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influence this. He also includes more generalreviews of dental and oral anatomy, and pro-vides an excellent summary of the processesof chewing and oral transport, viewed fromthe perspective of the mechanical propertiesof food,such as particle size and stickiness.

This food’s-eye view leads to numerousinsights and interesting ideas, such as Lucas’stheory of fracture scaling. Bigger animalshave bigger teeth, whose surface areas mightbe predicted to scale with body mass to thepower of 0.67 (because tooth area increasesto the power of two, and body mass increasesto the power of three, yielding a scaling ratioof 2/3). Yet tooth surface area in mammalstypically scales to the power of 0.61.Why thisis so remains elusive, but Lucas argues thatfracture mechanics plays a role.

The argument is complex,but boils downto the observation that once a crack is initiatedin an object, little additional energy is neededto finish the job, regardless of its size. Biggerfoods fracture at relatively low stress, whichhas several implications. One is that biggeranimals (assuming that they chew biggerfood) need relatively less muscle force (asquantified by muscle cross-sectional area),so this should only increase to the power of0.5 relative to body mass, although this hasyet to be tested. If tooth surface area does notincrease relative to bite force, then tooth sur-face area should also scale to 0.5 relative tobody mass. But teeth scale to the power of0.61, so other factors must also influencetooth size, including other complex aspectsof food mechanics also reviewed by Lucas.We can look forward to efforts to test thishypothesis and explore its implications.

Lucas does not consider in detail how dental function relates to tooth developmentand microstructure,or to the neuromuscularcontrol of chewing. But readers interested insuch topics as evolution,diet and ecology willenjoy his many other ideas about how vert-ebrate teeth work. The final chapter focusesmainly on mammals, creatively integrating

of species, in particular for the BSC and formost geography-based hypotheses of specia-tion. Coyne and Orr could be accused ofbeing ‘admayrers’, but that’s not the worstthing one can be called, in my opinion.Unlike Mayr in his early work, the authorsadmit, albeit with palpable hesitation, thatspeciation can also occur without geographicisolation, in overlapping or ‘sympatric’areas.Sympatric speciation, which for decades hadall the caché of a four-letter word, is increas-ingly seen to be responsible for the origin ofat least a minority of species.

Coyne and Orr also give renewed cre-dence to models of speciation that empha-size a role for sexual or natural selection,rather than viewing the origin of species aslittle more than a by-product of isolation.One currently popular model, ecologicalspeciation, de-emphasizes geographical set-tings and reaffirms the importance of localadaptations and natural selection in bring-ing about speciation. Reproductive isolationmay be brought about by ecological pro-cesses, such as habitat fragmentation or theuneven distribution of resources. In suchcases, interbreeding is prevented betweenpopulations that are limited — by behav-ioural, physiological and morphologicaladaptations — to a very particular set ofprey items, for example, or a particular treespecies that they need to build their nests.The absence of the homogenizing effect ofgene flow between individuals, not throughgeography but by the divergence ofadapted and ecologically important traits,possibly even in the same environment, thenleads to reproductive isolation. In this way,natural selection can play a prominent rolein speciation.

The most recent work, largely done onfish models, includes modern genomicapproaches, such as the analysis of quantita-tive trait loci. It concludes that reproductiveisolation and speciation may be a by-productof ecological differences and disruptiveselection on a surprisingly small number ofphenotypic traits,which are controlled by anequally small number of underlying genes.A role for selection can also be inferred frommolecular genetic data on hybrid incompati-bilities from models such as the fruitfly.These have yielded a few candidate ‘specia-tion genes’, which also show signs of naturalselection having been at work.

Performing this demanding duet in mas-terly harmony, Coyne and Orr present anauthoritative treatise on one of the mostlong-running debates in evolutionary biol-ogy. Speciation is an impressively up-to-dateand enlightening synthesis — and an enter-taining read. It deserves to join Darwin’s Onthe Origin of Species, and Mayr’s Systematicsand the Origin of Species on the bookshelf ofanyone who is interested in evolution. ■

Axel Meyer is in the Department of Biology,University of Konstanz, 78457 Konstanz, Germany.

