Tạp chí khoa học số 2006-01-27

27 January 2006 | $10
YYePG Proudly Presents, Thx for Support
TeAM
YYePG
Digitally signed by TeAM YYePG
DN: cn=TeAM YYePG, c=US,
o=TeAM YYePG, ou=TeAM
YYePG, email=
Reason: I attest to the accuracy
and integrity of this document
Date: 2006.02.02 16:33:29 +08'00'
YYePG Proudly Presents, Thx for Support

Quality | Selection | Performance | Results
R&D Systems is a trademark of TECHNE Corporation.
R&D Systems offers new
Proteome Profiler
™
Antibody
Arrays that are screening tools
to simultaneously detect
the relative level of phospho-
rylation of multiple proteins
in each sample. Each kit
contains buffers, detection

antibodies and four
nitrocellulose membranes
spotted with a carefully
selected panel of specific
capture antibodies.
www.RnDSystems.com | (800) 343-7475
U.S. & Canada
R&D Systems, Inc.
Tel: (800) 343-7475

Europe
R&D Systems Europe Ltd.

Tel: +44 (0)1235 529449

Germany
R&D Systems GmbH
Tel: 0800 909 4455

France
R&D Systems Europe
Tel: 0800 90 72 49

Proteome Profiler
™

Antibody
Arrays
from R&D Systems
For research use only. Not for use in diagnostic procedures.
RTK Array Kit
MAPK Array Kit
PRODUCT
Proteome Profiler
Phospho-Receptor Tyrosine
Kinase (RTK) Array Kit
Proteome Profiler
Phospho-Mitogen Activated Protein

Kinase (MAPK) Array Kit
SPECIES
Human
Human
DESCRIPTION
Contains 4 arrays - each spotted
(in duplicate) with antibodies
to 42 different RTKs.
Contains 4 arrays - each spotted
(in duplicate) with antibodies
recognizing 19 different MAPKs
and other kinases.

CATA LOG #
ARY001
ARY002
1 ERK1
2 ERK2
3 MSK2
4 RSK1
5 RSK2
6 GSK-3α/β
7 HSP27
PC PositiveControl
PC

D
1
2
3
4
5
6
7
PC
PC
C
A

B
Target Phosphorylation Site(s)
ERK1 T202/Y204
ERK2 T185/Y187
JNK1 T183/Y185
JNK2 T183/Y185
JNK3T221/Y223
JNK pan T183/Y185,T221/Y223
MSK2 S360
p38α T180/Y182
p38β T180/Y182
p38γ T183/Y185

p38δ T180/Y182
RSK1 S380
RSK2 S386
p70 S6K T421/S424
Akt1 S473
Akt2 S474
Akt3 S472
Akt pan S473, S474, S472
GSK-3α/β S21/S9
GSK-3β S9
HSP27 S78/S82
FIGURE 1. HeLa cells were incubated with no additions or with 200 nM PMA for 20 minutes either with or without

U0126 (a MEK1/2 inhibitor). R&D Systems Proteome Profiler Human Phospho-MAPK Arrays (Catalog # ARY002) were
incubated with (A) no lysate,(B) 175 μg of lysate from untreated cells, (C) 175 μg of lysate from PMA-treated cells,or (D)
175 μg of lysate from cells treated with PMA in the presence of U0126.
Pretreatment with U0126 diminishes the PMA-induced phosphorylation of downstream MEK1/2 pathway members
ERK1,ERK2, MSK2,RSK1 and RSK2, with little effect on the phosphorylation of non-members GSK-3α/β and HSP27.
Human Phospho-MAPK Array Panel
YYePG Proudly Presents, Thx for Support
Ni Sepharose
™
products from GE Healthcare give you greater flexibility and the highest
binding capacity available for histidine-tagged protein purification. They also assure
maximum target protein activity, thanks to their tolerance of a wide range of additives

and negligible nickel ion leakage.
His MultiTrap
™
prepacked multiwell plates let you directly apply unclarified lysate for greater
convenience and minimized degradation of sensitive target proteins. Ni Sepharose is also
available prepacked in His SpinTrap
™
, His GraviTrap
™
, HisTrap
™
and bulk packs to ensure

maximum flexibility in histidine-tagged protein purification.
www.gehealthcare.com/his
GE Healthcare
© 2006 General Electric Company - All rights reserved.
GE Healthcare Bio-Sciences AB, a General Electric Company.
Greater flexibility
in histidine-tagged
protein purification
GE01-06
YYePG Proudly Presents, Thx for Support
www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
425

CONTENTS
CONTENTS continued >>
DEPARTMENTS
431 Science Online
432 This Week in Science
437 Editors’ Choice
442 Contact Science
445 NetWatch
447 Random Samples
467 Newsmakers
482 AAAS News & Notes
542 New Products

543 Science Careers
COVER
A composite image of marine fish and
invertebrate development from egg through
late larval stages. As marine organisms grow
beyond the egg stage, they become capable
of swimming, first vertically for tens of meters,
then horizontally for hundreds to thousands
of meters. These behaviors influence how far
they disperse. See page 522.
Image: C. Guigand
EDITORIAL

435 Getting Serious About Biofuels
by S. E. Koonin
>> Review p. 484; Report p. 506
458
LETTERS
Where Next for Genome Sequencing? P. Raven et al. 468
Thinking About NASA’s Future M. Barratt; A. Hanson;
J. Plescia
Avoiding Climate Change J. E. Hansen
CORRECTIONS AND CLARIFICATIONS 470
BOOKS ET AL.
Breaking the Spell Religion as a Natural Phenomenon 471

D. C. Dennett, reviewed by M. Shermer
Plows, Plagues, and Petroleum How Humans Took 472
Control of Climate
W. F. Ruddiman, reviewed by J. White
EDUCATION FORUM
The Merits of Training Mentors 473
C. Pfund et al.
PERSPECTIVES
Loop Grafting and the Origins of Enzyme Species 475
D. S. Tawfik
>> Report p. 535
Climate Change and Human Evolution 476

A. K. Behrensmeyer
Rising Mountain Ranges 478
M. A. Poage and C. P. Chamberlain
>> Report p. 511
Making Better Ceramic Composites with Ice 479
J. Halloran
>> Report p. 515
Staying Connected in a Turbulent World 480
R. S. Steneck
>> Report p. 522
Volume 311, Issue 5760
473

NEWS OF THE WEEK
Fraud Upends Oral Cancer Field, Casting Doubt on 448
Prevention Trial
Scientists Keep Some Data to Themselves 448
U.S. Beckons Foreigners With Science Fulbrights 449
Measurement Schemes Let Physicists Tiptoe Through the Quanta 451
SCIENCESCOPE 451
Rare Tree Species Thrive in Local Neighborhoods 452
>> Report p. 527
Walk on the Wild Side Yields Supersensitive 452
Chemical Measurements
I Spy a Cold, Little Planet 453

U.K. Backs Off Reclassifying Cannabis as a Dangerous Drug 455
Researchers Caught Between Atoll and a Hard Place 455
Donors Draw Plans to Disburse $2 Billion War Chest for Bird Flu 456
Biobank Ties Cancer Genes to Rare Developmental Syndrome 456
>> Science Express Report by P. Rodriguez-Viciana et al.
Genomic Analysis Hints at H5N1 Pathogenicity 457
>> Science Express Research Article by J. C. Obenauer et al.
NEWS FOCUS
Special: Mental Health in Developing Countries
The Unseen: Mental Illness’s Global Toll 458
Mapping Mental Illness: An Uncertain Topography
China: Healing the Metaphorical Heart 462

A Spoonful of Medicine—and a Steady Diet of Normality 464
YYePG Proudly Presents, Thx for Support
YYePG Proudly Presents, Thx for Support
YYePG Proudly Presents, Thx for Support
YYePG Proudly Presents, Thx for Support
www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
427
CONTENTS continued >>
SCIENCE EXPRESS
www.sciencexpress.org
VIROLOGY
Large-Scale Sequence Analysis of Avian Influenza Isolates

J. C. Obenauer et al.
Sequences from 169 isolates of avian influenza viruses, including many different
strains, reveal that all have a motif located in a nonstructural gene that is necessary
for virulence.
>> News story p. 457
10.1126/science.1121586
MEDICINE
BREVIA: Prions in Skeletal Muscles of Deer with Chronic Wasting Disease
R. C. Angers et al.
Significant amounts of infectious prions are found in the muscles of deer infected with
chronic wasting disease, not just in the nervous tissues as in infected cattle.
10.1126/science.1122864

