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.

July 28, 2000 -- Vol. 4 Number 30

-----------------------------------------------

We are the strangest species. We question everything,
measure the stars, sift the sand through our fingers,
gauge the bowels of the Earth. It is our destiny and
it will not stop.
-- Anonymous

-----------------------------------------------

Contents of this Issue:

1. Computer Science:
Prospects in Molecular Electronics
----------------------------------
Within the next few decades a new technology will supplant the
transistor paradigm that currently forms the basis of computing
machines, and many believe this new technology will involve
molecular scale devices and the utilization of quantum effects
manifested at such scales.
(Includes related background material.)

2. Condensed-Matter Physics:
On the Optical Activity of Quantum Dots
---------------------------------------
Quantum dots are essentially artificial atoms, and quantum dots
that emit light are expected to form the basis of a new
generation of lasers.

3. Earth Sciences:
On Ocean Tides and Climate Change
---------------------------------
One of the important questions in geophysics is whether the
energy of ocean tides is dissipated in deep water or in shallow
coastal seas, the answer to this question having important
implications beyond tidal dynamics.
(Includes related background material.)

4. Evolutionary Biology:
On the Origin of the Cell Nucleus and the Woese-Mayr Controversy
----------------------------------------------------------------
A detailed hypothesis concerning the evolutionary origin of the
eukaryote nucleus is coupled with an argument against the 3-
kingdom approach of Woese and others.
(Includes related background material.)

5. Plant Biology:
On Photosynthesis
-----------------
Current research is delineating the details of light harvesting,
the first major event in photosynthesis.
(Includes related background material.)

6. Medical Biology:
Environment vs. Heredity in the Causation of Cancer
---------------------------------------------------
In a large-scale study of twins, the major contributor to the
causation of cancer was the environment rather than heredity.
(Includes related background material.)

7. Focus Report: On Cosmic Heat Death (James Jeans)

8. From the SW Archive:
Marietta Blau: The Destruction of a Career in Physics
-----------------------------------------------------
The physicist who invented the emulsion technique so important in
the early history of 20th century particle physics died poor and
unemployed.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

