Can the structures animals build - from the humble burrows of earthworms to towering termite mounds to the Great Barrier Reef - be said to live? However counter-intuitive the idea might first seem, this book demonstrates that many animals construct and use structures to harness and control the flow of energy from their environment to their own advantage.
Building on Richard Dawkins' classic, The Extended Phenotype, this book shows why drawing the boundary of an organism's physiology at the skin of the animal is arbitrary. Since the structures animals build undoubtedly do physiological work, capturing and channeling chemical and physical energy, such structures are properly regarded not as examples of 'frozen behavior' but as external organs of physiology. By challenging dearly held assumptions, a fascinating new view of the living world is opened to us, with implications for our understanding of physiology, the environment, and the remarkable structures animals build.
Scott Turner's beautifully written book puts empirical meat on the theoretical bones of Richard Dawkins's concept of the extended phenotype. He skillfully reviews how animal-built structures function as external organs of physiology of their builders, thus how they favor the survival and reproduction of the builders' genes. This is the first thorough review of the subject of 'external physiology' and as such is a work of major importance in biology.
Thomas D Seeley, Cornell University
The usual way of connecting organisms to their capabilities of controlling thermodynamics, fluid mechanics, and chemistry is to go within. In this profound work, Scott Turner inverts the usual direction and unfolds the connection outwards. In so doing, he gives us precision tools to re-think what organisms are and creates a paradigm that will prompt further research across a wide array of fields, from microbiology to ecology to biospherics
Tyler Volk, author of Gaia's Body: Toward a Physiology of Earth
Turner's lucid personal writing style leads the reader to the inescapable conclusion: the Earth's surface has a physiology. Manipulating midges and winter web weavers, like all life, shape and regulate the environment in accordance with the laws of nature.
Lynn Margulis, Distinguished University Professor, University of Massachusetts.
The impact of humans on the Earth is but one dramatic example of how organisms influence their environments. Scott Turner provides fascinating details on how organisms ranging from single cells to complex social insects effect change in their environments, influencing their success. Turner takes great care to be clear about complex mechanisms of function, underscoring the importance of other sciences to understand the biology of interactions between organisms and their environments.
Reed Hainsworth, Syracuse University
Turner brings to bear scientific incisiveness, humor, and a prose style that makes scientific minutiae fun to read ... The Extended Organism stands apart as a remarkably synthetic piece of scholarship.
Kurt Schwenk in the New York Times Book Review
A clever dissection of environmental physiology from a persistent and clever teacher. Like most good teachers, Turner manages to slip a huge range of information into your head along the way - information that helps change your view of organisms in their world.
Stephen R Palumbi in American Scientist
Turner's tales of the subtle ways organisms capitalize on the opportunities afforded them by their physical and chemical surroundings provide more than ample rason to read the book.
Steven Vogel in Nature
The apian way. New York Times Book Review, 10 December 2001, p 37. Kurt Schwenk, University of Connecticut
Amazing tales of electric lugworms. American Scientist 89: 266-268. May-June 2001. Stephen R Palumbi, Harvard University
The Extended Organism. Perspectives in Biology and Medicine 44 (2): 297-300 Spring 2001. Kevin Laland, Oxford University
The Extended Organism. Complexity 6 (2): 58-59 2001. Carl Anderson, Universität Regensburg (Germany)
Celebrating blurry boundaries. Nature 408 (2): 404-405 23 November 2000. Steven Vogel, Duke University
The Extended Organism. Ichnos 12: 309-310, 2005. Stephen K Donovan, Nationaal Natuurhistorisch Museum, Leiden, The Netherlands
Animals without boundaries. Ecology 82 (1): 304-305 2001. Holly Downing, Black Hills State University
The Extended Organism. Quarterly Review of Biology 76 2001. Albert D Carlson, Editor, Quarterly Review of Biology
Helpful extensions. EMBO Reports 11 (61) 2000. Jürgen Tautz, Universität Würzburg (Germany)
Fuzzing the boundary of animal life. Science 289 (5486): 1882 15 September 2000. Michael LaBarbera, University of Chicago
Darwin meets Gaia. The Times of London Literary Supplement 15 June 2001. Michael Hansell, Edinburgh University
The hills are alive. The Boston Globe Sunday Magazine 18 February 2001. Gareth Cook, Boston Globe
It's Alive. New Scientist 168 (2262): 30-33 28 October 2000. Kathryn Brown
The structures animals build, and why they build them, is the subject of this book. Traditionally, the study of animal-built structures has been the province of students of animal behavior or evolutionary biology, who have used these artefacts as "frozen behavior" - powerful probes into behavior, neurobiology and evolution. However, these structures also do things for the animals that build them, and what these things are is the theme developed in this book. Specifically, I argue that animal-built structures are properly external organs of physiology - devices to modify and control the flows of energy and matter between an organism and its environment. In developing this theme, I undertake a radical exploration of the nature of the organism and its relationship to its environment.
