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Gary Marcus

such as Bacon enthusiastically adopted the ar-tisanal epistemology, so that as Smith aptlynotes, it was the artisan’s practical power togenerate novel effects from nature, rather thanthe tricky technicalities of Copernican theory,that made the scientific revolution exciting tomany contemporaries.

The Body of the Artisan is a fascinatingand significant contribution to a more social,collective, and diversified history of scien-tific (and artistic) transformations in earlymodern Europe. The account of artisanalepistemology is convincing and innovatesthrough its focus on painters, sculptors, andengravers. However this makes the term “ar-tisanal” slightly misleading. Although Smithis at pains to avoid the anachronistic term“artist,” her choice of artisans with whom torepresent artisanal epistemology falls most-ly on an elite of decorative and fine artists.Absent are many of those traditionally dis-cussed in works on science and artisanry

such as gunners, clockmakers, and practi-tioners of the mechanical arts. Even if thelatter’s contributions have been widely dis-cussed before, many still remain hiddenfrom history. Smith ultimately sees a separa-tion of arts and sciences in the late 17th cen-tury, when experimentalists (having incor-porated artisans’ “active knowledge” intotheir new approach to nature) began deni-grating artisans as mere hands in contradis-tinction to their own superior heads. But it isnot clear that their aim was directed at thedelicate hands of painters and engravers, andit remains to be seen how the rougher handsof artisans such as cartwrights, foundrymen,carpenters, and blacksmiths contributed tothe emergence of modern science.

Reference1. F. Bacon, De dignitate et augmentis scientiarum

(London, 1623); translation from P. Rossi, Philosophy,Technology, and the Arts in the Early Modern Era(Harper & Row, New York, 1970), p.118.

To judge from some recent discussionsabout evolution, genes, and the mind, amother could be concerned that her

child, born with only about 30,000 genes,might have serious developmental problemsor at least be unlikely to follow a typical hu-man developmental pathway. Experts havemade much of the claim that 30,000 genesaren’t nearly enough to specify the vast num-ber of connections in the brain (the “geneshortage”) (1). Our genetic endowmentmight not even be sufficient to make us reli-ably human because, accord-ing to some, genes cannotspecify particular develop-mental outcomes (2, 3). Onecould get the impression thatall the genome can do, be-cause of its limited informa-tion capacity, is to specify thebasic properties that allow thebrain to be an “organ of plas-ticity” (4). Humans must behuman, on this view, becausesome parameter, like degree of plasticity ornumber of neurons, has been tweaked.Moreover, there has “not been enough time”for many new psychological capacities tohave evolved via changes in the genomesince the divergence of the human and chim-

panzee lineages (5). Such arguments havebeen widely invoked to downplay the role ofevolution in shaping the human mind as weobserve it today. They have also been used toargue against the view, associated with thegrowing field of evolutionary psychology,that the many specialized psychological abil-ities of humans are due to natural selectionspecifically for those abilities.

For our hypothetical mother, this mightbe worrying news indeed. Her child mightjust as easily turn out to have the brain of a

chimpanzee. The worriedparent will find such fears as-suaged by Gary Marcus’snew book, The Birth of theMind. With clarity and preci-sion, Marcus, a developmen-tal psychologist at New YorkUniversity, lays to rest the ru-mors of a gene shortage andalso rebuts the argument thatminds are too complex tohave been designed over evo-

lutionary time by the process of natural se-lection. He shows instead that minds arebuilt over the course of individual develop-ment by genetically regulated processes thathave been molded by natural selection tobuild brains that are functionally organizedin ways that promoted human survival andreproduction in the evolutionary past.

Marcus begins by observing that thebrain is far from the only place in the bodywhere our small genome gives rise to com-plex, functionally organized structures; the

H U M A N C O G N I T I O N

Dispelling Rumors of a Gene ShortageH. Clark Barrett

The reviewer is at the Center for Behavior, Evolution,and Culture and the Center for Culture, Brain, andDevelopment, Department of Anthropology, Uni-versity of California, Los Angeles, 341 Haines Hall, Box951553, Los Angeles, CA, 90095–1553, USA. E-mail:[email protected]

The Birth of the Mind

How a Tiny Number of

Genes Creates the

Complexities of

Human Thought

by Gary Marcus

Basic Books, New York, 2004.

288 pp. $26, C$36.95, £19.99.

ISBN 0-465-04405-0.

www.sciencemag.org SCIENCE VOL 304 11 JUNE 2004

B O O K S E T A L .

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liver or the heart, he notes, might just aseasily suffer from a gene shortage. He sur-veys the state of the art of our understand-ing of genes. Rather than static pictures orblueprints of phenotypes, genes are active“agents” that interact in precisely orches-trated ways to build organisms.

The author shows us how this view al-lows us to understand the fantastically com-plex, yet fantastically well-coordinated, gen-eration of the mind. In cognitive science, ithas long been customary to think of the brainas a computer. Marcus shows that the devel-opmental system that builds the brain can al-so be thought of as an algorithmic system,one that operates through frequent interac-tions with its internal and external environ-ments. He likens the genome to a com-pressed file, and the cellular machinery withwhich it interacts to a decompressor.However, this developmental system is fullof ingenious devices not typically found insilicon-based computers, including gradientsand switches that allow its operations to becontext-sensitive, feedback loops, and self-generated “test patterns” that allow the sys-tem to tune itself. Such phenomena chal-

lenge our standard notions of flexibility andplasticity as being fundamentally at oddswith genetic control. It is precisely becauseof genetically specified developmental pro-cedures that the brain is able to achieve itsastounding plasticity. Plasticity is not simplyresponsiveness to change (as when a basket-ball responds to being punctured) but re-sponsiveness that produces the correct out-come in diverse circumstances. As Marcusmakes clear, although we are vastly morecomplex than desktop computers and there-fore have potentially many more ways ofbreaking, the fact that our developmentalprocess is relatively far less prone to crashingwhile booting up from the zygote has every-thing to do with natural selection for specif-ic developmental outcomes.

Perhaps most important, Marcus tackles aquestion fundamental to current debatesabout the mind: How could so few genes ac-count for the large array of humans’ special-ized psychological skills? Here, argumentshave focused on the idea of modularity, thenotion that specific skills are handled by spe-cific areas or circuits in the brain. Evo-lutionary psychologists have argued, follow-

ing William James’s insight over a centuryago, that the flexibility and power of humanintelligence result from natural selectionhaving added, not removed, specialized ma-chinery to our minds. However, many haveintuited that there could not be very manymodules because of the gene shortage, a lackof evolutionary time, or both. Clearly, theblueprint idea of a one-to-one-mapping be-tween genes and modules (in which an en-tirely new suite of genes is required for everynew module) seems to lead inevitably to agene shortage. But Marcus shows that ourknowledge of developmental genetics de-bunks this simplistic view. He discussesways in which a complex regulatory systemcan build distinct units without an entirelynew set of instructions for each. For exam-ple, an animal with 60 legs would not neces-sarily need 10 times as many genes as a six-legged animal, and although human armsand legs differ considerably, we do not re-quire an entirely distinct set of genes for eachtype of limb. The same considerations applyto the components of the brain. Marcuspoints to many ways in which evolution cangenerate features of organisms’ phenotypesthat are modular in design without an equiv-alently modular genome. He also mentionsinteresting mechanisms for the generation ofnovel structures—such as duplication ofgenes within the genome, which allowsmodification of the copy without loss offunction of the original—that could provideuseful insights for those seeking to under-stand the origin of novel psychological ca-pacities in humans.