1. COMPUTER SCIENCE:
PROSPECTS IN MOLECULAR ELECTRONICS
It is apparent that within the next few decades there will be
developed a new technology that will supplant the transistor
paradigm that currently forms the basis of computing machines. It
is also apparent that this new technology will involve molecular
scale devices and the utilization of quantum effects manifested
at such scales. The basic science and engineering challenges are
enormous, but there is now such intense global hunger for
increased computing power (and excitement over the prospects)
that success in overcoming the obstacles seems highly probable.
... ... Craig S. Lent (University of Notre Dame, US) presents a
commentary on current efforts in this field, the author making
the following points:
     1) Modern computers are the result of two ideas: a) the use
of binary numbers to represent information in a machine, and b)
encoding the binary "1" and "0" as the "on" and "off" states of a
current switch. Prior to approximately 1940, electromechanical
relays were used as the current switch devices. Later, these
switches were replaced by vacuum tube triodes ("valves"), which
in turn were eventually replaced by the solid-state version of
the vacuum tube, the modern transistor. In general, representing
binary information by turning a current stream on or off has been
one of the most fruitful ideas in the history of technology.
     2) This idea, however, has serious drawbacks as device sizes
are reduced. The smaller the switch, the lower its ability to
cleanly turn the current off and on. Also, the current through
each single switch is reduced, making it more difficult to charge
up the interconnect lines between devices. Finally, switching
current requires electrons to move from the power supply through
a resistance to ground, resulting in considerable energy
dissipation. If present transistors could be magically shrunk to
the size of single molecules, a chip with phenomenal device
density could be fabricated, but the heat generated would cause
such a chip to melt as soon as it was turned on.
     3) It is thus clear that if electronic devices are to be
shrunk to the ultimate limit of molecular size, a new paradigm
must be developed. The Quantum-dot Cellular Automata (QCA)
paradigm retains the notion of a binary representation of
information, but this binary information is stored in the charge
configuration within a quantum-mechanical microscale system
("cell") rather than in the on/off state of a current switch. In
general, each cell consists of four "dots" and contains two
mobile electrons, the electrons occupying antipodal sites. In a
molecular implementation, each cell is a single molecule. No
current flows between cells. Instead, the Coulomb interaction
between cells tends to induce the same state in neighboring
cells, and this interconnection is sufficient to support general-
purpose computing. [Editor's note: For more on "quantum dots",
see related background material below and report #2 this issue.]
     4) At the present time, researchers are exploring a class of
molecules known as metal cluster carboxylates for use as QCA
molecules. Each of the four dots is composed of a cluster of
three metal atoms, with additional metal atoms forming a bridge.
Electrons hop from one outer dot to another through the central
cluster, which also acts structurally to place the four dots on a
plane. The molecules have been synthesized with several different
clusters and centers in an effort to understand the role of the
linkers in electron hopping and to design molecules with
appropriate switching behavior. Another experimental design
involves the use of single ruthenium atoms as the dots of a QCA
cell.
     5) The author concludes: "The QCA approach to molecular
electronics is very promising, but creating functional QCA
molecules is just the first step. In a device, the molecules need
to be attached to a surface in a predetermined geometry, inputs
and clocking signals need to be applied, and the state of the
output cells must be read. Each of these steps presents
substantial challenges. In addition, the whole approach to
circuit architecture must be rethought if circuits are going to
be based on QCA cells rather than transistors."
-----------
Craig S. Lent: Bypassing the transistor paradigm.
(Science 2 Jun 00 288:1597)
QY: Craig S. Lent [lent@nd.edu]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 28Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
COMPUTER SCIENCE:
ROOM-TEMPERATURE QUANTUM CELLULAR AUTOMATA
     The consensus view among computer scientists and
microelectronics engineers is that in the near future the rapid
growth of information processing capability will require radical
innovations in technology because of inherent limitations in
current microchip (integrated circuit) architecture and dynamics.
This has caused attention to focus on various possibilities for
the use of quantum mechanical effects in computing. One such
possibility involves the "single-electron transistor". A
single-electron transistor is a transistor of extremely small
dimensions isolated from its leads by potential barriers narrow
enough to permit electron tunneling, with a minute electron
source that is essentially a droplet of electrons. A
single-electron transistor switches on and off with the addition
of each electron, in contrast with the ordinary transistor which
sustains a switched-on state given a flow of added electrons.
This quantized behavior of the single-electron transistor is due
to its dimensions, the electron droplet essentially behaving as
an artificial atom or "quantum dot". As realized in the
laboratory, quantum dots are small electrically conducting
regions, typically less than 1 micron in diameter, that contain
from one to a few thousand electrons. Because of the small
volume, the electron energies within the dot are quantized, and
the behavior of the quantum dot is intermediate between that of
an atom and that of a classical macroscopic object.
     In general, in this context, the term "cellular automata"
refers to theoretical computer processing units consisting of a
large number of cells, each cell containing a relatively small
number of responding entities (devices), with each cell
communicating only with neighboring cells. The main advantage of
cellular automata systems is that they eliminate the requirement
for long interconnections between devices, a requirement that is
