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ScienceWeek
SCIENCE-WEEK
A Weekly Email Digest of the News of Science
A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy-makers.
August 18, 2000 -- Vol. 4 Number 33
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Every great scientific truth goes through three
stages. First, people say it conflicts with the Bible.
Next they say it had been discovered before. Lastly
they say they always believed it.
-- Louis Agassiz (1807-1873)
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Contents of this Issue:
1. Biological Engineering:
Analysis of Foot Adhesion in a Beetle
-------------------------------------
An account of a beetle whose primary defensive reflex is to
suddenly produce a strong adhesion to the substrate under it, an
adhesion so strong that predators cannot pry the beetle loose to
attack its vulnerable parts.
2. Anthropology:
Isotope Evidence of Neanderthals as Predators
---------------------------------------------
Analysis of Neanderthal bone isotopes suggests that Neanderthals
were primarily carnivore predators.
(Includes related background material.)
3. Medical Biology:
Link Between Home Pesticide Exposure and Parkinson's Disease
------------------------------------------------------------
Clinical evidence indicates that home and garden exposure to
insecticides and herbicides is associated with a substantial
increased risk of Parkinson's disease.
4. Astrophysics:
On the Cosmic Origin of Deuterium
---------------------------------
Measurements of the deuterium/hydrogen ratio at the Galactic
Center support the idea that most of the baryons in the Universe
are in the form of dark matter, and most of this dark matter is
non-baryonic.
5. Planetary Science:
New Evidence for Recent Underground Water on Mars
-------------------------------------------------
A high-resolution analysis of more than 20,000 orbiter images
suggests the presence of sources of liquid water at shallow
depths beneath the surface of Mars.
6. Materials Science:
Affinities of Peptides for Semiconductor Surfaces and Directed
Nanocrystal Assembly.
--------------------------------------------------------------
A new technique for identifying peptide sequences that bind to
specific semiconductor surfaces may have important applications
in future nanotechnology.
7. In Brief:
New Estimates of Deaths Attributed to Smoking
8. In Focus: On Definitions of Life
9. From the SW Archives:
On Beauty and Truth in Scientific Theories
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
1. BIOLOGICAL ENGINEERING:
ANALYSIS OF FOOT ADHESION IN A BEETLE
The beetles (Coleoptera) are a huge order of insects that
have fascinated entomologists for centuries and that continue to
provide an array of puzzles for evolutionary biologists. The
order of Coleoptera has more than 250,000 described species, more
than any other comparable group, with extreme diversity in size,
form, color, habits, and physiology. Beetles are found almost
everywhere on Earth where any insects are known, and species of
beetles exploit almost every habitat and type of food used by
insects.
A common feature among beetles is for the exoskeleton to
form an unusually hard and close-fitting suit of armor, the
forewings forming hard protective "elytra" under which the
delicate hindwings are normally folded in repose. In addition to
the armor, beetles have developed an enormous variety of special
defenses against predators, including color camouflage, secretion
of noxious chemicals, mimetic appearance, and appendage
retraction that causes the beetle to abruptly fall away from a
substrate ("drop-off reflex"). Here we consider a beetle whose
primary defensive reflex is to suddenly produce a strong adhesion
to the substrate under it, an adhesion so strong that predators
cannot pry the beetle loose to attack its vulnerable parts.
Hemisphaerota cyanea is a small blue beetle, oval-shaped,
the oval approximately 5 millimeters by 4 millimeters, the beetle
found on palmetto plants in the southeastern US. Ordinarily, the
beetle walks or rests with a loose hold on a palmetto frond, but
once disturbed it clamps down with such vigor that considerable
force is required to pry it loose.
... ... T. Eisner and D.J. Aneshansley (Cornell University
Ithaca, US) report a study of the magnitude of force that the
beetle H. cyanea is able to withstand, and of the mechanism by
which it effects defensive anchorage. The authors make the
following points:
1) H. cyanea responds to disturbance by activating a foot
(tarsus) adhesion mechanism by which it secures a hold on the
substrate. Its tarsi are oversized (approximately 0.5 millimeters
across) and collectively bear approximately 60,000 adhesive
bristles, each bristle with two terminal pads, each pad
approximately 3 microns in diameter. While walking, the beetle
commits only a small fraction of the bristles to contact with the
substrate, but when assaulted, the beetle presses its tarsi flat
down, thereby touching ground with all or nearly all of the
bristles. Once so adhered, the beetle can withstand pulling
forces of up to 0.8 grams (approximately 60 times its body mass)
for 2 minutes, and of higher magnitudes, up to more than 3 grams,
for shorter periods.
2) The authors report that adhesion in this beetle is
secured by a liquid, examined and characterized to be a probable
hydrocarbon oil. Analysis of samples of the oil indicate a
mixture of saturated and unsaturated hydrocarbons, of C(sub20) to
C(sub28) chain length, with (Z)-9-pentacosene as the principal
component.
3) The experimental apparatus used to measure adhesive
strength consisted of a platform on which the beetle was
positioned, and which could be subjected to a downward force,
either electronically with a solenoid or by hanging a weight
beneath it. The beetle was connected, by way of a hook attached
to its elytra, to a force transducer positioned directly above
it, the arrangement such that when a downward pull was applied to
the platform, the force was sensed by the transducer and relayed
electronically for visual display on an oscilloscope. The
solenoid permitted application of a linearly increasing force
(100 milligrams per second) to the platform; electronic feedback
from the force transducer insured that the output of the solenoid
remained linear. Such force application was used for measurement
of the adhesive strength of the beetle, defined as the force in
grams at which the beetle became detached from the platform.
