The Genesis of Animal Play:Testing the Limitsby Gordon M. BurkhardtMIT Press: 2005. 518 pp. $50, £32.95

Bernd Heinrich

A kitten batting a ball of yarn, kids on aswing, or an adult wielding a fishing-rod —few would disagree that these behaviourscan be described as play. Yet in the study of animal behaviour, the phenomenon ofplay is an anomaly. It is said to be adaptiveand yet it involves the expenditure of muchenergy, often with no apparent pay-off.When a certain behaviour is found to haveobvious pay-offs or functions it is, almostby definition, no longer ‘play’ but is definedby its function, such as foraging, predatoravoidance or mating.

According to the simplest, most short-term definition, play is ‘just for fun’. But inthe long term it may also be practice for afuture role, although the ultimate pay-offmay only be determined over a lifetime.Con-sider the activity of batting a ball around.That’s play, isn’t it? But if someone got paidfor it,would it still be play? Even without pay,it may be for practice.And what about otherswho expend time and resources to watch thissenseless activity? It would be difficult toassign adaptive value to these behaviours, orto measure them objectively. Should playthen be defined by internal motivation —pleasure, fun? But the motivation of internalpleasure can apply to many complex behav-iours, such as hunting, birdsong, sex or chasing a frisbee, although only the latter islikely to be called ‘play’. Is play then only‘senseless’ behaviour, or is it simply behav-iour for which an ultimate function has yet to be discovered?

Play may be plagued by paradoxes andenigmas, but it is a genuine behavioural phenomenon. It is an appropriate subject forenquiry, if only because we know so littleabout it, despite the interest of scholars whofor centuries have tried to define it, fix itsboundaries and fathom its functions.For themost part there has been little progress —instead, the subject has become entangled ina web of definitions and controversies. It isclearly time to re-examine play.

The Genesis of Animal Play does not reallyexplore the limits that I allude to above, butto date it is the most comprehensive and illuminating effort to come to terms with this enigmatic topic. Even though GordonBurkhardt claims his book “is not meant tobe a thorough review of play research in ani-mals or people on either a narrow or broadscale”, I believe nevertheless that it does

come close. Burkhardt reviews the literature(about 1,300 references are cited) and refersto most of the serious attempts to study play.In his attempt to understand its origins andnature, he incorporates both comparativeand multidisciplinary approaches.

In the first part of the book, Burkhardtexplores the diversity of play behaviour andthe history of various theories, definitionsand controversies surrounding it. He alsoproposes criteria for a modern definition ofplay. He champions the view of ethology laiddown by Niko Tinbergen,which says that anydefinition of a behaviour must encompassfour entirely different types of problem: itscausation or mechanisms; its adaptation orfunction; its development or ontogeny; andits evolution and phylogeny. Burkhardt addsa fifth category: the world of private experi-ence. Researchers using this last criterionwould ask whether all play is accompanied byone or a few specific emotions (presumablyafter play has already been identified, not toidentify it).

In the second half of the book, Burkhardtexamines the phylogeny of play, reviewingexamples from studies of mammals, birds,reptiles, fish and invertebrates. Most of theexamples of play in the literature come froma small number of placental mammals, inwhich play is clear-cut.However,because thefocus of the book is the origin and function

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of play, the most relevant examples are thoseat the boundaries where play is not readilydistinguished from non-play. Even amongthe mammals and the few birds studied,there is a great variety of play or potential play behaviour,so ecological,social and otherpotentially relevant factors may shed lighteven within this narrow taxonomic group-ing. At the borders, in fish and invertebrates,descriptions of putative play behaviourremain anecdotal. I suspect that few of thesewill sustain the five criteria for play that theauthor sets up, but he remains open-mindedto the possibility.

Burkhardt concludes by strongly backingthe ‘surplus resources’ theory as a way to predict where and when we might expect tofind playful behaviour. This idea is an elaboration of one proposed in 1795 by theGerman playwright Friedrich Schiller, whowrote: “An animal may be said to be at workwhen the stimulus to activity is some lack,and it may be said to be at play when the stim-ulus is sheer plenitude of vitality.” Schiller’sidea was further elaborated by HerbertSpencer in 1872. Burkhardt brings it into the social context and adds the adaptive significance — that play not only originatesfrom, but also creates, surplus resources thatmay be useful on subsequent occasions. I am not sure how or at what point in the life of an animal such surplus resources would

Just for fun?Working out why animals play is no easy task.

Dolphins are thought to engage in play-fighting — but is it just for fun or does practice make perfect?

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physicists are drowning in branes, as Kakuputs it, and that they are beginning to thinkthat M-theory itself must be part of some yetmore basic theory that is awaiting discovery.This is progress,Kaku assures us.

