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ScienceWeek
SCIENCE-WEEK
A Weekly Digest of the News of Science
July 3, 1998
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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. On Science and the Control of Aids
2. On Black Holes
3. Mars Pathfinder Mission: A Summary
4. On the Origin of Hydrothermal Megaplumes
5. On Polymer Rheology
6. Attraction Between Like-Charged Spheres in a Charged Pore
7. Origin of Life: A Model for the Universal Ancestor
8. On Prokaryotes in the Biosphere
9. Parenting and Survival in Anthropoid Primates
10. On Alcohol in the Western World
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1. ON SCIENCE AND THE CONTROL OF AIDS
Varmus and Nathanson (National Institutes of Health, US), in an
editorial in the journal *Science* assessing current efforts to
control AIDS, make the following points: 1) For the first time in
the history of the human immune deficiency virus (HIV) epidemic,
the US death rate attributable to AIDS has dramatically declined.
The explanation is almost entirely based on science: a logical
sequence of discoveries and tests has led to highly effective
antiviral therapies. 2) Qualifying this success are the
following: a) many drug failures; b) the expense of the drug
regimens; c) the continued high rate of viral transmission in the
US (especially among minority groups); d) the growing magnitude
of the epidemic in the poorer parts of the world (where the
successful drugs are simply unaffordable); e) the difficulties of
developing an HIV vaccine. 3) The progress made against HIV
exemplifies the potency of molecular medicine: disclosure of
viral genes, analysis of viral dynamics and pathogenesis, and
development of protein-targeted drugs. 4) The success in
developing treatments for AIDS has affirmed the vigor of the
biomedical research establishment, the system in which federal
agencies and private foundations largely fund investigator-driven
basic science, while the pharmaceutical industry and
biotechnology companies undertake most drug discovery and
development. 5) Developing a safe and effective vaccine is
probably the single most important long-term goal of current
research efforts. But a vaccine that fully prevents the
establishment of HIV infection is a daunting and perhaps
impossible goal. Even development of a vaccine that offers
significant reduction of disease and mortality appears to be a
difficult task, judging from the limited progress so far. 6) It
may be necessary to use vaccines with only modest efficacy while
development of more effective immunogens continues. 7) The
authors conclude: "The still expanding global dimensions of AIDS
are likely to be checked only if science can succeed as admirably
with vaccines as it has done with therapies."
QY: Harold Varmus, NIH, Bethesda, MD 20892-0148
(Science 19 Jun 98 280:1815) (Science-Week 3 Jul 98)
-------------------
Related Background:
ESTIMATED 20 MILLION INFECTED WITH AIDS IN SUB-SAHARAN AFRICA
There is perhaps too much of a tendency in many quarters to think
of a plague only as a state of affairs in which people drop dead
in expensive restaurants and get hauled away in trucks containing
piles of bodies. Our current plague, although not as dramatic as
some plagues of the past, is no less an international calamity.
The United Nations AIDS Program recently released a report
containing the following:
-- In 1997, 5.8 million people worldwide were newly infected with
HIV.
-- The number of new HIV infections this year rose 9% over 1996.
-- The total number of infected adults is now a little under 30
million, about 1% of the world's adult population.
-- This year, the total number of people infected with HIV
increased by 13%
-- More than 20 million people in sub-Saharan Africa are infected
with HIV, which is 7% of that adult population.
-- This year, 2.3 million people worldwide will have died of
AIDS, the consequent stage of HIV infection.
-- In South and Southeast Asia, 6 million people are infected
with HIV.
-- In Latin America, 1.3 million people are infected with HIV.
-- In North America, 860,000 people are infected with HIV.
-- In Western Europe, 150,000 people are infected with HIV.
(Nature 27 Nov 97) (Science-Week 19 Dec 97)
2. ON BLACK HOLES
In an essay on black holes, Martin Rees (Cambridge University,
UK) makes the following points: 1) Black holes are expected in
many theories of gravity, not just in Einstein's general
relativity theory. Indeed, black holes were in essence
conjectured more than 200 years ago, when in 1783 John Michell
presented a paper to the Royal Society of London concerning the
effect of gravity on light. 2) But the term "black hole" was not
coined until 1968, when John Wheeler described how an infalling
object "becomes dimmer millisecond by millisecond... light and
particles incident from outside... go down the black hole only to
add to its mass and increase its gravitational attraction." 3)
Viewed from the outside, black holes are exactly standardized
objects -- no traces persist to distinguish how a particular hole
formed or what kind of objects it swallowed. The combined efforts
of several theorists had proved this result by the early 1970s.
4) The paradoxes within a black hole are as fundamental, and as
far-reaching in their implications, as the puzzles that
confronted Einstein's contemporaries at the beginning of the 20th
century and triggered the development of relativity and the
quantum theory. Black holes preclude space and time being a
seamless continuum, and they may be gateways to other space-times
sprouting from our own. The existence of black holes not only
allows, but may even require, a broadening cosmic perspective
that envisions our universe as just a member of an ensemble. 5)
Ad hoc explanations for observed cosmic phenomena that do not
involve black holes can be devised, but they are generally too
contrived to be convincing, and black holes remain the most
plausible endpoints for certain types of stellar evolution. 6)
The evidence for supermassive extra-Galactic black holes is now
even more compelling than for black holes within our own galaxy.