Fixed forces in the form of weights hung beneath the platform
were used to determine the adhesive endurance of the beetle,
i.e., the length of time that the beetle withstood pulls of
different magnitude without detaching.
4) The authors suggest "there can be no question that the
extraordinary clinging ability of H. cyanea is defensive,
certainly against ants. The beetle is more persistent in its
clinging than the ant is in its attack, and it can maintain its
hold against forces exceeding by many times its body mass... It
should be noted that the beetle, because of its smooth
hemispheric shape, is intrinsically difficult to grasp for an
ant. By pressing itself down, the beetle provides yet another
measure of protection, because the edge of its body is then no
longer easily graspable and its legs are inaccessibly tucked
away."
5) The authors conclude: "The tarsi of many beetles,
including that of cassidine chrysomelids, bear a terminal claw by
which the beetle can secure anchorage. Measurements that we made
with one cassidine, Metriona bicolor, showed that by hooking
their tarsi into the leaf of their foodplant, these beetles can
withstand pulls upward of 4 to 5 grams, amounting to hundreds of
times their body mass. H. cyanea has tarsal claws, but these are
atrophied, as well they might be, given that they would be
inoperative on the hard surface of the palmetto frond. H. cyanea
has evolutionarily compensated for the atrophy of its claws by
expanding its tarsi and proliferating the bristles. M. bicolor,
with its functional claws, has only approximately 1000 adhesive
bristles per tarsus, in contrast to H. cyanea's 10,000."
-----------
T. Eisner and D.J. Aneshansley: Defense by foot adhesion in a
beetle (Hemisphaerota cyanea).
(Proc. Natl. Acad. Sci. US 6 Jun 00 97:6568)
QY: Thomas Eisner te14@cornell.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
2. ANTHROPOLOGY:
ISOTOPE EVIDENCE OF NEANDERTHALS AS PREDATORS
For many years after the discovery of the first Neanderthal
fossil in 1856, Neanderthal man was considered "a dim-witted
slouching brute". But Neanderthal fossil remains, in fact,
indicate Neanderthal man had a larger brain capacity (average
volume 1500 cubic centimeters) than modern humans (average volume
1360 cubic centimeters), and considering everything known about
the Neanderthals, many anthropologists now view Neanderthal man
as merely a group at one end of the spectrum of modern human
variation.
The Neanderthals have been found only in Europe and the
Middle East in sites dated at 120,000 to 35,000 years ago, and
perhaps up to 300,000 years ago in Spain. Neanderthals were
apparently culturally advanced in many ways. They made a variety
of tools and weapons from wood, bone, and stone, including
delicate arrowheads, hand axes, scrapers for removing fat from
animal skins, and tools for engraving designs on bone and stone.
Neanderthals also apparently made clothes from animal skins, used
fire extensively, lived in caves or bone and skin shelters, and
on the basis of burial remains, apparently had religious beliefs.
The Neanderthals apparently disappeared approximately 35,000
years ago, and whether they died off as a result of environmental
changes (e.g., retraction of the northern ice sheet), were killed
off by modern man, or were interbred with modern man and lost a
separate identity is still unresolved.
... ... M.P. Richards et al (6 authors at 6 installations, UK CA
US FR HR) present new evidence concerning Neanderthal diet, the
authors making the following points:
1) The authors point out that understanding Neanderthal diet
has implications for understanding Neanderthal land use, social
organization, and behavioral complexity. Yet despite the abundant
evidence for successful hunting techniques across Neanderthal
Eurasia, animal remains can indicate only hunting or scavenging
episodes; such remains cannot reveal predominant foods in the
diet over the long term. In contrast, the measurement of ratios
of the stable isotopes of carbon (C-13) and nitrogen (N-15) in
mammal bone *collagen provides an indication of aspects of diet
over the last few years of life, and such isotope evidence can
therefore provide direct information on Neanderthal diet.
2) The authors report that isotope analysis of two
Neanderthal fossils and associated animal fossils from Vindija
Cave, Croatia, indicate that the bulk of the dietary protein of
the Neanderthals came from animal sources. Comparison with animal
remains from this and other sites of similar age indicates that
the Vindija Neanderthal isotope values are similar to those of
other carnivores, and these results are very close to the results
for the earlier Late Pleistocene Neanderthals from France and
Belgium. Therefore, the authors suggest, the emerging picture of
the European Neanderthal diet indicates that although
physiologically the Neanderthals were presumably omnivores, they
behaved as carnivores, with animal protein the main source of
dietary protein. The authors suggest "this finding is in
agreement with the indirect archeological evidence and strongly
points to the Neanderthals having been active predators."
-----------
M.P. Richards et al: Neanderthal diet at Vindija and Neanderthal
predation: The evidence from stable isotopes.
(Proc. Natl. Acad. Sci. US 20 Jun 00 97:7663)
QY: Erik Trinkaus [trinkaus@artsci.wustl.edu]
-----------
Text Notes:
... ... *collagen: The term "collagen" refers to a group
of fibrous proteins of very high tensile strength that form the
main component of connective tissue, cartilage, and bones in
animals.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON THE NEANDERTHALS IN HUMAN EVOLUTION
About 10 kilometers east of Dusseldorf in Germany, in the valley
of the Dussel, there is a little town called Neander. One hundred
and forty-three years ago, in the summer of 1856, some workmen
broke into a cave to get at the limestone inside and discovered a
set of ancient bones. Most of the bones were smashed to bits by
the workmen, but some of the bones, including part of the skull,
survived, and the skeleton was soon recognized by anthropologists
as belonging to an ancient race of men who came to be known as
the Neanderthals. A Neanderthal fossil had actually been
discovered some years earlier in Gibraltar, but not recognized as
such. Neanderthal-like fossils have also been found in France,
Spain, Italy, Yugoslavia, Iraq, China, Java, and Israel. For more
than a century, one of the central questions in paleoanthropology
has been whether modern man evolved from this race -- or was the
Neanderthal a separate branch that became extinct?