one of the ultimate limitations of the speed of the conventional
computer microchip. What is of interest here is that quantum dots
can be configured as quantum cellular automata, and such
configurations have been shown to have the ability to perform
logic operations. Until now, however, these devices have worked
only at very low temperatures (millikelvins) -- unless the dots
are made extremely small (less than 2 nanometers in diameter).
... ... R.P. Cowburn and M.E. Welland (University of Cambridge,
UK) now report experimental development of quantum cellular
automata using relatively large quantum dots (approximately 100
nanometers) that work at room temperature, provided one uses
magnetic metals in the construction of the dots. The authors make
the following points:
     1) In the system developed by the authors, each quantum
cellular automata network consisted of a single elongated input
quantum dot followed by a chain of 69 circular dots. Each dot was
110 nanometers in diameter and placed so that the edge of each
dot was 25 nanometers from the edge of each neighboring dot
(i.e., pitch = 135 nanometers). The dots were 10 nanometers thick
and made from a common magnetic alloy (Supermalloy), which is
Ni(sub80)Fe(sub14)Mo(sub5)X, where X is other metals, all of the
dots on a single-crystal silicon substrate. The dots were
fabricated by high-resolution *electron-beam lithography.
     2) The authors point out that in electronic quantum cellular
automata, the term "quantum" is used because the system involves
*quantum mechanical tunneling of charge between dots to change a
logic state; classical electrostatics are involved thereafter in
the propagation of the change in logic state. The quantum
mechanical interactions in magnetic quantum cellular automata
networks are *exchange interactions between *spins within a
single dot in order to form a single giant classical spin. A
logic 1 is signaled when the magnetization vector of the dot
points to the right, for example, and a logic 0 when it points to
the left. The magnetic field emanating from such a magnetic
particle can be extremely large, with the result that one
magnetic dot is strongly influenced by the magnetic field
emanating from its nearest neighbor. These classical
magnetostatic interactions are then involved in the propagation
of information along the chain of dots. A further feature of
magnetostatic interactions is that they force the magnetization
to point along the length of the chain. The system is thus
intrinsically binary, with only right- and left-pointing
magnetization states being stable. An applied oscillating
magnetic field feeds energy into the system and serves as a
clock.
     3) The authors state: "These networks offer a several
thousandfold increase in integration density and a hundredfold
reduction in power dissipation over current microelectronic
technology."
-----------
R.P. Cowburn and M.E. Welland: Room temperature magnetic quantum
cellular automata.
(Science 25 Feb 00 287:1466)
-----------
Text Notes:
... ... *electron-beam lithography: In this context, lithography
is a technique used for integrated circuit fabrication, the
technique in general involving a silicon chip coated uniformly
with a radiation-sensitive film ("resist"), and an exposing
radiation source (e.g., ultraviolet light or an electron beam)
illuminating selected areas of the surface through an intervening
master template (mask) to obtain a particular pattern of resist-
coated surface after unexposed resist is washed away. Non-resist
coated portions of the silicon surface are then etched away by
acid. In electron-beam lithography, the radiation-sensitive film
used in microchip fabrication is placed in the vacuum chamber of
a scanning-beam electron microscope and exposed by an electron
beam under digital computer control. In the present report, the
quantum dots were fabricated by high-resolution electron-beam
lithography in a polymethylmethacrylate resist followed by
metalization and ultrasonically-assisted lift-off in acetone. The
report contains photographs of linear arrays of identical quantum
dots 110 nanometers in diameter fabricated by this method.
... ... *quantum mechanical tunneling: "Tunneling" is a quantum
mechanical phenomenon involving an effective penetration of an
energy barrier resulting from the width of the barrier being less
than the wavelength of the particle.
... ... *exchange interactions: In quantum mechanics, an
"exchange interaction" is an interaction represented by an
exchange of space or spin coordinates or both --  an interaction
that can be viewed as an effective exchange of particles.
... ... *spins: In quantum mechanics, electrons, protons, and
neutrons have an intrinsic angular momentum known as "spin", and
a *magnetic moment parallel or antiparallel to that angular
momentum. When electrons are combined together to form an atom or
ion, there is a resultant angular momentum which is a combination
of the intrinsic spin of the electrons and the angular momentum
due to their motion about the nucleus, and this is the "spin" of
the atom or ion. Atoms or ions with non-zero spin are magnetic
atoms or ions.
... ... *magnetic moment: (magnetic dipole moment) The intrinsic
spins of the electrons in an atom, together with the motion of
the electrons around the nucleus, give rise to a magnetic field
around the atom, and the magnitude of this field is related to
the magnetic dipole moment of the atom or ion.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 12May00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MATERIALS SCIENCE: QUANTUM DOTS
It is now possible to create extremely small crystals which
contain less than 1000 atoms, each crystal measuring a few
millionths of a millimeter across and thus in the nanoscale
domain. Certain of these nano-crystals, those of cadmium
selenide, for example, have peculiar attributes: crystals of
exactly the same composition but of different size exhibit quite
different properties, with the large nano-crystals of cadmium
selenide red in color, smaller crystals orange, and the smallest
(containing barely 100 atoms) yellow in color. The differences in
properties are due to quantum mechanical effects. These extremely
small atomic arrays are called "quantum dots", and there is a
current consensus that if quantum dots could be integrated onto a
chip, their unique electrical properties could be harnessed to
perform a function similar to a conventional transistor, while
requiring only a small fraction of the space. In consequence, the
creation of an appropriate regular array of quantum dots would
allow a computer processor many times more powerful than any
current supercomputer to be constructed on single chip.
... ... F. Remacle and R.D. Levine (2 installations, BE IL)
present a theoretical discussion of assemblies of metallic
quantum dots with each dot considered as an "atom". The dots are
taken as being packed close enough to be interacting. The authors
suggest that the key point is that such dots are essentially
"designer" atoms, since their electronic properties can be
controlled via the synthetic method used to prepare the dots. Of
direct significance are the size of the dot and the nature of the
ligands used to prevent coalescence of the dots. The energy
required to remove or add an electron to the dot is determined by
the size of the dot. The ligands control how closely the dots can
be packed and hence the strength of the coupling between adjacent
dots. An important parameter is the energy cost of adding an
electron to a dot: because of the large size of the dots, the
Coulomb repulsion of the added electron is low. Unlike most
ordinary atoms, quantum dots have a high capacity for
accommodating an additional electron.
-----------
F. Remacle and R.D. Levine: Architecture with designer atoms:
Simple theoretical considerations.
(Proc. Natl. Acad. Sci. US 18 Jan 00 97:553)
QY: R.D. Levine [rafi@fh.huji.ac.il]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 21Apr00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
MATERIALS SCIENCE: THE SEARCH FOR LOW-K DIELECTRICS
In general, a "transistor" is a semiconductor device in which it
is possible to control voltage or current in such a way as to
achieve gain or switching action. An "integrated circuit" is a
miniature electronic circuit produced within a single crystal of
a semiconductor such as silicon. Such devices, usually called
"chips", range from simple logic circuits to large-scale circuits
containing approximately 10^(6) components (transistors,
resistors, capacitors), and these devices are widely used in
memory circuits, microcomputers, pocket calculators, etc.,
because of their low cost and high speed.
... ... Robert D. Miller (IBM Almaden Research Center, US)
presents a review of current research in chip design, the author
making the following points:
     1) Within the next few years, high-performance chips
containing as many as 5 x 10^(8) transistors on a single chip
will be produced. These advanced chips may contain up to 10^(4)
meters of on-chip wiring. Such increased component and wiring
densities, however, cannot be achieved with currently used
materials. Although an intensive search is now underway for
materials that can replace silicon dioxide [SiO(sub2)] as the
insulator in these future devices, a clear candidate material has
yet to be identified.
     2) In a typical microchip, layers of copper-interconnect
wiring are separated by a dielectric insulator, traditionally
silicon dioxide. Both the resistance of the metal and the
capacitance of the insulator increase markedly as the wiring
dimensions and distances between chip components (pitch)
decrease, with resulting crosstalk, capacitative coupling between
metal-interconnect lines, and consequent increased signal delays.
Traditional aluminum-copper wiring can be replaced by pure
copper, which has a lower resistance, and then the performance
gain is limited primarily by interlayer and intralayer
capacitance, which in turn is dictated primarily by the
*dielectric constant of the insulator. Thus, there is now a
intensive search underway for new dielectric insulators with
lower dielectric constants than silicon dioxide. (The dielectric
constant (k) of silicon dioxide is in the range 3.9 to 4.2.)
     3) Any replacement low-dielectric constant material must
meet current requirements for integrated circuits: thermal
stability in excess of 400 degrees centigrade, good mechanical
properties, low ion content, breakdown fields in excess of 2
million volts per centimeter, low water uptake, lithographic
processability, low thermal expansion coefficients and film
stresses, good adhesion to a variety of substrates, and low
reactivity with conductor metals at elevated temperatures.
     4) Although the drive toward increased device densities and
improved performance in semiconductor devices makes the switch
from silicon dioxide on-chip insulators to low-dielectric
constant materials inevitable, no clear winner has yet emerged
among materials with dielectric constants less than 3.0. The
author concludes: "The switch to low-k on-chip insulators
continues to be a formidable challenge to chemists, physicists,
materials scientists, and integration engineers."
-----------
Robert D. Miller: In search of low-k dielectrics.
(Science 15 Oct 99 286:421)
QY: Robert D. Miller [rdmiller@almaden.ibm.com]
-----------
Text Notes:
... ... *dielectric constant: In general, a "dielectric" is a
substance that can sustain an electric field and act as an
insulator, e.g., a nonconductor of electric charge in which an
applied electric field causes a displacement of charge but not a
flow of charge. In physics, "permittivity" is the ratio of the
electric displacement in a dielectric medium to the applied
electric field strength, and "relative permittivity" refers to
the ratio of the permittivity of a medium to the permittivity of
*free space. Relative permittivities vary from 1 (for free space)
to over 4000 for certain ferromagnetic materials, but for most
materials, relative permittivities are less than 10. In general,
in physics, the term "dielectric constant" has been replaced by
the term "relative permittivity", but in the context of electric
circuits, the term dielectric constant is still used, and in this
context the term "dielectric constant" of a material is perhaps
best defined as the ratio of the capacitance of a capacitor
constructed of the material to the capacitance the capacitor
would possess if the material were replaced by free space.
... ... *free space: In physics, the term "free space" refers to
a region in which there is no matter and no electromagnetic or
gravitational fields, the region having a temperature of absolute
zero, unit refractive index, and the speed of light at its
maximum value.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 31Dec99
[For more information: http://scienceweek.com/swfr.htm]