In the centers of some galaxies, gas and stars are evidently
swirling into a black hole weighing as much as millions or even
billions of Suns. They manifest themselves as quasars or as
intense sources of cosmic radio emission. These supermassive
black holes have diameters as large as our solar system. 7) Rees
concludes with a quotation from the astrophysicist Roger Penrose:
"It is ironic that the astrophysical object which is the
strangest and least familiar, the black hole, should be the one
for which our theoretical picture is most complete."
QY: Martin Rees, King's College, Cambridge University, UK.
(Astronomy July 1998) (Science-Week 3 Jul 98)
-------------------
Related Background:
ON BLACK HOLES AS REAL ASTRONOMICAL OBJECTS
If the terminal stages of star death leave a remnant star mass
greater than 3 solar masses, the ultimate gravitational collapse
will produce a "black hole", a relativistic singularity. A black
hole is a localized region of space from which neither matter nor
radiation can escape. The Uhuru Satellite (uhuru is the Swahili
word for "freedom"), launched in 1970 and operating until 1973,
was the first artificial satellite for x-ray astronomy, producing
a catalogue containing 339 x-ray sources. ... ... G. Bisnovatyi-
Kogan (Space Research Institute Moscow, RU) reviews the papers
presented at a recent international conference on black holes
(11-17 January 1998, S.N. Bose National Centre for Basic Sciences
Calcutta, IN). This was perhaps the first conference devoted to
black holes as real astronomical objects. The first indications
for the actual existence of black holes came from x-ray observ-
ations of the UHURU satellite, but black holes were predicted
theoretically 60 years ago, and in fact Laplace in 1796 already
noted that light cannot leave a star when its free-fall velocity
as determined by the star's mass and radius is larger than the
speed of light as we have measured it. At the present time, if
the apparent mass of a discovered compact object exceeds the
limiting mass, and if we hold the theory of general relativity to
be valid, we say we have discovered a black hole. There are now
40 such objects that have been identified, 30 of them super-
massive objects each containing millions and billions of solar
masses and surrounded by dense stellar clusters in the strong
gravity of a black hole.
QY: G. Bisnovatyi-Kogan (gkogan@mx.iki.rssi.ru)
(Science 27 Feb 98) (Science-Week 20 Mar 98)
-------------------
Related Background:
GALACTIC BLACK HOLES: RADIATION AND PLASMA CONSUMPTION
If the terminal stages of star death leave a remnant star mass
greater than 3 solar masses, the ultimate gravitational collapse
will produce a black hole, a relativistic singularity, a mass
that has collapsed to such a small volume that its gravity
prevents the escape of all radiation. The boundary of the black
hole is called the "event horizon", because any event within the
boundary is invisible outside, the invisibility resulting from
the fact that no radiation can escape to be detected. The radius
of the black hole depends upon how much matter has fallen into
the region; it is called the "Schwarzchild radius", and it is
usually a few kilometers. In physics, a plasma is a fully ionized
gas consisting of free electrons and positive ions, the plasma
formed at high temperatures such as the temperatures in stars or
by photoionization (e.g., in interstellar gas). R. Genzel (Max
Planck Inst. for Extraterrestrial Physics, DE), in a short review
of galactic center black holes, suggests there is probably a
massive black hole at the center of our own galaxy, and that the
apparently low radiation of such galactic center black holes may
be due to plasma effects involving the conversion of gravitat-
ional energy into thermal energy of ions rather than into
radiation produced by electrons.
QY: Reinhard Genzel
(Nature 1 Jan 98) (cf. Narayan et al, Astrophys. J. 10 Jan 98)
(Science-Week 16 Jan 98)
-------------------
Related Background:
ANALYSIS OF A SUPERMASSIVE BLACK HOLE ACCRETION DISK
Matter with high angular momentum attracted to a black hole does
not fall directly into the black hole but forms a rapidly
spinning "accretion disk" around the black hole, and this can
produce considerable energy, particularly at x-ray wavelengths,
as the accretion disk loses angular momentum and spirals inward.
The dynamical evolution and fate of such accretion disks has been
the subject of much theoretical analysis and model simulations.
Supermassive black holes are black holes with masses of the order
of 10^(6) to 10^(9) solar masses and are believed to occupy the
centers of some galaxies. The term "iron-line emission" refers to
emission at the frequency characteristic (the "line") of iron
atoms in transit from excited states to lower energy states.
Because of the nature of nucleosynthesis -- the fusion reactions
in stars -- the cores of many stars consist of iron. Bromley et
al (3 authors at 3 installations, US RU) present an analysis of
the iron-line emission of galaxy MCG-6-30-15 that is independent
of parametric details of the disk model used, and they deduce
that from this galaxy there are being observed emissions from
gravitationally bound material in the strong-field region of a
supermassive black hole.