CHEMISTRY
A Molecular Jump Mechanism of Water Reorientation
D. Laage and J. T. Hynes
Simulations suggest that water molecules can rotate in large jumps as the broken
hydrogen bonds redistribute concertedly, not diffusively, among neighboring
molecules.
10.1126/science.1122154
GENETICS
Germline Mutations in Genes Within the MAPK Pathway Cause
Cardio-facio-cutaneous Syndrome
P. Rodriguez-Viciana et al.
Mutations that functionally alter an intensely studied cellular signaling pathway are

found in young patients with a developmental delay disorder.
>> News story p. 456
10.1126/science.1124642
TECHNICAL COMMENT ABSTRACTS
EVOLUTION
Comment on “Reconstructing the Origin 470
of Andaman Islanders”
M. g. Palanichamy et al.
full text at www.sciencemag.org/cgi/content/full/311/5760/470a
Response to Comment on “Reconstructing the Origin
of Andaman Islanders”
K. Thangaraj et al.

full text at www.sciencemag.org/cgi/content/full/311/5760/470b
REVIEW
CHEMISTRY
The Path Forward for Biofuels and Biomaterials 484
A. J. Ragauskas et al.
>> Editorial p. 435; Report p. 506
BREVIA
ASTRONOMY
The Orbital Period of the Ultraluminous 491
X-ray Source in M82
P. Kaaret, M. G. Simet, C. C. Lang
Periodic brightening of luminous X-ray source may be due to gas

supplied from a bloated star orbiting around a massive black hole.
RESEARCH ARTICLES
PHYSICS
Fermionic Superfluidity with Imbalanced 492
Spin Populations
M. W. Zwierlein, A. Schirotzek, C. H. Schunck, W. Ketterle
Cold clouds of atoms with unequal populations of atomic spins can
maintain a surprisingly robust superfluid state, which requires paired
spins.
>> Report p. 503
MICROBIOLOGY
Community Genomics Among Stratified Microbial 496

Assemblages in the Ocean’s Interior
E. F. DeLong et al.
Community genomic analysis indicates that the microbes near the
surface of the Northern Pacific are mobile and photosynthetic, while
those below 200 meters have pili and synthesize polysaccharides and
antibiotics.
REPORTS
PHYSICS
Pairing and Phase Separation in a Polarized 503
Fermi Gas
G. B. Partridge, W. Li, R. I. Kamar, Y. Liao, R. G. Hulet
Cold clouds of atoms with unequal populations of atomic spins can

maintain a surprisingly robust superfluid state, which requires paired
spins.
>> Research Article p. 492
CONTENTS
492 & 503
CREDIT (BOTTOM): MARTIN ZWIERLEIN/MIT
YYePG Proudly Presents, Thx for Support
Western Blotting
The Protein People
™
FREE
8 Steps to Better Blotting! Log

on to
www.piercenet.com
or call
800-874-3723 to request your
FREE Western Blotting Handbook!

SDS-PAGE
Antibodies & Other Probes
Precise
™
Precast Gels &
Ranger

™
MW Markers
Primary and secondary
antibodies with fluorescent
or enzymatic labels
Membrane
Treatment Products
Enzyme Substrates
MemCode
™
Stains, Qentix
™

Signal Enhancer & Miser
™
Antibody Extender
Pierce SuperSignal
®
, ECL
and 1-Step
™
Substrates
happy blotting.
Smile, and your blot smiles with you! A well-run Western blot
with a strong signal-to-noise ratio will put a smile on any

researcher’s face. Pierce has ALL the products you need to
achieve a happy Western blot.
Detection &
Enhancement Products
StartingBlock
™
, SuperBlock
®
& SEA BLOCK Buffers;
Casein and BSA
Restore
™

Stripping Buffer,
Erase-It
®
Background Eliminator
and CL-XPosure
™
Film
www.piercenet.com/imno22a
Blocking Buffers
Tel: 815-968-0747 or 800-874-3723 • Fax: 815-968-7316
Technical Assistance E-mail: • Customer Assistance E-mail:
© Pierce Biotechnology, Inc., 2006. Pierce products are supplied for laboratory or manufacturing applications only.

1-Step
™
, CL-XPosure
™
, Erase-It
®
, MemCode
™
, Miser
™
, Precise
™

, Qentix
™
, Ranger
™
, Restore
™
, StartingBlock
™
,
SuperBlock
®
and SuperSignal

®
are trademarks of Pierce Biotechnology, Inc.
SuperSignal
®
Technology is protected by U.S. patent # 6,432,662.
For European offices
and distributors,
visit www.perbio.com
For distributors outside
the U.S. and Europe,
visit www.piercenet.com
YYePG Proudly Presents, Thx for Support

www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
429
CONTENTS continued >>
REPORTS
CHEMISTRY
Ethanol Can Contribute to Energy and 506
Environmental Goals
A. E. Farrell et al.
A systems analysis shows that, contrary to some studies, biofuel ethanol
can yield more energy than is required for its synthesis; nevertheless,
better production technologies are needed.
>> Editorial p. 435; Review p. 484

CHEMISTRY
Optical Detection of DNA Conformational 508
Polymorphism on Single-Walled Carbon Nanotubes
D. A. Heller et al.
Metal ions in solution can change the way DNA wraps around a single-
walled nanotube and affect the tube’s fluorescence, providing a sensitive
detector.
GEOCHEMISTRY
Rapid Uplift of the Altiplano Revealed Through 511
13
C-
18

O Bonds in Paleosol Carbonates
P. Ghosh, C. N. Garzione, J. M. Eiler
A paleothermometer based on binding strength between rare C and O
isotopes within carbonates shows that the Bolivian Altiplano rose rapidly
about 8 million years ago.
>> Perspective p. 478
MATERIALS SCIENCE
Freezing as a Path to Build Complex Composites 515
S. Deville, E. Saiz, R. K. Nalla, A. P. Tomsia
Ice is used to template colloidal particles into forming bone and nacre-
like structures and then is easily removed, leaving a contaminant-free
substrate for further reinforcement.

>> Perspective p. 479
NEUROSCIENCE
The Cellular Basis of a Corollary Discharge 518
J. F. A. Poulet and B. Hedwig
Crickets “know” when they hear their own song because the neural
circuit for singing sends a corollary discharge to auditory neurons as well
as to the motor circuit for singing.
SCIENCE (ISSN 0036-8075) is published weekly on Friday, except the last week in December, by the American Association
for the Advancement of Science, 1200 New York Avenue, NW, Washington, DC 20005. Periodicals Mail postage (publication No.
484460) paid at Washington, DC, and additional mailing offices. Copyright © 2006 by the American Association for the Advancement
of Science. The title SCIENCE is a registered trademark of the AAAS. Domestic individual membership and subscription (51 issues): $139
($74 allocated to subscription). Domestic institutional subscription (51 issues): $650; Foreign postage extra: Mexico, Caribbean (surface

mail) $55; other countries (air assist delivery) $85. First class, airmail, student, and emeritus rates on request. Canadian rates with GST
available upon request, GST #1254 88122. Publications Mail Agreement Number 1069624. Printed in the U.S.A.
Change of address: Allow 4 weeks, giving old and new addresses and 8-digit account number. Postmaster: Send change of address to Science, P.O. Box 1811, Danbury, CT 06813–1811. Single-copy sales:
$10.00 per issue prepaid includes surface postage; bulk rates on request. Authorization to photocopy material for internal or personal use under circumstances not falling within the fair use provisions of
the Copyright Act is granted by AAAS to libraries and other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that $18.00 per article is paid directly to CCC,
222 Rosewood Drive, Danvers, MA 01923. The identification code for Science is 0036-8075/83 $18.00. Science is indexed in the Reader’s Guide to Periodical Literature and in several specialized indexes.
452 & 527
ECOLOGY
Scaling of Connectivity in Marine Populations 522
R. K. Cowen, C. B. Paris, A. Srinivasan
Larvae of coastal fish in the Caribbean typically disperse only 10 to 100
kilometers, less than had been thought, yielding more isolated

populations.
>> Perspective p. 480
ECOLOGY
Nonrandom Processes Maintain Diversity 527
in Tropical Forests
C. Wills et al.
Long-term census of trees in tropical forest plots shows that rare species
survive preferentially, leading to more species diversity as forests age.
>> News story p. 452
BIOCHEMISTRY
An Architectural Framework That May Lie 531
at the Core of the Postsynaptic Density

M. K. Baron et al.
A scaffolding protein, assisted by bound Zn
2+
, can assemble into
large sheets and may form a platform for the construction of the
postsynaptic density.
BIOCHEMISTRY
Design and Evolution of New Catalytic Activity 535
with an Existing Protein Scaffold
H S. Park et al.
A process that mimics natural protein evolution converts an enzyme
in the metallohydrolase superfamily into a new family member with

a different catalytic function.
>> Perspective p. 475
GENETICS
A Virus Reveals Population Structure and Recent 538
Demographic History of Its Carnivore Host
R. Biek, A. J. Drummond, M. Poss
An innocuous virus carried by cats shows that recent cougar populations
result from the expansion and merging of small isolated populations
that had been reduced by hunting.
508
CONTENTS
CREDIT (TOP): CHRISTIAN ZIEGLER

