granted that chimps and humans are almost 99% identical at DNA level, but points out that "humans and chimps have different amino-acid sequences in at least 55% of their proteins, a figure that rises to 95% for humans and mice. Thus we can't exclude protein-sequence evolution as an important reason why we lack whiskers and tails." [1] He also noted that nearly half of human protein-coding genes do not have homologues in fruit flies, so one could argue the opposite of Carroll's thesis and claim that "evolution of form is very much a matter of teaching old genes to make new genes." [1]
The review in BioScience noted that the book serves as a new Just So Stories , explaining the "spots, stripes, and bumps" that had attracted Rudyard Kipling's attention in his children's stories. The review praised Carroll for tackling human evolution and covering the key concepts of what Charles Darwin called the grandeur of [the evolutionary view of] life, suggesting that "Kipling would be riveted." [11]
The science writer Peter Forbes, writing in The Guardian , called it an "essential book" and its author "both a distinguished scientist ... and one of our great science writers." [13] The journalist Dick Pountain, writing in PC Pro magazine, argued that Endless Forms Most Beautiful was the most important popular science book since Richard Dawkins's The Blind Watchmaker , "and in effect a sequel [to it]." [2]
The paleobiologist Douglas H. Erwin, reviewing the book for Artificial Life, noted that life forms from fruit flies to humans have far fewer genes than many biologists expected – human beings have only some 20,000. "How could humans, in all our diversity of cell types and complexity of neurons, require essentially the same number of genes as a fly, or worse, a worm (the nematode Caenorhabditis elegans )?" [14] asks Erwin. He answered his own question about the "astonishing morphological diversity" of animals coming from "such a limited number of genes", praising Carroll's "insightful and enthusiastic" style, writing in a "witty and engaging" way, pulling the reader into the complexities of Hox and PAX-6 , as well as celebrating the Cambrian explosion of life forms and much else. [14]
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charles Darwin popularised the term "natural selection", contrasting it with artificial selection, which is intentional, whereas natural selection is not.
Evolutionary developmental biology is a field of biological research that compares the developmental processes of different organisms to infer how developmental processes evolved.
The modern synthesis was the early 20th-century synthesis of Charles Darwin's theory of evolution and Gregor Mendel's ideas on heredity into a joint mathematical framework. Julian Huxley coined the term in his 1942 book, Evolution: The Modern Synthesis. The synthesis combined the ideas of natural selection, Mendelian genetics, and population genetics. It also related the broad-scale macroevolution seen by palaeontologists to the small-scale microevolution of local populations.
In biology, homology is similarity due to shared ancestry between a pair of structures or genes in different taxa. A common example of homologous structures is the forelimbs of vertebrates, where the wings of bats and birds, the arms of primates, the front flippers of whales, and the forelegs of four-legged vertebrates like dogs and crocodiles are all derived from the same ancestral tetrapod structure. Evolutionary biology explains homologous structures adapted to different purposes as the result of descent with modification from a common ancestor. The term was first applied to biology in a non-evolutionary context by the anatomist Richard Owen in 1843. Homology was later explained by Charles Darwin's theory of evolution in 1859, but had been observed before this, from Aristotle onwards, and it was explicitly analysed by Pierre Belon in 1555.
Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth. It is also defined as the study of the history of life forms on Earth. Evolution holds that all species are related and gradually change over generations. In a population, the genetic variations affect the phenotypes of an organism. These changes in the phenotypes will be an advantage to some organisms, which will then be passed on to their offspring. Some examples of evolution in species over many generations are the peppered moth and flightless birds. In the 1930s, the discipline of evolutionary biology emerged through what Julian Huxley called the modern synthesis of understanding, from previously unrelated fields of biological research, such as genetics and ecology, systematics, and paleontology.
In evolutionary developmental biology, heterochrony is any genetically controlled difference in the timing, rate, or duration of a developmental process in an organism compared to its ancestors or other organisms. This leads to changes in the size, shape, characteristics and even presence of certain organs and features. It is contrasted with heterotopy, a change in spatial positioning of some process in the embryo, which can also create morphological innovation. Heterochrony can be divided into intraspecific heterochrony, variation within a species, and interspecific heterochrony, phylogenetic variation, i.e. variation of a descendant species with respect to an ancestral species.
Sean B. Carroll is an American evolutionary developmental biologist, author, educator and executive producer. He is a distinguished university professor at the University of Maryland and professor emeritus of molecular biology and genetics at the University of Wisconsin–Madison. His studies focus on the evolution of cis-regulatory elements in the regulation of gene expression in the context of biological development, using Drosophila as a model system. He is a member of the National Academy of Sciences, of the American Philosophical Society (2007), of the American Academy of Arts and Sciences and the American Association for Advancement of Science. He is a Howard Hughes Medical Institute investigator.