QY: B.C. Bromley
(Nature 1 Jan 98) (Science-Week 16 Jan 98)
3. MARS PATHFINDER MISSION: A SUMMARY
One year has passed since the Mars Pathfinder mission, and
various assessments of the mission have recently appeared. Jim
Bell (Cornell University, US), a member of the Mars Pathfinder
science team, reviews the mission with a particular focus on the
question of whether Pathfinder, as an instance of "faster and
cheaper" solar system exploration, also produced "better"
science. Bell makes the following points: 1) The Pathfinder
mission was a phenomenally successful demonstration of new
technologies and sheer engineering nerve -- a high-stakes gamble
that traded high risk for low cost and hit the jackpot. 2)
"Better" data means higher-quality data, not just more data, and
data that provides more definitive results than previous data.
The mission satisfies this definition of "better", and is viewed
by most scientists involved as a major scientific success in its
own right, and not merely a test flight. 3) The measurements
performed by Pathfinder fall into 5 categories: geology,
mineralogy/geochemistry, surface-material properties, atmospheric
science, planetary rotational dynamics. 4) Geology: Many of the
features observed at the landing site area are similar to
formerly flooded plains on Earth. But other processes involving
wind, volcanism, or impact could be responsible for many of the
observed landforms. A major geologic finding was that wind has
been an extremely important, and perhaps dominant, geologic
process on this part of Mars, and may have been the only major
agent of change for a huge span of time, conceivably several
billion years. 5) Mineralogy and geochemistry: The most striking
result was the finding by the Sojourner Alpha Proton X-Ray
Spectrometer that most of the rocks analyzed have a high silicon
content, higher than that of the Martian meteorite samples
gathered on Earth. If these Pathfinder site rocks are indeed
volcanic, there constituents suggest a more active subsurface
volcanic system than previously proposed. It was also found that
the dust of Martian dust storms has a high magnetic component,
and the data support the conclusion that the magnetic dust grains
consist at least partly of the iron oxide mineral maghemite. This
mineral is rare on Earth, usually forming in iron-rich water
solutions, which suggests that Martian dust may have formed in a
much wetter and perhaps warmer environment than exists today. 6)
Surface materials: The Pathfinder evidence indicates the
uppermost surface layer of soil at the site is extremely fine-
grained, like flour, consisting of particles only a few microns
in diameter. This top layer was probably formed by the gentle
settling of atmospheric dust. 7) Rotational dynamics: The data
from Pathfinder appear most consistent with Mars possessing a
relatively large metallic core, from 1300 to 2000 kilometers in
radius, which is approximately 40 to 60 percent of the overall
radius of the planet. In contrast, Earth's core occupies only 19
percent of its radius. 8) Atmospheric science: The Martian
atmosphere is complex and dynamic. For example, temperature at
the landing site increased by more than 20 degrees centigrade
after sunrise, and in the morning the air at the surface was more
than 10 degrees centigrade warmer than the air only a meter off
the ground. 9) The mission returned nearly 300 megabytes of data,
including more than 17,000 images. Only a fraction of the data
has yet been analyzed in detail or published in the peer-reviewed
literature. Analysis and interpretations are likely to continue
for some time.
QY: Jim Bell, Cornell University 607-255-2000.
(Sky and Telescope July 1998) (Science-Week 3 Jul 98)
4. ON THE ORIGIN OF HYDROTHERMAL MEGAPLUMES
Plate tectonics is the modern theory that unifies many of the
features and characteristics of continental drift and sea floor
spreading into a coherent model. Continental drift is the slow
movement of the Earth's land masses, a shifting across the
underlying molten material. Sea-floor spreading is the process
whereby sea floor is continuously created as the crustal plates
move apart and continuously destroyed where the plates push
against each other. The term "mid-ocean(ic) ridge" refers to a
topographic feature of a tectonic spreading center between
diverging oceanic plates. New crustal material is formed by
upswelling magma (molten material from which rock forms) as the
plates diverge. Basalt is a dark gray to black igneous rock of
volcanic origin that cools rapidly, and it is found as basement
rock on land, and on sea floor spreading from mid-ocean ridges. A
"pillow lava" is a lava with a distinctive shape acquired by
basalt that erupts into a submarine environment. The rapid
chilling of lava produces a series of convex basalt pods that
have the appearance of a stack of stone pillows. A "pillow
basalt" is a pod of basalt with a glassy outer skin and an inner
flow structure associated with the formative environment of a
pillow lava. Hydrothermal vents are fissures or opening through
which hydrothermal fluids escape from the Earth's crust, and
"hydrothermal megaplumes" are huge volumes of anomalously warm
water that are located up to 1000 meters above the sea floor and
appear to be generated at mid-ocean ridges. Hydrothermal
megaplumes were first discovered in 1986, and there has been
considerable debate concerning their origin. ... ... Palmer and
Ernst (University of Bristol, UK) use a theoretical model to
argue that the cooling of pillow basalts, which are erupted at
approximately 1200 degrees centigrade into sea water and are the
most common form of submarine volcanic activity, is responsible
for megaplume formation. The authors point out that the eruption
of pillow basalts onto the sea floor must involve thermal
perturbation of the overlying water column as the material erupts
at 1200 degrees centigrade and cools to ambient conditions
(approximately 2 degrees centigrade) within days to weeks. The
authors report they have examined the physical and chemical
features that might be expected from cooling of pillow basalts in
the deep oceans, and they conclude that this process is a viable
mechanism for the formation of hydrothermal megaplumes, and that
this simple explanation makes it possible to constrain more
closely the global flux and generation of megaplumes. The authors
also suggest that the wider radius of entrainment at the base of
megaplumes and their greater height above the sea floor compared
to chronic hydrothermal plumes means the megaplumes provide a
powerful mechanism for the dispersal of the larvae of organisms
endemic to hydrothermal vents, and that megaplumes may be of
particular importance in this regard on slow-spreading ridges.