YYePG Proudly Presents, Thx for Support
YYePG Proudly Presents, Thx for Support
www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
431
ONLINE
SCIENCENOW
www.sciencenow.org DAILY NEWS COVERAGE
Tick, Tock: Humans Have a Slow Molecular Clock
Recent evolutionary changes may explain why humans mature
slower than other primates.
Bumping Iron No Cure for Hookworms
Anemia caused by infection might actually be made worse with iron

supplementation.
Green Turtles Make a Comeback
Rumors of a South Atlantic population’s demise have been greatly
exaggerated, says new study.
SCIENCE’S STKE
www.stke.org SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT
REVIEW: Inhibition of Immune Responses by ITAM-Bearing
Receptors
J. A. Hamerman and L. L. Lanier
Inhibitory signals propagated through ITAMs may help to set the cell’s
activation threshold.
EVENTS

Plan your travels with this list of meetings, workshops, and conferences
related to cell signaling.
SCIENCE CAREERS
www.sciencecareers.org CAREER RESOURCES FOR SCIENTISTS
GLOBAL: Mind Matters—Driven to Distraction
I. S. Levine
Learn how to deal with personal business, chatty colleagues, and
other workday distractions.
MISCINET: Educated Woman, Ch. 47—The End Is Nearer
M. P. DeWhyse
It’s amazing what a few job offers will do for your morale.
US: The Other Microsoft

J. Kling
For 750 computer scientists at six facilities worldwide, Microsoft
Research is a great place to work.
GRANTSNET: International Grants and Fellowship Index
A. Kotok
Get the latest listing of funding opportunities from Europe, Asia,
and the Americas.
Taking the sting out of oxidants.
Cutting out distractions.
SCIENCE’S SAGE KE
www.sageke.org SCIENCE OF AGING KNOWLEDGE ENVIRONMENT
PERSPECTIVE: Prion 2005—Between Fundamentals and

Society’s Needs
C. Treiber
Conference goes a step further in coordinating and reinforcing
international research activities.
NEWS FOCUS: The Way of the Honeybee
M. Leslie
Bees turn reproductive protein into antioxidant.
Separate individual or institutional subscriptions to these products may be required for full-text access.
www.sciencemag.org
Immune receptor crosstalk.
YYePG Proudly Presents, Thx for Support
fer superfluids to be probed experimentally. Two

studies now address the quantum nature and the
phase transition of interacting Fermi gases of
lithium-6 in which unbalanced populations of two
different spins states are prepared (see the 23
December 2005 news story by Cho). Zwierlein
et al. (p. 492, published online 22 December
2005) examined the condensate fraction and
superfluidity as a function of spin imbalance and
found that superfluidity is remarkably stable
against population imbalance. Partridge et al.
(p. 503, published online 22 December 2005)
detail the spatial structure and polarization of the

mixed spin system.
Tracking a Turn to the Left
Semiconducting single-walled carbon nano-
tubes (SWNTs) exhibit band-gap fluorescence
in the near-infrared, and the dielectric envi-
ronment surrounding the SWNT can modulate
the band-gap energy. Heller et al. (p. 508)
show that this effect is sensitive enough to dis-
tinguish whether DNA wrapped around SWNTs
is in the native B form or has been shifted to
lower energies when the DNA
adopts the left-handed Z form in

the presence of divalent metal ions
such as mercury or cobalt. These
shifts were seen for the several dif-
ferent SWNT species present in a
buffer solution and were used to
detect micromolar levels of Hg
2+
in
highly scattering media such as
whole blood.
How High Was It?
Oxygen isotope fractionation in rain generally

decreases with elevation and temperature, and
Above-Ground Resources
With fossil-fuel supplies steadily waning, recent
research has focused on using plant-derived
materials as a renewable substitute (see the Edi-
torial by Koonin). Ragauskas et al. (p. 484)
review progress in this area, ranging from plant
genetics research for enhancing supply to enzy-
matic and other catalytic methods for breaking
down the biomass into practical fuels and fine
chemical precursors. Some of the economic chal-
lenges and benefits of changing the production

infrastructure on such a large scale are also
addressed. Ethanol is a renewable resource
already in use as a liquid fuel, but its production
from corn and cellulose is energy intensive, and
some analyses have found that the overall
process uses more energy than it creates. Farrell
et al. (p. 506) rigorously analyzed a variety of
relevant investigations, and found that the stud-
ies reporting negative net energy values are
flawed. All of the studies show that current corn
ethanol technologies reduce petroleum use sig-
nificantly relative to gasoline. However, new pro-

duction methods are needed if fuel ethanol is to
reduce greenhouse gas emissions significantly.
Unbalanced Superfluidity
The pairing of fermions lies at the heart of
superconductivity in metals and superfluidity in
helium-3, where the spin populations are gener-
ally equal. Exotic pairing states are expected to
arise for imbalanced spin populations, such as in
the pairing of quark matter in neutron stars and
in strongly magnetized superconductors, but
such systems are difficult to realize experimen-
tally. The availability of cold atom clouds of

mixed atomic spin states has allowed the
crossover regime between Bose-Einstein conden-
sates of molecules and Bardeen-Cooper-Schrief-
this effect can be used to determine changes in
elevation of a region over geological time. How-
ever, changes in the path of storms or the season
of precipitation add great uncertainty. Ghosh et
al. (p. 511; see the Perspective by Poage and
Chamberlain) have developed a thermometer
based on the binding of the temperature-
dependent binding of rate
13

C and
18
O isotopes
in carbonate minerals. This independent esti-
mate of temperature can be related to lapse rate
and other data used to infer elevation of miner-
als that form in soils. An analysis of soil carbon-
ates in Bolivia shows that the high plateau there
rose between 6 and 10 million years ago.
Marine Microbial
Gene Ecology
Depth stratification occurs in the open ocean

not only for large planktonic creatures but also
for microbial plankton. DeLong et al. (p. 496)
sampled and sequenced the microorganisms in
the water column in the North Pacific Subtropi-
cal Gyre with the aim of identifying sequences
that tracked major
environmental fea-
tures. Above 200
meters, distinct photic
zone sequences were
found characteristic
of photosynthetic and

mobile microorgan-
isms requiring iron,
mostly Prochlorococ-
cus (itself dividing
into high- and low-light−tolerant clades) and
Peligabacter, accompanied by Euryarchaea.
Strikingly, photic zone microbes showed evi-
dence of high rates of viral infection. Below
EDITED BY STELLA HURTLEY AND PHIL SZUROMI
27 JANUARY 2006 VOL 311 SCIENCE www.sciencemag.org
432
CREDITS (TOP TO BOTTOM): DEVILLE ET AL./MATERIAL SCIENCES DIVISION,LBNL; DELONG ET AL.

Frozen Forms
When water freezes, it can form hexagonal plates that grow at differ-
ent rates in different directions, and impurities can become trapped at
the water-ice interfaces. Deville et al. (p. 515; see the Perspective by
Halloran) exploited these effects to fabricate porous materials from
concentrated ceramic powder suspensions, which could also be back-
filled with a second material to make composites. The colloidal parti-
cles could then be etched away to leave a porous structure composed
of the second material such as alumina. Using nacre and bone as their
inspirations, the authors show how they can replicate these complex
composite materials.
YYePG Proudly Presents, Thx for Support

www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
433
CREDIT: PARK ET AL.
This Week in Science
200 meters, Chloroflexi, SAR202, Planctomycetales, and Crenarchaea were found, with sequences
suggesting a predominance of “adhesive” microbes that produce pili and synthesize polysaccha-
rides and antibiotics.
Dispersal Patterns of Marine Population
The scale of dispersal among marine populations, or “population connectivity,” has been a notori-
ously intractable problem. Cowen et al. (p. 522, published online 15 December 2005; see the cover
and the Perspective by Steneck) analyzed larval dispersal patterns for a suite of coastal fish species in
the Caribbean Sea, a large region with complex ocean currents. Typical dispersal distances were on

the scale of only 10 to 100 kilometers, and larval movement was a key factor in their dispersal poten-
tial. These robust estimates of population connectivity levels have broad relevance for the spatial
management of marine resources and for understanding the spread of invasive species and disease in
the marine environment.
The Not-So-Quiet Cricket
Our own behavior often generates intense sensory feedback, for example, during loud shouting.
How do we prevent self-induced desensitization of our auditory pathway and distinguish between
self-generated and external sounds? Inhibitory neural signals, called corollary discharges, are sent
from motor to sensory areas in the brain that suppress responses at the precise time that we gener-
ate sensory information. Using singing crickets as a model system, Poulet and Hedwig (p. 518)
identified the cellular basis for a corollary discharge that is indispensable in order to distinguish
self-generated sensory feedback from external information. The corollary discharge interneuron in

the cricket is driven by the song pattern generator and monosynaptically inhibits crucial elements of
the auditory pathway.
Working an Active Site into an Existing Scaffold
Designing enzymes that catalyze industrial reactions is one goal of protein engineering. Although
there has been progress in rational design, it is hindered by a limited understanding of structure-
function relations. Park et al. (p. 535; see the Perspective by Tawfik) have used a strategy that mim-
ics natural evolution to change the function of an
existing protein scaffold. By insertion, deletion,
and substitution of several active-site loops, fol-
lowed by point mutations, they introduced β-lac-
tamase activity into the αβ/βα metallohydrolase
scaffold of glyoxalase II. Extending the process to

