COMMENT SPRING BOOKS that the authors hew to the information metaphor. Breathlessly, Field and Davies survey the greatest hits and promises of genomics, including Jurassic Park-style reani- mation of extinct species, the microbiome and environ­mental engineering. The thin chap- ters blurt out strings of recent findings, each capped with a crescendo of sensational specu- lations that mostly rehearse familiar ethical questions. Critical distance is achieved with the time-honoured double negative: “Might a lawyer one day argue that deliberately not giving [our children] the best genes available is a form of abuse? It is not inconceivable to imagine a world where natural reproduction would seem primitive and even barbaric.” It concludes by exhorting us to set our sights on a global genome project to understand “the software that shapes our living planet”. The biocode is Gaia plus DNA. But two clichés do not make a right. Biocode simply extends the text metaphor to the macrocosm. The old metaphor is not wrong; it is incom- plete. In the new genome, lines of static code have become a three-dimensional tangle of vital string, constantly folding and rearrang- ing itself, responsive to outside input. The roots of this idea run deep. In her 1983 Nobel lecture, geneticist Barbara McClintock called the genome a “sensitive organ of the cell”. McClintock, who discovered mobile genetic elements in the 1940s, had named them con- myth that at first no one thought transposi- unbridled speculation and Panglossian opti- trolling elements because she thought they tion was real. The contested point was actu- mism. Junk DNA produces a lot of DNA junk. composed the regulatory system that gov- ally McClintock’s interpretation of mobile The idea that the many functions of non- erned gene action. In 1980, Ford Doolittle elements as controllers of gene action. coding DNA make the concept of junk DNA and Carmen Sapienza proposed that transpo- Parrington’s strongest chapters survey the obsolete oversells a body of research that is sons were molecular parasites, jumping into emerging view of gene regulation, includ- exciting enough. ENCODE’s claim of 80% genomes to propagate themselves. Parasitic ing DNA folding, epigenetics and regulatory functionality strikes many in the genome transposons are now textbook knowledge, but RNA. Overall, this is a faithful, engaging por- community as better marketing than science. McClintock’s larger point holds: the genome trait of the twenty-first-century genome. Still, as with McClintock, the larger point is dynamic, full of regulatory elements that Finally, Junk DNA, like the genome, is holds: the genome is more than a set of rules respond to environmental cues. crammed with repetitious elements and and parts descriptions. Finding apt imagery The Deeper Genome is the only book of superfluous text. Bite-sized chapters parade to replace the dead metaphor of the ‘instruc- the three that credits McClintock as a pro- gee-whizz moments of genomics. Carey’s The tion book of life’ could enable us to break free genitor of the three-dimensional genome. A Epigenetics Revolution (Columbia University of the cliché of nature versus nurture. It could scientist and journalist, Parrington covered Press, 2012) offered lucid science writing usher in a more democratic conception of life, the ENCODE story for The Times in 2012; and vivid imagery. Here the metaphors have in which all the world’s a cell, and all the genes his book enriches those accounts with his- been deregulated: they metastasize through and genomes merely players. ■ torical and scientific context. The science is an otherwise knowledgeable survey of non- better than the history. He provides a fine coding DNA. At one point, the reader must Nathaniel Comfort is professor of the discussion of recent support for McClintock’s run a gauntlet of baseball bats, iron discs, Vel- history of medicine at Johns Hopkins often-overlooked late work on how stress can cro and “pretty fabric flowers” to understand University in Baltimore, Maryland. He is activate transposition, but he perpetuates the “what happens when women make eggs”. The working on a biography of DNA. genome seems to provoke overheated prose, Twitter: @nccomfort NEW IN Neanderthal Man: In Search of Lost Genomes PAPERBACK Svante Pääbo BASIC 2015 Pioneer of ancient-DNA studies Svante Pääbo was inspired in his youth by ancient Highlights of this Egyptian history. Feeling that this field moved too slowly, he decided to study medicine season’s releases instead, and went on to sequence the first full Neanderthal genome in 2010. Here he details the technicalities of his life’s work and the incremental discoveries, such as genetic intimations that modern humans and Neanderthals had mixed, which generated our theories of human evolution. (See Henry Gee’s review: Nature 506, 30–31; 2014.) 