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

2. CONDENSED-MATTER PHYSICS:
ON THE OPTICAL ACTIVITY OF QUANTUM DOTS
One of the most significant developments in physics during the
past several decades has been the introduction of techniques for
manipulating small populations of electrons, and the
ramifications of this technology for both basic and applied
science have excited many physicists. At the present time, the
central player in this field is the so-called "quantum dot",
which essentially is an artificial atom. As described in the
previous report (SW 28 Jul 00 #1), quantum dots are small
isolated electrically conducting regions, typically less than 1
micron in diameter, that contain from one to a few thousand
electrons. Because of the small volume, the electron energies
within the dot are quantized, and the behavior of the quantum dot
is intermediate between that of an atom and that of a classical
macroscopic object.
... ... Daniel Gammon (Naval Research Laboratory, US) presents a
commentary on current research on electrons in artificial atoms,
the author making the following points:
     1) An electron in a quantum dot can be described by a
quantum wavefunction that is similar to that used for an electron
in a single atom, although the energy of the electron in the
quantum dot is spread in a coordinated way (spread "coherently")
over the lattice of atomic nuclei. The electronic wavefunctions
of quantum dots are often labeled with atomic notation, but
quantum dots are very much solid-state nanostructures that can be
tailored into different shapes. Recent studies (M. Bayer et al:
Nature 405:923 2000; R.J. Warburton et al: Nature 405:926 2000)
describe the optical behavior of individual quantum dots and
quantum rings, and such behavior is of considerable interest
because quantum dots that emit light are expected to form the
basis of a new generation of lasers.
     2) In these optical studies of quantum dots, the
semiconductor dots and rings are made from indium arsenide
embedded in gallium arsenide, and the structures were grown using
techniques developed within the past decade that allow much
smaller nanostructures to be created than were previously
possible. In these new experiments, electrons are introduced one
by one into individual quantum dots while the optical emission of
the dots is measured with great precision. These studies provide
new perspectives on the internal quantum-mechanical workings of
quantum dots; the ultimate goal is to create useful electronic
and optical nanomaterials that have been quantum-mechanically
engineered by tailoring the shape, size, composition, and
position of various quantum dots.
     3) Concerning the physics of quantum dots, adding even a
single electron to such a system requires a significant amount of
extra energy because of the repulsion between the negatively
charged electrons as they are forced into a smaller volume. One
result of this, called the "Coulomb blockade", is to make
possible a greater laboratory control of the number of electrons
in a quantum dot, i.e., researchers can tune the number of
electrons by manipulating input energy.
     4) In general, optical excitation of a semiconductor leads
to the creation of a quasi-particle known as an "exciton" -- a
negatively charged electron bound together with a positively
charged "hole". In contrast to the Coulomb blockade resulting
from electrical injection of electrons into a quantum dot, such
dots remain neutrally charged following optical excitation, and
the quantum dot exciton has been studied in detail by measuring
the light emitted when the hole and electron recombine.
     5) The author concludes: "Quantum dots have great
flexibility because their properties can be artificially
engineered, but this comes at a price. Nature has given us atoms;
scientists must make quantum dots. Further advances in this
exciting field of science and technology will depend heavily on
the creativity of physicists, chemists, and materials scientists
who make these tiny structures."
-----------
Daniel Gammon: Electrons in artificial atoms.
(Nature 22 Jun 00 405:899)
QY: Daniel Gammon, Naval Research Laboratory Washington, US)
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 28Jul00
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

