ScienceWeek August 25, 2007
Dan Agin
August 25, 2007
Vol. 11 - Number 32
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Do not undertake a scientific career in quest of
fame or money. There are easier and better ways to
reach them. Undertake it only if nothing else will
satisfy you; for nothing else is probably what you
will receive. Your reward will be the widening of
the horizon as you climb. And if you achieve that
reward you will ask no other.
-- Cecilia Payne-Gaposchkin (1900-1979)
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Contents (full text below):
1. Economics: Money Illusion and the Market
2. Neuroscience: The Threatened Brain
3. Geochemistry: The Oldest Fossil or Just Another Rock?
4. Social Science: Sacred Barriers to Conflict Resolution
5. Quantum Physics: On Photons and Waves
6. Materials science: On Complex System Self-Assembly
7. Statistics: Fallacies in Gender-Difference Analysis
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1.
Science 24 August 2007: Vol. 317. no. 5841, pp. 1042 - 1043 DOI:
10.1126/science.1143917
Economics: Money Illusion and the Market
Jean-Robert Tyran
Imagine a consumer who discovers to his surprise that the money
in his bank account and his salary have doubled overnight. Now
suppose that all prices have also doubled overnight. Will this
consumer be happy about being awash with money? Will he feel
richer today and buy more or different goods than he did
yesterday? Not according to standard economic theory. After all,
he has to work the same number of minutes to buy, say, a loaf of
bread, and can therefore afford to buy exactly the same set of
goods as he did yesterday. In short, the boost in purely
"nominal" terms (which inflates all monetary values by the same
factor) should not affect behavior because nothing has changed in
"real" terms (i.e. when taking this inflation properly into
account).
This is the textbook example that economists use to explain the
standard assumption that economic agents are free from money
illusion, i.e., that they think about economic transactions
exclusively in real terms. But now imagine a situation in which
all prices increase by 3.1% and nominal wages increase by, for
example, 2.3% over 1 year. Do people behave the same way in this
situation as in the effectively equivalent case when their
nominal wages fall by about 0.8% at constant prices? Or do some
people perceive these two situations differently because of
different nominal representations?
Despite increasing evidence that thinking in nominal terms is
common and that purely nominal changes can affect individual
choices (1, 2), economists have only started to understand when
and how money illusion affects market outcomes. Economists often
claim that learning and market forces eliminate distortions from
money illusion at the market level if irrational agents are
swiftly selected out of the market (e.g., because they go
bankrupt) or if rational agents can effectively take advantage of
irrational behavior. Yet, recent evidence, from both the
experimental laboratory and the field, suggests that money
illusion can affect market outcomes.
An intriguing example comes from the housing market. Housing
prices have reached unprecedented heights in recent years in
several countries. Sharp run-ups followed by busts are a common
feature of housing prices. Recently, Brunnermeier and Julliard
proposed that a particular type of money illusion, which results
from confusing nominal and real interest rates, could explain
such "housing frenzies" (3). They found that falling nominal
interest rates and inflation increased housing prices, and vice
versa, even when controlling for other factors that affect real
housing prices such as construction costs, housing quality,
property taxes, demographics, and general economic conditions.
The reasoning for this result is as follows. When inflation is
low, monthly nominal interest payments on mortgages are low
compared to the rent on a similar house. Because houses seem
cheap, illusion-prone investors entering the market tend to buy
rather than rent and cause an upward pressure on housing prices
when inflation declines. However, decreasing inflation not only
reduces entrants' current payments on the mortgage but also
increases the real cost of future mortgage payments. Investors
who base their decisions on the salient low nominal mortgage
payments, but ignore the less-visible effect of inflation on the
future real mortgage cost, are prone to an illusion. In a sense,
these investors act like a person who thinks that a car is
cheaper if the down-payment is spread over 4 years rather than 2
years because the monthly payments are lower. Some researchers
have suggested that a similar relationship between inflation and
real asset prices exists in the stock market, and have proposed
money illusion as a cause (4, 5).
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2.
Science 24 August 2007: Vol. 317. no. 5841, pp. 1043 - 1044 DOI:
10.1126/science.1147797
Neuroscience: The Threatened Brain
Stephen Maren
The world is a dangerous place. Every day we face a variety of
threats, from careening automobiles to stock market downturns.