The book, while physiological in outlook, is multidisciplinary and eclectic in its approach, drawing together concepts in thermodynamics, physics and chemistry, all explored in a rich context of natural history. The book should appeal to a wide range of readers, from the scientifically literate public - exemplified by readers of Smithsonian, Natural History, or Scientific American - to scientific specialists across a variety of disciplines. Students of animal behavior should enjoy seeing a physiological analysis of how animal-built structures work. Physiologists should enjoy seeing some novel ways physiology can be applied to questions in natural history and zoology. Evolutionary biologists will appreciate seeing the functional "flesh and bones" of Richard Dawkins' concept of the extended phenotype. Ecologists will enjoy seeing an return to their discipline's historical roots as a physiological science.
This chapter introduces the book's theme by a discussion of what constitutes the boundary between an organism and its environment. It introduces the notion that organisms are not tangible "things" but are ephemeral collections of organized matter and energy. What makes an organism living is how its presence influences and organizes this flow of matter and energy through the environment. The traditional outlook in physiology has been inward-looking, trying to understand how an organism's internal physiology - the collective actions of its internal organs, cells and molecules - organizes matter and energy. An outward look, however, reveals that organisms influence flows of matter and energy beyond the boundaries of the organism itself, and that structures built by animals often play a crucial role in this. Top
This chapter builds the idea of an external physiology that is, in principle, indistiguishable from the traditional idea of physiology as the workings of the "blood and guts" of an organism. It begins with a discussion of a fundamental thermodynamic principle - that the tendency of the universe is to disorder - and that to create order, work must be done. I illustrate this with a discussion of order and energy in the fundamental chemical reactions of life - the fixation of carbon dioxide by plants into sugar, and the metabolism of sugar by animals. I then discuss two physiological systems, one a "traditional" physiological system (operation of the kidneys of a freshwater fish), and an "extended" physiological function (deposition of calcium carbonate by reef-building corals) where the boundary between inside and outside the organism is not as clear. I try to make the point that these two systems are thermodynamically indistinguishable from one another. For those readers not familiar with the principles of thermodynamics, a brief sidebar article is included. Top
This chapter continues to build the notion of an external physiology and to explicitly posit the roles that animal-built structures might play in it. I begin by discussing an apparent logical flaw in Chapter 2, namely the supposed equivalence of all thermodynamic processes, whether living or inanimate. I formally introduce the concept of dual energy streams that can power physiological function: a "metabolic energy stream" that constitutes the flow of chemical energy through an organism that powers its internal physiology, and a parallel "physical energy stream" that, if captured properly, can also power physiological function. I assert that structures built by animals are crucial in capturing this physical energy stream and making it do physiological work. I conclude by broadly outlining the ways that the physical energy stream can be manipulated by structures. Top
This chapter begins to put flesh and bones onto the fairly theoretical arguments of the first three chapters. It is concerned with a remarkable example of how metabolic and physical energy streams flowing through a system interact to generate orderliness on a large scale. The example concerns so-called bioconvection phenomena, in which a culture of swimming microorganisms, like certain protozoa, spontaneously organizes itself into large-scale convection cells. This orderliness promotes respiratory gas exchange in the culture, and so constitutes the formation of a sort of "superorganismal" circulatory system. The chapter describes the origins of these phenomena in detail, and concludes with the assertion that such external physiology arises virtually inevitably when a metabolic energy stream interacts with large-scale potential energy gradients in the environment. Top
This chapter wraps up the theoretical part of the book, by making an explicit connection between the type of "spontaneous orderliness" of bioconvection cells with actual structures built by organisms. The chapter focuses on so-called modular structures of the types built by sponges and corals, and on how these structures are both shaped by, and exploit potential energy gradients in, the environment. The chapter outlines the peculiar modes of growth of these organisms, and attempts to put them into a context of development and evolution of body plans in the animal kingdom. Some modern models of growth of sponges and corals, involving fractal geometry and modular growth, are introduced, along with basic concepts like Fick's law and diffusion-limited-aggregation growth. The chapter argues that emergence of structures that "do" physiology is virtually spontaneous and should be a general feature of animals, irrespective of whether or not certain types of physiology have been appropriated by internal organs. The chapter concludes with an example of superorganismal physiology, the modification of the fractal dimension of coastlines by coral reefs. Top