The account Marcus offers will be re-freshing to those who are tired of simple-minded debates about the role of genes andevolution in shaping the human mind. If thereis a drawback to the book, it is that the authordoesn’t show us exactly how a tiny number ofgenes builds such a complex brain, only thatthey can. But he is hardly to blame for this,given that we have a long way to go before wehave a complete understanding of brain de-velopment. The strengths of The Birth of theMind lie in its sophisticated exposition ofhow genes guide development and its con-vincing argument that we need not hold outhope for some magical, as yet undiscovered,process to account for the brain’s complexity.Plain old natural processes, about which weknow much already, will do.

References1. P. Ehrlich, Human Natures: Genes, Cultures, and the

Human Prospect (Island, Washington, D.C., 2000).2. D. Buller, V. Hardcastle, Brain Mind 1, 307 (2000).3. R. Lickliter, H. Honeycutt, Psychol. Bull. 129, 819

(2003).4. J. L. Elman et al., Rethinking Innateness: Connect-

ionism in a Developmental Framework (MIT Press,Cambridge, MA, 1996).

5. M. Tomasello, The Cultural Origins of HumanCognition (Harvard Univ. Press, Cambridge, MA,1999). C

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The Cambrian Fossils of Chengjiang,

China.The Flowering of Early Animal Life.

Hou Xian-Guang, Richard J. Aldridge, Jan

Bergström, David J. Siveter, Derek J. Siveter,

and Feng Xiang-Hong. Blackwell, Oxford,

2004. 245 pp. $99.95, £60. ISBN 1-4051-

0673-5.

The 525-million-year-old gray mud-

stones of Yunnan province, south China, of-

fer a spectacular view into the diversifica-

tion of animal life. Exceptional preservation

has retained fine details of soft-bodied or-

ganisms. The many thousands of specimens

collected since Hou’s 1984 discovery of the

Chengjiang fauna document the bottom-

dwellers from a relatively shallow marine

environment. This rich Early Cambrian biota

was both older and more varied than the

renowned Burgess Shale fauna. The authors

offer anyone interested in paleontology or

evolutionary biology an excellent overview

of the setting, study, preservation, and paleoecology of the Chengjiang fauna as well as

brief descriptions, photographs, and reconstructions of more than 90 species. (Above, the

relatively abundant arthropod Fuxianhuia protensa, which reaches lengths of 11 cm.)

The New Quantum Universe. Tony Hey and Patrick Walters. Cambridge University Press,

Cambridge, 2003. 373 pp. $85, £55. ISBN 0-521-56418-2. Paper, $35, £19.99. ISBN

0-521-56457-3.

In The Quantum Universe (1987), the authors offered an accessible, nonmathematical

introduction to the physics and applications of quantum theory (especially the wave na-

ture of particles and the Pauli exclusion principle). In this updated edition, again copious-

ly illustrated, they have added accounts of quantum paradoxes, Schrödinger’s cat, and the

Bell inequality. They also discuss nanotechnology and quantum mechanics in computing,

cryptography, teleportation, and science fiction.

Image not available for online use.

11 JUNE 2004 VOL 304 SCIENCE www.sciencemag.org

B O O K S E T A L .

A recipe for the mindThe Birth of the Mind: How a TinyNumber of Genes Creates theComplexities of Human Thoughtby Gary MarcusBasic Books: 2004. 240 pp. $26, £19.99

Anthony P. Monaco

If the mind can be explained from theworkings of the brain, and the brain devel-ops by direction from our genes, then pre-sumably the mind can be explained fromour genetic make-up. But how can only30,000 genes make a brain with billions ofneurons and encode the particular aspectsof cognition that make us human?

The Birth of the Mind tries to unravel thiscomplex problem by first explaining what weknow about each component of the argu-ment: the mind, the brain, our genes and the environment. The breadth of examplesused to achieve this is impressive,encompas-sing 40 different organisms (from bacteria to chimpanzees), 30 different genes and 20different brain regions.

The author, Gary Marcus, spends muchof his efforts building up the reader’s knowl-edge base. It is difficult to make an argumentthat involves such diverse disciplines as evolution, genetics, gene expression, cellbiology, neurobiology and psychology with-out teaching the reader the bare essentials.Marcus does particularly well to make therelevant issues in these areas understandable

to the lay reader, and does an even better job of dispelling the myths that impede theway we think about genes and their role inmaking brains,and hence minds.

Marcus is a cognitive psychologist whounderstands genes. He has researched histopic well and describes the complex worldof genes in an entertaining and gripping way. He dispels the myth that there are toofew genes by explaining that single genes canencode several proteins with different func-tions, and more importantly that genes canbe turned on and off in groups in multiplecombinations to perform highly orches-trated and complex functions. He discardsthe analogy of genes as blueprints for build-ing a brain (or any other organ in the body),and prefers to think of genes as the ‘recipe’required for the correct development of thebrain.He explains heritability and the differ-ence between single-gene effects — and their resulting monogenic and relatively rare diseases — and complex genetic interactions,which cause more common diseases.

He also unravels the paradox of flexibility.How does the brain of a newborn, with itscomplex structures and connections,have theplasticity to enable it to respond to environ-mental influences as it develops further? Mar-cus disentangles the nature-versus-nurtureargument using many examples from neuro-science research that show that the brain isbuilt by genes in a self-organized way beforebeing reorganized and shaped by experienceand the environment. It is not a battle whereone side wins,but a vital interaction.

Having clarified these two paradoxesusing our current knowledge of genetics and

books and arts

NATURE | VOL 427 | 19 FEBRUARY 2004 | www.nature.com/nature 681

During his three-month sojourn with the British Antarctic Survey, artist JohnKelly experienced the polar region as sublime but often darkly ominous. Thispainted-over photomontage — part of a six-part series called Silent Sea —

portrays the Antarctic’s threatening beauty. It is part of an exhibition of hiswork, “Due South: Art and the Antarctic”, which runs from 24 February to 1 August at the Natural History Museum in London. Alison Abbott

Art

Go with the floe

neuroscience, can we explain how genesmake minds? The story is only beginning.This book shows that genes build brains andthat brains are designed to be flexible and tolearn,but the jump from genes to the mind isan indirect one. The question cannot yet beanswered, and it is not entirely clear wherethe answer will come from.

Will geneticists pinpoint genes and genepathways that will inform us about humancognition? This is already happening but willprovide only part of the answer and confirmthat genes are directly influencing mentalabilities. Will cognitive scientists detail therelationship between neural structures andmental structures? This area of research isexpanding,thanks to modern brain-imagingtechniques that enable researchers to ‘see’thebrain in action. The path ahead to integratethese disciplines to gain a fuller understand-ing is optimistically vague,and anyone inter-ested in the topic would be encouraged toread this book.

Lay readers may be daunted by the sheercomplexity of the science — even with the best intentions of explanations in lay terms,a glossary and an appendix to explain thegenes. But the more scientifically minded,especially those with a background in eithergenetics or neuroscience, would gain muchfrom the book. It would at least dispel somemyths and paradoxes, leaving the possibili-ties open for an eventual understanding ofhow 30,000 genes can provide the recipe for the mind. ■

Anthony P. Monaco is director of the WellcomeTrust Centre for Human Genetics, University ofOxford, Headington, Oxford OX3 7BN, UK.