other scaffolds may allow creation of new enzyme
activities with practical applications.
Maintaining Different Trees in the Forest
Frequency-dependent models for the maintenance of high species diversity of trees in tropical forests
predict that locally rare species survive preferentially when compared with common species. Wills et al.
(p. 527; see the news story by Pennisi) present a longitudinal survey of species frequencies from a
network of large plots (50 hectares) in seven tropical forest sites in the Old and New Worlds. In all of
the sites, the diversity of recruits into large size classes did increase as the forests aged. Forests suffer-
ing from limited, temporary disturbance should have the ability to recover former levels of diversity,
and selection processes should favor increasing differences between species.
Viruses Reveal the Secrets of the Cougar
Conservationists and research scientists have discussed the idea that pathogens could be used as

genetic tags to record changes in the demography of the host population, but until now have
failed to get to grips with any specific system. Biek et al. (p. 538) have characterized the spatial
and temporal distribution of nonpathogenic feline immunodeficiency virus (FIV) and its natural
host, the cougar, as the cats’ populations recovered from heavy hunting pressure in the first half
of the 20th century. Fast-evolving RNA viruses such as FIV provide insights into what the host
population has been doing on an ecological time scale, despite the slow pace of chance of the
host population.
Conference
Frontiers in Live
Cell Imaging
April 19-21, 200 6
Natcher Conference Center

National Institutes of Health
Bethesda, Maryland, USA
Conference Chairs. YL Wang
(Massach
usetts) and AF Horwitz (Virginia)
Keynote Lectures. "The Future o f Live Cell
Imaging" – RY Tsien (HHMI, UCSD)
"Astronomical Optics and Ligh
t Microscopy:
Common Challenges and Di v e rse
Opportunities" – RRagazzoni
(Osservatorio d i Arcetri, Florence)

Scientific Sessions and Speak
ers:
Probes and Sensors. RM Dickson (Georgia
Tech), KM Hahn (North Carolina), G Marriott
(Wisconsin), A Miyaw a ki (RIKEN), AYTing
(MIT
)
New Directions in Optical Imaging.
E Betzig (HHMI), EGratton (UCIrvine),
C Larabell (LBNL, UCSF), JW Sedat (UCSF),
Wilson (Oxford)
, XS Xie (Harvard)T

Imaging Single Molecules. T Ha (Illinois),
WE Moerner (Stanford), PSchwille (TU
Dresden), NL Tho mpson (North Carolina),
TYanagida (Osaka), X Zhuang (Harvard)
Molecular Dynamics in Single Cells.
R Heald (Berkeley), A Kusumi (K yoto),
JLippin
cott-Schwartz (NIH NICHD),
ED Salmon (North Carolina), SM Simon
(Rockefeller), CM Waterman-Storer (Scripps)
Structural and Cellular Dynamics in
Tissues. JS Condeelis (Albert Einstein),

SEFraser (Caltech), P Fr i edl (Würzburg),
RC Reid (Harvard), EHKStelzer (EMBL)
Extracting Inf
ormation from Images.
GDanuser (Scripps), DL Donoho
(Stanford),
R Eils (German Cancer Research Center),
RF Murphy (Carnegie Mellon)
P
oster Sessions.
New NIH Funding Opportunities. NIH Staff
Information and Registration

www.cellimaging.org
National Institute of General
Medical Sciences
(www.nigms.nih.gov)
Cell Migration Consortium
(www.cellmigration.org)
YYePG Proudly Presents, Thx for Support
©2006 Promega Corporation. 13284-AD-CR
P R OMEGA COR POR ATION • www.prom ega.co m
Measure as few as 10 cells in less than 10 minutes—with a single-step protocol
for quantifying intracellular ATP. From basic research to high-throughput drug
screening, the CellTiter-Glo Assay is judged the best. It enables you to easily

estimate cell number, m
easure cell viability or quantitate cytotoxic effects.
Discriminating scientific minds agree;
C
ellTiter-Glo is the perfect assay.
See for yourself. For a FREE SAMPLE visit: www.promega.com/celltiterglo
Dynamic range from less than
10 cells to over 10,000 cells.
Luminescence (RLU)
Cells per Well
0 100 200 300 400
0

10
20
0
400
800
1,200
1,600
2,000
10k 20k 30k 40k 50k
0
3171MC
YYePG Proudly Presents, Thx for Support

Getting Serious About Biofuels
ALTHOUGH RUDOLF DIESEL IMAGINED THAT HIS EPONYMOUS ENGINE WOULD BE FUELED BY VEGETABLE
oils, the widespread availability of inexpensive petroleum during the 20th century determined other-
wise. The world is now seriously revisiting Diesel’s vision, driven by surging global oil demand, the
geographical concentration of known petroleum reserves, the increasing costs of finding and produc-
ing new reserves, and growing concerns about atmospheric greenhouse gas (GHG) concentrations.
Liquid hydrocarbons are well suited for transport uses because of their high energy density and han-
dling convenience. Although fossil fuels will be required and available for many decades, producing
supplementary fuels from biomass can simultaneously address three important societal concerns with-
out requiring substantial modification of existing vehicles or of the fuel distribution infrastructure: secu-
rity of supply (biofuels can be produced locally in sustainable systems),
lower net GHG emissions (biofuels recycle carbon dioxide that was extracted

from the atmosphere in producing biomass), and support for agriculture.
The 2% of today’s transportation fuels derived from biomass and blended
with fossil fuels are produced either by the fermentation to ethanol of food-
derived carbohydrates (such as cane sugar or cornstarch) or by the processing
of plant oils to produce biodiesel. Unfortunately, current practices based on
food production models do not maximize energy or GHG benefits (because
they use fossil fuels) and are not economically competitive with fossil fuels at
today’s energy prices.* Nevertheless, many nations (including the United
States, European Union, and India) are expecting that some 5% of their road
fuels will be bioderived within the next 5 years.
Credible studies show that with plausible technology developments, bio-
fuels could supply some 30% of global demand in an environmentally

responsible manner without affecting food production. To realize that goal, so-called advanced bio-
fuels must be developed from dedicated energy crops, separately and distinctly from food. This is a
multidisciplinary task in which biologists, agronomists, chemical engineers, fuel specialists, and
social scientists must work to integrate and optimize several currently disjoint activities.
There are major technological challenges in realizing these goals. Genetic improvement of energy
crops such as switchgrass, poplar, and jatropha has barely begun. It will be important to increase the
yield and environmental range of energy crops while reducing agricultural inputs. Plant development,
chemical composition, tolerance of biotic and abiotic stresses, and nutrient requirements are important
traits to be manipulated. The combination of modern breeding and transgenic techniques should result in
achievements greater than those of the Green Revolution in food crops, and in far less time.
The cost of biomass transport determines the supply area of a biofuels processing facility and
thus its scale and economics. But unlike most food crops, there is no need to keep biomass intact.

That means that in-field densification, pelletization, drying, and pyrolysis are among the technology
opportunities to reduce transport costs. Fuel production from the lignocellulosic component of bio-
mass will be a very important improvement. Its particular challenges of chemical recalcitrance
and utilization of the constituent sugars to produce optimal fuel molecules and co-products are not
intractable to current biotechnology. Similarly, process integration comparable to that of a modern
petroleum refinery is a plausible chemical engineering goal.
Intertwined with the technology of large-scale biofuels production are the social and policy
issues. The balances between natural vegetation and cultivation, arable and marginal land use,
mechanized agriculture and employment opportunities, and food and energy crops will be impor-
tant matters of discussion in many different forums. Whatever the outcomes, technologies will have
to be sufficiently robust to accommodate a diversity of needs around the globe.
There is substantial technology “headroom” for advanced biofuels to enhance energy security, reduce

GHG emissions, and provide economical transport. It exists largely because the world’s scientific and
engineering skills have not yet been focused coherently on the challenges involved. It is now time to do
that through a coordination of government, university, and industrial R&D efforts, facilitated by respon-
sible public policies. In the jargon of the petroleum industry, the “size of the prize” is too large to ignore.
—Steven E. Koonin
10.1126/science.1124886
*Brazil is a singular counterexample, where favorable agricultural conditions and a flexible processing infrastructure allow
the majority of the country’s road transport to be powered economically with cane-derived ethanol.
Steven E. Koonin is chief
scientist for BP, London,
UK. He is a theoretical
physicist from the

California Institute of
Technology, Pasadena,
CA, USA, where he also
served as provost from
1995 to 2004. E-mail:

com
www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
435
CREDITS (LEFT TO RIGHT): CALTECH; BRETT HAMPTON/ARS
EDITORIAL
YYePG Proudly Presents, Thx for Support

