Does the internal physiology of animals imply a harmony of structure and function?
By Mary Beth Saffo
March 1, 2007
The Tinkerer’s Accomplice: How Design Emerges from Life Itself by J. Scott Turner, Cambridge, $27.95
The biologist Ward Watt once wrote that “adaptation is a central but troublesome concept in evolutionary biology.” It might say something about the state of evolutionary biology, or perhaps about the nature of Big Ideas in general, that a similar statement could be made about several other central concepts in this field as well. Evolutionary biology is full of important questions so contentious that biologists often do not agree about the significance of particular phenomena, much less the mechanisms behind them. That contentiousness is, in most ways, a sign of a vital, dynamic discipline and of important problems worth arguing about. But it’s also a reminder that these Big Questions are hard questions, too, not solvable by superficial thinking, casual observations, quick experiments, or easy answers.
In a new book, The Tinkerer’s Accomplice, animal physiologist J. Scott Turner tackles one of the biggest and most troublesome biological issues, the problem of design in biology. Turner approaches this problem from the perspective of an animal physiologist and works to link a central concept in animal physiology—homeostasis—with that of design. In its classic definition, homeostasis is a mechanism that regulates the internal environment of animals, maintaining equilibria of such factors as salt concentration, fluid content, muscle tension, and (in some animals) body temperature. Turner seeks to demonstrate that agents of homeostasis can “impart design in living systems.” In my view, he does not succeed in doing so.
The perspective of The Tinkerer’s Accomplice has much in common with that of Turner’s earlier book, The Extended Organism. Homeostasis is a theme of both books, as is a laudable emphasis on the importance of whole-organism perspectives in biological research. But the two books also differ: The Extended Organism concentrates on the physiological implications of animal-built structures, while The Tinkerer’s Accomplice focuses on internal physiology. The Extended Organism is by far the more successful of the two books.
One of the many challenges of evolutionary biology is to infer from the fossil record, and from our still-growing understanding of life on earth today, the events of evolutionary history as well as the mechanisms that have brought about major, long-term evolutionary change. This effort demands every experimental, observational, and conceptual skill biologists can bring to the table. But, most of all, it demands an ability to think about organisms at different scales of organization and about evolution at different scales of time and space. It is a conceptual as well as experimental challenge to extrapolate the consequences of DNA mutations observed over the tiny time slices of a laboratory experiment to inferences of the mechanisms and direction of long-term evolutionary change; to assess the impact of natural selection on the genetics, physiology, architecture, and interactions of organisms, and the impact of large-scale and small-scale environmental factors on the outcomes of natural selection; and to understand the full import of the interplay between life and environmental changes throughout the history of the earth.
Paralleling the conceptual challenges of viewing life at different temporal and physical scales is the equal challenge of finding a language to formulate these perspectives. A common problem arises when an identical term is used to describe similar, but not necessarily identical, phenomena in different biological contexts, or at different scales of time and space. The word design is one of those troublesome words with multiple biological and cultural connotations, and Turner gets into trouble on this score with his very first sentence: “This book is about why organisms work well, or to put it another way, why they seem to be ‘designed.’” The first half of the sentence implies an emphasis on the mechanics of organism function; the second half implies a focus on the causative factors of that function.
In an apparent effort to establish his intentions, the author next brings up “intelligent design,” asserting that his book is not about that highly politicized issue. But even mention of “intelligent design” adds unnecessary confusion, especially since the author explicitly notes his central interest in “the fraught problems of intentionality and purposefulness,” and he chastises other biologists for shying away from these problems in their own scholarly work. Later attempts at clarification include his coinage of the conceptually unnecessary and aesthetically unfortunate term designedness to refer to the “harmonious integration of structure and function.”
As Turner notes later, “It depends on what the meaning of ‘designed’ is.” Well, exactly. The initial semantic confusion about this word alone sets the conceptual tone for the rest of this interesting, maddening, and highly problematic book.
The Tinkerer’s Accomplice is an agglomeration of diverse topics. On the way to the concluding chapters on “intentionality” and “design,” Turner offers up the works of David Hume, termite mounds, the biomechanics of muscle physiology, the formation of blood vessels and bones, Spiderman, tattoos, embryonic development, flotation mechanisms, gut physiology in sea anemones and mammals, mad cow disease, the components of vision, and the biology of addiction.
It makes for a rich mix, and some of the components of the mix are satisfying indeed. Turner’s description of the work of fibroblasts and angioblasts in blood vessel operations brought these cells alive for me in a way that standard anatomical treatments have never done. I also learned a lot about antler growth and was intrigued by his homeostatic perspective on such mental disorders as schizophrenia, adhd, and drug addiction. Flashes of humor brighten the book throughout.
But The Tinkerer’s Accomplice also has many difficulties, on both biological and philosophical levels. Turner takes a disappointingly narrow, animal-based view of regulatory mechanisms, promoting the view that animals are “more interestingly designed than other creatures,” incorrectly stating that epithelia are unique to animals, and wrongly implying that animals that regulate their internal fluids or external habitat are evolutionarily superior to those organisms that cope with environmental variation in other, often impressive and equally successful ways. This narrow view robs him of the opportunity to bring up pertinent examples from other parts of the biosphere, including structural architecture of seaweeds and terrestrial plants; the developmental legerdemain of sponge epithelia; flotation devices in seaweeds and unicellular algae; and ionic regulation in microbes and other organisms. A broader view would have yielded richer physiological and evolutionary insights.
A lesser complaint is the author’s simplistic portrayal of neo-Darwinists as determinedly “atomistic” in their thinking, utterly uninterested in the developmental, physiological, or environmental dimensions of genetic change over time. While some geneticists of that sort do exist, they are vastly outnumbered by a growing body of developmental biologists, evolutionary biologists, and population geneticists whose life’s work is centered on studying the mechanisms of genetic change in their fullest developmental, physiological, and/or ecological context.
Given that issues of adaptation and natural selection are inextricably, profoundly bound up with the problem of the design of organisms, it is also puzzling that both phenomena receive, at most, only cursory attention throughout the book. Even a brief but formal discussion of these topics would have made The Tinkerer’s Accomplice a deeper and more coherent book. The essays and books of Stephen Jay Gould, the several books by Steven Vogel on biomechanics, and even Henry Petroski’s books on engineering design have all managed to explain these principles succinctly and accurately for lay audiences. I recommend all of these authors to any readers left confused by the design discussions in The Tinkerer’s Accomplice.
Most seriously, Turner does not manage to link homeostasis to “intentionality” and “design” beyond his repeated assertions that such links exist. Neither of the two overtly philosophical chapters forged convincing connections between the author’s physiological examples and the “intentionality” and “purposefulness” purported to be, in the book’s conclusion, “life’s fundamental attribute.” Turner did give me some food for thought and also offered some tidbits of truly interesting biology along the way. But in the end the worthwhile material in this book is badly in need of, yes, better design.
Mary Beth Saffo is a biologist at work on a book about parasitic and beneficial symbiosis, tentatively titled "Lives of the Infectious and the Infected."
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