Arguably, one of the most important functions of the brain and
nervous system is to evaluate threats in the environment and then
coordinate appropriate behavioral responses to avoid or mitigate
harm.
Imminent threats and remote threats produce different behavioral
responses, and many animal studies suggest that the brain systems
that organize defensive behaviors differ accordingly (1). On page
1079 of this issue, Mobbs and colleagues make an important
advance by showing that different neural circuits in the human
brain are engaged by distal and proximal threats, and that
activation of these brain areas correlates with the subjective
experience of fear elicited by the threat (2). By pinpointing
these specific brain circuits, we may gain a better understanding
of the neural mechanisms underlying pathological fear, such as
chronic anxiety and panic disorders.
To assess responses to threat in humans, Mobbs and colleagues
developed a computerized virtual maze in which subjects are
chased and potentially captured by an "intelligent" predator.
During the task, which was conducted during high-resolution
functional magnetic resonance imaging (fMRI) of cerebral blood
flow (which reflects neuronal activity), subjects manipulated a
keyboard in an attempt to evade the predator. Although the
virtual predator appeared quite innocuous (it was a small red
circle), it could cause pain (low- or high-intensity electric
shock to the hand) if escape was unsuccessful. Brain activation
in response to the predatory threat was assessed relative to
yoked trials in which subjects mimicked the trajectories of
former chases, but without a predator or the threat of an
electric shock. Before each trial, subjects were warned of the
contingency (low, high, or no shock). Hence, neural responses
evoked by the anticipation of pain could be assessed at various
levels of threat imminence not only before the chase, but also
during the chase when the predator was either distant from or
close to the subject.
How does brain activity vary as a function of the proximity of a
virtual predator and the severity of pain it inflicts? When
subjects were warned that the chase was set to commence, blood
oxygenation level-dependent (BOLD) responses (as determined by
fMRI) increased in frontal cortical regions, including the
anterior cingulate cortex, orbitofrontal cortex, and ventromedial
prefrontal cortex. This may reflect threat detection and
subsequent action planning to navigate the forthcoming chase.
Once the chase commenced (independent of high- or low-shock
trials), BOLD signals increased in the cerebellum and
periaqueductal gray. Activation of the latter region is notable,
as it is implicated in organizing defensive responses in animals
to natural and artificial predators (3, 4). Surprisingly, this
phase of the session was associated with decreased activity in
the amygdala and ventromedial prefrontal cortex. The decrease in
amygdala activity is not expected, insofar as cues that predict
threat and unpredictable threats activate the amygdala (5, 6).
However, activity in these brain regions varied considerably
according to the proximity of the virtual predator and the shock
magnitude associated with the predator on a given trial (see the
figure). When the predator was remote, blood flow increased in
the ventromedial prefrontal cortex and lateral amygdala. This
effect was more robust when the predator predicted a mild shock.
In contrast, close proximity of a predator shifted the BOLD
signal from these areas to the central amygdala and
periaqueductal gray, and this was most pronounced when the
predator predicted an intense shock. Hence, the prefrontal cortex
and lateral amygdala were strongly activated when the level of
threat was low, and this activation shifted to the central
amygdala and periaqueductal gray when the threat level was high.
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3.
Science 24 August 2007: Vol. 317. no. 5841, pp. 1046 - 1047 DOI:
10.1126/science.1146923
Geochemistry: The Oldest Fossil or Just Another Rock?
John M. Eiler
The history of the past 542 million years of life on Earth can be
read from shells, bones, teeth, and leaf casts preserved in the
geological record. For the preceding 4 billion years, more subtle
clues, such as remnants of microbial cells, biomolecules, and the
impressions left by soft-bodied organisms, may be preserved in
sedimentary rocks. But in sediments deposited in the first
billion years of Earth history, these traces have been destroyed
by metamorphism (recrystallization without melting, often
accompanied by reaction and chemical exchange). Here, the only
widely recognized evidence for life comes from measurements of
carbon isotopes in kerogen and graphite (1). Because metabolic
carbon fixation discriminates against 13C, the 13C/12C ratio in
biogenic carbon is ~3% lower than in inorganic carbon. This
signature can be preserved through metamorphic processes that
destroy microfossils and biomolecules.