... ... I. Tattersall and J.H. Schwartz present a review of
recent research in this area, the authors making the following
points:
1) Although many paleoanthropologists have lately begun to
look favorably on the view that Neanderthals merit species
recognition in their own right as Homo neanderthalensis, at least
as many paleoanthropologists still regard the Neanderthals as no
more than a strange variant of our own species, Homo sapiens.
This difference in viewpoint represents far more than a simple
matter of taxonomic hair-splitting, since if the Neanderthals are
considered as a single species they must be analyzed and
understood on their own terms. In contrast, if the Neanderthals
are merely subspecies variants of ourselves, they can be
dismissed as little more than an evolutionary epiphenomenon, a
minor and ephemeral appendage to the history of Homo sapiens.
2) Recently, Duarte et al (1999) proposed that the skeleton
of a 4-year-old child, unearthed in late 1998 at the 24,500-year-
old site of Lagar Velho in Portugal, represents not merely a
casual result of a Neanderthal/modern human mating, but rather is
the product of several millennia of hybridization among members
of the resident Neanderthal population and the invading Homo
sapiens.
3) In general, "Neanderthals" is the informal designation of
a morphologically distinctive group of large-brained *hominids
who inhabited Europe and western Asia between approximately
200,000 and less than 30,000 years ago. They are sharply
distinguished from modern humans by a wide range of cranial and
*postcranial characteristics, although they do share a number of
derived bony features with other members of the European/western
Asian hominid *clade that diversified in this part of the world
after approximately 500,000 years ago. Subsequent to
approximately 150,000 years ago, the Neanderthals appear to have
been the sole surviving species of this clade.
4) The Neanderthals were apparently highly successful over a
large region for a substantial period of time, but this situation
changed dramatically with the arrival in Europe of the first
modern humans, Homo sapiens. The evidence is that these "Cro-
Magnons" had begun to arrive both in eastern Europe and in the
far northeast of the Iberian Peninsula by approximately 40,000
years ago, and within little more than 10,000 years, the
Neanderthals were gone. The mechanism of their eviction has long
been debated, but there are four main possibilities. The first
and second of these possibilities, that the Neanderthals were
eliminated by the moderns in direct conflict or by indirect
economic competition, both imply the separate species status of
the Neanderthals, as does any combination of these two
possibilities. The alternative possibilities, that the
Neanderthals had simply evolved rapidly into moderns, or that the
genes of the invading moderns simply "swamped" those of the
Neanderthals, both imply some form of species continuity.
5) The authors suggest that the analysis by Duarte et al of
the Lagar Velho child's skeleton is "a brave and imaginative
interpretation" which the majority of paleoanthropologists will
consider unproven. The archeological context of Lagar Velho is
that of a typical *Gravettian burial, with no sign of *Mousterian
cultural influence, and the specimen itself lacks not only
derived Neanderthal characteristics, but also lacks any
suggestion of Neanderthal morphology.
6) the authors conclude: "The probability must thus remain
that this is simply a chunky Gravettian child, a descendant of
the modern invaders who had evicted the Neanderthals from Iberia
several millennia earlier. However, in this contentious and
poorly documented field, any new data are eagerly sought, and
Duarte et al's courageous speculations will doubtless spur much-
needed new research."
-----------
I. Tattersall and J.H. Schwartz: Hominids and hybrids: The place
of Neanderthals in human evolution.
(Proc. Natl. Acad. Sci. US 22 Jun 99 96:7117)
QY: Ian Tattersall [iant@amnh.org]
-----------
Text Notes:
... ... *hominids: In general, any primate in the human family.
... ... *postcranial: In general, this refers to the skeleton
behind the cranium in a quadruped and below the cranium in a
biped.
... ... *clade: A "clade" is a cluster of taxa derived from a
single common ancestor.
... ... *Gravettian: A paleolithic culture in Europe extending
from approximately 30,000 to approximately 22,000 years ago.
... ... *Mousterian: Neanderthals lived by hunting and gathering,
probably in small, nomadic groups, an existence that evidently
required extraordinary strength. Their tool technology involved
the so-called "*Levallois technique" to produce flakes that were
then further worked to yield as many as 60 different implements.
For the Neanderthals, this Middle Paleolithic technology is
termed "Mousterian" after a cave at Le Moustier, France.
Mousterian flakes could be used for many purposes, including
cutting flesh, scraping hides, and working wood.
... ... *Levallois technique: Named after the site in France
where the first examples of such tools were found. This tool-
making technique involves the preparation of a large stone "core"
with a flat upper surface and a convex lower surface. Broad
flakes are detached from the core by striking the core sharply at
an angle on an anvil. The resulting flakes are broad and thin.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 3Sep99
-------------------
Related Background:
ON MODERN HUMAN ORIGINS
The study of human origins, the field called paleoanthropology,
has intrinsic difficulties because of the relative scarcity of
data, but these difficulties are magnified enormously by the
simple fact that paleoanthropology, in essence, represents a
species attempting to reconstruct its own early history. As might
be expected, an objective reconstruction, one without biases and
preconceptions, is far from easy. The human group we call the
"Neanderthals" lived in much of Europe, part of Asia, and the
Middle East between 150,000 to probably less than 30,000 years
ago. Neanderthals were the first fossil humans to be discovered,
and they have long been the focus of anthropological
investigation. More bones of Neanderthals are known than for any
other human-related (hominine) fossil group, including 30 nearly
complete skeletons, so the preoccupation of the anthropology
community with the Neanderthals is perhaps understandable. One of
the important questions concerning the Neanderthals is what
happened to them? Hypotheses have shifted back and forth since
the first discovery in 1856 of Neanderthal bones, with two major
views. One view is that the Neanderthals were the direct
ancestors of modern Europeans. The other view regards the
Neanderthals as a side branch of human evolution, with extinction
as their fate. This latter view is apparently the majority view
in the paleoanthropology community.
