If you are interested in how living things work down at the cellular level, then this is a good time to be alive. It is not, however, an equally good time to be reading popular-science books. While evolution gets a lot of ink devoted to it, in part because it is fascinating and in part because some people, absurdly, continue to see it as problematic, the molecular processes that evolution shapes go comparatively unsung. Books seeking to explain quarks or superstrings are easy to find, reflecting the belief that physics is more profound the smaller the scale at which it occurs. But a similar approach doesn't hold for biology, and books seeking to explain the building of a cell wall, or the mechanics of replicating a DNA molecule, or the central importance of adenosine triphosphate to everything you will ever do, are hard to come by.

This is one of the reasons why Carl Zimmer's elegant and engaging Microcosm is so welcome. The promise of the title is that highly specific knowledge about the workings of one unobtrusive and unspectacular creature can reveal fundamental things about the world at large, and the promise is fulfilled in more ways than most readers would, I suspect, think possible. It shows quite nicely that, in the right hands, molecular biology is a lot more revealing about life in general than particle physics is about stuff in general.

The organism in question is Escherichia coli, an unremarkable and mostly benign denizen of the human gut that has become a remarkably revealing collaborator in the laboratory. E. coli first came to the notice of the 19th-century paediatrician Thomas Escherich on the basis of its capacity for “massive, luxurious growth” when transferred from stools to the flask or the Petri dish, and this proclivity for growing as much as anyone could wish when given the opportunity has made it a key participant in and witness to the great intellectual triumph of 20th-century biology - the lab-based realisation that, for all the bewildering variation seen in nature, a great many basic mechanisms of life are common to it all. As the great molecular biologist Jacques Monod put it, providing a slogan for Zimmer's project, “What's true for E. coli is true for the elephant.”

Zimmer uses E. coli to look at genetics and evolution, at the ways cells use energy and husband resources, at the ways proteins provide structure, at the need for life to adapt to and modify its environment, at the virtues of having different strategies for different circumstances, at the relationships between predators and prey, and at the clear evidence against religious explanations of creation. In doing so, he demonstrates not just a deep knowledge of contemporary research on E. coli - parts of this book are really bang up to date - but also of a broad range of contemporary biology (Zimmer's previous books include popular studies of parasitism, of evolution and of developing theories of the mind, and the range of subject matter he explores in The New York Times and on his blog is broader still). He knows his elephants as well as he understands the inside of a Petri dish.

In such an ambitious project there are some missteps. Of the three increasingly inexact ways that the microcosm can stand for the macrocosm (by embodying a process common to everything in the macrocosm, which is what Monod meant, by providing an analogy to some other process happening in the macrocosm, or through metaphor), the book may sometimes overreach at the level of analogy. For example, the similarities between E. coli's metabolic pathways and the structure of networks such as the internet are skimmed over a bit too quickly to convince. Zimmer's resolute embrace of brevity is in most places a plus, but there are times when he could afford to stop and unpack things a bit further.

In metaphor, though, he comes up with turns of phrase and images that are deep delights. The ways in which the structure of the cell depends on the tempo of different molecular processes give it a “geography of rhythms”; the building of a flagellum, which takes longer than the bacterium's replication, is like building a medieval cathedral, in that “a new microbe inherits a partially built tail and passes it on, still unfinished, to its descendants”. (Another flagellar delight is the way in which Zimmer shows that, far from being a structure that could not evolve stepwise, as proponents of intelligent design would have you believe, this complex corkscrew actually reveals its evolved status clearly down at the molecular and genetic level.) Perhaps the phrase that will resonate with me longest, though, is the one he uses to frame the discussion of E. coli as a workhorse of biotechnology and a proving ground for the more ambitious redesigns of life - “playing nature” - so much richer in its implications than the tediously Faustian “playing God”. If you want to get a clearer idea of the sort of nature that science can now play with, this is the book for you.

Microcosm by Carl Zimmer
Heinemann £20 pp243 Buy the book from Books First £18.00 including free delivery

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