Although he has every confidence thatthe quest for a theory of everything will suc-ceed, perhaps in just a few decades, Kaku isvague about what success will look like. Hedescribes how observations of gravitationalwaves or of temperature fluctuations in thecosmic microwave background, or perhapsexperiments at CERN’s upcoming LargeHadron Collider, might reveal tiny signs ofM-theory seeping from higher dimensionsinto our own poor world. Then again, theymight not, in which case we have to fall back on neopythagorean arguments of puremathematical consistency to let us knowwhich is the right theory. If that theory isunique, we would “know the mind of God”,says Kaku, borrowing a favourite phrase ofEinstein’s. Or there could be lots of legit-imate theories, so that our Universe would be merely one of many possible universes.(I suppose this means that even God couldn’tmake his mind up.)

Whatever universe we live in, it is boundto end badly. Stars die and cosmic expansioncan only lead to a cold, utterly attenuatedemptiness. But we can escape this dreary fate, Kaku says. Once physicists have figuredout the theory of everything, they will be ableto manipulate space-time to create a worm-hole through which we can pass to a new universe and start over again. Or maybe, ifit is too difficult to send our physical selves to another universe, we can capture our

civilization’s entire sum of information andconvey it down the wormhole in the memoryof a quantum nanobot. This is the big pay-off: by fully understanding physics, intelli-gence can escape its cosmic doom.

Parallel Worlds slides from even-handeddiscussion of what physicists and cosmol-ogists are actually doing into areas that are, shall we say, a touch speculative. Kakumentions problems and difficulties along theway, but he gives the distinct impression thatthe prospects described in his final chaptersare, if not exactly within our grasp, at leastreasonable extrapolations.Some readers willno doubt be entranced by the grand vision,the great sweep of imagination. For me, theparade of mind-boggling ideas breezily por-trayed here — the Big Bang as a collision ofbranes, time travel around massive rotatingcylinders, matter as holographic projectionfrom higher to lower dimensions — createda different cumulative impression. The greatenterprise of fundamental physics began toseem larky,whimsical and not quite serious.

String theory and its cosmological impli-cations embody, for the moment, a researchprogramme much more than a genuine theory of physics. Getting from one to theother demands detailed and diligent effort.There is no guarantee that it will all work outas desired. But Kaku takes the truth of the big ideas more or less for granted, and racesahead to the most far-reaching and literallycosmic conclusions. This is intellectualentertainment — brane candy, if you like —but will it ever be more than that? ■

David Lindley is a freelance science writer inAlexandria, Virginia, USA.

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To infinity andbeyond!Parallel Worlds: The Science ofAlternative Universes and OurFuture in the Cosmosby Michio KakuAllen Lane/Doubleday: 2005. 448 pp.£20/$27.95

David Lindley

Michio Kaku is an enthusiast. In the breath-less introductory chapters of Parallel Worlds,he speeds through the history of cosmologyand fundamental physics to persuade usthat science has never been as thrilling as it is now. Edmund Halley may have been“shocked beyond belief” and “staggered” byNewton’s calculation of planetary orbits,but that’s small potatoes compared with thestaggering science that goes on nowadays.String theory is staggering; quantum com-puters are truly staggering; the recent dis-covery of accelerating cosmic expansion leftscientists dumbfounded; their minds reel at the idea of parallel universes. And whenthey’re not reeling and staggering, they haveto contend with the “insane conclusions ofquantum theory”.

Melodrama aside, Kaku’s book provides a sprightly and generally efficient account ofour present understanding of the Universe,in which astronomical observation and ele-mentary physics combine to give a coherent,if rather bizarre, picture of the cosmos. Plainordinary matter, such as we are made of,is tame stuff. The Universe is mostly darkmatter and dark energy, both revealed by the dynamics of galaxies. As yet there is noconvincing explanation for either.

But string theory will take care of that.Beginning with the now familiar idea that allparticles are in fact little wiggly loops inhab-iting extra dimensions, Kaku sketches howgravity may one day be unified with quan-tum mechanics. Then we will understandspace-time and all the matter and forces in it.There was a time when string theory seemedunique: only one version of it could possiblywork. But more versions appeared, to be subsumed some years later into M-theory,which unifies string theories at the cost ofintroducing fundamental surfaces of higherdimensions (called ‘branes’).

It is a little unsettling now to learn that

manifest themselves or how an ethologistcould demonstrate their existence. However,the idea surely applies to the activity ofscientific research, and perhaps even to thewriting of a book. ■

Bernd Heinrich is in the Department of Biology,University of Vermont, Burlington,Vermont 05405, USA

Brane teaser: if parallel universes exist, they might take the form of bubbles in different dimensions.

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useful. This discussion is pertinent not only to wildlife science but to all spheres of enquiry.

