vertical posture. But unless such traitsimprove the fitness of both males and females(in which case natural selection alone can do the job), sexual selection will produce differences between the sexes, as it probablydid with human body size. Why, then, don’twe see knuckle-walking women with chim-panzee-sized brains? Although we may neverknow why humans became erect and brainy,sexual selection seems among the least plausible of many alternative theories.

Despite its considerable merits, TheAncestor’s Tale seems the least compelling of

Dawkins’ works. Given the author’s talents,however, this may be akin to judging Corio-lanus Shakespeare’s least compelling play.Thankfully, Dawkins returns to top form inthe final chapter, a philosophical overview ofthe extraordinary events he’s just recounted.Here he grapples with questions of whetherevolution would produce similar creatures ifit began anew (a qualified yes), and whetherevolution itself promotes “evolvability”,making species even more likely to respondto future selection (another qualified yes).

His final sentences are quintessential

Dawkins, with language at its most lambentand elegant,used simply to express profoundtruths:“The fact that life evolved out of nearlynothing … is a fact so staggering that I wouldbe mad to attempt words to do it justice.Andeven that is not the end of the matter. Notonly did evolution happen: it eventually led to beings capable of comprehending theprocess, and even of comprehending theprocess by which they comprehend it.” ■

Jerry A. Coyne is in the Department of Ecologyand Evolution, University of Chicago, Chicago,Illinois 60637, USA.

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First steps in scienceCurious Minds: How a ChildBecomes a Scientistedited by John BrockmanPantheon: 2004. 256 pp. $23.95, £16.99

Paul L. Harris

John Brockman asked 27 distinguished sci-entists from diverse fields, includingphysics, psychology, biology, mathematicsand robotics, to write a short biographicalsketch, describing their childhood and whatgot them hooked on science. The hetero-geneity of the essays they wrote serves as an antidote to easy speculation about therebeing any essential precursors to scientificaccomplishment.

Is a scientifically oriented family impor-tant? It looks that way at first as you readthrough the opening piece by psychologistNick Humphrey. One of his early memories— vividly described — is of being taken byhis grandfather on Boxing Day to dissect afrog in the empty, silent anatomy depart-ment of University College, London. Thegrandfather, as it happens, has a Nobel prizein physiology,and is just one family figure in adistinguished panoply. Humphrey candidlywrites: “What I gained from this childhoodenvironment was a sense of intellectual en-titlement — a right to ask questions, to pry,to provoke, to go where I pleased in pursuit of knowledge.”

That sense of intellectual entitlement isechoed by cognitive scientist Alison Gopnik.She writes of her parents’ devotion to theirchildren’s intellectual lives,not with a view to“enrichment” or “achievement”, but with agift for making such intellectual activity “theaccepted, ordinary, happy way that civilizedpeople went about their lives”. Ray Kurzweil,an inventor, recalls a similarly intense intel-lectual life in his family circle: “The intenseand animated discussions were invariablyabout new ideas, usually those of intellectu-als I had never heard of.The way for me to getattention was to have an idea.”

But consider, by contrast, the childhood

of the computer scientist Jaron Lanier. Hismother died when he was nine and he wasraised by an indigent father with an interestin psychic phenomena. For a while they livedin tents in southern New Mexico beforemoving into a fragile geodesic domedesigned by his father. Such an eccentricupbringing might nurture intellectual inde-pendence, but it’s a long way from the sci-entific dynasty described by Humphrey orthe high-minded but nurturing family inwhich Gopnik was raised. NeuroscientistJoseph LeDoux describes an equally unpro-pitious start. His father was a bull rider in therodeo and hoped that his only child wouldemulate him.

Another plausible candidate for later sci-entific accomplishment is a keen childhood

interest in some branch of the natural world:insects, stars, fossils or electricity. Some con-tributors do display such a passion.Computerscientist Rodney Brooks, for example, wasalready fascinated by electric circuits at theage of seven. And Lynn Margulis, a biologist,writes of lying on her belly to watch antcolonies. Yet there are disconcerting excep-tions. Another biologist, Richard Dawkins,tells an amusing story about mistaking a blue tit for a chaffinch. Shocked at the boy’serror, his grandfather turned to Dawkins’father and remonstrated: “Good God, John— is that possible?”

The conclusion that does emerge fromthis collection is that a huge number of dif-ferent paths lead to a successful scientificcareer. Some can be tentatively traced back

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to early childhood,but others receive a bumpstart later in life from a mentor or teacher,and many illustrate how chance encountersprovoke a dramatic new direction. Withoutproviding any general conclusions, theseessays offer the idiosyncrasy and curiosityvalue that we expect of good, narrative his-tory,combined with much fine writing.

Two contributors — Stephen Pinker andJudith Harris — adopt a scientistic stancetoward the whole narrative enterprise. Don’ttrust our childhood recollections, they cau-tion, and certainly beware of any causal con-nections that we infer. Psychologicalresearch on the unreliability of childhoodmemories and our frequent lack of intro-spective access to potent influences on ourchoices lend weight to their cautionaryremarks. But few readers will feel comfort-able reading these accounts so sceptically.Many of the contributors revisit their child-hood with gusto — and with palpablecuriosity. What they write is quirky, absorb-ing and persuasive in just the way that goodstories are. ■

Paul L. Harris is at the Harvard Graduate Schoolof Education, 503A Larsen Hall, Appian Way,Cambridge, Massachusetts 02138, USA.