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About half of the estimated 30,000-odd genes in the human genomeare expressed in the brain. Among these genes is hidden the explana-tion for our unique human cognitive abilities, and for many of thedifferences between individual people. Developmental neurobiologyis the essential bridge for connecting genome to behavior, but despiteits obvious importance, there has not yet been a popular bookdevoted to this subject.

The Birth of the Mind is an ambitious attempt to fill this gap. Theauthor, Gary Marcus, is a cognitive scientist, but he has learned a lotabout developmental neurobiology and has written a concise and veryreadable introduction to the field. By drawing on related disciplinessuch as genetics, cognitive science and evolution, he provides anoverview of how the interaction between genome and environmentgives rise to the human brain—and by extension the human mind.

Marcus gives as clear an account as I have ever seen of the natureversus nurture ‘debate’. In fact, most biologists no longer regard thisas a debate (genes and environment are both important), and thefact that it is still perceived as such by the public may reflect the lackof clear popular account, which this book now provides. The con-cepts of pleiotropy, heritability and the interaction between genesand environment are also clearly explained. The popular press lovesto announce the discovery of ‘genes for’ everything from adultery tozoophilia, and this will probably continue as long as there is ademand for light scientific entertainment; anyone who reads thisbook, however, will understand why this is a misrepresentation ofwhat genes actually do.

I found the discussion of innate behaviors particularly insightful.These are often described as ‘hardwired’, the implication being thatthey are inflexibly determined by the genome. But as Marcus empha-sizes, there is a distinction between ‘hardwired’ and ‘prewired’. Just ascomputer software often comes with default settings that can be cus-tomized by the user, so the brain develops with prewired patterns thatcan be modified by later experience. The failure to distinguish these

two situations has led to endless confusion in the debate betweennativism (the belief that cognitive abilities are prewired) and empiri-cism (the opposite), and Marcus does a nice job of recasting the dis-cussion in a more constructive way.

He also dispels a more recent myth, namely that there is a ‘geneshortage’ that precludes genes from encoding complex behaviors. It isadmittedly surprising that we have only 30,000 genes but 100 billionneurons, particularly given that the nematode C. elegans has nearly asmany genes yet only 302 neurons. But as Marcus makes clear, genesare complex individually and give rise to even greater complexity byacting in combination; moreover, the truth is that we have no basis forsurprise, absent a theory to explain how many genes are needed for agiven degree of biological complexity.

Einstein famously advised that everything should be made assimple as possible, but no simpler. Marcus takes this to heart, andhis book contains many simplifications but few misrepresenta-tions. Where to simplify is a matter of taste, and not everyone willagree with his decision to avoid the complexities of transcriptionaland posttranscriptional regulation. He compares genes to Booleanlogic gates; IF a certain combination of transcription factors ispresent, THEN make this protein. This is a useful analogy for thegeneral reader, but it may be a violation of Einstein’s maxim. Genessometimes behave as analog rather than digital devices; that is, theyshow graded rather than on/off expression. An important issue forthe emerging field of systems biology is to develop theoreticalframeworks for understanding gene interaction networks, and it isnot clear whether discrete models will suffice or whether morecomplex continuous models will be needed. But Marcus’s formula-tion is certainly provocative and probably not seriously misleadingfor his target audience.

The book is enjoyable to read. Marcus writes with a light touch (hismentor was Steven Pinker, and it shows), and if he occasionally goestoo far (e.g., “without genes, learning would not exist”, p. 170), anoccasional vapidity seems preferable to the ponderous academicprose by which too many scientists express themselves.

I have one reservation, however; despite the book’s title, anyonelooking for philosophical insights into the mind/brain relationshipwill be disappointed. Marcus announces this at the outset. Referringto Francis Crick’s ‘astonishing hypothesis’ that our thoughts are deter-mined by physical events within our brains, he says: “I can’t say that Iam astonished. To many people of my generation, it has become obvi-ous (maybe even banal) that our thoughts are the product of ourbrains.” I wonder whom he has been talking to. In my experience, thegreat majority of lay people are dualists, and some find the materialistviewpoint profoundly disconcerting. Even those of us who considerourselves hard-nosed materialists sometimes sense the chasm thatseparates our scientific beliefs from our sense of self. Marcus seemsuntroubled by such thoughts, and his book will be of little help tothose who are.

But overall, The Birth of the Mind is a fine general introduction andI have no hesitation recommending it to students, scientists fromother disciplines, or lay readers wanting to learn something about thisfascinating and fast-developing field. �

Charles Jennings is Executive Editor of the Nature Research Journals.

e-mail: [email protected]

Building brains from genesThe Birth of the Mind: How a TinyNumber of Genes Creates theComplexities of Human Thought

by Gary Marcus

Basic Books, 2004288 pp. hardcover, $26ISBN 0465044050

Reviewed by Charles Jennings

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about 10–15% of cases of horrific trauma, such as rape orcombat battle. Moreover, it is often delayed in its onset.These observations have led McGaugh and other neuro-scientists to speculate that perhaps a post-trauma drugcould be given to trauma victims that would block theaction of stress hormones, which might attenuate (oreven prevent) the development of PTSD. Early workreveals the promise in this original idea. As a result,ethical issues have already risen to public discussion.Should we be giving people pills to purposefully dampenpainful, unwanted memories? Critics of this approach worrythat such dimming or erasing of painful memories mightdisconnect people from who they really are. But others havewanted such a ‘cure’ for people who are racked by painfulmemories. And they have wanted the cure for hundreds ofyears if we draw a liberal inference from Shakespeare’sMacbeth. It is there that a doctor is urged to treat LadyMacbeth and rid her of painful memories of the past:

‘Canst thou not minister to a mind diseas’d,Pluck from the memory a rooted sorrow,Raze out the written troubles of the brain…with some sweet oblivious antidote…’

If Shakespeare could read Memory and Emotion, he’d besmiling at his own foresight.

References

1 Neisser, U. and Harsch, N. (1992) Phantom flashbulbs: false recollec-tions of hearing the news about Challenger. In Affect and Accuracy inRecall: Studies of ‘Flashblub’ Memories (Winograd, E. and Neisser, U.,eds), pp. 9–31, Cambridge University Press

2 Loftus, E.F. (2003) Our changeable memories: legal and practicalimplications. Nat. Rev. Neurosci. 4, 231–234

3 Nourkova V.V., Bernstein D.M., Loftus E.F. Altering traumaticmemories. Cogn. Emotion (in press)

1364-6613/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.doi:10.1016/j.tics.2004.03.005

Blueprints, Swiss Army knives, and other metaphorsThe Birth of the Mind: How a Tiny Number of Genes Creates the Complexities of Human Thought, by Gary Marcus, Basic Books

(Perseus) 2004. $26.00 (278 pp.) ISBN 0 465 04405 0

Timothy Justus

Department of Neurology, VA Northern California Health Care System, Martinez, CA 94553-4668, USA

In 1975, a set of experiments wasperformed that has impacted manydebates concerning the differencesbetween humans and our closest pri-mate relatives. The experiments werecarried out by Mary-Claire King, work-ing in the laboratory of Allan Wilson atBerkeley. The methodology involveddetermining the temperature at which

two pieces of single-stranded DNA, one sample from ahuman and the other from a chimpanzee, would ‘melt’ orseparate from each other. The greater the similaritybetween chains, the tighter the chemical fit betweenthem and the higher the temperature required for theseparation. In this case, the high temperature that wasrequired suggested that over 98% of the human andchimpanzee genomes were identical [1].