Something to chew onDental Functional Morphology:How Teeth Workby Peter W. LucasCambridge University Press: 2004. 372 pp.$130, £75

Daniel E. Lieberman

Science has made substantial progress sinceAristotle wrote (apparently without doingmuch research) that women have fewerteeth than men. The sheer volume of pub-lished research on teeth since may lead someto conclude that we have over-compensatedfor Aristotle’s ignorance. Yet teeth merit allthis attention because of their tremendousbiological importance — not to mention thedreadful pain they can cause. Dental devel-opment and function are the focus of muchclinical attention. And for evolutionary biol-ogists, teeth are invaluable sources of infor-mation about taxonomy, phylogeny andmany other aspects of animal biology.

There are already many excellent texts ondental function and development within thecontext of craniofacial development andclinical dentistry, as well as several goodreviews of dental variation and evolutionamong vertebrates. But Dental FunctionalMorphology provides a fresh perspective ondental function. Peter Lucas’s basic argu-ment is that because the primary function ofteeth is to reduce the size of food particles,dental morphology must be analysed in thecontext of how teeth fracture food, and how foods resist this. So the book reviews in detail many of the key mechanical propertiesof food, such as toughness and elasticity,which influence how teeth initially deformfood items and generate cracks in them tobreak down large particles. Lucas then con-siders how variations in tooth size and shape

400 NATURE | VOL 431 | 23 SEPTEMBER 2004 | www.nature.com/nature

Grabbing a bite: the main role of teeth is to break down large items of food into smaller ones.

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biomechanics, anatomy, ecology and taxon-omy in order to reconsider the evolution ofdental adaptations for generating fracturesin food for animals that eat insects, grasses,leaves, fruit and other animals. Primates,especially humans, get special attention. Ingeneral, we chew our food like other mam-mals, but the invention of cooking and otherforms of food processing have drasticallydecreased the particle size and toughness of the food we eat. Palaeoanthropologists are still arguing about when cooking firstevolved, but Lucas provides new reasons tosuggest that the first species of the genusHomo, which had small teeth, was the firsttrue chef of the animal world. Lucas calcula-tes that your molars can be between 56% and82% smaller to eat a cooked potato ratherthan a raw one, depending on whether youeat the skin and whether you roast or boil it.

Teeth often appear messy, confusing anddull to non-specialists, but Lucas succeeds in conveying his enthusiasm for the chal-lenges of learning about the biology andecology of organisms from such a small andhumble organ. Although the book containsplenty of mechanics, the equations are pre-sented clearly and well explained.

Lucas has filled the text with fascinatingobservations, humorous asides and wonder-fully detailed footnotes.One particularly funbonus is a flick-art animation running on thebottom corner of the book’s pages thatdepicts the evolutionary transformation of aprimitive single-cusped tooth into a humanmolar.Flicking through this cartoon will giveyour copy a thumb-worn look that Aristotlemight have envied. ■

Daniel E. Lieberman is in the Department ofAnthropology, Harvard University, 11 DivinityAvenue, Cambridge, Massachusetts 02138 , USA.

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interdisciplinary subject between biologyand geography. It is certainly taught in bothsets of departments, which once caused me a little difficulty as an external examinerbecause students had been taught essentiallythe same course twice. But biogeography is abranch of biology, of population and com-munity ecology, and covers genetical andevolutionary topics as well as pure ecologicalones. It is certainly an important branch,although the editors exaggerate its impor-tance to Darwin and Wallace in discoveringnatural selection. It is nevertheless a branchwith unusually fuzzy edges, differing fromthe related bits of biology largely by anemphasis on maps and geology.

With so many editors involved, the stan-dards of the commentaries and the editingare both a bit variable, though it is mildlyamusing to be told about “Louis Carroll’sThrough the Looking Glass” (two errorsthere) or that the muskrat “was introducedin 1905 into what was then Czechoslovakia”.More seriously, in my view, the editorialboard (who are all biologists) would havebeen well advised to seek the opinions ofhistorians of science on the works frombefore 1950. Using facsimiles that have beenstandardized to a fixed page size means thatsome of the text is hard to read and somehalf-tones would have been better omitted.The cross-referencing is a bit weak, too.Some of the commentaries are excellent.

