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The Extended Organism: The Physiology of Animal-Built Structures

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In _The Extended Organism: The Physiology of Animal-Built Structures_ (Harvard University Press), J. Scott Turner gives plenty of surprising examples to show that animals indeed use the environment outside in ways that would qualify the outside as part of their physiology. He intends us to take a broader view that organisms are not just tangible things wrapped up in skin or chitin or scales. An organism is, instead, an ephemeral collection of organized matter and energy. An organism is busy all its life influencing the flow of matter and energy through itself, but also through the environment. He argues that the reductionism of molecular and evolutionary biology may give way to a more holistic view, and winds up with the controversial idea of Gaia, the hypothesis that earth can be viewed as a single living organism. He says he doesn't want to air the arguments pro and con of this idea, but if organisms modify their environments into becoming part of their physiology, then it is not much of a step to saying that the Earth has a physiology of its own.

Perhaps. Turner's book is well argued and full of good ideas, and it may presage a neo-holism. Whether it accomplishes that, though, is less important than what it does manage to do. Turner is astonishingly encyclopedic in his explanations of his many surprising examples of out-of-body physiology. He draws upon thermodynamics, hydrodynamics, chemistry, electrical circuits, fractals, acoustics, and much more to put his audacious ideas onto a sound scientific foundation. This does not make for easy reading, but he is a genial guide and he tries his best to explain complicated ideas simply; the book is not for those, however, who can't stand equations mixed with the text. The best parts of the book are the examples of animals that have as good as made their surroundings part of their innards. There are lots of examples. In addition to the beetles that grab a bubble of air to use as scuba gear, there are beetles that not only do that, but if there is a current moving over them, their hydrodynamic form causes a suction, so that if they face into the current (which they of course habitually do), a bubble forms, pulled out of the water itself. They make this their gills, and they never have to go to the surface. Spittlebugs make a frothy white spittle attached to plants. The spittle isn't spittle, of course, but a froth of sap from the plant, processed by the digestive tract, excreted, and inflated with bubbles. Turner makes the case that since the bugs have a diet of protein-rich sap, they have a lot of ammonia as a waste product, and they cannot detoxify it as other animals do. The spittle enables the ammonia to be carried away; in other words, it functions as an exterior kidney. Earthworms, Turner shows, are fundamentally aquatic animals that only manage to get around when the water content of soils is perfectly balanced for them. (Turner reminds us that Darwin got enormous satisfaction for his last great work concerning earthworms and what they do to soils; before Darwin, earthworms were regarded as pests which ate plant roots.) The burrowing activities of the earthworm actually make the soil itself more favorable to the narrow needs of their own survival, and they use the soil as an organ to maintain a proper salt and water balance inside them.

There are many examples even before Turner gets to bees and to termites, which are his own particular enthusiasm and which use their homes to regulate temperature, oxygen content, and more. It is inarguable that these creatures really do shape their environment, and in ways that are not obvious. With clarity, humor, and a broad scientific understanding, Turner has done much to advance an argument to his holistic view.

In relatively short time, the reader is introduced to a new paradigm of external+internal animal physiology. Turner, just as Vogel (Life in Moving Fluids, Life's Devices, etc.) has the rare gift of teasing out complicated animate-inanimate interactions, be they hydrodynamic or thermodynamic, and presenting them to the reader in well-designed graphics and often humorous anecdotes. However, the book does not 'dumb-down' the material to a series of over-simplifications. In reading this book I had both the wondrous sense of seeing common structures such as ant hives and hearing 'amplified crickets' with a new respect for the underlying physics. The Extended Organism is an enlightening read for any curious person, researcher or not.

We are particularly excited with the comments, suprisingly coincident with our book 'Immune Crossover' 1998 that already converted into a fourth edition. I'll start reading today to review it later