The relevance of this finding is intuitive and immediate:if humans and chimpanzees are genetically 98% the same,how are we to reconcile the seemingly vast cognitivedifferences between the two species – for example, thehuman species’ ability to produce language, art, technol-ogy, and so forth – with the remaining mere two percent ofthe genome? In his new book, The Birth of the Mind, GaryMarcus quickly dispels the blueprint metaphor that leadsmany non-biologists astray when thinking about genes.The problem with this metaphor is that, unlike a genome,a blueprint contains a one-to-one mapping between theelements on the plan and in the finished product; an

alteration of an architectural blueprint creates an equiv-alent amount of change in the constructed building.

This difficulty we face in understanding how subtledifferences between genomes are amplified into dramaticphenotypic differences between species recurs in the formof the ‘gene shortage’ problem, which Marcus attributes tobiologist Paul Ehrlich [2]. The shortage refers to the ratiosbetween the size of the genome (in humans, by currentestimates, some 30 000 genes) and the number of neuronsin the brain (some 100 billion or 1011), with even higherorders of magnitude for the number of synapses betweenneurons, which give rise to our mental representations. Anempiricist argument here might be: how could suchelaborate representations be determined by such a smallset of genes? The appeal of such a rhetorical device alsostems from the same implicit blueprint metaphor thatmight lead one to expect a less dramatic ratio between thenumber of genes and the number of neuronal connections.

The simple answer to both of these shortages (either interms of the absolute number of genes or the differencesbetween genomes) is to realize that genotype–phenotyperelationships are exponential. If we consider any numberof developmental disorders that have been studied geneti-cally, such as Williams Syndrome or the speech andlanguage disorder exhibited by the KE family, it becomesimmediately apparent that changes in a handful of genes,or even a single gene, can lead to exponentially largerchanges in phenotype. The question then is one of how thegenome ‘unpacks’ to orchestrate human development, inparticular the development of the human brain. Marcus isquite up to the job of reviewing the current knowledge onCorresponding author: Timothy Justus ([email protected]).

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the subject, and in doing so integrates a large body of workacross genetics, developmental biology, cognitive psychol-ogy, neuroscience and linguistics. As a cognitive scientist,Marcus writes particularly appropriately for that audi-ence. Those with heavier biological training will probablyfind the bulk of the material familiar, but the level ofintegration across fields should still leave most readerswith some novel insights and new questions.

First off, Marcus provides us with a more accurate (andmore cogsci-friendly) alternative to the blueprint meta-phor to help us imagine the genome in action: the ‘if-then’statements of a computer program. The aptness of thismetaphor can be seen in work on what are known asregulatory proteins – proteins that control the degree ofexpression of other genes and the proteins they encode,many of which are themsleves also regulatory proteins.Such protein if-then statements are what allow a researcherto ramp up expression of a single master control gene in,for example, the antennae of a fruit fly and modulate theactivity of hundreds of other genes to result in an extra eye[3]. Similar embedded cascades of gene expression under-lie the differences between a normally developing childand one with a genetic developmental disorder, and eventhe differences between closely related species likehumans and chimps, whose genomes differ by seeminglyinsignificant proportions.

For this reader, the more engaging sections of the bookare the instances where Marcus takes a stand on some ofthe current conceptual challenges facing cognitive psy-zchology as it tries to integrate sensibly the increasinglyavailable genetic data into theories of human cognitiveorganization. I would like to examine three conceptualissues that, in particular, beg reconsideration in light of asmall, data-compressed genome.

The first of these issues concerns the distinctionbetween the developmental process and the mentalrepresentations that result from that process, particularlywith regard to the issue of domain-specificity. Marcustouches on this point in a discussion that contrasts thelogic of association and dissociation following brain lesions(which are disruptions of previously developed represen-tations) and the logic of association and dissociation indevelopmental disorders (which are disruptions of thedevelopmental process itself). Marcus suggests thatalthough the failure to find neuropsychological dis-sociations might provide evidence against domain-specificrepresentations, the failure to find developmental dis-sociations probably does not. This is because the loss of agene affects a multitude of genetic cascades in disparateareas of the brain, and can result in the disruption ofdevelopmental processes that in normal developmentwould have culminated in domain-specific represen-tations. It seems here that Marcus is envisioning a brainthat develops domain-specific representations (e.g. forlanguage), but he breaks from more hard-core nativistaccounts by allowing the genetic constraints involved notto be themselves domain-specific. If this is true, Marcusmay be close to meeting the ‘anti-modularists’ – whom heoften pits himself against – halfway; Annette Karmiloff-Smith, along with her colleagues Jeffrey Elman andElizabeth Bates, has long advocated a view of development

in which the domain-specificity of developmental pro-cesses and that of their products, mental representations,are dissociated in a very similar manner [4,5].

The second issue where there seems to be someconvergence concerns the realization that the expressionof a gene is not likely to be specific to one representation,one cortical region, or even the nervous system. Togetherwith Simon Fisher, Marcus nicely illustrated this in arecent and much needed review of the FOXP2 gene, theaberrant gene in the speech-disordered KE family [6]. Thisissue is relevant because on first impression one mightexpect that more modular views of brain organizationwould require some degree of genetic specificity. Marcuspoints to a 1998 article by Karmiloff-Smith [7] that he feelsis an example of genetic naıvete of this kind. I think thatKarmiloff-Smith’s article is worth a second read, becauseit is not only more sophisticated than Marcus gives creditfor, but also reflects a view of brain development that isactually strikingly similar to Marcus’s own. Both authorsdescribe ‘unique-marker’ genes as implausible. Bothauthors also describe a developmental process in whichgenetic constraints largely establish different corticalregions with, in Marcus’s words, the ‘subcomponents forcomputation, not complete systems for single-handedlysolving complex cognitive tasks’ (p. 133, italics original).Thus, the two are in agreement to a surprising extent overthe way in which the genome contributes to the establish-ment of mental representations, and both even allow someof these end representations to be specific to differentcognitive domains. The real tension in this debate, itseems, stems from the ‘Swiss-Army-knife’ view of thebrain, and what this metaphor implies, not only abouthuman development but also human evolution.