With this chapter, the book turns to specific examples of animal-built structures and how these can act as organs of external physiology. I begin with very simple structures, tubes dug in mud by worms. Many intertidal and marine invertebrates dig tunnels into bottom muds, and these potentially perform important physiological functions for them. The energy source that is exploited by these tunnels appears to be gradients in oxidation potential that exist across a boundary common in marine muds, the redox potential discontinuity layer (RPDL). By digging a tunnel that spans the RPDL, marine worms introduce electron acceptors into the highly reducing environment of anoxic muds. The resulting redox potential gradient sets in motion an energetic cascade which provides food energy to the worms, with relatively little effort on the part of the worms themselves. The emergence of the RPDL and of the burrowing habits of marine worms is put into the context of "grand" evolutionary events in the history of the Earth, including the origins of photosynthesis, the response of the original anaerobic biota of the Earth, and the proliferation of the Metazoa around the Precambrian and Cambrian periods. Top
This chapter continues the theme of tunnels and their roles in the physiology of the animals that dig them. Here, I turn to the problem of earthworms and how they alter the structure of the soils they live in. I begin by making and defending the assertion that earthworms are physiologically aquatic animals that are poorly equipped physiologically for life on land. Part of this discussion includes a detailed description of the water balance organs of the annelids. I continue by examining the problem of how water moves in soils, introducing in the process the important concept of the water potential. From there, I develop a simple water balance model that describes the energy costs to earthworms of living in soil habitats, leading to the conclusion that earthworms can survive only in a fairly narrowly delimited set of soil types. The chapter ends with a discussion of how the burrowing activities of earthworms modify the soil to expand the volume of the types of soil habitats favorable to their own survival. I conclude by making the assertion that earthworms are essentially co-opting the soils they live in as accessory water-balance organs, in which the structure and distributions of the tunnels they build are crucial features of the earthworm's own salt and water balance. Top
Beginning with this chapter, the book turns from simple structures like tunnels or burrows, and turns to the more complex structures, specifically woven structures built by arthropods. The discussion is centered around the use of bubbles as gills, and begins with a description of the aquatic spider, Argyroneta aquatica, and its use of a web as a diving bell. From there, I begin a more general discussion of the use of bubble by aquatic arthropods. In so doing, I develop a general outline of gas exchange between bubbles and the environment, and how certain aquatic insects exploit these physical principles to turn bubbles into gills. I wrap this phase of the chapter up with a discussion of the plastron gill, and the physical principles underlying its operation. From there, I go on to discuss three examples of unusual plastron gills, each of which rely on structures built by animals. The first is a parasitic wasp, Agriotypus, which inhabits caddis houses. These wasps line the caddis-house with a tightly-woven envelope of silk, which is then evacuated of water and filled with air. One of the curious architectural features of these coccoons is a long silken ribbon that extends into the water, and which acts as an "oxygen sponge" to draw oxygen into the coccoon. The second is an African aquatic beetle, Potamodytes, which exploits kinetic energy in flowing water to maintain its plastron gill, and which often uses structural features of its environment, like pebbles or twigs, to increase the efficiency of capture of this kinetic energy. The final example turns the tables and examines a plastron gill that works as an accessory kidney. Spittle bugs construct foamy nests of spittle, often at great expense to themselves. Commonly, spittle nests are thought to be adaptations to prevent desiccation. I show this to not be the case, and build an argument that these are plastron kidneys, which help promote the loss of ammonia gas from the bug. Top