QY: M.R. Palmer (m.r.palmer@bris.ac.uk)
(Nature 18 Jun 98 393:643) (Science-Week 3 Jul 98)
5. ON POLYMER RHEOLOGY
Rheology is the study of the flow and alterations of matter in
response to applied forces. Two laws dating back to the 17th
century are of importance in rheology: a) Hooke's law describes
the behavior of an elastic solid, relating the stress to the
deformation via a constant elastic modulus (coefficient of
elasticity); b) Newton's law describes the behavior of a linear
viscous fluid, relating the shear stress to the rate of
deformation via a constant viscosity coefficient. The objective
of current rheology is to describe the more complex behavior of
most real materials when they are examined over a wide range of
stresses and deformations. ... ... De Kee and Wissbrun (2
installations, US) review the history and present status of
polymer rheology, and make the following points. 1) The greatest
advances in rheology occurred with the advent, starting in the
1930s, of technologies based on synthetic high-molecular weight
polymers. These materials display a wide variety of readily
observed unusual rheological phenomena, and probably a majority
of rheological research in the past 50 years has been devoted to
the study of polymeric materials. 2) In all fluid mechanics
problems, it is necessary to solve the momentum and energy
conservation equations subject to boundary conditions that define
the geometry of the problem and subject to a mathematical
description of the fluid. That description is called a
constitutive equation, a rheological equation of state that
relates the time-dependent stresses and strains. 3) The behavior
of polymeric fluids falls somewhere between that of a purely
viscous material and that of a perfectly elastic material. A
volume element of an elastic material has a perfect memory of its
undeformed shape; that of a viscous fluid has no memory at all.
Polymer solutions and melts are viscoelastic; a volume element of
such a material has a partial memory that fades with time after a
deformation is imposed. The viscoelastic character of polymeric
materials is responsible for a number of significant phenomena
not observed with *Newtonian fluids. 4) At the present time, the
development of appropriate constitutive equations to describe the
stress state of viscoelastic liquids is an area of active
research and controversy. No theory is yet available that
adequately describes all of the observed phenomena in a variety
of flows. The authors suggest the following three paths as the
near-future of polymer rheology: a) The study of materials, such
as *dendrimers, that are more complex than homogeneous linear
polymers. b) Observations of the structures of materials while
they are being deformed. c) Numerical simulation on all scales,
from molecular to macroscopic, as an adjunct to classical
theoretical and experimental studies.
QY: Daniel De Kee, Tulane University 504-865-5731.
(Physics Today June 1998) (Science-Week 3 Jul 98)
... ... *Newtonian fluid: A simple fluid in which the state of
stress at any point is proportional to the time rate of strain at
that point. The proportionality factor is the viscosity
coefficient.
... ... *dendrimers: Highly branched macromolecules synthesized
by successive reactions of polyfunctional monomers around a core,
with the result that the number of end groups increases
geometrically.
6. ATTRACTION BETWEEN LIKE-CHARGED SPHERES IN A CHARGED PORE
A colloid is a system of particles 1 to 1000 nanometers in
diameter dispersed in another phase, and such systems,
particularly systems of electrically charged colloids, have
important practical significance and are also of considerable
theoretical interest. The existence of long-range attractive (as
opposed to the expected repulsive) electrostatic forces between
particles of like charge is one of the current major
controversies of colloid science. The established classical
theory (Derjaguin-Landau-Vervey-Overbeek) of colloidal
interactions predicts that an isolated pair of like-charged
colloidal spheres in an electrolyte should experience a purely
repulsive *screened electrostatic (coulombic) interaction. Direct
measurements of such interactions have shown quantitative
agreement with the classical theory, but recent experiments have
provided evidence that the effective interparticle potential can
have a long-range attractive component in more concentrated
suspensions and for particles confined by charged glass walls.
This long range attraction in concentrated systems is apparently
due to multi-body interactions. Theoretical explanations have
been proposed but remain the subject of controversy.
... ... Bowen and Sharif (University of Wales, UK) now present a
quantitative theoretical explanation of the attractive forces
between confined colloidal particles, the theory based on direct
solutions of the classical nonlinear Poisson-Boltzmann equation
for two like-charged spheres confined in a cylindrical charged
pore. The calculations show that the attraction may be explained
by the redistribution of the electric double layer of ions and
counterions in solution around the spheres, owing to the presence
of the wall. The authors suggest there is thus no need to revise
the established concepts of underlying theories of colloidal
interactions. [Editor's Note: The theoretical result in this
paper is unequivocal: the calculation shows that for the given
boundary conditions, the force between two particles of like
charge dips below zero (i.e., becomes attractive) before
returning to zero at infinite distance.]