This brings us to the third issue, which concerns theimplications of small numbers of genes and comparativegenetic differences for evolutionary psychology. The realproblem of the ‘gene-shortage’ is not that it underminesthe truism that brain development proceeds under geneticguidance, but it does however call into question the Swiss-Army-knife view of the mind that currently dominatesevolutionary psychology [8]. According to this view, thebrain does not merely end up with dozens of differentdomain-specific representations, but is believed to havebeen designed for acquiring those representations bydozens of selection pressures acting on specific, adaptivecognitive abilities. The small number of genes separatinghumans from the last common ancestor is highly sugges-tive of a scenario long advocated by Stephen Jay Gouldand Richard Lewontin [9], which proposes that many ofhumanity’s unique cognitive abilities (or the capacity todevelop them culturally) were not directly selected, butwere instead consequences of other selection pressures.Given the strong data compression found in the genome,natural selection of a master control gene in response toone trait or behaviour might result in an ‘unintended’reorganization of multiple other systems. Marcus himselfhints at such a scenario with regard to the evolution oflanguage: ‘But since…a single change can induce a newcascade or block an old one, phenotypic changes need notbe gradual. A single mutation (or duplication) can have alarge effect on the phenotype… if language arose by a

Update TRENDS in Cognitive Sciences Vol.8 No.5 May 2004202



novel combination of existing elements – such as neuralstructures for memory, the automatization of repeatedactions, and social cognition – it is possible that it couldhave developed relatively quickly.’ (p. 140). Marcus’sprimary point in this passage concerned the pace oflanguage evolution, but that scenario certainly also begsquestions about what physical traits or behaviours droveit. Despite Marcus’s sophistication in critiquing the ‘genefor’ concept, my main disappointment with The Birth of theMind was that Marcus was not so cautious in his use of theSwiss-Army-knife view of the brain, with its very explicit‘evolved for’ connotation. Perhaps the Swiss Army knife islike the blueprint when it comes to human developmentand evolution: a metaphor in need of replacement.

References

1 King, M.C. and Wilson, A.C. (1975) Evolution at two levels in humansand chimpanzees. Science 188, 107–116

2 Ehrlich, P.R. (2000) Human Natures: Genes, Cultures, and the HumanProspect, Island Press, Washington DC

3 Halder, G. et al. (1995) Induction of ectopic eyes by targeted expressionof the eyeless gene in Drosophila. Science 267, 1788–1792

4 Karmiloff-Smith, A. (1992) Beyond Modularity: A DevelopmentalPerspective on Cognitive Science, MIT Press

5 Elman, J.L. et al. (1996) Rethinking Innateness: A ConnectionistPerspective on Development, MIT Press

6 Marcus, G.F. and Fisher, S.E. (2003) FOXP2 in focus: what can genestell us about speech and language? Trends Cogn. Sci. 7, 257–262

7 Karmiloff-Smith, A. (1998) Development itself is the key to under-standing developmental disorders. Trends Cogn. Sci. 2, 389–398

8 Tooby, J. and Cosmides, L. (1992) The psychological foundations ofculture. In The Adapted Mind: Evolutionary Psychology and theGeneration of Culture (Barkow, J.H. et al., eds), pp. 19–136, OxfordUniversity Press

9 Gould, S.J. and Lewontin, R.C. (1979) The spandrels of San Marco andthe Panglossian paradigm: a critique of the adaptationist programme.Proc. R. Soc. Lond. Ser. B 205, 581–598


|Corrigendum

Corrigendum: Shared representations between selfand other: a social cognitive neuroscience view

Trends in Cognitive Sciences 7 (2003) 527–533

In the article by J. Decety and J.A. Somerville,published in the December 2003 issue of TICS, we wishto correct the following with respect to two of theillustrations.

In Box 2 on p. 529, Figure I is not adapted fromreference [39] as stated, but is from an unpublished studythat contrasted ‘social emotion’ conditions with neutralconditions. The appropriate figure to illustrate subjectiveperspective-taking can be found in reference [38].

Also, in Figure 1 on p. 530, two activations, one in thelateral view and one in mid-sagittal, marked as yellow

hexagons in the frontal cortex (anterior) as being‘Imagining action’ from reference [38], were not in factfound in that study. An activation at this location in medialprefrontal cortex was found in reference [39] in a conceptualperspective-taking task. Reference [38] found an activationin the frontopolar cortex (Brodmann area 10).

We apologise to readers for this incorrect information.doi of original article: 10.1016/j.tics.2003.10.004


Endeavour

Coming soon in the quarterly magazine for

the history and philosophy of science:

The future of electricity in 1892 by G.J.N. Gooday

The First Personal Computer by J. November

Sherlock Holmes the Scientist by L. Snyder

Locate Endeavour in the BioMedNet Reviews collection (http://reviews.bmn.com) or on ScienceDirect (http://www.sciencedirect.com)

Update TRENDS in Cognitive Sciences Vol.8 No.5 May 2004 203



Evolutionary Psychology human-nature.com/ep – 2005. 3: 275-278 ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ Book Review A major feat of intelligent synthesis A review of The Birth of the Mind: How a tiny number of genes creates the complexities of human thought by Gary Marcus. New York: Basic Books, 2004. Michael Peters, Professor of Psychology, University of Guelph, Guelph, ON, Canada. Email: [email protected].

The title and subtitle of this book raise the expectation that we will find out something about the relation between genes and the mind, suggesting that it provides a new perspective on the mind/body problem. I have to confess that when I first read through Marcus’s volume I had the same experience I had when reading Popper and Eccles’ “The Self and its Brain” some years ago. After patiently following Eccles’ careful description of this and that neurophysiological mechanism, I felt I had somehow missed the connection when all of a sudden he switched into talking about the mind as if he had built a satisfactory and convincing bridge from the neurophysiology of the brain to the “mind”. In the case of Marcus’ book I initially had the same difficulty, in this case going from ”gene” to “mind”. However, things became clearer when pausing to reflect on how Marcus uses the term “mind”. He avoids all manner of metaphysical complications by restricting himself to the use of “mind” as short-hand for the sorts of things that take place in Popper’s world 2, the “world of mental processes”, such as thinking, perceiving and remembering. Marcus follows the sage maxim that if you cannot define what a thing is, try at least to describe what you think it does. So, be warned: his book does not claim to illuminate the reader on the mind/body issue, in spite of the title (indeed, at one point, Marcus confesses “I use the term “mental gene” as a bit of a joke” p. 80). What Marcus sets out to do, and he does so very successfully, is to describe how a deceptively small number of genes can create the conditions conducive to the development of the mind in the sense in which most of us, by common understanding, use the term. This is an important book for evolutionary psychologists, and especially for born-again evolutionary psychologists. By “born-again” I mean individuals who have come to evolutionary thinking somewhat late in their academic life, with a background in social psychology or in Skinnerian behaviorism. Having been raised in a setting where sole emphasis was on the organizing and instructive effects of the environment on the organism, this group, after floundering about for decades without notable progress, literally had an epiphany when encountering evolutionary