Stalking life’ssecond secretThe Proteus Effect: Stem Cellsand their Promise for Medicineby Ann B. ParsonJoseph Henry Press: 2004. 304 pp. $24.95

Lee M. Silver

On 28 February 1953, Francis Crickfamously burst into a Cambridge pub withJim Watson in tow and exclaimed trium-phantly: “We have found the secret oflife!” The rest, as the cliché goes, is history.Both scholarly and popular accounts of thepersonalities and events surrounding thediscovery of the double helix, and subsequent advances in molecular genetics,have appeared in tens of thousands ofbooks and articles. The DNA story is taughtin school biology classes to eight-year-oldchildren. Several DNA-based Nobel prizeshave already been won, and more are nodoubt waiting in the wings.

Genes and genomes, however, representonly one of two pillars of likely twenty-first-century progress in biomedicine.The secondis stem-cell biology. And yet, while everyoneknows of Watson and Crick, hardly anyonehas heard of Leroy Stevens and other earlystem-cell pioneers. Indeed, many scientistsare unaware of the five decades of advancesthat occurred before the 1998 isolation ofhuman embryonic stem cells. In her newbook The Proteus Effect, journalist Ann

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Parson fills the gap with a breezy,easily acces-sible narrative of the people, results andideas that have shaped the field.

Parson traces the birth of mod-ern stem-cell research back to1953, the same year that thedouble helix made its debut.Although the means for com-posing and reproducing life’sgenetic recipes had been a funda-mental secret of life, it was not theonly one. A second mystery was theprocess by which a microscopicembryo could develop into a fullyfunctional human being or othermammal. Embryologists knew thatdevelopment occurred throughthe controlled growth, divisionand specialization of individualcells, but they didn’t know how devel-opmental control was asserted. Manyassumed, without evidence, that a perma-nent loss of biological components or capa-bilities was responsible for the narrowing ofcellular potential. By implication, it seemedthat a postembryonic mammalian cellshould never be able to reverse course andreturn to an embryonic state.The exceptionswere the germ cells (eggs and sperm), whichstill had the potential to retrace normaldevelopment only after combining with eachother.

Goal-oriented unidirectional develop-ment was easily accepted as scientificdogma because it aligns neatly with tradi-tional Judaeo-Christian-derived religiousdoctrine, which permeates Western culture.As recently as 2002, Princeton professorRobert George — a defender of strictCatholicism and member of PresidentBush’s Council on Bioethics — claimed themantle of science when he wrote that thedirection of a human embryo’s growth “isnot extrinsically determined, but is in accordwith the genetic information within it … It is clear that from the zygote stage forward,the major development of this organism is controlled and directed from within, that is, by the organism itself ” (George’semphases). Consequently, according toGeorge and others on the council and in theBush administration, human zygotes andblastocysts (newly fertilized embryos thathave just started to divide) are “already liv-ing human beings” deserving of protectionfrom the murderous pursuits of biomedicalscientists. Perhaps George would come torealize how outdated his views of embry-ology are if he read Ann Parson’s book (andthen again, perhaps not).

In the winter of 1953, Leroy Stevens wassearching for morphological differencesamong inbred mice at the Jackson Labora-tory in Bar Harbor, Maine, when he chancedupon the observation of an enlarged testiclein about 1% of adult males of the 129 strain.The cause of the enlargements was an inde-

pendently growing mass of a type previouslyfound only in human patients. It was called ateratoma because of its monster-like charac-teristics. Human teratomas are typically covered with skin and hair, and contain abizarre diversity of tissues and organs nor-mally found in other parts of the adult body,including synaptically connected neurons,muscle, beating heart tissue, bone, teeth andsometimes eye-like entities or whole limbs.Stevens realized that the 129 strain’s pre-disposition to develop teratomas gave him aunique tool for tackling the mystery of theirorigin, which could provide insight into normal developmental processes.

Two years and 17,000 animals later,Stevens had dissected his way back throughyounger and younger mice, and ultimatelyfetuses, to discover that random genital-ridge cells occasionally flew off-course anddeveloped like the innards of early embryosbefore exploding into teratomas. In otherstrains, females were predisposed to tera-toma formation. Ovarian cells morphed, bythemselves, into an organism that Stevenssaid “looked just like a normal embryo, butthen it would all get mixed up. It became disorganized and you had a tumour insteadof a baby mouse.” Stevens didn’t think thatmutant genes were the main trigger ofthis aberrant development, and when heplaced normally fertilized embryos intounusual environments, such as the kidneycapsule, they also became teratomas insteadof mice.

Teratomas are not ordinary tumours.Along with their adult tissues, some containcells that can grow and divide for years with-out becoming specialized. When dispersedand injected into mouse abdomens, thesecells developed into “thousands of smallstructures resembling 5- or 6-day mouseembryos floating freely”. Stevens was con-vinced that such “embryonic carcinoma”

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