Friday, January 8, 2010

In The Beat of a Heart

Over Christmas break, I read In the Beat of a Heart: Life, Energy, and the Unity of Nature, by John Whitfield. I had mixed feelings about the book. I didn't have much interest in the parts dealing with biodiversity in tropical forests and skimmed through them rather quickly. But other parts I found fascinating. One of the main topics explored in the book is Kleiber's law (metabolic rate scales as the 3/4th power of body mass), which Russ Hobbie and I discuss in Chapter 2 of the 4th edition of Intermediate Physics for Medicine and Biology. But the book has a broader goal: to compare and contrast the approaches of physicists and biologists to understanding life. The main idea can be summarized by the subtitle of the textbook I studied biology out of when an undergraduate at the University of Kansas: The Unity and Diversity of Life. Intermediate Physics for Medicine and Biology lies on the "unity" side of this great divide, but the interplay of these two views of life makes for a remarkable story.
The book begins with a Prologue about D'Arcy Thompson (Whitfield calls him "the last Victorian scientist"), author of the influential, if out-of-the-mainstream, book On Growth and Form.
"This is the story--with some detours--of D'Arcy Thompson's strand of biology and of a century-long attempt to build a unified theory, based on the laws of physics and mathematics, of how living things work. At the story's heart is the study of something that Thompson called 'a great theme'--the role of energy in life... The way that energy affects life depends on the size of living things. Size is the most important single notion in our attempt to understand energy's role in nature. Here, again, we shall be following Thompson's example. After its introduction, On Growth and Form ushers the reader into a physical view of living things with a chapter titled 'On Magnitude,' which looks at the effects of body size on biology, a field called biological scaling."
In the Beat of a Heart examines Max Rubner's idea that metabolism scales with surface area (2/3rd power), and Max Kleiber's modification of this rule to a 3/4th power. It then describes the attempt of physicist Geoffrey West and ecologist Brian Enquist to explain this rule by modeling the fractal networks that provide the raw materials needed to maintain metabolism. While I was familiar with much of this story before reading Whitfield's book, I nevertheless found the historical context and biographical background engrossing. Then came the lengthy section on forest ecology (Zzzzzzzzz). I soldiered on and was rewarded by a penetrating final chapter comparing the physicist's and biologist's points of view.
"Finding a unity of nature would not make studying the details of nature obsolete. Indeed, finding unity depends on understanding the details. The variability of life means that in biology the ability to generalize is not enough. If you've measured one electron, you've measured them all, but, as I saw in Costa Rica, to understand a forest you must be able to see the trees, and that takes a botanist. Thinkers such as Humboldt, Darwin, and Wallace gained their understanding of how nature works from years of intimate experience of nature in the flesh and the leaf. And yet they were not just interested in what their senses told them: they also tried to abstract and unify. The combination of attributes--intrepid and reflective, naturalist and mathematician--strikes me as rather rare, and becoming more so. These days scientific lone wolves such as D'Arcy Thompson are almost extinct, and it would take a truly awesome polymath to acquire the necessary suite of skills in natural history, ecology, mathematics, and physics to devise a theory as complex as fractal networks."
The book ends with a provoking question and answer that sums up the debate nicely:
"Is nature beautifully simple or beautifully complex? Yes, it is."
More about In the Beat of a Heart can be found at the book's website: http://www.inthebeatofaheart.com.

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