616 | NATURE | VOL 520 | 30 APRIL 2015 © 2015 Macmillan Publishers Limited. All rights reserved ORIGINS OF LIFE An improbable journey Adrian Woolfson enjoys two studies on microbial life’s trek towards complexity. n 1676, the Dutch merchant and amateur rise to bacteria and archaea, which have no The Vital Question: Why is Life the Way it is? scientist Antoni van Leeuwenhoek sub- nucleus or other sub-cellular organelles. NICK LANE mitted an essay to the Royal Society of The evolutionary engine of life then seems Profile: 2015. ILondon detailing a singular discovery. This to have got stuck, idling along at the unicel- Life’s Engines: How Microbes Made Earth was the world of unicellular organisms, lular level for another 2 billion to 3 billion Habitable which he observed using a self-designed years. Falkowski explains how unicellu- PAUL G. FALKOWSKI microscope. Three hundred years later, lar organisms, although morphologically Princeton Univ. Press: 2015. Leeuwenhoek’s “animalcules” were shown challenged, managed to perfect the basic to hold the secret to the evolution of complex biochemical ‘engines’ that would power all ancestral archaean host engulfed a small life on Earth. forms of life on Earth. According to Lane, population of symbiotic bacteria, resulting In his imaginative and beautifully written the stagnation occurred because the molec- in the first eukaryotic cell, the forebear of The Vital Question, evolutionary biochem- ular motors that drive the biochemistry of complex life. ist Nick Lane defines a genealogy that links bacteria and archaea were unable to cross Lane recounts how over time, the engulfed the descendants of the Cambrian explosion the energetic threshold necessary for the bacteria jettisoned most of their genes that — the first appearance of morphologically evolution of complex form. This energetic were unrelated to energy production; these complex animals in the fossil record, were either lost permanently or relo- about 540 million years ago — to the cated to the cell nucleus. There they simple organisms that preceded them. continued to fulfil their original func- In so doing, he persuades us that com- THE EVOLUTIONARY ENGINE tions, or formed the raw material for prehending the structure, function, the evolution of new genes with unex- behaviour, genetics and evolution of GOT STUCK, pected roles, such as transcription fac- microorganisms is necessary for a tors — proteins that bind to DNA. This deep understanding of complex life, IDLING ALONG AT THE allowed embryonic stem cells to be and of the processes that undermine it, patterned in three-dimensional space. including diseases and ageing. This vis- UNICELLULAR LEVEL. What remained of the imbibed bacte- ceral insight into the largely uncharted ria, with their pared-down genomes expanses of microbial existence could and surrounding membranes, became also form the basis of a predictive science constraint on life is the central focus of The energy-generating mitochondria. The acqui- enabling us to speculate about the nature of Vital Question. sition of these organelles enabled eukaryotic potential life on other planets. It derives, Lane explains, from two princi- cells to expand their volume by up to 15,000 Biophysicist Paul Falkowski’s entertain- pal design features that all living things use times that of the average bacterium, and to ing, easy-to-read and historically rich Life’s to power themselves. The first is the use of support a genome around 5,000 times larger. Engines, meanwhile, uses the work of micro- high-energy molecules of ATP, the chemi- Lane’s important realization is that this also biologist Carl Woese to trace complex life cal currency of energy transfer. The second gifted eukaryotic cells with about 200,000 back to its three lines of descent: bacteria, is the idiosyncratic ‘chemiosmotic’ force, times more energy per gene than the aver- archaea and eukaryotes. By studying the which moves protons and facilitates the age prokaryotic cell. This over-cranking RNA sequences of ribosomes — the cellular continuous generation of ATP. Both Lane of the evolutionary engine allowed for the machines that make proteins — Woese was and Falkowski describe these molecular development of a baroque diversity in the able to show that Charles Darwin was cor- processes compellingly. Although adequate nature and extent of cellular gene and pro- rect in suggesting that all life arose from a to power single bacteria-sized cells, the tein expression. single, now-extinct, common ancestor. method constrains the allowable surface- Although readily accommodated by It remains unclear how and when life first to-volume ratio of a living cell. Lane argues, classic Darwinian evolutionary theory, the originated on Earth, but we know that the however, that around 1.5 billion years ago horizontal, sudden and co-operative nature first unicellular organism emerged between this energetic constraint was overcome by of Lane’s evolutionary narrative differs from 3.6 billion and 2.7 billion years ago, giving an improbable endosymbiosis event: an the incremental, vertical and competitive The Homing Instinct: Meaning and Mystery in The Accidental Species: Misunderstandings of Animal Migration Human Evolution Bernd Heinrich MARINER 2015 Henry Gee UNIV.