There is a class of structures that are built by one animal hijacking the activities of another organism. One of the most obvious examples of this is the stimulation of plant galls by the arthropod parasites that cause them. Plant galls are a type of developmental anomaly among plants that result when a pathogen (often an arthropod) attacks the plant and activates developmental programs in the plant that normally are quiescent. In many galls, the resulting growth is apparently chaotic, but in the case of many leaf galls, can result in surprisingly orderly structures. These structures are explored in light of their effects on leaf microclimate and heat and water balance of the parasitized leaves. I conclude with a rather speculative discussion of the forces that have driven the evolution of plant galls. Top
Auditory signals are common modes of communication among insects. These provide external channels for information exchange and control that are, in principle, no different from the neurological and chemical signaling that goes on inside the body. This chapter is concerned with auditory communication among crickets, in particular mole crickets, which construct singing burrows, acoustical structures that aid in the projection and refinement of the acoustical signals of the song. This chapter requires the laying of a fair bit of groundwork in acoustical theory, which I try to do in the context of the question: how do crickets produce loud sounds? As part of the groundwork, I discuss the mechanisms of sound production by crickets, what the acoustical limitations are on sound production, and various ways one can get around these limitations with clever acoustical devices, like baffles. I conclude with a description of one of these devices, a Klipsch horn, which bears an uncanny resemblance to the singing burrows of mole crickets. I then discuss the acoustical performance of these burrows, introducing along the way some of the structural variation among different species and how this variation affects the ways crickets use their acoustical signals to attract mates. The chapter concludes with a discussion of how such a "high-performance" structure could evolve, in the context of the problem of "organs of extreme perfection." Singing burrows present an interesting challenge because these are external "organs of extreme perfection" that must evolve in the absence of any genetic template that natural selection could act directly on. I assert that the high performance is the result of a feedback loop that extends outside the body of the cricket that enables the male to "tune" its burrow as the high performance structure it is. Top
Many social insects build nests to house their colonies. Some of these structures, like the nests of the fungus-growing termites of southern Africa or the leaf cutter ants of the New World are among the most spectacular animal-built structures on the planet. This chapter deals with how these remarkable structures function in the respiratory physiology of the colonies they house, and discusses the engineering and physical principles at work in the structure and function of these nests. The chapter goes on to confront a long-standing issue in the biology of social insects, whether or not social insect colonies can be "superorganisms", collections of animals that can engage collectively in behaviors that are organismal in nature. Advocates of the superorganism concept have long pointed to structures like these to bolster their arguments, because they supposedly demonstrate such a high degree of structural integration that it is almost a form of "engineering." The chapter concludes with a discussion of the ups and downs of the superorganism concept, and uses the author's recent work on termite mounds in Africa to shed new light on the notion of insect engineering. Top
This is a wrap-up chapter, devoted to a reprise of the general lessons that have been learned, and concluding with a discussion of the future of environmental physiology. I begin with a general discussion of the problem of orderliness, introducing the doctrine of vitalism, the supposedly moribund doctrine that asserts that life is a qualitatively unique phenomenon that is not amenable to the dominant reductionist approach that has characterized 20th century biiology. I then introduce the essentially neo-vitalist doctrine of Gaia, the hypothesis of James Lovelock and Lynn Margulis that the Earth is a single living organism. I devote much of the chapter to a discussion of the problem of orderliness in the context of the scientific critique of Gaia. Along the way, I attempting to develop some general ideas in control systems theory and new developments in theory of chaos, so that we may have a critical way of evaluating the claim that the Earth, and not just the organisms in it, has physiology. I make the claim that, indeed, the Earth does, and that Gaia may indeed mark the resurgence of a scientifically credible vitalism. Central to this is the ability of organisms to structurally modify their environments in ways that enable them to control the flows of matter, energy and information between them - in short, the principal thesis of this book. I conclude the chapter with a few thoughts on the future of biology, which, I suggest, lies "beyond the organism", away from the radical reductionism that has dominated 20th century biology. Top