3. EARTH SCIENCES:
ON OCEAN TIDES AND CLIMATE CHANGE
The gravitational forces of the Sun and Moon deform the shape of
the Earth, causing tides in the oceans, atmosphere, and solid
body of the Earth, with the most visible tidal effects the
displacements of the ocean surface. For many years one of the
important questions in geophysics is whether the energy of ocean
tides is dissipated in deep water or in shallow coastal seas, the
answer to this question having important implications beyond
tidal dynamics.
... ... Carl Wunsch (Massachusetts Institute of Technology, US)
presents a commentary on recent research in this field, the
author making the following points:
     1) The author points out that the Moon is receding from the
Earth at approximately 4 centimeters per year, as measured by
laser reflectors left on the Moon by astronauts. One question
concerns how this motion is related to ocean circulation.
According to Kepler's laws, the recession of the Moon from the
Earth implies there is a continuing loss of energy in the Earth-
Moon system of 3 x 10^(12) watts (3 terawatts), mostly in the
ocean. But where in the ocean is this energy dissipated, and what
are its effects? Recent work by G.D. Egbert and R.D. Ray (Nature
405:775 2000) has produced evidence that dissipation of tidal
energy in the deep sea, and the resulting mixing, are controlling
features of the overall ocean circulation.
     2) The current picture of the oceans includes a wind-driven
upper circulation that gives rise to massive near-surface flows
such as the Gulf Stream, and superimposed on this circulation is
an ocean circulation whose driving forces are not yet clear. One
hypothesis, based on previous considerations and on the new data,
is that both wind- and tide-driven controls determine the rates
at which the ocean transports heat and fresh water, and if this
hypothesis survives further tests, the author suggests there are
several implications: a) This hypothesis brings into question the
extent to which current uniform mixing models of the ocean
circulation can either reproduce the present-day circulation or
predict responses to external changes. b) This hypothesis also
suggests that the rate-limiting factor for oceanic heat transport
is not primarily the surface density gradient imposed on the
ocean (producing the so-called "*thermohaline circulation"), but
rather it is the strengths and patterns of the wind and the
distribution of the tides.
     3) The author proposes the following consequences of the
wind/tide hypothesis: a) Atmospheric wind patterns must be known
in considering past and future climate change. b) Changes in
tidal distributions and the consequent mixing must be understood
over geological time: over longer periods in the past, the entire
continental configuration was different, with radically different
tidal distributions and mixing.
     4) The author concludes: "It appears that the tides are,
surprisingly, an intricate part of the story of climate change,
as is the history of the lunar orbit."
-----------
Carl Wunsch: Moon, tides, and climate.
(Nature 15 Jun 00 405:743)
QY: Carl Wunsch [cwunsch@pond.mit.edu]
-----------
Text Notes:
... ... *thermohaline circulation: The term "thermohaline" refers
to the joint activity of salinity and temperature in the oceans,
and thermohaline circulation refers to the convective process
produced by thermohaline gradients.
-------------------
Related Background:
GEOPHYSICS:
TIDAL CYCLES AND RAPID CLIMATE CHANGE
     Over the course of geologic history, the environment on
Earth has been far from static. Geologic evidence suggests that
600 million years ago the atmosphere lacked sufficient oxygen to
support animal life. More recently, as indicated by sediments
recording conditions over the past 500,000 years, the climate of
the planet varied between at least two different states. The
record from the past 150,000 years is particularly well-
preserved, offering details concerning repeated climate changes.
Between approximately 131,000 and 114,000 years ago, a warm
period similar to the climate of today occurred. This was
followed by what is called the "Wisconsin ice age", which ended
approximately 12,000 years ago when the current relatively warm
*Holocene period began.
     Records of changes in Earth's climate are particularly clear
in high-resolution ice cores, which can preserve histories of
local climate (as reflected in snowfall and temperature),
regional climate (as reflected in wind-blown dust, sea salt,
etc.), and broader climate (as reflected in trace gases deposited
from the atmosphere) -- all on a common time scale that can
demonstrate synchrony of climate changes over wide regions.
     High resolution ice-core and deep-sea sediment-core records
over the past million years show evidence of abrupt changes in
climate superimposed on slow alternations of ice-ages and
interglacial warm periods.
     The term "solar irradiance" refers to the amount of solar
irradiation received from the Sun, and this can vary considerably
and with a complex of periodicities. In 1920, the meteorologist
Milutin Milankovic (1879-1958) proposed that small changes in
Earth's orbit, *precession, and *inclination affect the heat
balance and modify climate (the alterations called "solar
forcing"). The Milankovic hypothesis was not taken seriously
until 1976, when teams studying sediment cores from the ocean
floor constructed a history of ocean temperature that matched the
predictions of the Milankovic hypothesis, with two different
ocean cores providing similar results.
... ... C.D. Keeling and T.P. Whorf (University of California San
Diego, US) present a proposal to explain sudden climate changes
on the scale of thousands of years, the authors making the
following points:
     1) Variations in solar irradiance are generally believed to
explain climatic change on 20,000- to 100,000-year time-scales in
accordance with the Milankovic theory of the ice ages, but there
is no conclusive evidence that variable solar irradiance can be
the cause of abrupt fluctuations of climate on time-scales as
short as 1000 years.
     2) The authors propose that such abrupt millennial changes,
seen in ice and sedimentary core records, were produced in part
by well characterized almost periodic variations in the strength
of the global oceanic tide-raising forces caused by resonances in
the periodic motions of the Earth and Moon. A well-defined 1800-
year tidal cycle is associated with gradually shifting lunar
declination from one episode of maximum tidal forcing on the
centennial time-scale to the next. An amplitude modulation of
this cycle occurs with an average period  of approximately 5000
years, associated with gradually shifting separation intervals
between *perihelion and *syzygy at maxima of the 1800 year cycle.
     3) The authors propose that strong tidal forcing causes
cooling at the sea surface by increasing vertical mixing in the
oceans. The authors suggest that on the millennial time-scale,
this tidal hypothesis is supported by findings, from sedimentary
records of *ice-rafting debris, that ocean waters cooled close to
the times predicted for strong tidal forcing.
-----------
C.D. Keeling and T.P. Whorf: The 1800-year oceanic tidal cycle: A
possible cause of rapid climate change.
(Proc. Natl. Acad. Sci. US 11 Apr 00 97:3814)
QY: Charles D. Keeling [cdkeeling@ucsd.edu]
-----------
Text Notes:
... ... *Holocene period: The most recent epoch of the geologic
time scale, from approximately 10,000 years ago to the present.
... ... *precession: In general, the wobbling motion of a
spinning top or gyroscope in which the axis of rotation gradually
sweeps out a conical volume. The spinning Earth undergoes a slow
precession due to the combined gravitational attraction of the
Sun, Moon, and planets.
... ... *inclination: In general, the angle between the orbital
plane of a body and the reference plane centered on the object
around which the body is revolving.
... ... *perihelion: The point in an elliptical orbit around the
Sun which is nearest the center of the Sun.
... ... *syzygy: In this context, those points in the orbit of
the Moon where the Moon, Earth, and Sun are in a straight line.
... ... *ice-rafting debris: In general, in this context, "ice-
rafting" is the transport of rock particles and other materials
by floating ice.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Jun00
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

