The Story of Life. Richard Southwood. Oxford University Press, Oxford, United Kingdom, 2003. 272 pp., illus. $28.00 (ISBN 0198525907 cloth).
I have long looked for a book that describes life's record on Earth in a manner that covers evolutionary biology, paleontology, geology, genetics, and whatever other scientific fields pertain to the subject. Not being a card-carrying specialist in these dimensions of prehistory, I have wanted the book to be integrative across disciplines and accessible to a scientist who specializes in being a generalist. I have also wanted the book to highlight the remarkable array of life forms that have been generated by almost four billion years of evolution's powers. Above all, I have wanted it to be informed with a spirit that reflects the wonder of life's very existence from shortly after the emergence of the planet itself—what has been viewed as such an unlikely event that it has been described as the “impossible phenomenon.” With the appearance of Richard Southwood's The Story of Life, I need look no further.
Southwood's account begins with the formation of Earth, followed by the primordial planet's suffering an asteroid bombardment, both intensive and extensive, for fully 100 million years. Eventually there emerged the first rudimentary flickerings of life. Then, after just 15 million years (a mere moment in evolutionary time), more complex life forms began to appear. After this biotic breakthrough, 3 billion years or more passed with few significant advances: Life's manifestations were largely a case of “the same as before, only more so.” Then, around 540 million years ago, there was a sudden explosion of new species, arriving in huge numbers and with highly diversified forms: “Modern life” came into its own. From that point on, and for only the last eighth of life's history, Earth has featured animals with skeletons, jointed legs, a panoply of body plans, and numerous other major adaptations. This final phase rightly occupies threequarters of Southwood's account.
In the main body of the book, Southwood takes us through one period after another, with extended accounts of life's development during the Permian, Triassic, Jurassic, Cretaceous, and Tertiary. During this last period, Southwood documents that “the main bands of vegetation, which we still have today, became clearly established: the tundra, coniferous forest, deciduous forest, grassland, and tropical rainforest.” Most of our present plantscapes-arose in less than the last 1 percent of life's history, and their associated animal communities arose during an even shorter time.
Southwood ends his account with detailed descriptions of the eruptions of new life forms during the Quaternary period, right up to the Holocene. This final phase, a mere 11,000 years, could be better termed the Homocene in light of the homogenizing impacts of Homo sapiens—for example, the grand-scale transformation of forests and grasslands to make way for agriculture. But the depauperizing debacle began rather earlier, notably during the late Pleistocene, with its mini–mass extinctions of “charismatic mega-vertebrates.” Especially enlightening is Southwood's assessment of the debate on the predominant cause of the recent widespread extinctions: human hunters or climate change? Or both together, possibly working in conjunction to exert compounded impacts?
Whatever the cause or causes, the last few tens of thousands of years have seen a sharp end to the heyday of mammals and birds, and especially of their outsize creatures. Humans will never again set eyes on the Americas' mammoths, rhinoceroses, and camels, or on their sabertoothed cats, 16-foot-long ground sloths, and two-ton armadillos. Nor will they see Australia's 16-foot-high birds and 20-foot-high kangaroos, or similar giant species in Madagascar, New Zealand, and elsewhere. In all, two-thirds of the large mammals in the Americas have vanished, as have four-fifths of those in Australia.
Southwood confronts the reader with a series of basic questions. For instance, how did life ever emerge? Why did the dinosaurs go extinct at all, let alone so suddenly, after some 200 million years of dominance? Was their extinction caused entirely by an asteroid, or were other factors at work? Another key question that Southwood discusses at illuminating length: Are we humans precipitating another mass extinction, largely confined to a single century by contrast with the far longer periods for the five mass extinctions of the past? The “overnight” demise of the dinosaurs probably extended over thousands of years.
Southwood raises many other and more esoteric-sounding questions: For example, what was “snowball Earth”? Answer: an exceptionally glaciated planet with sea-level ice reaching far into the tropics. Also worth more than a page or two are such diverse and obvious topics as protists, algae, lampshells, tectonics, Gondwanaland, bipedalism, and Cro-Magnons. Less well-known phenomena, such as chemoautotrophs, pachycephalosaurs, conodonts, and cyanobacteria, are likewise covered in engaging detail. Not discussed, however, are certain central and controversial questions such as punctuated equilibrium: Do evolutionary processes proceed, generally speaking, in smooth progression (not the same as progress, if indeed there is any such thing in evolution)? Or is long-term stasis sometimes punctuated by phases of instant-seeming shifts to new stable morphologies?
Such, then, is the scope of this exhilarating account of life's record—exhilarating because Southwood himself can hardly contain his enthusiasm for his subject. Well might he write with such reader-friendly spirit: He has long served as chairman of zoology at Oxford University (and as head of the university), making him an expert's expert and an academic's academic. But he is more than that. He tells his story with scholarly passion, almost as if he were freshly acquainted with paleobiology rather than a cognoscente who has studied the field for half a century. His exuberant style is not surprising: The book is based on a first-year student course that Southwood taught for many years, attracting students in droves. He excels at presenting complex material in an eminently digestible fashion. His book is packed with abstruse findings, arcane theories, and authoritative viewpoints, but it is more immediately enlightening than a textbook. Moreover, it is admirably illustrated with numerous maps charting the movements of the continents, with line drawings of animals and plants both extinct and extant, and with graphs and tables in profusion. All of this goes to make the book both erudite and entertaining.
I would like to have seen more discussion of one aspect of the chemical processes that first sparked life. Given that the primordial soup was presumably to be found in many places, could life have first come into being, then been extinguished—it was long a fragile affair— before being generated a second time? And if more than one origin occurred, could several origins have existed side by side until they finally coalesced into the splendidly mongrel outcome we witness today?
As Southwood emphasizes, humans are the only species to have existed with the power to deliberately drive another species extinct; and humans are the only species with the power to save another species from becoming extinct. Janusfaced as we are, we need to decide whether we are to be regarded by our descendants millions of years ahead (supposing Homo sapiens persists that long) as the single generation in human history to have precipitated a mass extinction. All this is spelled out in graphic detail in the book's final chapter, in which Southwood urges Homo to be sapiens enough to safeguard the millions of fellow species that share the planet with us, albeit they may not view us as showing much fellow spirit.
Of course, and as Southwood repeatedly asserts, new species will eventually be generated by evolutionary processes of speciation. Unfortunately, we may eventually find we have depleted certain of these basic processes by destroying tropical forests and wetlands, which have served as the main sources of new species in the wake of mass extinctions in the prehistoric past. The loss of these evolutionary powerhouses could mean that the recovery time required for mass speciation will prove longer than the few million years of past bounce-backs. The future story of life may well turn out to be a tale of biotic impoverishment such as the planet has not known for 65 million years, since the dinosaurs and associated species were eliminated. As Michael Soulé and Bruce Wilcox stated, “Death is one thing, an end to birth is something else” (Soulé and Wilcox 1980, p. 8).
As scholarly as any textbook, the book would make a ready read on an airplane trip. It can be heartily recommended to the aficionado and the student alike. It should even appeal to that eclectic readership, the general public, so that people can gain an insight into the astonishing abundance and variety, and the pedigree, of our planet's chief feature.