© Copyright 2005 Thomson. EndNote is
a registered trademark of Thomson.
All trademarks are the property of theirrespectivecompanies.
800-722-1227
•
760-438-5526
Fax: 760-438-5573
rs
EndNote,used by millions of researchers, students, professors,
librarians and writers worldwide, is knownfor introducing
innovative featuressuch as the ability to search online bibliographic
databases, organize references and images, and create instant

bibliographies.With EndNote 9, you can work faster with increased
performance, connectto more data sources worldwide, and share
cu
stomized libraries with colleagues easily. EndNote is easy to use,
easy to learn and isseamlessly compatible with Microsoft
®
Word for
Windows
®
and Mac
®
OSX.There simply is no better way to manage

yourreferences and build instant bibliographies.
Download your Free demoor buy onlinetoday.
www.
endnote.com
EndNote. Where millions of
researchers, librarians and
students begin.
Learnabout new
tools for your
research andpublishing—
Onfolio
™

Organize RSS feeds and Web research
RefViz
™
Visualize references
sciPROOF
™
Proof your manuscript
YYePG Proudly Presents, Thx for Support
firmed this pattern, with SSSS students outper-
forming SSST and STTT students when tested
right away but with the rankings reversed after
1 week. Notably, the repeated-study students

had read the text four times more than the
repeated-test students had, yet they retained
significantly less of the information. — GJC
Psychol. Sci. 17, 249 (2006).
CHEMISTRY
Using Silver to Sugarcoat DNA
One strategy for wiring nanodevices together is
to make the desired connections with DNA
strands, which can then be metallized. For
molecular electronics, it would be useful to cre-
ate metal-free gaps in these wires, and for the
chemical reduction of silver with aldehyde-

modified DNA, such gaps can be created by
binding large proteins to the DNA, which then
act as a resist.
Burley et al. describe an alternative
approach in which modified DNA molecules are
synthesized using Pwo polymerase with modi-
fied dTTPs bearing acetylenic groups. A pro-
tected aldehyde, in the form of a galactose that
has been modified with an azide group, can
then react with the acetylenic side chains via
“click” chemistry. Treatment of a 318–base pair
modified DNA with silver salt solution (Tollens’

www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
437
CREDITS (TOP TO BOTTOM): LONGINO ET AL., BIOTROPICA 37, 670 (2005); PHOTOS.COM
EDITORS’CHOICE
EDITED BY GILBERT CHIN
PSYCHOLOGY
Post-Testanic Potentiation
Tests are an inescapable part of schooling,
though generally less prevalent now than in days
of yore. Two reasons for administering tests are
(i) to assess student achievement and aptitude,
and (ii) to impel students to study, and presum-

ably to learn, the subject matter.
Roediger and Karpicke demonstrate that
the actual taking of a test, as opposed to simply
preparing to take it,
has beneficial conse-
quences. After being
allowed to study a
reading comprehension
passage (preparation
material for the Test of
English as a Foreign
Language), students

either were tested for
retention of the ideas
or allowed a second
study session; students
in both groups were
then tested 5 min, 2
days, or 1 week later. The study-study (SS)
group performed better at first but did not
score as well as the study-test (ST) group on
the later test dates. An expanded protocol con-
reagent) and then with a developer solution
deposited silver nanoparticles on the DNA,

which was confirmed by atomic force
microscopy. — PDS
J. Am. Chem. Soc. 10.1021/ja055517v (2006).
VIROLOGY
HIV Hijacks Exosomes
Understanding the mechanisms by which HIV
infects cells is a key step in developing effective
treatments. Wiley and Gummuluru describe
how immature dendritic cells of the immune
system can capture HIV particles and, soon
after internalization, transmit them to T cells
without themselves becoming infected.

Dendritic cells are one of the first immune
cell types encountered by incoming virus
particles in the mucosa. HIV particles bind to
dendritic cells and are internalized, ending up
in multivesicular endosomes. Dendritic cells
constitutively release some of the internal
vesicles from multivesicular endosomes—
so-called exosomes—into the extracellular
milieu. For dendritic cells that have recently
internalized HIV, it appears that the exosomes
contain intact infectious HIV particles, which
can then infect CD4

+
target T cells. Indeed, the
exosome-associated virus particles are up to
ECOLOGY/EVOLUTION
Taking In the Welcome Mat
Ants are ubiquitous in tropical forests, and they
exhibit a wide variety of nesting and foraging
behaviors that have fascinated naturalists and
ecologists ever since the pioneering of scientific
exploration in the tropics. Despite many
decades of intense study and the high visibil-
ity of ants, Longino has managed to unearth

previously unreported nesting habits in two
endemic Costa Rican ant species in the
genus Stenamma.
These ants build nests in the vertical clay
banks of streams, and the entrance to the nest
is formed by a tunnel through the center of a shal-
low dish sitting atop a pedestal of clay or through a
similarly shaped disk of soil lying on a mound of small
stones. In both types of dwelling, a spherical pebble near
the entrance can be retrieved and used to plug the doorway
in times of danger. Each ant colony maintains several such
nests, but occupies only one at a time. Because of their colo-

nial habit, ants attract predators, and much of their
nesting repertoire revolves around defense. Hence, it
appears that the elaborate constructions of Stenamma may
minimize the chances of attack by marauding hordes of
army ants, which are one of the dominant forces shaping
tropical forest ecosystems. — AMS
Biotropica 37, 670 (2005).
Taking tests to learn.
Nest entrance and Stenamma alas.
HIGHLIGHTS OF THE RECENT LITERATURE
Continued on page 439
YYePG Proudly Presents, Thx for Support

Enhanced RNA Am plification
MessageAmp™ II-
Biotin Enhanced
Single Round aRNA
Amplification Kit
High Yields from Low Inputs.
With just 50 ng of RNA input, a
single round of amplification
yields enough biotin labeled
amplified RNA for Affymetrix
®
GeneChip

®
analysis.
• Enhanced Efficiency –
Single round of amplification from just 50 ng of RNA
• Enhanced Yields –
Upto10X greater yields than leading competitor
• Enhanced Sensitivity –
Highest Present calls of any linear amplification kit
• Enhanced Convenience –
Includes optimized NTP mix containing biotin-UTP
Detect More Genes.
Ambion’s new MessageAmp™

II-Biotin Enhanced kit
consistently produces higher
percent Present calls than the
leading competitor, from 50
ng and just a single round of
amplification.
Ambion, Inc.
U.S. 800-888-8804 • Canada 800-445-1161
fax +1-512-651-0201
For a list of Ambion direct free
phone numbers and distributors
in your country, go to

www.ambion.com/contact
Ambion K.K. (Japan)
tel +81 (0)3-5638-2181
fax +81 (0)3-5638-2182
Ambion (Europe) Ltd
tel +44 (0)1480-373-020
fax +44 (0)1480-373-010
Save up to 40% on Reaction Costs
MessageAmp II-Biotin Enhanced
is a complete single round amplifi-
cation and labeling kit validated for
Af fymetrix

®
GeneChip
®
analysis.
www.ambion.com/prod/ma2biotin
YYePG Proudly Presents, Thx for Support
www.sciencemag.org SCIENCE VOL 311 27 JANUARY 2006
439
17050 Montebello Road
Cupertino, California 95014
Email:
On the Web: www.betchartexpeditions.com

Call for trip brochures &
the Expedition Calendar
(800) 252-4910
We invite you to travel with
AAAS in the coming year.
You will discover excellent
itineraries and leaders, and
congenial groups of like-
minded travelers who share a
love of learning and discovery.
Spring in Sardinia
April 17-29, 2006

Explore archaeological sites and
spectacular countryside from Cagliari
to Cabras, Santa Teresa Gallura to
Aighero as you discover the unique
heritage of Sardinia. $3,450 + air.
Alaska
June 3-10, 2006
Explore southeast Alaska from Sitka
to Glacier Bay and Juneau on board
M/V Sea Lion. $4,390 + free air from
Seattle.
Backroads China

April 14-30, 2006
With FREE Angkor Wat Tour
Join our very talented guide David
Huang, and discover the delights of
Southwestern China, edging
18,000-foot Himalayan peaks,
the most scenic, spectacular,
and culturally rich area in
China. $3,295 + air.
Tibetan Plateau
July 7-25, 2006
Discover Tibet, a place of

fascination for naturalists &
explorers for centuries. $3,295 + air.
Costa Rica/Panama
March 4-11, 2006
Discover the wildlife of the tropical
rainforests and the Osa Peninsula.
Transit the Panama Canal. From
$3,850 including air from Miami.
Copper Canyon, Mexico
April 8-15, 2006
Discover Mexico's greatest canyon
system and the Tarahumara,

famous for their long distance
running games. $2,495 +
2-for-1 air from Tucson.
Aegean Odyssey
May 24–June 7, 2006
Discover the history of
Western Civilization as you
explore Athens, Delphi, Delos,
Mykonos, Santorini, and Knossos,
led by Dr. Ken Sheedy. $3,695
plus 2-for-1 air from JFK.
EDITORS’CHOICE

10-fold more infectious per particle than are
cell-free virus preparations. The remaining den-
dritic cell–associated virus is transported from
multivesicular endosomes to lysosomes and
degraded. This exosomal pathway may explain
how HIV can evade immune destruction even
after having entered the wrong target cell of
the immune system. The relative importance of
this pathway—in comparison to the so-called
infectious synapse, wherein dendritic cells
directly pass HIV on to target T cells—remains
to be established. — SMH

Proc. Natl. Acad. Sci. U.S.A. 103, 738 (2006).
CHEMISTRY
A Guide to Achieving Closure
Epoxides are versatile intermediates in both
enzymatic and laboratory syntheses of complex
organic compounds. These three-membered
rings, composed of an oxygen and two substi-
tuted carbon atoms, are strained and can be
opened readily by scission of a C-O bond. More-
over, the liberated oxygen can attack another
epoxide in the same molecule, forming a larger
and more stable cyclic ether in the process.