A major feat of intelligent synthesis

psychology. They were bowled over by the apparent simplicity and power of this (to them) new approach. However, they came to this new way of looking at things without a solid foundation in either evolutionary thinking or understanding of the genetics and functional aspects of the biological substrate thought to underlie behavior. This created a situation in which a near-fundamentalist fervor was paired with large gaps in the knowledge that is necessary to fully appreciate “how things might work”. Marcus’ book helps link gene action to behavior, and may be considered a sine qua non for serious evolutionary psychology. One of the reasons why Marcus’ book is so valuable, not only for the layperson but also someone immersed in the field, lies in its unusual amount of reference documentation. Fully 1/3 of the book is taken up by references, glossaries and an appendix, all of which deepen the reader’s involvement and understanding. Although many of the references are familiar to me (such as my favorite didactic vehicle for explaining gene/behavior relations to students, the Aplysia egg-laying hormone story), many others were not, and I owe much to Marcus’ breadth of reading, which has enriched my understanding of gene action. This review will not cover the book chapter and verse, but will focus on its most salient aspects. This, I hope, will give the reader a sufficient impression of those delights that the book holds for the evolutionary psychologist. Marcus begins his exploration, appropriately, with the nature/nurture question, and by posing his two paradoxes: 1) how can a small number of genes guide the development of brains that contain tens of billions of neurons and which are characterized by a rather invariant general architecture across our species and 2) how can the brain be as flexible as it is, given this invariant architecture? In addressing these paradoxes, Marcus places great emphasis on the interaction between nature (genes) and nurture (environment), because he is convinced that the interaction holds the key to the reconciliation between the two paradoxes. Indeed, the interaction between processes guided by genetic instructions and their modification via feedback from the environment can be considered the dominant theme of the book. Throughout, Marcus describes interactions at all levels and in different contexts. For instance, when the mRNA leaves the nucleus, its effects are for naught if the proper mix of amino acids - among other things - is not available in the soma of the cell. Marcus points out, more topically, that the dream of reconstructing dinosaurs from dinosaur DNA, a lá Jurassic Park, is likely to remain a dream because the DNA will not find in its immediate environment (that is, the “modern” cell into which it is implanted) the appropriate biochemical substrate that can interact with the signals generated by the dinosaur DNA. In the chapter “wiring the mind”, the developmental aspects of interaction between neurons of the unfolding brain and their immediate environment are described, with many current and beautiful examples. Here, the interaction takes the form of, if-then prepositions, e.g., “if this protein or factor is encountered, the growing cell will differentiate in that direction, or move its processes in that direction, or come to rest in this layer”. Of course, interactions extend beyond that level. Throughout, Marcus stresses that the

Evolutionary Psychology – ISSN 1474-7049 – Volume 3. 2005. - 276 -


brain and the genome that underlies brain function is responsive to the external environment. In the earlier chapters, in which differentiation of the unfolding nervous system is discussed, there are examples of how in the development of the sensory machinery of brain, external influences interact with the unfolding neural substrate. That substrate unfolds on its own, to a point, but in order to end up with a useful working brain, it is informed and modified by external inputs.

Ultimately, even the social environment has a direct impact, not only in the development of the brain but in the continued life span functioning of the brain. As Marcus puts it “genes aren’t just for kids, they are for life” (p. 169). By this, he means that environmental inputs feed back signals to the DNA which, in turn, produces proteins that modify the response to the environmental inputs; this happens throughout the life span, as distinct from the earlier DNA/surround interactions that take place in shaping the brain. A specific example is learning at the cellular level, in which environmental input activates stretches of neuronal DNA which in turn produce changes, via structural proteins, in the receptor membrane that modify the neuron’s responsivity to further input. Another example concerns changes in daylight duration that gain access to DNA which responds by sending out proteins or polypeptides that initiate, in many species, a cascade of changes that affect hormone levels and reproductive behaviors. To return to the first paradox - how a small number of genes can direct the development of an entire large brain - Marcus provides an extensive answer in “Paradox resolved”. Illustrating these elements with numerous examples, Marcus summarizes several points that capture the way in which small numbers of genes can give rise to complexity:

• Genes do not provide blueprints of structure but, rather, a guide to process. • Genes work in combination. In the conventional view, 100 genes code for

100 proteins, but if one considers that each gene codes for two sets of 50 proteins, their effects may lead to 50 x 50 combinations of proteins. Clearly, the possible number of permutations is gigantic.

• The same set of instructions can be used everywhere in the body; Marcus uses the analogy of compression schemes in computer languages that specify simple procedures. The analogy suggests that genetic instructions for certain recurrent schemes do not have to be reinvented, depending on where in the body they occur, but can be expressed flexibility anywhere where they are needed.

• The same genetic instruction can be used recurrently so that, for example, each of the legs of a centipede does not have to be constructed with different DNA specifications, but shares common code with the other legs. (p. 157).

In the context of the “Evolution of mental genes”, Marcus addresses many important evolutionary aspects of gene action. Just a couple are mentioned here. For




instance, he provides a number of suggestions of how new gene functions arise through simple mechanisms such as gene duplication. Thus, different mutations in the gene that duplicates the code for photoreceptors could lead to specialization for different wavelengths. In the context of evolution, Marcus also addresses the issue of matching genes between species and the somewhat surprising realization that so much of, let us say, chimpanzee DNA lines up with human DNA. Here, the huge percentage of matching DNA code is deceptive because the difference most likely lies in regulatory genes that can bring about very large differences in spite of constituting a small amount of DNA. Are there any quibbles? Only minor ones, concerning differences in emphasis rather than fact. Marcus tends to focus on proteins coded by DNA stretches and allows for more than one protein per gene. But it is also useful to emphasize that precursors for particular proteins can be chopped into numerous polypeptides, many of them very small, just a few amino acids long. As a common example, the pro-opio-melano-cortin stretch coded by DNA serves as a precursor that contains the instructions for the production of longer and even very short polypeptides (such as enkephalins) that can have physiological effects by themselves or as part of larger functional portions of the code. These polypeptides can be separated out by restriction enzymes. Minor changes in nucleotide base sequences in the code for the formation of the polypeptides can produce polymorphisms (RFLPs = Restriction Fragment Length Polymorphisms) that are themselves subject to selective pressures. It seems to me that Marcus, although making brief mention of the general principle (p. 81), does not sufficiently exploit this important contribution to the plethora of ways in which a gene can contribute to great complexity. While reading the book it occurred to me that a group of individuals who might benefit from reading Marcus’ book are the proponents of Intelligent Design. Their creationist credo holds that complex forms must have been created de novo because they could not have arisen by chance. Such an argument could perhaps have been more easily maintained with the “one gene/one enzyme” scenario. However, any objective reading of the material provided by Marcus makes it very difficult, and perhaps intellectually dishonest, to persist in the suggestion that chance and selection cannot produce immense complexity in biological systems. In summary, a most satisfying book. Marcus represents important ideas in a fluid and entertaining style, without compromising scientific content. There is an impressive breadth in his synthesis, as noted also by other reviewers, and he meets the ultimate goal of writers of books that span the bridge from the popular to the specific: that the book can be read at different levels by readers with different levels of background information. Although evolutionary psychologists can get the bits and pieces of what Marcus offers spread across texts and journal articles, I am not aware of any other work that informs so elegantly, comprehensively and clearly about current work in the basics of gene/behavior interactions. A major feat of intelligent synthesis!

The Birth of the MindHow a Tiny Number of Genes Creates theComplexities of Human Thoughtby Gary MarcusBasic Books, 2003