In 1996, Mojzsis et al. reported the oldest indications of life
on Earth to date (2) in a rock collected from a patch of
intensely folded and metamorphosed quartz-rich rocks on Akilia, a
tiny, barren island off the southwest coast of Greenland. The
authors suggested that these quartz-rich rocks are banded iron
formations (a type of iron-rich marine sediment) deposited more
than 3860 million years ago, and that at least one of them
contains 13C-poor graphite derived from organic matter. Rocks
nearly this old from elsewhere also contain 13C-depleted carbon
(1).
The graphitic, quartz-rich rocks on Akilia have been widely
discussed and intensely scrutinized. Much of this scrutiny has
been critical and has eroded confidence in the original finding
(3-11). But this year, the authors of the original study have
punched back in a pair of papers (12, 13) that address the
critics' most serious charges.
The ages of old, metamorphosed sediments can be constrained
through isotope dating of igneous rocks that cut through, or
contain inclusions of, those sediments. The originally reported
age of the Akilia quartz-rich rocks [(2) and references therein]
was based on the isotopic age of the mineral zircon in such a
cross-cutting granitoid (an igneous rock rich in quartz and
feldspar). But these zircons could be minerals from an unknown
older rock that were entrained in the igneous rock while it was
still liquid (3). It has also been suggested that the intense
deformation undergone by nearly all Akilia island rocks prevents
confident identification of places where granitoids cross-cut
older volcanic or sedimentary rocks (4).
Manning et al. (12) refute the first criticism by showing that
the trace-element contents of the suspect zircons (redated at
3820 to 3840 million years ago) are consistent with them having
crystallized from their host rocks; thus, at least some
granitoids on Akilia very likely are as old as originally
claimed. The authors also strive to address the second critique,
but against long odds: No crosscutting relations between
granitoids and the quartz-rich rocks have been observed. In some
places, granitoids to cross-cut volcanic strata that are part of
the same original set of strata as the quartz-rich rocks,
providing a minimum age for the whole stratigraphic section.
However, even these cross-cutting relations are partially
obscured or otherwise ambiguous. Barring discovery of further
cross-cutting relations, it is difficult to foresee how this part
of the debate can be more definitively resolved.
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4.
Science 24 August 2007: Vol. 317. no. 5841, pp. 1039 - 1040 DOI:
10.1126/science.1144241
Social Science: Sacred Barriers to Conflict Resolution
Scott Atran, Robert Axelrod, Richard Davis
Efforts to resolve political conflicts or to counter political
violence often assume that adversaries make rational choices (1).
Ever since the end of the Second World War, "rational actor"
models have dominated strategic thinking at all levels of
government policy (2) and military planning (3). In the
confrontations between nation states, and especially during the
Cold War, these models were arguably useful in anticipating an
array of challenges and in stabilizing world peace enough to
prevent nuclear war. Now, however, we are witnessing "devoted
actors" such as suicide terrorists (4), who are willing to make
extreme sacrifices that are independent of, or all out of
proportion to, likely prospects of success. Nowhere is this issue
more pressing than in the Israeli-Palestinian dispute (5). The
reality of extreme behaviors and intractability of political
conflicts there and discord elsewhere--in the Balkans, Kashmir,
Sri Lanka, and beyond--warrant research into the nature and depth
of commitment to sacred values.
Sacred values differ from material or instrumental ones by
incorporating moral beliefs that drive action in ways dissociated
from prospects for success. Across the world, people believe that
devotion to core values (such as the welfare of their family and
country or their commitment to religion, honor, and justice) is,
or ought to be, absolute and inviolable. Such values outweigh
other values, particularly economic ones (6).
To say that sacred values are protected from trade-offs with
economic values does not mean that they are immune from all
material considerations. Devotion to some core values, such as
children's well-being (7) or the good of the community (8), or
even to a sense of fairness (9), may represent universal
responses to long-term evolutionary strategies that go beyond
short-term individual calculations of self-interest, yet advance
individual interests in the aggregate and long run. Other such
values are clearly specific to particular societies and
historical contingencies, such as the sacred status of cows in
Hindu culture or the sacred status of Jerusalem in Judaism,
Christianity, and Islam. Sometimes, as with cows (10) or forests
(11), the sacred may represent accumulated material wisdom of
generations in resisting individual urges to gain an immediate
advantage of meat or firewood for the long-term benefits of
renewable sources of energy and sustenance. Political leaders
often appeal to sacred values as a way of reducing "transaction
costs" (12) in mobilizing their constituents to action and as a
least-cost method of enforcing their policy goals (13).