In general, an epoxide can be opened via
attack at either carbon, and substituents intro-
duced to favor one path over the other can
prove difficult to remove from the desired
product. Simpson et al. have found that the
tetracyclic core common to the ladder poly-
ethers (marine natural products associated
with red tides) can be prepared efficiently via a
base-catalyzed epoxide-opening cascade that
is guided by trimethylsilyl substituents. Attack
by the oxygen is favored at the silyl-substi-
tuted carbon of the adjacent epoxide, yielding

the naturally occurring six-membered rings
over the kinetically favored five-membered
ones. Furthermore, including a fluoride salt in
the reaction mixture has the happy conse-
quence of eliminating the pendant trimethylsi-
lyl group after each ring closes. — JSY
J. Am. Chem. Soc. 10.1021/ja057973p (2006).
MICROBIOLOGY
A Stomach Full
Until hints to the contrary in several recent stud-
ies, the stomach was conventionally thought of
as being almost as uninhabitable as Mars. Upon

analysis of small-subunit 16S ribosomal RNA
libraries prepared from endoscopy samples col-
lected from 23 individuals, Bik et al. discovered,
living in the human stomach, a zoo of microor-
ganisms of which a significant proportion had
been identified previously as residing in the
mouth and 10% were previously unsuspected
denizens. Indeed, a member of the genus that
includes the notoriously radiation-resistant
Deinococcus radiodurans was found, perhaps
reflecting the tough physicochemical environ-
ment of the stomach. Nineteen of the people

were found to be positive for Helicobacter pylori
but otherwise showed significant variation in
their gastric ecosystems. In all, 128 phylotypes
were discovered, with Streptococcus and Pre-
votella spp. being the most abundant after H.
pylori. The authors proffer the suggestion that
there are multiple ecological niches in the stom-
ach, each with its own demographic, although
currently we can only guess at the roles these
organisms play in health and disease. — CA
Proc. Natl. Acad. Sci. U.S.A. 103, 732 (2006).
APPLIED PHYSICS

Gated Spin Control in Carbon
Nanotubes
The growing fields of molecular electronics and
spin electronics offer the future possibility of
high-density electronic devices, but with
the advantage of avoiding the prob-
lem of how to dissipate the heat that
builds up in such densely packed
structures. Nagabhirava et al. have
combined the two approaches using
a carbon single-walled nanotube (c-
SWNT) to bridge the gap between the

ferromagnetic source and drain con-
tacts. With the gap reduced to
around 10 nm in order to reduce
spin-scattering events along the nan-
otube, they show that the magnitude and sign of
the magnetoresistance, a measure of the flow of
polarized electrons through the carbon nan-
otube in response to an external magnetic field,
can be reproducibly modified from +10% to
–15% by application of a bias on a back gate.
The results provide strong evidence for spin
transport through c-SWNTs and promise for the

spin transistor, a device in which a gate bias con-
trols the flow of spin-polarized current between
the source and drain contacts. — ISO
Reaction scheme yielding the tetrahydropy-
ran core.
CREDIT: SIMPSON ET AL., J. AM. CHEM. SOC. 10.1021/JA057973P (2006)
Continued from page 437
YYePG Proudly Presents, Thx for Support
J.T.Baker
®
is a trademark of Mallinckrodt Baker, Inc.
Mallinckrodt

®
is a trademark of Mallinckrodt Inc.
©2006 Mallinckrodt Baker, Inc. All rights reserved.
Enter the
Mallinckrodt
Baker
“Big Hits”
Sweepstakes.
Win a Classic
Jukebox!
Just enter our “Big Hits”
Sweepstakes, and you could

be the proud owner of a
beautiful, 50s style jukebox.
To enter, visit
www.mallbaker.com/lab
Quality
◆
Choice
◆
Value
Career advice,
insight and tools.
Turn to the experts for the big picture.

Visit www.ScienceCareers.org
Your career is too important to leave to chance. So to find
the right job or get career advice, turn to the experts. At
ScienceCareers.org we know science. And we are committed to
helping take your career forward. Our knowledge is firmly
founded on the expertise of Science, the premier scientific
journal, and the long experience of AAAS in advancing science
around the world. Put yourself in the picture with the experts in
science. Visit www
.ScienceCareers.org.
ALBERT EINSTEIN and related rights ™/© of
The Hebrew University of Jerusalem, used

under license. Represented by The Roger
Richman Agency, Inc., www.albert-einstein.net.
YYePG Proudly Presents, Thx for Support
J.T.Baker
®
is a trademark of Mallinckrodt Baker, Inc. Mallinckrodt
®
is a trademark of Mallinckrodt Inc.
©2006 Mallinckrodt Baker, Inc. All rights reserved.
J.T.Baker
®
and Mallinckr odt

®
.
Two great bra nds. One unique source for chemicals.
Every day, thousands of laboratories around the globe put
their trust in chemicals from Mallinckrodt Baker. Our diverse
product line offers a match for virtually any
application you’re working on. Plus, our
chemicals deliver consistent results…
time after time.
To request copies of the
new Mallinckrodt and
J.T.Baker catalogs, please

visit www.mallbaker.com/lab
Mallinckr odt Baker.
We’ve been a hit with chemistsfor 130 years.
Quality
◆
Choice
◆
Value
YYePG Proudly Presents, Thx for Support
27 JANUARY 2006 VOL 311 SCIENCE www.sciencemag.org
442
John I. Brauman, Chair, Stanford Univ.

Richard Losick, Harvard Univ.
Robert May, Univ. of Oxford
Marcia McNutt, Monterey Bay Aquarium Research Inst.
Linda Partridge, Univ. College London
Vera C. Rubin, Carnegie Institution of Washington
Christopher R. Somerville, Carnegie Institution
George M. Whitesides, Harvard University
R. McNeill Alexander, Leeds Univ.
Arturo Alvarez-Buylla, Univ. of California, San Francisco
Richard Amasino, Univ. of Wisconsin, Madison
Meinrat O. Andreae, Max Planck Inst., Mainz
Kristi S. Anseth, Univ. of Colorado

Cornelia I. Bargmann, Rockefeller Univ.
Brenda Bass, Univ. of Utah
Ray H. Baughman, Univ. of Texas, Dallas
Stephen J. Benkovic, Pennsylvania St. Univ.
Michael J. Bevan, Univ. of Washington
Ton Bisseling, Wageningen Univ.
Mina Bissell, Lawrence Berkeley National Lab
Peer Bork, EMBL
Dennis Bray, Univ. of Cambridge
Stephen Buratowski, Harvard Medical School
Jillian M. Buriak, Univ. of Alberta
Joseph A. Burns, Cornell Univ.

William P. Butz, Population Reference Bureau
Doreen Cantrell, Univ. of Dundee
Peter Carmeliet, Univ. of Leuven, VIB
Gerbrand Ceder, MIT
Mildred Cho, Stanford Univ.
David Clapham, Children’s Hospital, Boston
David Clary, Oxford University
J. M. Claverie, CNRS, Marseille
Jonathan D. Cohen, Princeton Univ.
F. Fleming Crim, Univ. of Wisconsin
William Cumberland, UCLA
George Q. Daley, Whitehead Institute

Caroline Dean, John Innes Centre
Judy DeLoache, Univ. of Virginia
Edward DeLong, MIT
Robert Desimone, MIT
Dennis Discher, Univ. of Pennsylvania
Julian Downward, Cancer Research UK
Denis Duboule, Univ. of Geneva
Christopher Dye, WHO
Richard Ellis, Cal Tech
Gerhard Ertl, Fritz-Haber-Institut, Berlin
Douglas H. Erwin, Smithsonian Institution
Barry Everitt, Univ. of Cambridge

Paul G. Falkowski, Rutgers Univ.
Ernst Fehr, Univ. of Zurich
Tom Fenchel, Univ. of Copenhagen
Alain Fischer, INSERM
Jeffrey S. Flier, Harvard Medical School
Chris D. Frith, Univ. College London
R. Gadagkar, Indian Inst. of Science
John Gearhart, Johns Hopkins Univ.
Jennifer M. Graves, Australian National Univ.
Christian Haass, Ludwig Maximilians Univ.
Dennis L. Hartmann, Univ. of Washington
Chris Hawkesworth, Univ. of Bristol