Hox genes, a subset of homeobox genes, are a group of related genes that specify regions of the body plan of an embryo along the head-tail axis of animals. Hox proteins encode and specify the characteristics of 'position', ensuring that the correct structures form in the correct places of the body. For example, Hox genes in insects specify which appendages form on a segment, and Hox genes in vertebrates specify the types and shape of vertebrae that will form. In segmented animals, Hox proteins thus confer segmental or positional identity, but do not form the actual segments themselves.
A body plan, Bauplan, or ground plan is a set of morphological features common to many members of a phylum of animals. The vertebrates share one body plan, while invertebrates have many.
Biological or process structuralism is a school of biological thought that objects to an exclusively Darwinian or adaptationist explanation of natural selection such as is described in the 20th century's modern synthesis. It proposes instead that evolution is guided differently, basically by more or less physical forces which shape the development of an animal's body, and sometimes implies that these forces supersede selection altogether.
Ontogeny and Phylogeny is a 1977 book on evolution by Stephen Jay Gould, in which the author explores the relationship between embryonic development (ontogeny) and biological evolution (phylogeny). Unlike his many popular books of essays, it was a technical book, and over the following decades it was influential in stimulating research into heterochrony, which had been neglected since Ernst Haeckel's theory that ontogeny recapitulates phylogeny had been largely discredited. This helped to create the field of evolutionary developmental biology.
Wallace Arthur is an evolutionary biologist and science writer. He is Emeritus Professor of Zoology at the University of Galway. His most recent book is Understanding Life in the Universe, published by Cambridge University Press, which focuses on the likely extent and nature of extraterrestrial life. He was one of the founding editors of the journal Evolution & Development, serving as an editor for nearly 20 years. He has held visiting positions at Harvard University, Darwin College Cambridge, and the University of Warmia and Mazury in Olsztyn, Poland.
In evolutionary developmental biology, the concept of deep homology is used to describe cases where growth and differentiation processes are governed by genetic mechanisms that are homologous and deeply conserved across a wide range of species.
Evolutionary thought, the recognition that species change over time and the perceived understanding of how such processes work, has roots in antiquity—in the ideas of the ancient Greeks, Romans, Chinese, Church Fathers as well as in medieval Islamic science. With the beginnings of modern biological taxonomy in the late 17th century, two opposed ideas influenced Western biological thinking: essentialism, the belief that every species has essential characteristics that are unalterable, a concept which had developed from medieval Aristotelian metaphysics, and that fit well with natural theology; and the development of the new anti-Aristotelian approach to modern science: as the Enlightenment progressed, evolutionary cosmology and the mechanical philosophy spread from the physical sciences to natural history. Naturalists began to focus on the variability of species; the emergence of palaeontology with the concept of extinction further undermined static views of nature. In the early 19th century prior to Darwinism, Jean-Baptiste Lamarck (1744–1829) proposed his theory of the transmutation of species, the first fully formed theory of evolution.
Alessandro Minelli is an Italian biologist, formerly a professor of zoology in the Faculty of Mathematical, Physical and Natural Sciences of the University of Padova, mainly working on evo-devo subjects.
The Extended Evolutionary Synthesis (EES) consists of a set of theoretical concepts argued to be more comprehensive than the earlier modern synthesis of evolutionary biology that took place between 1918 and 1942. The extended evolutionary synthesis was called for in the 1950s by C. H. Waddington, argued for on the basis of punctuated equilibrium by Stephen Jay Gould and Niles Eldredge in the 1980s, and was reconceptualized in 2007 by Massimo Pigliucci and Gerd B. Müller.
Heterotopy is an evolutionary change in the spatial arrangement of an animal's embryonic development, complementary to heterochrony, a change to the rate or timing of a development process. It was first identified by Ernst Haeckel in 1866 and has remained less well studied than heterochrony.
The evo-devo gene toolkit is the small subset of genes in an organism's genome whose products control the organism's embryonic development. Toolkit genes are central to the synthesis of molecular genetics, palaeontology, evolution and developmental biology in the science of evolutionary developmental biology (evo-devo). Many of them are ancient and highly conserved among animal phyla.
How the Snake Lost Its Legs: Curious Tales from the Frontier of Evo-Devo is a 2014 book on evolutionary developmental biology by Lewis I. Held, Jr. The title pays homage to Rudyard Kipling's Just So Stories, but the "tales" are strictly scientific, explaining how a wide range of animal features evolved, in molecular detail. The book has been admired by other biologists as both accurate and accessible.