Matters of principle or "sacred honor," when enforced to a degree
far out of proportion to any individual or immediate material
payoff, are often seen as defining "who we are." After the end of
the Vietnam War, successive U.S. administrations resisted Hanoi's
efforts at reconciliation until Hanoi accounted for the fate of
U.S. soldiers missing in action (14). Granted, the issue was
initially entwined with rational considerations of balance of
power at the policy-making level: The United States did not want
to get too close to Hanoi and so annoy Beijing (a more powerful
strategic ally against the Soviet Union). But popular support for
the administration's position, especially among veterans, was a
heartfelt concern for "our boys," regardless of numbers or
economic consequences.
The "who we are" aspect is often hard for members of different
cultures to understand; however, understanding and acknowledging
others' values may help to avoid or to resolve the hardest of
conflicts. For example, at the peaceful implementation of the
occupation of Japan in 1945, the American government realized
that preserving, and even signaling respect for, the emperor
might lessen the likelihood that Japanese would fight to the
death to save him (15).
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5.
Nature 448, 872-873 (23 August 2007) | doi:10.1038/448872a;
Published online 22 August 2007
Quantum Physics: On Photons and Waves
Luis A. Orozco
When measuring photons, it's a case of 'wanted, dead' - catching
them alive is not an option. But we can observe how a
superposition of many photon waves progressively collapses as it
interacts with a beam of atoms.
Earlier this year, a team from the Ecole Normale Supérieure in
Paris recorded jumps of light heralding the birth and death of a
photon trapped in a cavity1. As they describe in this issue
(Guerlin et al., page 889)2, the same researchers have now
performed a similar, more complex trick - recording exactly how a
coherent state of many photons collapses as it is measured.
A measurement process differs fundamentally between the classical
and quantum worlds. In the classical realm, there is no explicit
limitation on a measurement's accuracy. In the quantum domain, by
contrast, accuracy is constrained by the Heisenberg uncertainty
principle: a measurement will produce a definite result, but one
whose value is distributed according to the laws of probability.
What is more, the measured object will itself be fundamentally
altered by the measurement. Thus, the clicking sound produced
when a photon is caught by a detector says two things: yes, a
particle was detected; but sorry, the way you detected it killed
it, and its energy was converted into an electric pulse.
But the quantum world has more subtle states to investigate than
a single photon. Photons, or the probabilistic wavefunctions
associated with them, can add together, or superpose. If they
superpose coherently (in phase), their combined wavefunction
begins to look like a classical wave. This coherent
electromagnetic field is the complex beast whose collapse was
monitored by Guerlin et al.2.
But how did they achieve this feat, given the difficulties of
measuring a quantum object without instantly destroying it? The
authors' 'quantum non-demolition measurements' in a cavity
quantum-electrodynamical (QED) system required profound
understanding of quantum mechanics, continuous theoretical
elucidation of subtle details of cavity QED, and unprecedented
dedication in realizing a simple theoretical model in the
laboratory. This model3 first required the development of a pair
of superconducting mirrors for the walls of the cavity whose
losses are low enough that light remains captured between them
for the length of time it would take the light to circle Earth at
the Equator.
The second pivotal ingredient is individual rubidium atoms in a
'Rydberg' state in which one electron is highly excited. These
atoms are like little planetary systems, with the excited
electrons on a distant orbit around a remote atomic nucleus. They
can oscillate between two different excited states, and the
regularity of this oscillation makes them excellent timekeepers.
The frequency of that oscillation is easily disturbed in the
presence of light - to the extent that it can be used to detect
the presence of a single photon non-destructively1.
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6.
Nature 448, 876-877 (23 August 2007) | doi:10.1038/448876a;
Published online 22 August 2007
Materials science: On Complex System Self-Assembly
David J. Pine
Take silicon, soak in water, add acid - and stir. This simple new
recipe for the self-assembly of complex microstructures belies an
involved sequence of hydrophobic, electrostatic and van der Waals
interactions.