Review by Lloyd A. Wells, Ph.D., M.D. on Apr 30th 2004

This is a wonderful book which I heartily recommend to any interested readers who want toexplore either genomics or the workings of the mind/brain. In fact, I loved this book and thinkthat many readers will view it similarly. Throughout the book, which is written for reasonable well-educated lay-readers, Marcuspoints out the misconceptions which are rife in most peoples' views of genomics andespecially psychogenomics and explains how just 30,000 genes can and do encode theincredibly complex brains of human beings, with billions of neurons and trillions of neuronalconnections. He makes the major point that "what is good enough for the body is goodenough for the brain", and that the genes which build the body overlap with and work in thesame way as the genes which build the brain, using many examples throughout the bookfrom ocular dominance columns and other areas. In nine short chapters he covers a great deal of ground, and the chapter titles themselveskeep us reading - "Born to Learn", "Brainstorms", Aristotle's Impetus", "Copernicus' Revenge"and "Paradox Lost", among others. He begins with a quote from Richard Dawkins: "The genetic code is not a blueprint forassembling a body from a set of bits; it is more like a recipe for baking one from a set ofingredients. If we follow a particular recipe, word for word, in a cookery book, what finallyemerges from the oven is a cake. We cannot now break the cake into its component crumbsand say: this crumb corresponds to the first word in the recipe; this crumb corresponds to thesecond word in the recipe, etc." Genes "work" with one another, and they have majorinterfaces with the environment as well. Thinking and behavior are not completelydetermined by the genes, which are necessary but not sufficient conditions. Marcus uses MIND rather than BRAIN in his title, but immediately cites Pinker's definition ofmind as "what the brain does." He is a fan of Crick's fascinating book, The AstonishingHypothesis, so this is not a dualistic book, and the author dismisses dualism without reallyconsidering its arguments. He extends Crick's thesis, arguing that the mind has its origin inthe brain, and the brain has its origin in the genes, and he points out that consideration ofgenes has been very deficient even in recent work on theory of mind. At the same time, he isvery careful to point out that genes do not control our destiny - they contribute importantly, asdo all kinds of internal and external environmental factors. After this introduction, Marcus turns to the question of the mind/brain of human neonatesand argues about what is encoded and what is plastic. He next turns to the structure of thebrain and its flexibility. He provides a wonderful description of genes and proteins anddevelops the concept of "genetic recipes". He argues well that the role of genes in the brainis the same as in all other organs. He moves on to the interaction of genes and theenvironment in brain function - an excellent and well-informed discussion. He follows with awonderful chapter on evolution which clarifies more than anything I have read why, with98.5% genomic similarity to chimpanzees, human beings are so different. Finally, he arguesthat vague concepts such as "nature and nurture" are truly on the verge of being replaced by"a synthesis of biology and the cognitive sciences".

Throughout the book, he downplays a special role for genes in the brain vs other organs,and he is very convincing. "In fact, I use the term 'mental gene' as a bit of a joke. Althoughmany genes affect our mental life... 'mental genes' are pretty much the same as othergenes: self-regulated instructions for building parts of a very complex biological structure...Many of them ... are the same. From the perspective of the toolkit of biology, there is littledifference between a gene expressed in the brain and a gene expressed elsewhere. A geneis a gene is a gene." And this, for Marcus, is an organizing principle. Our genes lead to oursense of self, and our sense of self realizes that it shares its genes with others throughout theanimal kingdom: he (and I) find this unifying, gratifying - solace, in fact. The chapter on evolution is the heart of the book, in some ways, and a truly outstandingdiscussion. Our genes add to survival value by making our brains and our selves flexibleenough to adapt and care for ourselves. Marcus considers many important topics but has anespecially fascinating view of the role and place of language in our evolutionarydevelopment, which is central, crucial, and certainly imperfectly understood and still verycontroversial. The author presents the arguments of Fodor, who believes that formallanguage is distinct from a "language of thought" in the brain, and Gleitman, who points outthe lack of cognitive differences in people who speak different languages and argues that apre-existing conceptual component of the brain produces what we view as language as itsmental representation. (There are many opposing arguments about this issue, of course.) Marcus points out that the "genes for language" reported by the media are not unique tolanguage, and that our "language genes" do not just come from the 1.5% of genes we do notshare with chimpanzees but from the other 98.5% as well. He also makes explicit the rolesof many genes in determination of mental traits and downplays the idea that we shall find onegene for depression, for example. He provides a very brief but fascinating overview of real and potential ethical issues,especially in regard to "designer babies". Marcus provides an excellent appendix providing interested readers with a good account ofmethods used in genomic research - an excellent introduction to this topic. There is anoutstanding glossary, seventeen pages long, defining common terms of molecular biologyand genomics for the general reader. The chapter notes which follow are useful and areannotated in many cases. There are thirty pages of references which really provide a majorresource for scientific and medical readers who wish to pursue the book's topics in moredetail. I cannot find any significant aspect of this book to criticize. It is well written, and the authorhas a sense of humor, which can be very helpful in a book like this. For example, he alludesto a "study" allegedly finding that human infants are stupid, which is a wonderful, satiricalpiece in The Onion. He realizes that psychogenomics is in its infancy and makes anoccasional delightful comment such as, "Scientists are a lot better at 'finding' genes forcomplex mental traits than they are at replicating their findings." This is a superb book, and Irecommend it most highly.

Lloyd A. Wells, Ph.D., M.D., Mayo Clinic, Rochester, MN

1

To Appear in Language

The birth of the mind: How a tiny number of genes creates the complexities of

human thought. By Gary Marcus. New York: Basic Books, 2004. Pp. 278. ISBN 0-

465-04405-0. $26 US.

Reviewed by Wendy K. Wilkins, Michigan State University

It is relatively commonplace for linguists to assume that language is in the mind

and that the mind is the result of the activity of the brain. But how do mental phenomena,

like language, actually arise from the biology? Gary Marcus has provided a highly

readable introduction to the relevant science, informed by questions important to both

linguists and psychologists, that discusses how the mind/brain derives from the genes. A

credible theory of the mind, and therefore of language, must at some point deal with, or at

least rest comfortably with, basic biological matters, and in contemporary biology, this

necessarily involves genetics. Rational though this may sound, it remains highly unusual

for researchers to directly address the genetic basis of mental phenomena in humans. M

has provided a most valuable resource that takes on this issue, and he has done it with

sophistication, readability, and even a good dose of humor—a rare and welcome

combination. M’s book is a must-read for any linguist who cares about the psychological

and biological reality of grammar, and for any scholar who wishes to gain some insight to

the even broader questions (‘paradoxes’ as M refers to them) of how the mind can be

2

both richly structured and at the same time highly flexible, and how it can emerge from

such a (relatively) small genome of only 30,000 or so genes.

A question of enduring interest, whether in consideration of language acquisition

or of the basic nature of linguistic knowledge, involves the relative contributions of

nature (innate capacities, the genes) and nurture (environment, the input data). As M

explains, these are not separable: absent an environment, genes are useless; absent its

genes, no organism can use the environment. A further important lesson provided in Ch.

1 is that the genome-as-blueprint metaphor is highly misleading.

Ch. 2 addresses the fact that humans, sensitive to the statistical properties of the

world and also able to both imitate and generalize from given information, come

equipped with the mental mechanisms (nature) that allow us to learn from what is out

there in the world (nurture). Humans are born able to learn language, and to do so under

almost any circumstances. For M, there is no real debate about whether language

acquisition is innate, but rather about which learning mechanisms are special for

language.

The human newborn’s brain has the same overall organization as the adult brain.

Nature provides an initial configuration that nurture (experience) then modifies. The

main point of Ch. 3 is that the newborn brain is prewired, not hardwired. Young brains

adapt and change, but they are organized in advance of experience. Neurons are subject

to how developmental rules—genes—work. They are influenced by their neighbors but

can also reflect their source. Hence, just as there are initial (prewiring) constraints, there

are limits on plasticity.

3

Ch. 4 gives a succinct conceptual history of the gene and then explains how genes

provide recipes for proteins, including information about when the protein is to be made.

‘Understanding how genomes contribute to the construction of body and brain is … a

matter of understanding how the two parts of every gene—the regulatory if and the

protein template then—work together to guide the fates of individual cells’ (60). Cells

are not distinguished by what genes they contain, but by which ones are switched on.