... ... G.A. Clark (Arizona State University, US) presents a
review of current research controversies and methods concerning
the transition from early humans to modern humans that apparently
occurred during the period from 50,000 to 10,000 years ago
(Middle-Upper Paleolithic transition). A central question is
whether the transition occurred abruptly or gradually. The author
makes the following points:
1) Insufficient data is only part of the reason the question
of human origins remains unresolved. Researchers in this area
come from various research traditions, and in each of these
traditions different assumptions about the remote human past
determine what is considered relevant data, which questions are
asked of the data, and how the data are interpreted. More data do
not remove the paradigmatic bias implicit within each research
tradition, and in consequence people from the different relevant
fields fail to communicate effectively.
2) The disciplines that contribute to the field (archeology,
human paleontology, and molecular biology) tend to be discovery-
driven and focused on methodology. The result is a common absence
of concern for the logic of inference underlying claims of
knowledge. European archeological studies of modern human origins
are a particularly good example of such epistemological naivete.
These studies are based on a century-old typological systematics
that emphasizes retouched stone tools, coupled with a set of
biases and preconceptions concerning the relationships between
developments in tool-making and developments of cultures.
3) On the surface, the voluminous literature produced by the
debate concerning modern human origins suggests an informed and
sophisticated interdisciplinary research in which data are
absorbed and digested, arguments assimilated, and methodologies
understood, compared, and evaluated. The author suggests "this is
a gross simplification of a much more complex reality."
4) The author concludes: "We are, in effect, consumers of
one another's research conclusions, but we select among
alternative sets of research conclusions in accordance with our
biases and preconceptions. These biases and preconceptions must
be subjected to critical scrutiny. As long as there is no
explicit concern with the logic of inference -- how we know what
we think we know about the past -- there can be no consensus."
-----------
G.A. Clark: Highly visible, curiously intangible.
(Science 26 Mar 99 283:2029)
QY: G.A. Clark [gaclark@asu.edu]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 28May99
-------------------
Related Background:
HUMAN EVOLUTION: THE FATE OF THE NEANDERTHALS
The current consensus in paleoanthropology is that the
Neanderthals were an extinct side-line of human evolution.
European Neanderthals are thought to have diverged from the
lineage that gave rise to modern humans at least 500,000 years
ago. The current view is that approximately 30,000 to 40,000
years ago the Neanderthals were replaced by modern populations,
probably from an ultimately African source. A present debate
concerns how this population replacement occurred.
... ... Paul Mellars, in a short review of a recent conference
(28-30 Aug 1998, Gibraltar, UK) on the Neanderthals, makes the
following points: 1) The current consensus is that in the
southern part of the Spanish peninsula, roughly to the south of
the Ebro valley, the local Neanderthals survived for at least
5000 to 10,000 years after the arrival of modern populations in
the adjacent parts of northern Spain and the Mediterranean coast.
2) The most likely explanation for the prolonged coexistence of
these two populations lies in the ecological differences between
the northern and southern parts of the Iberian peninsula. 3)
Studies of Neanderthal skeletal remains reinforce the conclusion
that the Neanderthals were a divergent lineage that probably made
no contribution to the evolution of anatomically modern humans.
This is consistent with the DNA evidence that the two lineages
separated at least 500,000 years ago, and even longer divergence
times are favored by some researchers. 4) The impression at the
end of the conference was that the Neanderthals were really quite
different from humans -- well adapted to survive in the harsh
glacial environments of Europe, but with distinct anatomical and
behavioral patterns different from their modern human successors.
The author concludes: "The eagerness of some scientists to claim
close kinship with the Neanderthals could come close to denying
that human evolution actually took place."
-----------
Paul Mellars (University of Cambridge, UK)
The fate of the Neanderthals.
(Nature 8 Oct 98 395:539)
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 6Nov98
-------------------
Related Background:
FIRST ANALYSIS OF DNA FROM A NEANDERTHAL BONE
... For more than a century, one of the central questions in
paleoanthropology has been whether modern man evolved from this
race [the Neanderthals] -- or was the Neanderthal a separate
branch that became extinct? Until recently, the primary
laboratory method of investigation of such a question was
analysis of the morphology of bone fragments. This week, the
field of paleoanthropology has apparently crossed an important
watershed, as M. Krings et al (University of Munich, DE;
Pennsylvania State University, US) report the first analysis of
DNA from an extinct human, in this case DNA extracted from the
actual Neanderthal skeleton found near Dusseldorf in 1856. The
key to the investigation was the analysis of mitochondrial rather
than nuclear DNA. Mitochondrial DNA is usually present in
concentrations two or three orders of magnitude greater than
nuclear DNA, and they were able to find enough of it still intact
to amplify with the PCR technique and piece together a total DNA
sequence of 379 base pairs. Comparison of this sequence with
contemporary human sequences leads to the conclusion that
Neanderthal and modern man are separate evolutionary lines, and
that the latter did not evolve from the former. The work will
have to be replicated with other Neanderthal fossils, but most
paleoanthropologists are excited by the results and expect them
to be confirmed. The technology of evolutionary paleoanthropology
has evidently now progressed from caliper measurements of bones
to measurements of bone DNA fragments.