In folding its proteins and constructing its complex membranes,
nature uses self-assembly: bathed in water or another liquid,
tiny building-blocks come together by virtue of their shape and
interactions. As they report in the journal Small, Onoe et al.1
adapt these natural processes for their own designs. They
describe a method for assembling parts just 10 micrometres across
into complex, three-dimensional objects, and go on to build up
chains of interlocking rings. The research is another step
towards the ultimate goal of building electrical or optical
circuits, or even microscopic machines, from components at
micrometre and smaller scales.
The folding of a protein molecule from a long, linear sequence of
linked amino acids is one of nature's more spectacular
demonstrations of self-assembly. In a watery environment, certain
amino acids along the chain can attract each other by various
means - van der Waals attraction, hydrogen bonding or hydrophobic
interactions. Others might repel each other through their
electrical charges or hydrophilic interactions. Geometrical
constraints limit which amino acids along the chain can interact
with each other, so which amino acid occupies a given position in
the chain is crucial to the final topology and shape of the
protein. Geometry thus conspires with attractive and repulsive
forces to fold the amino-acid chain into the complex shape that
gives a protein its particular function.
Simpler examples of self-assembly also abound. Soap molecules, or
'surfactants', are one. These consist of a water-loving
(hydrophilic) head connected to a water-hating (hydrophobic)
tail. When placed in water, the hydrophobic tails of different
surfactant molecules bunch together to form the core of a sphere,
with their hydrophilic heads at the surface. This way, both heads
and tails get to live in their desired surroundings. While
arranging themselves, the tails often corral a particle of dirt,
isolating it so that it can be washed away.
Onoe and colleagues1 exploit the same ideas of self-assembly,
except that their building-blocks are not organic molecules, but
particles of silicon formed into slightly tapered cylinders 10
microm in diameter at the wider end. This wider base is coated
with a layer of hydrophobic molecules, whereas a thin layer of
silicon dioxide (SiO2) forms naturally through oxidation of the
remaining surfaces in air. When placed in water with a nearly
neutral pH of 6.5, the SiO2 surfaces become negatively charged
and repel each other when two particles come close. The
hydrophobic bases of two cylinders, by contrast, can avoid
contact with the water by pairing up flush against each other.
And this is exactly what happens when the water is stirred to
bring particles close to one another: the hydrophobic surfaces
pair up to form barrel-shaped 'dimers' (Fig. 1a).
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7.
Nature 448, 849 (23 August 2007) | doi:10.1038/448849a; Published
online 22 August 2007
Statistics: Fallacies in Gender-Difference Analysis
Claire Ainsworth
Unsound analyses are common in gender genetics papers.
Most claims that men and women are affected differently by
disease-associated gene variations are poorly founded. A team of
researchers has found that the data supporting such claims are
often poorly analysed statistically or come from studies that
were not adequately designed to show these links.
"The abysmal standard of statistical analysis in much of genetic
epidemiology is little short of scandalous," says David Balding,
professor of statistical genetics at Imperial College London, UK,
who was not involved in the study. "This paper reveals an entire
industry of prominently reported results that are largely
unjustified and probably mostly false."
John Ioannidis and his colleagues at the University of Ioannina
School of Medicine in Greece evaluated 432 claims in 77 research
papers (N. Patsopoulos et al. J. Am. Med. Assoc. 298, 880-893;
2007). The team applied a set of criteria to determine whether
the papers' authors had performed the correct analysis, such as
comparing like with like, and had taken steps to show that the
association was not due to chance. Worryingly, only 12.7% of
claims satisfied these criteria. "There is quite a gap between
what should have been done and what the journals and reviewers
should have asked for, compared with what the authors did," says
Ioannidis.
Many studies were not designed to test for a link between sex and
gene variants, with researchers trying to extract associations
from their data after the fact. Sample sizes were at least ten
times smaller than they needed to be to yield statistically
robust results, Ioannidis adds.
"This paper tells us that we don't have a clue whether gender is
a real biomarker for any of the clinical areas assessed," says
Howard McLeod, director of the UNC Institute for Pharmacogenomics
and Individualized Therapy in Chapel Hill, North Carolina.
"Gender, as well as age and race, are crude ways of understanding
the complex factors regulating clinical effect," he adds.
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