QY: W. Richard Bowen (r.bowen@swansea.ac.uk)
(Nature 18 Jun 98 393:663) (Science-Week 3 Jul 98)
... ... *screened: Screening is a reduction of the effective
electric field at a point, the reduction due to the space charge
of ambient charged particles of sign opposite to the source of
the field.
7. ORIGIN OF LIFE: A MODEL FOR THE UNIVERSAL ANCESTOR
Biologists have long subscribed to the idea that all life on
Earth arose from a common ancestor. Until recently, nothing
concrete was said about this ancestor, but it was intuitively
assumed to be simple, often likened to a *prokaryote, and
generally held to have had little or no *intermediary metabolism.
Only when biology became defined on the level of molecular
sequences did it become possible to seriously consider the nature
of this ancestor. ... ... Carl Woese (University of Illinois
Urbana-Champaign, US) presents a "genetic annealing" model for
the universal ancestor of all extant life. Physical annealing
involves a first stage heating to a high temperature followed by
a slow cooling of the system to produce new structures,
particularly special crystalline forms. The term "annealing" is
also used in molecular biology to refer to the separation of DNA
strands by heating and the recombination of complimentary strands
by cooling. In Woese's model, the term "annealing" is used in
still a third sense. In the author's model, in the evolutionary
counterpart of physical annealing, the elements of the system are
primitive cells, mobile genetic elements, and so on, and physical
temperature becomes "evolutionary temperature", the evolutionary
"tempo". The evolutionary analog of "crystallization" is
emergence of new structures, new cellular subsystems that are
refractory to major evolutionary change. The author defines the
entities in which *translation had not yet developed to the point
that proteins of the modern type could arise as "progenotes", and
the era during which these were the most advanced forms as the
"progenote era". Concerning "evolutionary temperature", the
author points out that macroscopic evolutionists recognized long
ago a relationship between the "tempo" (rate) of evolution and
its "mode" (a measure of the outcomes). When microbial evolution
finally came into the picture, a similar phenomenon was
encountered on the molecular level, suggesting that this
tempo/mode relationship was a fundamental manifestation of the
evolutionary process. Because of high mutation rates and other
factors, the progenote era is proposed as one of very high
evolutionary tempo. In the author's model, progenotes were very
unlike modern cells, their component parts with different
ancestries, and the complexion of their components changing
drastically over time. Progenotes possessed the machinery for
gene expression and genome replication and at least some
rudimentary capacity for cell division, but the ordinary cellular
functions had no genealogical continuity, since they were too
subject to the confusion of *lateral gene transfer. According to
the author, the transition from progenotes to genotes turned upon
the evolution of translation, the conversion of messenger RNA
code into the specific amino acid sequences of specific proteins.
The author proposes the genetic annealing model as "an attempt to
develop a consistent general picture of the universal ancestor...
The ancestor cannot have been a particular organism, a single
organismal lineage. It was communal, a loosely knit, diverse
conglomeration of primitive cells that evolved as a unit... The
universal ancestor is not an entity, not a thing. It is a process
characteristic of a particular evolutionary stage." The author
concludes with a conjecture that genomes resulting from episodes
of rapid evolution will contain an abnormally high proportion of
foreign genes, and a suggestion that "genome sequences will soon
be available in sufficient number to properly test whether the
tempo/mode relationship (rapid evolution) invariably links
increased mutation rate and increased levels of lateral gene
transfer or vice versa."
QY: Carl Woese (carl@ninja.life.uiuc.edu)
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:6854)
(Science-Week 3 Jul 98)
... ... *prokaryote: Prokaryotes are cells without a cell nucleus
and other membrane-bound organelles.
... ... *intermediate metabolism: The sum of all metabolic
reactions between the uptake of nutrients and the excretion of
waste products.
... ... *lateral gene transfer: This refers to the "horizontal"
transfer of genetic information between individuals of the same
generation, the mechanism involving the incorporation by the
genome of accessible new genetic elements. The process is common
among primitive life forms such as bacteria.
-------------------
Related Background:
BIOCHEMICAL EVOLUTION: POLYMERIZATION ON MINERAL SURFACES
J. Smith (University of Chicago, US) proposes a conceptual
framework for consideration of the origins of replicating
biopolymers. Although extended Darwinian natural selection
coupled with Mendel-Watson-Crick genetic inheritance/mutation
provides a plausible framework for integrating the patchy
paleontological record with the increasingly complex biochemical
zoo of the present Earth, the actual chemical beginning of "life"
still poses major challenges. How could the first replicating and
energy-supplying molecules have been assembled from simpler
materials that were undoubtedly available on the early proto-
continents? Catalysis at mineral surfaces might generate replic-
ating biopolymers from simple chemicals supplied by meteorites,
volcanic gases, and photochemical gas reactions. But many ideas
are implausible in detail because the proposed mineral surfaces
strongly prefer water and other ionic species to organic ones.
