Tuesday, August 25, 2015

Book Review: A New History of Life by Peter Ward and Joe Kirschvink

A New History of Life is a  natural history that stands out because of its large timescale (4.567 billion years, to be precise) and broad intended audience. Overall, it delivers on the promise of its title adjective, describing new findings and hypotheses connecting paleontology and geology, and offering genuine but grounded scientific speculation for future work. For the general reader, it provides a wealth of new information, but because its overall scientific narrative lacks momentum and internal connection, it may be most appropriate for a scientifically literate audience.

It is impressive to watch the authors address the central challenge of this genre, which I have faced myself in my writing for a general audience:  How do you filter oceans of information and translate it into general terms? Authors Ward and Kirschvink set up their filter by emphasizing physical evidence, and rocks and bones in particular. Their geological and paleontological emphasis gives this story a different tone and tempo than other natural histories that start with the Big Bang (physics) or the characteristics of life (biology). My own discipline, chemistry, is not as deeply integrated as a result – here, chemistry plays a role in dating the rocks and bones, and in transforming the environment, but the authors focus most attention on the change and flow of continents (and other aspects of geology) and body plans (developmental biology).

The flip side of the authors’ emphasis is their deemphasis. Ward and Kirschvink deemphasize evidence from genetic clocks and other results from molecular biology, which leads them a chain of reasoning that is mostly geological in nature. For example, they favor a very late evolution of water photosynthesis. Personally, I trust the genetic clocks that show how many forms of photosynthesis, including water photosynthesis, evolved much earlier than Ward and Kirschvink allow. But this is a moot point -- a few hundred million years one way or the other doesn’t change the story much for the general reader.

A New History of Life reads at the level of an undergraduate science course. Ward and Kirschvink recount the back-and-forth narrative of scientific discovery and rebuttal as hypotheses are set forward and discarded.  If the reader already understands how science works, these sections depict the drama of science in enjoyable detail. Sometimes the details seem more superfluous, as when some sections list other scientists in the field but without enough detail to make them distinct characters. A surprising number of the images in the book depict scientists working in the field but would not convey much information to the non-specialist.

The scientific detail is both an advantage and disadvantage. For example, the first chapter is all about geological nomenclature, which is too dry for a general reader. Throughout the book, the authors provide precise biological and geological terms for organisms and places, but more description of these would make the story more relevant. A photo of a fossil skull is not clearly connected to the chapter around it, and lists of details on dinosaur names and the shapes of lagoon habitats provide detailed “dots” of data, but they do not seem connected.

At such points, the book becomes more like a required course assignment than the flowing story it could be. On page 80 the authors write “We apologize for the complex chemistry necessary in the preceding section. But to get this story right requires complexity.” If this was placed before the section it described, the general reader would read that section differently – as it is, it amounts to locking the barn door after the horse is gone.

These narrative nits having been picked, this book is indeed new and interesting, both substantial and helpful for the prepared reader. In the chapters on the origin of life, the authors focus on the “RNA world” hypothesis, and include new findings that support this hypothesis, such as the nucleotide synthesis discovered half a decade ago by Sutherland and colleagues, but fail to cover recent experiments that point to “metabolism-first” explanations. The “new” hypothesis in this section is that life started on Mars, which is interesting and possible, but given the difficulties and distances, more speculative than other new proposals in the book.

Another “new” hypothesis the authors develop in several places is that major events like the Cambrian explosion and particular extinctions were started by “true polar wander” events. One true polar wander event coincided with the Cambrian explosion, but my enthusiasm is tempered by the fact that there have been thirty or so of these events throughout history, which is number large enough that the timing may be more coincidence than cause. A graph of the thirty events would have addressed my own skepticism but was not included.

The hypothesis I’m most attracted to appears throughout the book, but may have been deemphasized by the authors because it is not all that “new.” Ward and Kirschvink frequently allude to the power of oxygen, both at and after the Cambrian explosion. They connect oxygen to animal diversification and extinction more intimately than any other general text, and oxygen’s influence is found in nearly every chapter. This is an exciting and intriguing thread to follow throughout the narrative, but could have been emphasized more.

Curiously, in a section on dinosaur morphology, they downplay the power of oxygen. On page 266, they begin a paragraph with the statement, “No evolutionary history can even be pinned on one factor.” The paragraph ends, “Nevertheless, oxygen levels must have played a part.” This apparent underselling of the organizing chemical power of oxygen brought to my mind the stories of how Einstein resisted the Big Bang because of its implication that the universe had a beginning. But, as is common for popular science, philosophical and theological implications are kept implicit.

Another major theme of this book that is powerful (but not really new) is the generative power of past extinction events. As Ward and Kirschvink put it, “Over and over, however, it really looks like a dominant theme in the history of life is that times of crisis promote new innovation.” Many scientists from many fields, including myself, have converged on this finding, and it deserves to be repeated many times. What does that tell us about what kind of universe we call home?

The authors close the book by extrapolating the billion-year trends of change in carbon dioxide and oxygen levels into the distant future. This is an obituary for the future earth in which CO2 runs slowly out of the atmosphere, like air running out of a balloon.

In a book that tends to avoid large metaphors, this section stands out: “The fate of the nautilus is a metaphor for all animal life. Sooner or later evolution, competition, and the natural changing of our Earth and sun as they age will make any body plan obsolete.” The authors describe a bleak future that gives the sense of the universe running down and flickering out, which is accurate as far as science goes, but philosophically and theologically truncated.

In summary, this book is an excellent example of recent evidence in the history of life, with special emphases on geology and paleontology. Anyone with an interest in those two sciences will find new ideas and directions in these pages. The most powerful conclusions --  the emerging consensus on the driving role of oxygen and the creative power of even the most devastating extinctions -- give a sense of the vitality of life and the orderliness of creation that is somewhat at odds with the deflating final chapter. Here, new evidence is presented well, and its ultimate implications are left for the reader to ponder.

No comments: