The evolutionary blackbird

Nature, April 24, 2003

The poet Wallace Stevens wrote about 13 ways of looking at a blackbird. Perhaps someday another poet will write about 13 ways of looking at the history of life. I can certainly think of 13 different scientists who have written books on the subject, each of which is coloured by its author’s expertise. Books by vertebrate palaeontologists are dominated by animals with bones, despite the fact that vertebrates make up a tiny proportion of the world’s biodiversity today — not to mention the fact that they didn’t exist for the first 3 billion years or so of life’s history.

The Precambrian expert Andrew Knoll has looked at those first 3 billion years in great detail in his new book Life on a Young Planet (to be reviewed in Nature shortly), leaving the details of dinosaurs and mastodons to others. For yet another take, try The Major Transitions in Evolution by John Maynard Smith and Eörs Szathmáry. For them, the essence of life’s history is the emergence of new kinds of complexity. Instead of fossils, you get equations.

In The Story of Life, Oxford ecologist Richard Southwood takes his own look at the evolutionary blackbird. Southwood is a leading figure in ecology, thanks to his seminal work on insects and his landmark book Ecological Methods. For 18 years he taught an introductory course on the history of life, and out of that experience has sprung The Story of Life. Not surprisingly, Southwood sees the history of life in an ecological light, not as a single-file parade of new life forms but as a network of species whose links are being perpetually reworked.

This network first took shape over 3 billion years ago, as early microbes cooperated to harness the energy in their environment. The network grew more complex as animals and other multicellular organisms evolved, and as reefs offered new ecospaces for species to colonize. Southwood recounts how dry land was transformed over hundreds of millions of years, as bacterial crusts gave way to forests that offered a new ecospace as vast as that of coral reefs. Over time, ecosystems change like gently tapped kaleidoscopes, Southwood writes, although mass extinctions give them a good shake from time to time.

Southwood displays an impressive sweep of knowledge about life, from the fauna of hydrothermal vents to the anatomy of plant-eating birds’ digestive tracts. For the most part, he has kept abreast of the latest developments in evolutionary research, although from time to time he slips back into comfortable textbook explanations. Describing the great domains of life, for example, he writes: “The Archaebacteria also fall into two groups, both of which have lifestyles that are very unusual, but which could have been maintained on the ancient earth.” These microbes (which are now generally called Archaea, not Archaebacteria) can indeed be found in strange places, such as geysers and oxygen-free swamps. But they can also be found in ordinary places, such as grassland soil and the open ocean, where they outnumber bacteria. Archaea got a reputation for being bizarre only because scientists discovered their more unusual members first.

A more serious shortcoming in The Story of Life is the scant attention paid to DNA, which has revolutionized our understanding of evolution’s course. The ecological changes that Southwood details were made possible by changes to genes, and scientists are starting to get some hints of what those changes were, from the promiscuous gene swapping between early microbes to the recruitment of old genes to make new structures such as jaws and fingers.

Despite these grumbles, I recommend The Story of Life to those looking for a swift, efficient delivery of the most important information we have on how life has blossomed on Earth. Southwood is succinct and clear, and his narrative rarely gets bogged down with historical digressions or personal anecdotes. Although this style has its strengths, it also has its weaknesses. At the beginning of his book, Southwood claims that the story of life “provides a bench-mark for judgments on the environmental problems of today”. But when Southwood finally reaches our own age, he seems almost indifferent as he zips through the ways that we are altering the climate and the planet’s ecosystems. A little more passion would have been welcome. After all, these days the evolutionary blackbird is beginning to look more like a canary in a coal mine.