The molecular sieve silicalite (Union Carbide; = Al-free Mobil
ZSM-5 zeolite) has a 3-dimensional 10-ring channel system whose
electrically neutral silicon-oxide surface strongly adsorbs
organic species over water, and the ZSM-5 type zeolite mutinaite
has recently been found in Antarctica. The author proposes that
zeolites with similar structures may have existed on the surface
of Earth during its life-origin phase, and that polymer migration
along weathered silicic surfaces of micrometer-wide channels of
feldspars might have led to assembly of replicating catalytic
biomolecules and perhaps primitive cellular organisms. The author
suggests that weakly metamorphosed Archaean rocks might retain
microscopic clues to the proposed mineral adsorbent/catalysts,
and that other frameworks are also possible, including ones with
laevo/dextro one-dimensional channels.
QY: Joseph V. Smith (smith@geol.uchicago.edu)
(Proc. Natl. Acad. Sci. US 31 Mar 98 95:3370)
(Science-Week 8 May 98)
-------------------
Related Background:
ORIGIN OF LIFE: THE PRESENT STATUS OF CHEMICAL THEORY
The essential question involved in the origin of what we call
life is how can order arise from disorder? At the present time,
this question is approached on two fronts: 1) study of the
principal features of self-organizing systems, systems in which
order does arise from disorder, systems in which order is indeed
demanded from disorder on thermodynamic grounds; and 2) study of
the detailed chemistry of such systems, the chemistry of
organization and the chemistry of components. In the case of
components, it is essential that appropriate self-organizing
components exist in the first place if they are to become self-
organized, and such candidate components are thus the focus of
much chemical research in this area. In 1953, the chemist Stanley
Miller reported what soon became a famous experiment. To water
under a gas mixture of methane, ammonia, and hydrogen, he added
an electrical discharge. After one week of continuous electrical
discharge, he found that a number of important biological
molecules, including amino acids, had been formed. Miller
proposed his experiment as a model for the conditions under which
the essential compounds necessary for life originated . The
Miller experiment was a watershed, and it began a new era of
experimentation and analysis of possible primordial components.
Coupled with this, were the new important discoveries by
astrophysicists of the presence of organic molecules in the
interstellar medium and in meteorites. In a review of origin of
life theories, P. Radetsky (Univ. of California Santa Cruz, US)
points out that the Miller theory is no longer the consensus
theory, that contemporary geologists believe the primordial
atmosphere consisted primarily of carbon dioxide and nitrogen,
which are less reactive than the gases in the Miller experiment,
and that the field is currently embroiled in controversy fueled
for the most part by an absence of hard fact. QY: Peter Radetsky,
Univ. of California Santa Cruz 408-429-4008 (Earth February
1988)
(Science-Week 2 Jan 98)
-------------------
Related Background:
RNA POLYMERIZATION A FOCUS AT ORIGIN OF LIFE MEETING
If the complex molecules necessary for life originated on Earth
rather than elsewhere, then a natural question is how? How and
under what conditions did the first polymerizations occur? Under
ordinary laboratory conditions, without special outside agencies
such as catalysts, RNA monomers, for example, will not assemble
into polymers unless the monomer concentration is impossibly
large. So how was polymerization achieved on the early Earth?
Such questions are now the essential questions in the origin-of-
life branch of biological science, and at a recent regional
meeting of the American Chemical Society, a group of researchers
in this area presented results of their latest studies. David
Usher et al have used a "day-night machine", an apparatus that
exposes solutions to alternating cycles of daylight and darkness,
and have apparently found evidence of RNA polymerization from
monomers, the polymerization dependent on the alternating cooling
and heating produced by the light-dark cycles. James Ferris and
Gozen Ertem (Rensselaer Polytechnic Institute, NY US) presented
evidence that clay or pyrite minerals can catalyze polymer
formation from RNA monomers by serving as adsorption templates.
And Tom Waddell et al (University of Tennessee Chattanooga, US)
reported that if intermediates of the citric acid cycle, so vital
in biological processes, are exposed to sunlight, the production
of other intermediates in the cycle is catalyzed. The hunt for
efficient catalysts for RNA polymerization that may have been
present on primeval Earth continues. (Science 22 Aug 97)
(Science-Week 5 Sep 97)
8. ON PROKARYOTES IN THE BIOSPHERE
Prokaryotes (bacteria) are unicellular life forms lacking a
membrane-bound nucleus, structured chromosomes, and complex
internal organization. They are invisible to the naked eye, but
they are an essential component of the Earth's biota. They
catalyze unique and indispensable transformations in the
biogeochemical cycles of the biosphere, produce important
components of the Earth's atmosphere, and represent a large
portion of life's genetic diversity. Although the abundance of
prokaryotes has been estimated indirectly, the actual number of
prokaryotes and the total amount of their cellular carbon on
Earth has never been directly assessed. ... ... Whitman et al (3
authors at University of Georgia, US) present an array of
calculations based on analysis of various habitats, and make the
following points: 1) The number of prokaryotes and the total
amount of their cellular carbon on Earth are estimated to be 4-6
x 10^(30) cells and 350-550 x 10^(15) grams of carbon,
respectively. The total amount of prokaryotic carbon is thus 60
to 100 percent of the estimated total carbon in plants, and
inclusion of prokaryotic carbon in global models will almost
double estimates of the amount of carbon stored in living
organisms. 2) In addition, the Earth's prokaryotes contain 85-130
x 10^(15) grams of nitrogen, and 9-14 x 10^(15) grams of
phosphorus, or about 10-fold more of these nutrients than do
plants, and represent the largest pool of these nutrients in
living organisms. 3) Most of the Earth's prokaryotes occur in the
open ocean, in soil, and in oceanic and terrestrial subsurfaces,
where the numbers of cells is of the order of 10^(29) to 10^(30).