Lewis does not mince his words. Forinstance, he observes that neither Raghaven-dra Gadagkar of the Centre for EcologicalSciences in Bangalore nor US ecologists such as E. O. Wilson “are willing to abandontheoretical ecology to take up taxonomythough. Gadagkar encourages students to do so, and Wilson ecologists of the devel-oping world to do the same. Neither will do it himself.” And while talking about differences between India and the West, he writes that villages in India,“even those wholose crops and occasionally relatives, haveexisted in close contact with dangerouswildlife for centuries without driving thoseanimals to extinction. Before the British

there was no evidence of Indian ‘predatorelimination hunts’ in the style of the Texasrattlesnake drives or the turn-of-the-centurywolf bounties in the United States, aimed atthe eradication of every member of a givenspecies.” There is something irresistiblyrefreshing about Lewis’s willingness to speakhis mind.

In keeping with his seemingly earnestdesire to faithfully reproduce all his findings,all of his conversations (or rather, the rele-vant sections of them) seem to be recordedverbatim. The book is thus peppered withquotes in ‘Hinglish’, and misplaced modi-fiers, fractured sentence construction andother endearing linguistic idiosyncrasies are rife.

Despite its scholarly character, this bookis user-friendly for lay-readers, thanks in no

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small measure to the author’s superb story-telling ability. The more informed readermight skip over a couple of pages here andthere with a ‘been there, done that’ shrug,but I suspect that few ecologists are privy tothe intricate history of their chosen field ofwork. The book thus serves to round outtheir education by providing a historical and philosophical perspective. ■

Deepak Apte is head of the ConservationDepartment, Bombay Natural History Society,Hornbill House, S. B. Singh Road,Mumbai 400 023, India.

ErratumWe apologize to Gordon M. Burghardt formisspelling his name in the recent review of hisbook The Genesis of Animal Play (Nature 434,273–274; 2005).

Martin Kemp

Foyer sculptures — those big lumps of arty stuffcommissioned to hang or stand in the entrancespaces of large modern buildings — don’t tend tooccupy a high rank in the pantheon of contempo-rary art. There is often an inverse relationshipbetween the size of the object and the attention itcommands from those who come and go. Gener-ally decided by committees, which are inherentlyuncreative, these sculptures typically occupy anunsatisfying middle ground: just modern enoughto seem adventurous without imposing them-selves demandingly on the viewer.

In this context, it is good to see that the massivepiece commissioned from Thomas Heatherwick,which adorns a seven-story space in the WellcomeTrust’s new headquarters in London (designed by Hopkins Architects), is a technical, visual and conceptual tour de force .

The statistics are impressive enough in them-selves: there are almost 150,000 glass spheres;26,732 stainless steel wires, 0.5 mm in diameter,and the same number of springs; the sculpture is nearly 30 metres in height; and it has a totalweight of 14 tonnes. Needless to say, such a workis not the product of an archetypal artist workingin romantic isolation in a studio-garret. The team-work required is akin to that in the workshop of amajor Renaissance artist–engineer.

Even more impressive, for those who enter,leave and pass by the building, are the beguilingvisual effects and complex associations embed-ded within the sculpture. Each of the glass beads is composed of two hemispheres sur-rounding a piece of dichroic film that generates a range of floating effects, from clear to turquoise,pink, green, yellow, violet and orange. The glassand film together ensure that the visual impact is continually transformed as the light changes

and the spectator moves through the space. The overall form is the result of a self-organizing

process. Heatherwick and his team experimentedwith a range of viscous molten substances, drop-ping them into water and watching them solidify in shapes that are unpredictable yet observe certain material parameters. Such configurations,suggestive of organic entities, were among thoseconsidered by D’Arcy Thompson in his great 1917book, On Growth and Form. Metal proved mostamenable, and, after some 400 tests,a small piece of solidified white metalwas selected. This small model wasthen translated digitally by a screenmatrix into an overall configuration of suspended beads.

The work that arose from thisprocess does not have one singlemeaning. The parameters of inter-pretation are set in part by its pres-ence in the headquarters of one ofthe world’s major medical researchcharities. Parallels of the structurewith molecular models are almostinescapable.

The German title, Bleigiessen,has strong associations with health.‘Lead-guessing’ is a New Year’s Everitual in central Europe. Molten lead is poured into water and the result-ing shapes are divined as signalling a person’s fortune. Yet Heatherwickdid not intend this as a meaning from the beginning. It was only late in the process of design that he learnt about ‘lead-pouring’ from hisGerman grandmother.

The end result is that the inherentunpredictability of the process ofcooling molten metal in water

belongs simultaneously to modern science and to folk intuitions about the vagaries of fortune that govern all our lives. Henry Wellcome, founderof the trust, would have been delighted by thisunanticipated conjunction of modern scientificknowledge with the superstitions behind traditionalcustoms.Martin Kemp is professor of the history of art at theUniversity of Oxford, Oxford OX1 1PT, UK, and co-director of Wallace Kemp Artakt.

Science and culture

Science and superstitionThomas Heatherwick’s sculpture for the Wellcome Trust’s new building in London.

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