Martin Heimann, Max Planck Inst., Jena
James A. Hendler, Univ. of Maryland
Ary A. Hoffmann, La Trobe Univ.
Evelyn L. Hu, Univ. of California, SB
Meyer B. Jackson, Univ. of Wisconsin Med. School
Stephen Jackson, Univ. of Cambridge
Daniel Kahne, Harvard Univ.
Bernhard Keimer, Max Planck Inst., Stuttgart
Alan B. Krueger, Princeton Univ.
Anthony J. Leggett, Univ. of Illinois, Urbana-Champaign
Michael J. Lenardo, NIAID, NIH
Norman L. Letvin, Beth Israel Deaconess Medical Center

Olle Lindval, Univ. Hospital, Lund
Richard Losick, Harvard Univ.
Andrew P. MacKenzie, Univ. of St. Andrews
Raul Madariaga, École Normale Supérieure, Paris
Rick Maizels, Univ. of Edinburgh
Michael Malim, King’s College, London
Eve Marder, Brandeis Univ.
George M. Martin, Univ. of Washington
William McGinnis, Univ. of California, San Diego
Virginia Miller, Washington Univ.
H. Yasushi Miyashita, Univ. of Tokyo
Edvard Moser, Norwegian Univ. of Science and Technology

Andrew Murray, Harvard Univ.
Naoto Nagaosa, Univ. of Tokyo
James Nelson, Stanford Univ. School of Med.
Roeland Nolte, Univ. of Nijmegen
Helga Nowotny, European Research Advisory Board
Eric N. Olson, Univ. of Texas, SW
Erin O’Shea, Univ. of California, SF
John Pendry, Imperial College
Philippe Poulin, CNRS
Mary Power, Univ. of California, Berkeley
David J. Read, Univ. of Sheffield
Colin Renfrew, Univ. of Cambridge

Trevor Robbins, Univ. of Cambridge
Nancy Ross, Virginia Tech
Edward M. Rubin, Lawrence Berkeley National Labs
Gary Ruvkun,
Mass. General Hospital
J. Roy Sambles, Univ. of Exeter
David S. Schimel, National Center for Atmospheric Research
Georg Schulz, Albert-Ludwigs-Universität
Paul Schulze-Lefert, Max Planck Inst., Cologne
Terrence J. Sejnowski, The Salk Institute
George Somero, Stanford Univ.
Christopher R. Somerville, Carnegie Institution

Joan Steitz, Yale Univ.
Edward I. Stiefel, Princeton Univ.
Thomas Stocker, Univ. of Bern
Jerome Strauss, Univ. of Pennsylvania Med. Center
Tomoyuki Takahashi, Univ. of Tokyo
Mark Tatar, Brown Univ.
Glenn Telling, Univ. of Kentucky
Marc Tessier-Lavigne, Genentech
Craig B. Thompson, Univ. of Pennsylvania
Michiel van der Klis, Astronomical Inst. of Amsterdam
Derek van der Kooy, Univ. of Toronto
Bert Vogelstein, Johns Hopkins

Christopher A. Walsh, Harvard Medical School
Christopher T. Walsh, Harvard Medical School
Graham Warren, Yale Univ. School of Med.
Colin Watts, Univ. of Dundee
Julia R. Weertman, Northwestern Univ.
Daniel M. Wegner, Harvard University
Ellen D. Williams, Univ. of Maryland
R. Sanders Williams, Duke University
Ian A. Wilson, The Scripps Res. Inst.
Jerry Workman, Stowers Inst. for Medical Research
John R. Yates III, The Scripps Res. Inst.
Martin Zatz, NIMH, NIH

Walter Zieglgänsberger, Max Planck Inst., Munich
Huda Zoghbi, Baylor College of Medicine
Maria Zuber, MIT
John Aldrich, Duke Univ.
David Bloom, Harvard Univ.
Londa Schiebinger, Stanford Univ.
Richard Shweder, Univ. of Chicago
Ed Wasserman, DuPont
Lewis Wolpert, Univ. College, London
EDITOR-IN-CHIEF Donald Kennedy
EXECUTIVE EDITOR Monica M. Bradford
DEPUTY EDITORS NEWS EDITOR

R. Brooks Hanson, Katrina L. Kelner Colin Norman
EDITORIAL SUPERVISORY SENIOR EDITORS Barbara Jasny, Phillip D. Szuromi;
SENIOR EDITOR/PERSPECTIVES Lisa D. Chong; SENIOR EDITORS Gilbert J. Chin,
Pamela J. Hines, Paula A. Kiberstis (Boston), Beverly A. Purnell, L. Bryan
Ray, Guy Riddihough (Manila), H. Jesse Smith, Valda Vinson, David Voss;
ASSOCIATE EDITORS Marc S. Lavine (Toronto), Jake S. Yeston; ONLINE EDITOR
Stewart Wills; ASSOCIATE ONLINE EDITOR Tara S. Marathe; BOOK REVIEW EDITOR
Sherman J. Suter; ASSOCIATE LETTERS EDITOR Etta Kavanagh; INFORMATION
SPECIALIST
Janet Kegg; EDITORIAL MANAGER Cara Tate; SENIOR COPY EDITORS
Jeffrey E. Cook, Harry Jach, Barbara P. Ordway; COPY EDITORS Cynthia
Howe, Alexis Wynne Mogul, Jennifer Sills, Trista Wagoner;

EDITORIAL
COORDINATORS
Carolyn Kyle, Beverly Shields; PUBLICATION ASSISTANTS
Ramatoulaye Diop, Chris Filiatreau, Joi S. Granger, Jeffrey Hearn,
Lisa Johnson, Scott Miller, Jerry Richardson, Brian White, Anita Wynn;
EDITORIAL ASSISTANTS E. Annie Hall, Lauren Kmec, Patricia M. Moore,
Brendan Nardozzi, Michael Rodewald;
EXECUTIVE ASSISTANT Sylvia S.
Kihara;
ADMINISTRATIVE SUPPORT Patricia F. Fisher
NEWS SENIOR CORRESPONDENT Jean Marx; DEPUTY NEWS EDITORS Robert Coontz,
Jeffrey Mervis, Leslie Roberts, John Travis;

CONTRIBUTING EDITORS Elizabeth
Culotta, Polly Shulman;
NEWS WRITERS Yudhijit Bhattacharjee, Adrian Cho,
Jennifer Couzin, David Grimm
, Constance Holden, Jocelyn Kaiser, Richard
A. Kerr, Eli Kintisch, Andrew Lawler (New England), Greg Miller, Elizabeth
Pennisi, Robert F. Service (Pacific NW), Erik Stokstad; Katherine Unger
(intern);
CONTRIBUTING CORRESPONDENTS Barry A. Cipra, Jon Cohen (San
Diego, CA), Daniel Ferber, Ann Gibbons, Robert Irion, Mitch Leslie
(NetWatch), Charles C. Mann, Evelyn Strauss, Gary Taubes, Ingrid
Wickelgren;

COPY EDITORS Linda B. Felaco, Rachel Curran, Sean Richardson;
ADMINISTRATIVE SUPPORT Scherraine Mack, Fannie Groom BUREAUS: Berkeley,
CA: 510-652-0302, FAX 510-652-1867, New England: 207-549-7755,
San Diego, CA: 760-942-3252, FAX 760-942-4979, Pacific Northwest:
503-963-1940
PRODUCTION DIRECTOR James Landry; SENIOR MANAGER Wendy K. Shank;
ASSISTANT MANAGER Rebecca Doshi; SENIOR SPECIALISTS Jay Covert, Chris
Redwood
PREFLIGHT DIRECTOR David M. Tompkins; MANAGER Marcus
Spiegler;
SPECIALIST Jessie Mudjitaba
ART DIRECTOR Joshua Moglia; ASSOCIATE ART DIRECTOR Kelly Buckheit;

ILLUSTRATORS Chris Bickel, Katharine Sutliff; SENIOR ART ASSOCIATES Holly
Bishop, Laura Creveling, Preston Huey;
ASSOCIATE Nayomi Kevitiyagala;
PHOTO RESEARCHER Leslie Blizard
SCIENCE INTERNATIONAL
EUROPE () EDITORIAL: INTERNATIONAL MANAGING
EDITOR
Andrew M. Sugden; SENIOR EDITOR/PERSPECTIVES Julia Fahrenkamp-
Uppenbrink;
SENIOR EDITORS Caroline Ash (Geneva: +41 (0) 222 346
3106), Stella M. Hurtley, Ian S. Osborne, Stephen J. Simpson, Peter Stern;
ASSOCIATE EDITOR Joanne Baker EDITORIAL SUPPORT Alice Whaley; Deborah