4) The numbers of heterotrophic prokaryotes (bacteria that feed
on organic material) in the upper 200 meters of open ocean, the
ocean below 200 meters, and soil are consistent with average
turnover times of 6-25 days, 0.8 years, 2.5 years, respectively.
An uncertain estimate for the average turnover time of
prokaryotes in the subsurface is of the order of 1000 to 2000
years. 5) The cellular production rate for all prokaryotes on
Earth is estimated at 1.7 x 10^(30) cells per year and is highest
in the open ocean. The authors suggest that the large population
size and rapid growth of prokaryotes provides and enormous
capacity for genetic diversity, and that given the numerical
abundance and importance of prokaryotes in biogeochemical
transformations, the absence of detailed knowledge of prokaryotic
diversity is a major omission in our knowledge of life on Earth.
QY: William B. Whitman (whitman@uga.cc.uga.edu)
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:6578)
(Science-Week 3 Jul 98)
9. PARENTING AND SURVIVAL IN ANTHROPOID PRIMATES
Allman et al (4 authors at 2 installations, US) present an
analysis of the relationship between parenting and survival in 10
species of anthropoid primates, including humans, and make the
following points: 1) Most anthropoid primates are slow to
develop, their offspring are mostly single births, and the
interbirth intervals are long. To maintain a stable population,
parents must live long enough to sustain the serial production of
a sufficient number of young to replace themselves, while
allowing for the death of offspring before they can reproduce.
However, in many species there is a large differential between
the sexes in the care provided to offspring. 2) The authors
hypothesized that in slowly developing species with single
births, the sex that bears the greater burden in the care of
offspring will tend to survive longer. Males are incapable of
gestating infants and lactating, but in several species fathers
carry their offspring for long periods. The authors predicted
that females tend to live longer than males in the species where
the mother does most or all of the care of offspring, that there
is no difference in survival between sexes in species in which
both parents participate about equally in infant care, and that
in the species where the father does a greater amount of care
than the mother, males tend to live longer. 3) The hypothesis of
the authors was supported by analysis of survival data for males
and females in the following anthropoid primate species:
chimpanzee, spider monkey, orangutan, gibbon, gorilla, human,
goeldi's monkey, siamang, owl monkey, titi monkey.
QY: John Allman (cebus@cheiro.bio.caltech.edu)
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:6866)
(Science-Week 3 Jul 98)
-------------------
Related Background:
ON GRANDMOTHERING, MENOPAUSE, AND HUMAN EVOLUTION
Hawkes et al (5 authors at 2 installations, US) present a
hypothesis that the long postmenopausal lifespans that disting-
uish humans from all other primates may have evolved with mother-
child food sharing, a practice that allowed aging females to
enhance the fertility of their daughters, the practice thereby
increasing selection against senescence. The authors suggest
their hypothesis also accounts for human late maturity, small
size at weaning, and high fertility, and that the hypothesis has
implications for past human habitat choice and social organiz-
ation, and for ideas about the importance of extended learning
and paternal provisioning in human evolution.
QY: E.L. Charnov, Univ. of Utah, Dept. of Biology 801-581-5636
(Proc. Natl. Acad. Sci. US 3 Feb 98)
(Science-Week 20 Feb 98)
10. ON ALCOHOL IN THE WESTERN WORLD
The consumption of alcohol (ethanol) is recognized as a major and
potentially preventable health problem. In general, a linear
correlation exists between the intensity of alcohol abuse in
terms of duration and dose and the development of a wide spectrum
of pathologies, especially liver disease. As little as 200 ml
wine or 60 ml whiskey in women, 1200 ml of 5% beer in men, when
consumed on a daily basis over years, can produce liver injury.