(Cell 11 July 97) (Science-Week 18 Jul 97)
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. MEDICAL BIOLOGY:
LINK BETWEEN HOME PESTICIDE EXPOSURE AND PARKINSON'S DISEASE
Parkinson's disease (also called Parkinson disease) is a
slowly progressive degenerative central nervous system disorder
characterized by decreased movement, muscular rigidity, resting
tremor, and postural instability. The disease was first described
by James Parkinson in 1817 and is now known to be associated with
degeneration of one or more specific regions of the brain
(dopaminergic neuron groups) and resultant loss of neural
connections (projections) from these groups to several important
brain centers. Dopaminergic neurons are nerve cells that use
dopamine as a *neurotransmitter substance. Dopamine is found in
several major areas of the brain, and it is the degeneration of
so-called dopamine neurons that is apparently involved in
Parkinson's disease.
One must distinguish "parkinsonism" from Parkinson's
disease. Parkinsonism is a syndrome (a complex of symptoms; in
this context, a complex of various movement symptoms) that may be
caused by Parkinson's disease, but which may also be caused by
infectious, vascular, pharmacological, toxic, metabolic,
structural, and various degenerative disorders. In other words,
not every individual with parkinsonism has Parkinson's disease.
The major differentiating characteristic is the response to the
drug "*levodopa", which is converted by the body into dopamine.
Individuals with parkinsonism who respond to levodopa treatment
receive a diagnosis of Parkinson's disease. At the present time,
Parkinson's disease is the 4th most common neurodegenerative
disease of the elderly. It affects approximately 1 percent of
people older than 65 years, and 0.4 percent of people between 40
and 65 years.
... ... Joan Stephenson (J. Amer. Med. Assoc., US) reviews a
presentation by Lorene Nelson (Stanford University) at a recent
meeting of the American Academy of Neurology, at which meeting
Nelson presented evidence of a link between home pesticide use
and Parkinson's disease. Stephenson makes the following points:
1) The study involved 496 patients diagnosed with
Parkinson's disease within the Kaiser Permanente Medical Care
Program of Northern California during the years 1994-1995, and
541 age- and sex-matched controls from the same population. Using
in-person structured interviews, a research team collected
information about lifetime history of exposure to home pesticides
(herbicides, insecticides, and fungicides) prior to diagnosis.
2) After controlling for known risk factors such as family
history of the disorder, occupational exposure to pesticides and
herbicides, and cigarette smoking, the investigators found that
home exposure to insecticides and herbicides were associated with
an increased risk of Parkinson's disease. Fungicide exposure was
not linked with an increased risk of the disorder.
3) Individuals with high-level herbicide exposure had a 70
percent increased risk compared with those who were not exposed.
People who used insecticides in the garden showed a 50 percent
increased risk compared to those who had never been exposed to
home pesticides of any type. In-home use of insect-killing
chemicals was associated with a 70 percent increased risk of
Parkinson's disease compared with no use of pesticide.
4) In her report to the American Academy of Neurology,
Lorene Nelson, a neuroepidemiologist, pointed out that the idea
that pesticides might be linked with Parkinson's disease is
biologically plausible, since many pesticides are neurotoxic and
may affect various aspects of central nervous system function,
possibly even resulting in the death of specific nerve cells.
Previous studies have found a substantially increased rate of
Parkinson's disease among city dwellers who gardened for a hobby.
-----------
Joan Stephenson: Exposure to home pesticides linked to Parkinson
disease.
(J. Amer. Med. Assoc. 21 Jun 00 283:3055
QY: Joan Stephenson editors@jama.com
-----------
Text Notes:
... ... *neurotransmitter substance: Neurotransmitters are
chemical substances released at the terminals of nerve axons in
response to the propagation of an impulse to the end of that
axon. The neurotransmitter substance diffuses into the synapse,
the junction between the presynaptic nerve ending and the
postsynaptic neuron, and at the membrane of the postsynaptic
neuron the transmitter substance interacts with a receptor.
Depending on the type of receptor, the result may be an
excitatory or an inhibitory effect on the postsynaptic nerve
cell.
... ... *levodopa: (L-dopa) The biologically active form of
"dopa", which is converted into dopamine. Dopamine = 3,4-
dihydroxyphenylethylamine. Dopa = 3,4-dihydroxypheynylalanine.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
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4. ASTROPHYSICS:
ON THE COSMIC ORIGIN OF DEUTERIUM
The Big Bang theory is the general cosmological model that
proposes that all matter and radiation in the universe originated
in an explosion at a finite time in the past. "Nucleosynthesis",
the creation of elements by nuclear reactions, began when the
temperature of the primitive Universe dropped to approximately
10^(9) degrees kelvin. According to the current model, this
occurred approximately 100 seconds after the Big Bang. A fraction
of protons (hydrogen nuclei) fused with neutrons to form
deuterium (heavy hydrogen) nuclei, and deuterium nuclei could
then fuse to form the two isotopes of helium. Most of the helium
in the Universe was formed at this time, along with deuterium and
lithium, but very little of the heavier elements. According to
the current consensus model, this primeval nucleosynthesis era
ended approximately 1000 seconds after the Big Bang, when the
Universe became too cool for nuclear reactions. Nucleosynthesis
also occurs in stars, but during the early minutes after the Big
Bang, stars did not yet exist.