If your class reading list calls for some-thing on Linnaeus, Buffon, de Candolle, vonHumboldt and Hooker at one end of the timespan, along with MacArthur and Wilson’stheory and developments in the 1970s, this2-kg set will be very useful. ■

Mark Williamson is in the Department of Biology,University of York, York YO10 5DD, UK.

Colin Martin

The installation by Dutch artist Zeger Reyers in thebasement of the GEM Museum of ContemporaryArt in the Hague, the Netherlands, acknowledgesthe prior claim of water on the museum’s site. Theland was drained by previous generations.

Reyers’ work frequently creates new biotopes,which display the vagaries of biological processes.At the 2003 Havana Biennial he released 200 white laboratory mice onto a 15-metre-long whitetabletop covered with 5,000 kg of white porcelain.Their colouring made them difficult to spot, creat-ing an installation that referenced protective adaptation in nature. Other previous installationscovered interior spaces with living fungi.

To reach Aqua Boogie, visitors descend a staircase that has a view across a large pond

outside, conveying a feeling of being below waterlevel. They enter an irregular, 220-square-metrespace, flooded with dark, non-reflecting water andcriss-crossed with pine duckboards (right). As wellas allowing viewers to explore the aqueous bio-tope more closely, this grid recalls Victory Boogie Woogie, a painting by Piet Mondrian, as the instal-lation’s title suggests.

The biotope affects many of the senses. “It hasthe thin fragrance of living water, like you smell whenentering a canal,” says Reyers. “The water alsodampens sounds, making it a quiet, serene place.”Beneath the surface, 35 leather carp, selected byReyers because their dark colouring makes thempractically invisible, go about unseen business.Like all Reyers’ work, Aqua Boogie is accessible,but offers multiple levels of interpretation. It can dis-concert viewers by challenging their perceptions of

a familiar environment, experienced out of context.On two occasions during the installation, which

can be seen until 7 November, Reyers will recreatea 2001 work, Mussel Chair. A Parisian pavementcafé chair, encrusted with mussels after havingbeen submerged in the Eastern Scheldt estuary fortwo years, will be brought to the museum, cleanedup and steamed. The cooked shellfish will beoffered to visitors to eat, adding taste to the othersensory experiences offered by Aqua Boogie.Colin Martin is a writer based in London.

Science in culture

Awash with artZeger Reyers saturates the senses with his installation Aqua Boogie.

The geography of lifeFoundations of Biogeography:Classic Papers with Commentariesedited by Mark V. Lomolino, Dov F. Sax &James H. BrownUniversity of Chicago Press: 2004. 1,291 pp.$135, £94.50 (hbk); $45, £31.50 (pbk)

Mark Williamson

Collections of papers are useful both toundergraduates and their lecturers. Here isa set of 72 pieces on biogeography, 30 ofwhich are excerpts from books. They werechosen and edited by a committee of 19biologists, 13 of whom have contributed tothe commentaries that precede the eight sec-tions. Except for the first section, on early(mostly nineteenth century) classics, theseare arranged by topic, which is helpful. Inmuch the same way that a camel is a horsedesigned by a committee, the selection oftopics has some strange bumps and depres-sions, but the resulting animal is neverthe-less useful in the appropriate circumstances.

The editors suggest that biogeography is arecent discipline and that nine of the authorswould not have called themselves biogeogra-phers. But biogeography is a nineteenth-cen-tury term. Darwin wrote of the geographicaldistribution of organic beings, and AlfredRussel Wallace wrote of geographical zool-ogy. And in the twentieth century, RobertMacArthur and Edward O. Wilson are inprint saying “we both call ourselves biogeog-raphers” and are “unable to see any real dis-tinction between biogeography and ecology”.

Biogeography might appear to be an

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