The mechanisms by which alcohol damages the liver are still
unclear, but the damage is undisputed. Given all of the above,
however, it is a fact that alcohol consumption has been an
important aspect of Western civilization for thousands of years,
and has probably existed for at least 10,000 years in various
communities. In an essay on the role of alcohol consumption in
the Western world, Bert L. Vallee (Harvard University, US) makes
the following points: 1) Ethanol (ethyl alcohol) is a
multifaceted entity: it may be social lubricant, sophisticated
dining companion, cardiovascular health benefactor, or agent of
destruction. 2) For most of the past 10,000 years in the Western
world, alcoholic beverages may have been the most popular and
common daily drinks, indispensable sources of fluids and
calories in a world of contaminated and dangerous water
supplies. 3) The experience of the East differed greatly. For at
least the past 2000 years, the practice of boiling water,
usually for tea, has created a potable supply of non-alcoholic
beverages. In addition, genetics plays an important role in
making Asia avoid alcohol: approximately half of all Asian
people metabolize alcohol differently than non-Asians, making
the experience of drinking alcohol quite unpleasant [see
background material below]. 4) Beer and wine became staples in
Western societies and remained there until the end of the last
century. Indeed, throughout Western history, the normal state of
mind may have been one of inebriation. 5) Although yeasts
produce alcohol, they can tolerate concentrations of only about
16 percent, so that fermented beverages had a natural maximum
proof. Distillation, introduced by the Arabs about 700 A.D.,
circumvented the fermentation limit by taking advantage of
alcohol's boiling point being lower than water (78 vs. 100
degrees centigrade) to boil off and then condense the alcohol
from fermented mixtures. 6) Presently, alcohol contributes to
100,000 deaths in the US each year, making it the 3rd leading
cause of preventable mortality. 7) Each year, approximately
12,000 children of drinking mothers are born with the physical
signs and intellectual deficits associated with full-blown fetal
alcohol syndrome, and thousands more suffer lesser effects. 8)
Alcoholism, in historical terms, has only just been understood
and accepted as a disease, and we are still coping with the
historically recent arrival of concentrated alcohol. The author
concludes: "Alcohol today is a substance primarily of
relaxation, celebration and, tragically, mass destruction. To
consider it as having been a primary agent for the development
of an entire culture [Western civilization] may be jolting, even
offensive to some. Any good physician, however, takes a history
before attempting a cure."
QY: Bert L. Vallee, Harvard Univ. Medical School 617-432-1550.
(Scientific American June 1998) (Science-Week 3 Jul 98)
-------------------
Related Background:
... ... Ethanol is readily absorbed from the gastrointestinal
tract, and more than 90 percent is metabolized by the liver
through oxidative mechanisms involving mainly the enzyme alcohol
dehydrogenase and certain other enzymes. Alcohol cannot be stored
and all of it is metabolized. Alcohol dehydrogenase oxidizes
alcohol to acetaldehyde. Apparently, approximately 85 percent of
the Japanese population has an atypical alcohol dehydrogenase
that operates about 5 times faster than the same enzyme does in
non-Japanese. Other Asian groups may exhibit the same phenomenon.
Consumption of alcohol by such persons leads to the accumulation
of acetaldehyde, resulting in extensive vasodilation, facial
flushing, and compensatory tachycardia (rapid heartbeat > 100 per
minute).
-------------------
Related Background:
COMPLEXITIES IN ALCOHOL CONSUMPTION MORTALITY RISK
The question of the beneficial vs. harmful effects of moderate
alcohol consumption in adults is not at all settled, despite
media trumpeting that moderate alcohol consumption reduces
mortality of middle-aged and older people. The provocation for
the media attention was the appearance of an article in the New
England Journal of Medicine of 11 Dec 97. Now 4 letters appear in
the same journal (one a response from the authors of the original
article), and it appears that conclusions from this study that
forms the basis of current popular views concerning alcohol may
not be firm. One letter writer, John D. Potter, who wrote an
editorial on the subject in the NEJM issue of 11 Dec 97, now says
"perhaps it is time to reexamine our conclusions about any
benefits that accrue from alcohol; it is certainly time to renew
attention to its deleterious health consequences."
(New England J. Med. 7 May 98 338:1385) (Science-Week 15 May 98)
-------------------
Related Background:
ALCOHOL CONSUMPTION AND MORTALITY: A NEW MASSIVE STUDY
Ethyl alcohol is widely used as a psychoactive drug and has been
for thousands of years. That ethyl alcohol has a deleterious
effect on individual biological cells is known to any biologist
who has ever mixed ethyl alcohol into a drop containing living
cells under a microscope. In the body, however, the deleterious
cellular effects of ethyl alcohol are complicated by the systemic
detoxification mechanisms that result in the breakdown or trans-
formation of ethyl alcohol into innocuous substances, and the
result of this is that the systemic toxicity (and psychoactive
effects) of ethyl alcohol is a question of how much intact ethyl
alcohol is actually circulating in the blood, rather than how
much has been imbibed. As a further complication, there is
evidence that low levels of ethyl alcohol are protective against
heart disease and stroke, perhaps due to the ethyl alcohol
affecting the complexing of cholesterol with lipoproteins. Now
Thun et al (7 authors at 2 installations, US UK) report an
analysis of mortality data of 490,000 men and women (mean age 56
years, range 30 to 104) who reported their alcohol and tobacco
use in 1982. The authors followed this group from 1982 to 1991,
and they report the evidence indicates that moderate alcohol
consumption slightly reduced overall mortality, the benefit
increasing with age. The background cardiovascular risk with
increased alcohol consumption was far smaller than the large
increase in risk produced by tobacco. The authors suggest the
implications of their findings for social policy are beyond the
scope of their report. QY: Michael J. Thun, American Cancer
Society, 1599 Clifton Road NE, Atlanta, GA 30329-4251 US
(New England J. Med. 11 Dec 97) (Science-Week 19 Dec 97)
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