Central to current cosmological considerations are the
distinctions between the geometries of a "flat" (uncurved;
infinite in both extent and lifetime), "closed" (spherical;
finite in both extent and lifetime), and "open" (*hyperbolic;
infinite and expanding forever) Universe. An important quantity
is the Omega parameter, defined as the ratio of the density of
matter (or energy) in the Universe to the theoretical density
required for flatness. An Omega with a value of greater than 1
implies a closed Universe; a value less than 1 implies an open
Universe; a value equal to 1 implies a flat Universe. The problem
for the past 60 years has thus been to obtain an estimate of the
mass density of the Universe from observations. The current
standard conception is that the geometry of the Universe is flat.
In general, a baryon is a nuclear particle (e.g., a proton)
built from 3 quarks (fundamental particles that combine to make
up protons, neutrons, and mesons). In this context, the term
"dark matter" refers to material whose presence can be inferred
from its effects on the motions of stars and galaxies, but which
cannot be seen directly because it emits little or no radiation.
It is believed that at least 90 percent of the mass in the
Universe exists as some form or dark matter. The term "non-
baryonic dark matter" refers to a hypothetical form of matter not
containing baryons, i.e., without protons or neutrons. Non-
baryonic dark matter has been suggested as a possible component
of the apparently "missing" mass of the Universe.
Since nucleosynthesis in stars destroys rather than creates
deuterium, nearly all the extant deuterium in the Universe is
believed to have been produced during the primeval
nucleosynthesis era. A critical point is that the fraction of
deuterium produced during that era, the ratio deuterium/hydrogen,
should be dependent on mass density, since it is density and
temperature that determine fusion probabilities for protons and
neutrons. Measurements of deuterium/hydrogen ratios, therefore,
may allow estimates of the primeval and present mass density of
the Universe, and help our understanding of the history and
future of the Universe.
The term "astration" refers, in general, to the cycle in
which interstellar material forms into stars, is enriched with
heavy elements as a result of nuclear reactions, and is then
returned to interstellar space via *stellar winds, *planetary
nebulae, or *supernovae.
In astrophysics, a "metal" is any element heavier than
hydrogen or helium, and the abundance of such heavy elements in
celestial objects is termed their "metallicity".
The term "Galactic Center" refers to the central region of
our Galaxy, dense with stars and gas, which may contain a massive
black hole of some millions of solar masses.
... ... D.A. Lubowich et al (7 authors 5 installations, US UK)
present a study of deuterium in the Galactic Center, the authors
making the following points:
1) The authors point out that the Galactic Center is the
most active and heavily processed region of the Galaxy, so it can
be used as a stringent test for the abundance of deuterium (a
sensitive indicator of conditions in the first 1000 seconds in
the life of the Universe). As deuterium is destroyed in stellar
interiors, chemical evolution models predict that its Galactic
Center abundance relative to hydrogen should be 5 x 10^(-12),
unless there is a continuous source of deuterium from relatively
primordial (low-metallicity) gas.
2) The authors report the detection of deuterium (in the
molecule DCN) in a molecular cloud only 10 *parsecs from the
Galactic Center. The data, when combined with a model of
molecular abundances, indicate a D/H ratio of (1.7 +- 0.3) x
10^(-6), which is 5 orders of magnitude larger than the
predictions of evolutionary models with no continuous source of
deuterium. The authors suggest the most probably explanation is
recent infall of relatively unprocessed metal-poor gas into the
Galactic Center. The measured D/H ratio is 9 times less than the
local interstellar value, and the lowest D/H ratio observed in
the Galaxy. The authors suggest the observed Galactic Center
deuterium is cosmological, with an abundance reduced by stellar
processing and mixing, and there is no significant Galactic
source of deuterium.
3) The authors suggest that if all the Galactic deuterium is
indeed primordial, and current astration models are correct, then
the primordial or early Galactic D/H ratio should be 5 x 10^(-5).
For this D/H ratio, standard Big Bang nucleosynthesis models
imply that the baryon density of the Universe is less than the
critical density necessary to close the Universe. The authors
conclude: "Thus the fraction of the critical density contributed
by baryons... requires most of the baryons to be in the form of
dark matter, and most of this dark matter to be non-baryonic."
-----------
D.A. Lubowich et al: Deuterium in the Galactic Center as a result
of recent infall of low-metallicity gas.
(Nature 29 Jun 00 405:1025)
QY: D.A. Lubowich dlubowic@aip.org
-----------
Text Notes:
... ... *hyperbolic: This is a negative curvature, like the
surface of a saddle, and it is sometimes called a "saddle"
Universe. In such a geometry, the sum of the angles of a triangle
is less than 180 degrees. In a spherical (closed) geometry, the
sum of angles is more than 180 degrees; in a flat geometry, the
sum of angles is exactly 180 degrees.
... ... *stellar winds: In general, the term "stellar wind"
refers to the outflow of gas from the surface of a star. The Sun,
for example, loses approximately 10(-14) of its mass each year
via such a wind ("solar wind").
... ... *planetary nebulae: A "planetary nebula" is a nebula
formed when a star (red giant or supergiant) sheds its outer
layers in the last stage of its evolution, leaving a hot core
that ionizes the expunged gas. The size of planetary nebulae
range from approximately the diameter of our solar system to a
light year across. Their lifetime is only about 10,000 years, and
they are all expanding with speeds of approximately 20
kilometers/second. In this context, the term "planetary" has
nothing to do with planets: the term is historical, the first
planetary nebulae discovered so named because they gave the
impression of planetary disks around stars when viewed in small
telescopes.
... ... *supernovae: Supernovae are stellar explosions in which
virtually an entire star is disrupted. The estimate is that in
our own Galaxy approximately 1 supernova occurs every 30 years,
with most of the supernovae obscured by galactic dust.
... ... *parsecs: 1 parsec equals 3.262 light-years, or 30.86 x
10^(12) kilometers.