4. EVOLUTIONARY BIOLOGY:
ON THE ORIGIN OF THE CELL NUCLEUS AND THE WOESE-MAYR CONTROVERSY
     Confronted with the enormous diversity of biological
organisms on this planet, a diversity compounded by biological
organisms living harmoniously within biological organisms, and
even biological organisms living within biological organisms that
live within biological organisms, biologists have devoted much
effort during the past few centuries to classification, the
search for categorization schemes that would not only facilitate
studies of biological systems, but hopefully also reveal
fundamental truths. And as might be expected, classification
schemes are often in conflict, producing controversy, disputes
that often rage for decades. Such "science wars" exist in every
branch of science, and one current intense and sometimes
vituperative war in biology, the Woese-Mayr controversy, which
might be called the "War of the Kingdoms", is now occupying the
attention of many biologists.
     In general, the Woese-Mayr controversy concerns the broad
classification of all living systems into either two or three
kingdoms, and although to the non-biologist the controversy might
seem overdrawn, it does in fact in its details have serious
implications for our understanding of the evolution of life on
Earth, and it is a controversy both substantive and intriguing.
It is also a controversy, in outline at least, between
interpretations of recent data in molecular biology (with an
emphasis on chemistry) and interpretations of classical data in
cell biology (with an emphasis on morphology).
     In this context, the term "eukaryotes" refers to biological
cells that contain a cell nucleus, and the term "prokaryotes"
refers to biological cells that do not contain a cell nucleus,
and we are concerned here with single-celled microorganisms, the
primeval biological systems from which all life on Earth evolved.
     In biology, the term symbiosis refers to an intimate and
protracted association of individuals of different species, and
the term "symbiogenesis" refers to the genetic integration of
long-term associated members of different species.
     The archaebacteria (also called the Archaea) are prokaryotes
considered to be ancient compared to other kingdoms, and 
possibly the most ancient life forms and the ancestors of all
eukaryotes. They typically exist in extreme environments, and
include the methane-producing bacteria (methanogens), the
"salt-loving" bacteria (halophilic bacteria), and the sulfur-acid
tolerant thermoacidophilic bacteria.
     All prokaryotes other than archaebacteria are called
"eubacteria", the term referring to a large and diverse group of
bacteria lacking photosynthetic pigments and marked by a
sensitivity to particular antibiotics and by the incorporation of
muramic acid into their cell walls.
     "Mitochondria" are double-membrane enclosed organelles of
cells that are involved with several important biochemical
pathways, including electron transport and oxidative metabolism.
Various types of eukaryotic cells may contain from none to a few
to several thousand mitochondria in each cell type. The
mitochondria are relatively large cylindrical structures up to 10
microns long and up to 2 microns in diameter, and they are
believed to have originated as organisms that became symbiotic
with eukaryotic cells.
     The term "protists" (Proctista) refers to one of the
phylogenetic kingdoms, this category defined mostly by exclusion
and containing all the eukaryotic nucleated organisms that cannot
be classified as animal, plant, or fungus. Protists include
protozoans, algae, kelps, slime molds, and many obscure
eukaryotes. The term "amitochondriate protist" refers to a
protist without mitochondria.
     In this context, a "chimera" is any cell or organism with
genetic material from two or more genotypes (e.g., two or more
species). 
... ... L. Margolis et al (3 authors at 2 installations, US ES)
present a detailed hypothesis concerning the evolutionary origin
of the eukaryote nucleus, their analysis coupled with a critical
discussion of the Woese-Mayr controversy. The authors make the
following points:
     1) The authors propose that the common ancestor of all
eukaryotes originated by genome fusion of two or more different
prokaryotes that became chimeras via symbiogenesis. Long-term
physical association between metabolically dependent consorting
bacteria led, by genetic fusion, to this chimera. In particular,
the chimera originated when an archaebacterium (specifically, a
thermoacidophil) and a motile eubacterium emerged under selective
pressure characterized by oxygen threat and scarcity both of
carbon compounds and electron acceptors. The authors suggest the
earliest descendant of this momentous merger, if alive today,
would be recognized as an amitochondriate protist. The authors
further suggest that their specific model of *syntrophic chimeric
fusion "can be proved by sequence comparison of functional
domains of motility proteins isolated from candidate taxa."
     2) The authors state their analysis requires the 2-domain
system (Bacteria/Eukarya) rather than the 3-domain system
(Archaea/Eubacteria/Eukarya). [Editor's note: For details, see
related background material below]. The authors state that the
prokaryote vs. eukaryote dichotomy, which replaced the animal vs.
plant dichotomy in biology, so far has resisted every challenge,
and that the molecular biology-based threat of the
microbiologists to the prokaryote vs. eukaryote evolutionary
distinction "seems idle." The authors state that in a history of
contradictory classifications of microorganisms since 1820, J.M.
Scamardella (1999) noted that Woese's entirely nonmorphological
system ignores symbioses. The authors (Margolis et al), however,
suggest that bacterial consortia and protist endosymbioses
"irreducibly underlie evolutionary transitions from prokaryotes
to eukaryotes." Although some prokaryotes are intermediate
between eubacteria and archaebacteria, no organisms intermediate
between prokaryotes and eukaryotes exist. The authors suggest
these facts render the nonmorphological taxonomies of Woese and
others inadequate. The authors suggest "only all-inclusive
taxonomy, based on the work of thousands of investigators over
more than 200 years on live organisms suffices for detailed
evolutionary reconstruction."
     3) The authors suggest that when Woese insists "there are
actually three, not two, primary phylogenetic groupings of
organisms on this planet" and claims that they, the
Archaebacteria (Archaea) and the Eubacteria, are "each no more
like the other than they are like eukaryotes," he denies the
various intracellular motile structures (e.g., the *mitotic
apparatus) absent in all prokaryotes and present in all
eukaryotes. The authors state: "He [Woese] minimizes these and
other cell biological data, sexual life histories including
cyclical cell fusion, fossil record correlation, and protein-
based molecular comparisons. The tacit, uninformed assumption of
Woese and other molecular biologists that all heredity resides in
nuclear genes is patently contradicted by embryological,
cytological, and cytoplasmic heredity literature... Many
eukaryotes, but no prokaryotes, regularly ingest entire cells,
including, of course, their genomes, in a single *phagocytic
event. This invalidates any single measure alone, including
*ribosomal RNA gene sequences, to represent the evolutionary
history of a lineage."
-----------
L. Margolis et al: The chimeric eukaryote: Origin of the nucleus
from the karyomastigont in amitochondriate protists.
(Proc. Natl. Acad. Sci. US 20 Jun 00 97:6954)
QY: Michael F. Dolan [mdolan@geo.umass.edu]
-----------
Text Notes:
... ... *syntrophic: The term "syntrophism" refers to the mutual
dependence of organisms for nutritional needs, especially between
strains of microorganisms.
... ... *mitotic apparatus: In general, the term "mitosis" refers
to the ordered process by which a cell nucleus and cytoplasm
divide into two progeny, and the term "mitotic apparatus" refers
to the dynamic cytoskeletal architecture involved in the temporal
staging of the process and the actual physical separation of
components.
... ... *phagocytic: Literally, "cell eating". A cell capable of
phagocytosis (e.g., an amoeba) has a mobile boundary which can
engulf particles or smaller cells, followed by incorporation of
the particles or smaller cells into the engulfing cell interior.
... ... *ribosomal RNA gene sequences: A ribosome (not to be
confused with riboZYME) is a small particle, a complex of various
ribonucleic acid component subunits and proteins that functions