Importantly, the then of one gene can satisfy the if of another, turning it on, and thus,

through iterations of this process, a single gene can cause a cascade of hundreds of

thousands of others. The switching on of one gene can result in a large and significant

development.

Genes work to create the brain just as they do any other part of the body; neurons

do have special qualities but they are just specializations of the general plan for all cells.

Ch. 5 reviews the structure and function of neurons, and builds the case that alterations in

the human genome can lead to differences in mind and behavior. Behaviors are the

products of many neural circuits, and every cell is the product of many proteins and

hence many genes. Genes build structure, but it is the neurons that handle real-time

actions. It is unlikely that there is a single gene for any complex behavior (like

language), and there are likely to be many genes that profoundly influence such complex

traits. Few genes are uniquely expressed in a single cortical area, but gradients

(‘signaling molecules that diminish in concentration as they move away from their

source’ [85]) could play roles in determining boundaries between areas, and particular

areas (perhaps, we might speculate, even certain ones specialized for language) could

emerge by means of combinations of overlapping molecular markers. Importantly, as M

4

stresses here and throughout the book, ‘[a]lthough the mind is significantly influenced by

genes, it is not fixed by the genes—recall the difference between rigid hardwiring and

flexible prewiring’ (79).

In Ch. 6, M says that, ‘the wiring between neurons is arguably the single thing

that makes the brain most special’ (89). What the brain does can be understood as a

function of the connections among the (billions) of neurons. The process by which brain

wiring is established is a gradual one, directed not by diagram but by algorithm. Axons

(outputs) and dendrites (inputs) are both active: by the functioning of signals and

receptors, they find each other. All genetic processes are triggered by signals, and some

of these come from internal instructions (including some generated by neural activity

before birth) and others from the external environment. Thus M returns to the issues of

nature versus nurture and learning: animals can learn because they can alter their nervous

systems based on experience. However, not just anything can be learned. What is

learnable is determined by genetic mechanisms (different in different species), or in other

words, the particular ifs and thens of the genome. Learning also necessarily involves

information storage and memory specialized for the sort of information to be stored, as

well as the ability to orient to what is relevant in the learning environment. These too are

guided by neural circuitry. For M, genes are as important to learning as they are to so-

called innate development.

Ch. 7, The Evolution of Mental Genes, is the one of most direct potential interest

to linguists. Here M considers the evolutionary context that explains how humans, but

not chimpanzees whose genome is so similar, are able to speak and acquire complex

culture. Thus, he addresses how humans potentially evolved to have language, not

5

through considering what the brain evolved for, but focusing on the how, and to some

extent, the when. M reviews the various ways in which the genome can mutate

(insertion, deletion, inversion of nucleotides, or of larger chunks of the chromosome), but

directs most of the focus to duplication (of single genes or even whole chromosomes), an

evolutionary process that often can provide a distinctly beneficial option for the organism

or the species. ‘The coordinated processes of duplication and divergence have played an

important role in nearly every step in the evolution of the brain. New forms in evolution

almost never arise from scratch; they are almost always varieties on a preexisting theme’

(114). In brain evolution, there are several critically important general stages. The first

major step was the development of electrical signaling. Then came the trend toward

centralization and bilateralization, resulting in a division of labor between central and

peripheral, and left and right; the evolution of glial cells and myelin for insulating the

axons, allowing them to be more densely packed and energy efficient; which in turn

allowed for larger brains, which came to be divided into fore-, mid-, and hindbrain. This

was later accompanied by a general trend toward increased neural specialization.

Mammals developed a neocortex and increasingly specialized cortical areas, and all

mammals share a general overall neural organization and system of developmental

timing.

M then turns to addressing what is uniquely human. He believes that language is

key and provides the most powerful tool for learning: ‘the mother of all learning

mechanisms and the single thing that makes humans different’ (124). Skirting the

temptation to propose a basic purpose for language, M discusses connections between

language and communication, thought, memory, and complex culture. Noting that some

6

scientist or other has proposed just about every imaginable hypothesis about the evolution

of language, M, recognizing that we can’t make progress on evolutionary matters without

understanding the biology that underlies the behavior or the trait, points to the fact that

we haven’t really figured out yet how the brain accomplishes language acquisition or use.

Language is not as localized in the brain as originally thought, and it is not obvious how

our brains differ from those of chimpanzees (except in sheer size, which in and of itself is

not a determining factor). M reviews what is known about the few apparent differences

and concludes that while some may have been found, they probably do not provide

sufficient conditions. We are not yet able to identify what makes the brain uniquely

human. This should not be interpreted, however, as the end of the innateness hypothesis

(as some have concluded), but it should encourage us to rethink modularity in light of a

deeper understanding of evolution—a process that rarely creates something new, but

typically tinkers with what is already in place.

A language module may depend on a few dozen or a few hundred

evolutionarily novel genes, but it is also likely to depend heavily on

genes—or duplicates of preexisting genes—that are involved in the

construction of other cognitive systems, such as the motor control system,

which coordinates muscular action, or the cognitive systems that plan

complex events. At the genetic level, figuring out what gives humans the

unique gift of language will be a matter not just of finding out about those

(perhaps relatively few) genes that are unique to people, but also a matter

of finding out how those unique genes interact with all the others that are

part of our common primate heritage. Essentially the same can be said at

7

the brain level: Understanding language will be a matter not just of

understanding unique bits of neural structure but also a matter of

understanding how those unique structures interact with other structures

that are shared across the primate order (132).

This is M’s ‘specialization-through-reconfiguration’ (134) view and, I would suggest, the

theory that best fits the known linguistic and biological facts. M concludes Ch. 7 with a

discussion of the potential for learning more about the basis of language and language

acquisition through the study of genetic, or potentially genetic, disorders. He discusses

the increasingly well-known FOXP2 gene, and stresses that, although genetic change is

gradual (e.g. one duplication at a time), each step can have a large and noticeable, and

apparently abrupt, effect on the phenotype.

Ch. 8 returns to the two big questions alluded to in Ch. 1. The understanding of

genes as self-replicating recipes helps resolve these two fundamental issues: how it is that

‘innateness and flexibility coexist’ and ‘[h]ow it is that a genome with far fewer than

100,000 genes can guide the growth of billions of neurons (not to mention the trillions of

connections between those neurons)’ (147). Ch. 9 addresses the importance of

interdisciplinary work, combining biology and the cognitive sciences, for truly

understanding nature and nurture. It is followed by a brief appendix on reading the

genome.

The space allotted for a book review allows only a brief recapping of what is

already a very condensed discussion of an immensely complicated topic. Lost is one of

the things that makes the book most special: the flavor of M’s prose. This is the quickest,

most enjoyable, introduction to genetics you are likely to find. And an understanding of

8

what M has to tell us about the genes should profoundly impact the way we think and

write about both language in the mind/brain and the origins of linguistic capacity.

Especially in this last arena, we have for too long been content with discussions that

address language behavior or linguistic precursors as behavioral repertoires that exist in

some nonmaterial ether. M provides us the understanding of genetics which should allow

us to demand explanation based, if not in genetic reality, then at least in biological

plausibility.

Department of Linguistics and Germanic, Slavic, Asian, and African Languages

A614 Wells Hall

Michigan State University

East Lansing, MI 48824

Documents

Academic Reviews of The Birth of the Mind Science Nature Nature