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Summary & Notes by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
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5. PLANETARY SCIENCE:
NEW EVIDENCE FOR RECENT UNDERGROUND WATER ON MARS
Life as we know it requires water, so the presence or absence of
water on a planet or other astronomical body is an important
issue. As our nearest neighbor, Mars is of most interest, and
sooner or later Mars will be explored, will be visited by
astronauts and researchers who will be able examine the surface
of Mars as the surface of the Earth has been examined. Meanwhile,
our major geological studies of Mars are photographic, and as the
photographic technology improves, new information concerning Mars
continues to become available.
... ... M.C. Malin and K.S. Edgett (Malin Space Science Systems,
US) report a high-resolution (2 to 8 meters/pixel) analysis of
more than 20,000 images relayed by the Mars Orbiter Camera since
1997. The authors make the following points:
1) Mars is now a desert world on which liquid water, because
of ambient conditions, is not likely to be found at the surface:
average temperatures are below 273 degrees kelvin and atmospheric
pressures are at or below water's triple-point vapor pressure of
6.1 millibars. However, in 1972 the Mariner 9 orbiter mission
photographed evidence -- in the form of apparent giant flood
channels and arborized networks of small valleys -- that liquid
water might have been stable in the surface environment at some
time in the past. Analysis of Mars 4 and Mars 5 data, Viking
orbiter images (1976-1980), and observations of flood terrain by
Mars Pathfinder in 1997 supported this conclusion.
2) The Mars Global Surveyor orbiter reached the planet in
1997, and one of the most important early results of the Mars
Orbiter Camera investigation was the absence of evidence for
precipitation-fed overland flow of water. For example, there are
no contributory rills, gullies, and/or small channels associated
with the martian valley networks. Whatever the explanation for
the absence of these features, the possibility that liquid water
flowed across the martian surface in a sizable volume for an
extended period of time, and especially in the recent past, now
seems quite remote.
3) The authors, however, report that relatively young
landforms on Mars, seen in high-resolution images acquired by the
Mars Global Surveyor Mars Orbiter Camera since March 1999,
suggest the presence of sources of liquid water at shallow depths
beneath the martian surface. Found at middle and high martian
latitudes (particularly in the southern hemisphere), gullies
within the walls of a very small number of impact craters, south
polar pits, and two of the larger martian valleys display
geomorphic features that can be explained by processes associated
with ground-water seepage and surface runoff. The relative youth
of the landforms is indicated by the superposition of the gullies
on otherwise geologically young surfaces, and by the absence of
superimposed landforms or cross-cutting features, including
impact craters, small polygons, and wind-formed (eolian) dunes.
The limited size and geographic distribution of the features
argue for constrained source reservoirs.
3) The authors conclude: "Although the available evidence
suggests that the processes that created these landforms acted in
the relatively recent past and could even be contemporary, the
absence of old, degraded, or cratered examples remains a
mystery."
-----------
M.C. Malin and K.S. Edgett: Evidence for recent groundwater
seepage and surface runoff on Mars.
(Science 30 Jun 00 288:2330)
QY: Michael C. Malin, Malin Space Science Systems, PO Box 910148,
San Diego, CA 92191-0148 US.
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Summary by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
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6. MATERIALS SCIENCE:
AFFINITIES OF PEPTIDES FOR SEMICONDUCTOR SURFACES AND DIRECTED
NANOCRYSTAL ASSEMBLY
In biological systems, organic molecules exert control over
the nucleation and mineral phase of a number of inorganic
materials such as calcium carbonate and silica, and also exert
control over the assembly of crystallites and other nanoscale
building blocks into various complex structures required for
biological function. This ability to direct the assembly of
nanoscale components into controlled and sophisticated structures
has motivated intense efforts in materials science to develop
assembly methods that mimic or exploit the recognition
capabilities and interactions found in biological systems. Of
particular interest are methods that could be applied to
materials with interesting electronic or optical properties.
Biological assembly systems, however, have evolved by natural
evolution, and evolution has not selected for interactions
between biomolecules and materials of interest in electronic and
optical engineering. Nevertheless, peptides with limited
selectivity for binding to metal surfaces and metal oxide
surfaces have been successfully "selected" in the laboratory.
... ... S.R. Whaley (5 authors at 2 installations, US) now report
that *combinatorial phage-display libraries can be used to evolve
peptides that bind to a range of semiconductor surfaces with high
specificity, with binding depending on the crystallographic
orientation and composition of the surface. The phage-display
libraries used in this work were based on a combinatorial library
of random peptides containing 12 amino acids. Approximately
10^(9) different peptides were investigated. The experiments used
5 different single-crystal semiconductors. The authors suggest
that since various electronic devices contain structurally
related materials in close proximity, such peptides may find use
in the controlled placement and assembly of a variety of
practically important materials, and thus broaden the scope of
"bottom-up" fabrication approaches.
... ... In a commentary on this work, C.A. Mirkin and T.A. Taton
(Northwestern University, US) state as follows: "In principle,
[the approach of Whaley et al] applies to all materials, so they
may have discovered a way of directly interfacing biomolecules
with any inorganic structure. Moreover, different parts of the
same biomolecule could be designed to selectively recognize and
organize multiple inorganic building blocks, creating structures
with even greater spatial control. Although the work is at a
preliminary stage and practical applications are some way off,
this approach is likely to become a powerful technique for the
design of materials in years to come."
-----------
S.R. Whaley: Selection of peptides with semiconductor binding
specificity for directed nanocrystal assembly.
(Nature 8 Jun 00 404:665)
QY: Angela M. Belcher belcher@mail.utexas.edu
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C.A. Mirkin and T.A. Taton: Semiconductors meet biology.