Dennison
ADMINISTRATIVE SUPPORT Janet Clements, Phil Marlow, Jill White;
NEWS: INTERNATIONAL NEWS EDITOR Eliot Marshall DEPUTY NEWS EDITOR Daniel
Clery;
CORRESPONDENT Gretchen Vogel (Berlin: +49 (0) 30 2809 3902, FAX
+49 (0) 30 2809 8365);
CONTRIBUTING CORRESPONDENTS Michael Balter
(Paris), Martin Enserink (Amsterdam and Paris), John Bohannon (Berlin);
INTERN Michael Schirber
ASIA Japan Office: Asca Corporation, Eiko Ishioka, Fusako Tamura, 1-8-
13, Hirano-cho, Chuo-ku, Osaka-shi, Osaka, 541-0046 Japan; +81 (0)
6 6202 6272, FAX +81 (0) 6 6202 6271; ;

ASIA NEWS
EDITOR
Richard Stone +66 2 662 5818 () JAPAN NEWS
BUREAU
Dennis Normile (contributing correspondent, +81 (0) 3 3391
0630, FAX 81 (0) 3 5936 3531; );
CHINA REP-
RESENTATIVE
Hao Xin, + 86 (0) 10 6307 4439 or 6307 3676, FAX +86 (0)
10 6307 4358; ;
SOUTH ASIA Pallava Bagla
(contributing correspondent +91 (0) 11 2271 2896; )

www.sciencemag.org
1200 New York Avenue, NW
Washington, DC 20005
Editorial: 202-326-6550, FAX 202-289-7562
News: 202-326-6500, FAX 202-371-9227
Bateman House, 82-88 Hills Road
Cambridge, UK CB2 1LQ
+44 (0) 1223 326500, FAX +44 (0) 1223 326501
SUBSCRIPTION SERVICES For change of address, missing issues, new orders
and renewals, and payment questions: 800-731-4939 or 202-326-
6417, FAX 202-842-1065. Mailing addresses: AAAS, P.O. Box 1811,
Danbury, CT 06813 or AAAS Member Services, 1200 New York Avenue,

NW, Washington, DC 20005
INSTITUTIONAL SITE LICENCES please call 202-326-6755 for any
questions or information
REPRINTS: Author Inquiries 800-635-7181
Commercial Inquiries 803-359-4578
Corrections 202-326-6501
PERMISSIONS 202-326-7074, FAX 202-682-0816
MEMBER BENEFITS Bookstore: AAAS/BarnesandNoble.com bookstore
www.aaas.org/bn; Car purchase discount: Subaru VIP Program
202-326-6417; Credit Card: MBNA 800-847-7378; Car Rentals:
Hertz 800-654-2200 CDP#343457, Dollar 800-800-4000 #AA1115;
AAAS Travels: Betchart Expeditions 800-252-4910; Life Insurance:

Seabury & Smith 800-424-9883; Other Benefits: AAAS Member Services
202-326-6417 or www.aaasmember.org.
(for general editorial queries)
(for queries about letters)
(for returning manuscript reviews)
(for book review queries)
Published by the American Association for the Advancement of Science
(AAAS), Science serves its readers as a forum for the presentation and
discussion of important issues related to the advancement of science,
including the presentation of minority or conflicting points of view,
rather than by publishing only material on which a consensus has been
reached. Accordingly, all articles published in Science—including

editorials, news and comment, and book reviews—are signed and reflect
the individual views of the authors and not official points of view adopted
by the AAAS or the institutions with which the authors are affiliated.
AAAS was founded in 1848 and incorporated in 1874. Its mission is to
advance science and innovation throughout the world for the benefit
of all people. The goals of the association are to: foster communication
among scientists, engineers and the public; enhance international
cooperation in science and its applications; promote the responsible
conduct and use of science and technology; foster education in science
and technology for everyone; enhance the science and technology
workforce and infrastructure; increase public understanding and
appreciation of science and technology; and strengthen support for

the science and technology enterprise.
INFORMATION FOR CONTRIBUTORS
See pages 102 and 103 of the 6 January 2006 issue or access
www.sciencemag.org/feature/contribinfo/home.shtml
SENIOR EDITORIAL BOARD
BOARD OF REVIEWING EDITORS
BOOK REVIEW BOARD
EXECUTIVE PUBLISHER Alan I. Leshner
PUBLISHER Beth Rosner
FULFILLMENT & MEMBERSHIP SERVICES () DIRECTOR
Marlene Zendell; MANAGER Waylon Butler; SYSTEMS SPECIALIST Andrew
Vargo;

SPECIALISTS Pat Butler, Laurie Baker, Tamara Alfson, Karena Smith,
Vicki Linton;
CIRCULATION ASSOCIATE Christopher Refice
BUSINESS OPERATIONS AND ADMINISTRATION DIRECTOR Deborah Rivera-Wienhold;
BUSINESS MANAGER Randy Yi; SENIOR BUSINESS ANALYST Lisa Donovan; BUSINESS
ANALYST
Jessica Tierney; FINANCIAL ANALYST Michael LoBue, Farida Yeasmin;
RIGHTS AND PERMISSIONS: ADMINISTRATOR Emilie David; ASSOCIATE Elizabeth
Sandler;
MARKETING: DIRECTOR John Meyers; MARKETING MANAGERS Darryl
Walter, Allison Pritchard;
MARKETING ASSOCIATES Julianne Wielga, Mary Ellen

Crowley, Catherine Featherston, Alison Chandler;
DIRECTOR OF INTERNATIONAL
MARKETING AND RECRUITMENT ADVERTISING
Deborah Harris; INTERNATIONAL
MARKETING MANAGER
Wendy Sturley; MARKETING/MEMBER SERVICES EXECUTIVE:
Linda Rusk; JAPAN SALES Jason Hannaford; SITE LICENSE SALES: DIRECTOR
Tom Ryan; SALES AND CUSTOMER SERVICE Mehan Dossani, Kiki Forsythe,
Catherine Holland, Wendy Wise;
ELECTRONIC MEDIA: MANAGER Lizabeth
Harman;
PRODUCTION ASSOCIATES Sheila Mackall, Amanda K. Skelton, Lisa

Stanford, Nichele Johnston;
APPLICATIONS DEVELOPER Carl Saffell
ADVERTISING DIRECTOR WORLDWIDE AD SALES Bill Moran
PRODUCT (); MIDWEST Rick Bongiovanni:
330-405-7080, FAX 330-405-7081 •
WEST COAST/W. CANADA B. Neil
Boylan (Associate Director): 650-964-2266, FAX 650-964-2267 •
EAST
COAST/E. CANADA
Christopher Breslin: 443-512-0330, FAX 443-512-0331 •
UK/EUROPE/ASIA Tracey Peers (Associate Director): +44 (0) 1782 752530,
FAX +44 (0) 1782 752531

JAPAN Mashy Yoshikawa: +81 (0) 33235 5961,
FAX +81 (0) 33235 5852
ISRAEL Jessica Nachlas +9723 5449123 •
TRAFFIC MANAGER Carol Maddox; SALES COORDINATOR Deiandra Simms
CLASSIFIED (); U.S.: SALES DIRECTOR Gabrielle
Boguslawski: 718-491-1607, FAX 202-289-6742;
INSIDE SALES MANAGER
Daryl Anderson: 202-326-6543; WEST COAST/MIDWEST Kristine von Zedlitz:
415-956-2531;
EAST COAST Jill Downing: 631-580-2445; CANADA,
MEETINGS AND ANNOUNCEMENTS
Kathleen Clark: 510-271-8349; LINE AD

SALES
Emnet Tesfaye: 202-326-6740; SALES COORDINATORS Erika Bryant;
Rohan Edmonson Christopher Normile, Joyce Scott, Shirley Young;
INTERNATIONAL: SALES MANAGER Tracy Holmes: +44 (0) 1223 326525, FAX
+44 (0) 1223 326532;
SALES Christina Harrison, Svitlana Barnes; SALES
ASSISTANT
Helen Moroney; JAPAN: Jason Hannaford: +81 (0) 52 789
1860, FAX +81 (0) 52 789 1861;
PRODUCTION: MANAGER Jennifer Rankin;
ASSISTANT MANAGER Deborah Tompkins; ASSOCIATES Christine Hall; Amy
Hardcastle;

PUBLICATIONS ASSISTANTS Robert Buck; Natasha Pinol
AAAS BOARD OF DIRECTORS RETIRING PRESIDENT, CHAIR Shirley Ann Jackson;
PRESIDENT Gilbert S. Omenn; PRESIDENT-ELECT John P. Holdren; TREASURER
David E. Shaw; CHIEF EXECUTIVE OFFICER Alan I. Leshner; BOARD Rosina
M. Bierbaum; John E. Burris; John E. Dowling; Lynn W. Enquist; Susan
M. Fitzpatrick; Richard A. Meserve; Norine E. Noonan; Peter J. Stang;
Kathryn D. Sullivan
YYePG Proudly Presents, Thx for Support