(Nature 8 Jun 00 405:627)
QY: Chad A. Mirkin camirkin@chem.northwestern.edu
-----------
Text Notes:
... ... *combinatorial phage-display libraries: Bacteriophage
(phage; bacterial virus) is a virus that infects bacteria, the
virus consisting essentially of naked DNA or RNA surrounded by a
complex polyhedral shell ("capsid") composed mainly of
glycoproteins. The smallest phages are approximately 25
nanometers in diameter. In general, a chemical "combinatorial
library" is any system capable of producing a large number of
different substances from a small number of building blocks. In
this context, a "fusion protein" is essentially a protein
expression product resulting from the laboratory fusion of two
genes. In general, a "phage-display library" is a gene library
encoding fusion proteins consisting of a foreign polypeptide
sequence and a coat protein of a particular phage. When cloned,
the engineered phage displays on its surface the foreign
polypeptide sequence fused with the phage coat protein, with each
phage clone randomly expressing a single polypeptide sequence. In
the work discussed here, sequences are selected ("evolved") for a
particular binding characteristic by serially allowing the phages
expressing the various sequences to bind to substrate, separating
phages that bind, allowing selected phages to replicate in their
natural bacterial host, and at exposure to substrate invoking
increasingly stringent binding requirements for selection. After
a number of passes, phage with strong binding properties to the
substrate have been evolved. The genomes (in this case, DNA) of
these strong-binding phages are then sequenced, and the
corresponding fusion-protein foreign peptide sequences
identified.
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Summary & Notes by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
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7. IN BRIEF:
NEW ESTIMATES OF DEATHS ATTRIBUTED TO SMOKING
In the US, an estimated 4 million people will die this year from
tobacco-related illness. The tobacco industry has criticized
estimates by the US Centers for Disease Control and Prevention
(CDC) of the number of deaths in the US attributable to smoking,
stating the estimates are adjusted only for age and sex and lack
adjustment for socioeconomic and behavioral factors. Using data
from the same population-based study used by the CDC, M.J. Thun
et al (3 authors at American Cancer Society, US) report that
after adjusting for age and controlling for education,
occupation, race, alcohol consumption, and various dietary
factors, the overall estimate of deaths attributable to smoking
in the US decreased by only approximately 1 percent from the CDC
estimate.
-----------
M.J. Thun et al: Smoking vs. other risk factors as the cause of
smoking-attributable deaths.
(J. Amer. Med. Assoc. 9 Aug 00 284:706)
QY: Michael J. Thun mthun@cancer.org
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Summary by SCIENCE-WEEK http://scienceweek.com 18Aug00
For more information: http://scienceweek.com/swfr.htm
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8. IN FOCUS: ON DEFINITIONS OF LIFE
"Whatever may be our ultimate conclusions, we may do well to
adopt at least as a temporary expedient the policy of
resignation; with Sir Edward Schaefer we may abandon the attempt
to define life. Perhaps, in doing this, we are following
historical precedents: Geometers have had to resign themselves to
the fact that Euclid's parallel axiom cannot be proved. But as
the reward of this resignation came the new geometries of Bolyai,
Lobatchewski, and Riemann. Enlightened inventors have abandoned
the attempt to build a perpetual motion machine; but again,
resignation is rewarded with the recognition of a fundamental
law, the law of conservation of energy. Physicists, following
Einstein, have abandoned for the time being at any rate, the
attempt to determine experimentally the Earth's absolute motion
through space. The reward has been the theory of relativity, one
of the greatest events in the history of science. The whole
development of science, especially in recent years, is a record
of tearing down barriers between separate fields of knowledge and
investigation. Little harm, and perhaps much gain, can come from
a frank avowal that we are unable to state clearly the difference
between living and non-living matter. This does not in any way
commit us to the view that no such difference exists. For the
present, then, we shall adopt the position that the problem is
essentially one of definition. The question is not so much 'What
is life?' but rather 'What shall we agree to call life?' And the
answer, for the present at any rate, seems to be that it is
immaterial how we define life; that the progress of science and
our understanding of natural phenomena is quite independent of
such a definition."
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Alfred J. Lotka: Elements of Mathematical Biology
(Dover Publications, New York 1956)
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9. FROM THE SW ARCHIVES:
ON BEAUTY AND TRUTH IN SCIENTIFIC THEORIES
There is an old adage, particularly in the physical sciences,
that of two theories arising from the same set of facts, one
theory beautiful and the other theory ugly, the beautiful theory
is more likely to be correct. There are indeed theories that are
difficult or impossible to test that have extensive and expansive
lives because of their aesthetic appeal, and that are discarded
with great reluctance when testing of the theory does eventually
become possible. ... ... J. McAllister (University of Leiden,
NL), in a review of the relation between the aesthetic properties
of scientific theories and their acceptance by the scientific
community, notes that many scientists claim to be able to tell by
means of aesthetic judgment how close a theory is to the truth,
but that in fact it often happens that a theory that is
aesthetically innovative strikes most scientists as ugly when it
is first put forward. For example, Kepler's theory of planetary
motions was initially considered ugly because it involved
ellipses rather than circles; Newton's theory of gravitation was
considered ugly because it postulated action at a distance;
quantum electrodynamics was first considered ugly for relying on
nonstandard mathematical operations for renormalization; and,
indeed, there is the famous rejection of quantum theory by
Einstein because he felt it lacked aesthetic appeal. Noting that
what is called beautiful changes as society and science change,
McAllister concludes the evidence that any aesthetic property of
theories is a sign of truth is at present scarce.
-----------
QY: James W. McAllister mcallister@rullet.leidenuniv.nl
(American Scientist Mar/Apr 1998) (Science-Week 27 Feb 98)
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