as the site of protein synthesis. The tripartite kingdom proposal
of Woese and others is primarily based on gene sequence analysis
of particular ribosomal RNA fractions.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 28Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
EVOLUTIONARY BIOLOGY: ON THE PRIMEVAL KINGDOMS
During most of the past 100 years, the consensus view among
biologists was that all life on Earth evolved from a universal
common ancestor, a primitive cellular form that lived
approximately 3.5 to 3.8 billion years ago. This view capped
centuries of detailed classifications of living systems, with
relationships between organisms deduced and revised and revised
again as new discoveries were made. Detailed analysis of many
traits indicated, for example, that primates in the human family
(hominids) shared a common ancestor with apes, that this common
ancestor shared an earlier common ancestor with monkeys, and that
that common ancestor, in turn, shared an even earlier common
ancestor with primitive primates (prosimians; e.g., lemurs), and
so on. The view was thus of a "tree of life", with discrete
branches rising ever higher, but with all branches deriving from
a single primeval trunk. The known organisms that might have
comprised the primeval trunk and its lowest branches, however,
did not provide enough organismic information to define detailed
relationships, so that biologists were left with apparent
mysteries concerning radical evolutionary innovations between
primitive cells and more complex cells, between the first
biological cells and the appearance of multicellular fungi,
plants, and animals.
... ... W. Ford Doolittle (Dalhousie University, CA) presents a
review of recent changes in evolutionary theory concerning
primeval origins, the author making the following points:
     1) In the mid-1960s, Zuckerkandl and Pauling proposed a
revolutionary strategy that might supply the missing information
concerning evolutionary branching. The essential idea was that
instead of investigating anatomy and physiology, family trees of
living organisms should be based on differences in the monomer
sequences in selected genes or proteins. This approach became
known as "molecular phylogeny", and its essential basis was that
as a result of changes in genes caused by mutations, as two
species diverge from an ancestor, the gene sequences they share
will also diverge, and as time passes, the genetic divergence
will increase. Researchers could thus reconstruct the
evolutionary past of living species by assessing the apparent
history of divergence of genes or proteins isolated from those
species. Protein studies completed in the 1960s and 1970s
demonstrated the general utility of molecular phylogeny by
confirming and then extending the already established family
trees of well-studied groups such as the vertebrates.
     2) A new research development occurred in the late 1970s,
when Carl Woese proposed that the two-domain view of life that
divided living organisms into a) bacteria and b) cells with
internal membrane-bound organelles (eukaryotes) was no longer
tenable on the basis of molecular analysis. Woese suggested that
certain so-called "bacteria" formed a distinct third primary
group -- the archaea -- and that members of this group were as
different from other bacteria as bacteria were different from
eukaryotes. Woese suggested that although certain cells without
internal membrane-bound organelles (prokaryotes) classified as
bacteria might look like bacteria, they were genetically much
different, and their *ribosomal RNA (rRNA) supported an early
evolutionary divergence.
     3) Once the idea of three rather than two primeval domains
was accepted by researchers, an important question was which of
the two structurally primitive groups -- bacteria or archaea --
gave rise to the first eukaryotes? Because of evidence indicating
an apparent kinship between the gene expression/protein synthesis
machinery of archaea and eukaryotes, the consensus was that
eukaryotes diverged from the archaea.
     4) One important result of research in molecular phylogeny
during the past 15 years has been the production of strong
evidence supporting the "endosymbiont hypothesis". In biology,
the term "symbiosis" refers in general to an intimate and
protracted association of individuals of different species, and
"endosymbiosis" refers to a symbiotic association between cells
of two or more different species in which a smaller cell inhabits
a larger host cell. The endosymbiont hypothesis in evolutionary
biology, now a consensus view, proposes that the mitochondria
components of eukaryotes, so essential for eukaryote metabolism,
formed when an early eukaryote engulfed and then retained one or
more primitive bacteria of a certain type (alpha-proteobacteria).
Eventually, these bacteria relinquished their ability to live on
their own and transferred some of their genes to the nucleus of
the host cell, and these bacteria then evolved into the extant
mitochondria. In addition, and similarly, the hypothesis proposes
that some mitochondria-bearing eukaryotes ingested bacteria
capable of producing oxygen during photosynthesis
(cyanobacteria), and these resident symbiotic bacteria
subsequently evolved into the chloroplasts, the present internal
structures that drive photosynthesis in certain eukaryotes (e.g.,
in plant cells).
     5) Until very recently, therefore, the consensus view in
biology could be summarized as follows: The early descendants of
the last universal common ancestor -- a small prokaryote cell --
divided into two prokaryotic groups: the bacteria and the
archaea. Later, the archaea gave rise to the eukaryotes.
Subsequently, the eukaryotes gained valuable energy-generating
organelles -- mitochondria and (in the case of plants, for
example) chloroplasts -- by taking up and retaining certain
symbiotic bacteria.
     6) Several years ago, however, the consensus view stated
above became complicated by a large amount of evidence concerning
the phenomenon of "lateral gene transfer" (horizontal gene
transfer). Biologists recognize two types of gene transfer from
one organism to another: vertical and horizontal. Vertical gene
transfer occurs between parents and offspring, and horizontal
gene transfer is the transfer that may occur between organisms
otherwise. It is in bacteria that horizontal gene transfer has
been studied most extensively, particularly in the last decade.
Three types of horizontal gene transfer are known: conjugation,
transduction, and transformation. Conjugation is a type of sexual
reproduction exhibited by some bacteria, the process involving
the exchange of genetic material by means of a tube or bridge,
the transfer of DNA occurring either in one direction or in both
directions. Transduction involves the transfer of genetic
material from one bacterium to another with the intermediation of
a virus. Essentially, when the virus infects one bacterium, it
often carries away pieces of that bacterium's genome, and those
pieces, upon the infection of a new bacterium, become
incorporated into the second bacterial genome. Finally,
transformation is the process involving the uptake or
incorporation of DNA fragments (plasmids) by a bacterium, first
observed in 1944 by Oswald Avery. In this context, the important
aspect of horizontal gene transfer is that in primitive cells
such as prokaryotes it is now apparent that horizontal gene
transfer readily occurs across species. As a consequence of the
new evidence, the consensus view of the interrelations between
the primeval three kingdoms has now been seriously destabilized.
     7) In general, the current situation concerning the
evolutionary "tree of life" is as follows: The conceptual tree-
like structure with discrete branches is retained at the top of
the eukaryote domain, and also retained is the idea that
eukaryotes obtained mitochondria and chloroplasts from bacteria.
But the lower parts of the tree are now seen to involve an
extensive anastomosis of branches -- branches joining other
branches in a complex network of intersecting links -- resulting
from extensive horizontal gene transfer of single or multiple
genes, the horizontal gene transfer known to be common in
unicellular organisms. Thus, the author (Doolittle) suggests that
the "tree of life" lacks a single organism at its base, and that
"the three major domains of life probably arose from a population
of primitive cells that differed in their genes."
-----------
W. Ford Doolittle: Uprooting the tree of life.
(Scientific American February 2000)
QY: W. Ford Doolittle, Dalhousie Univ., Halifax, Nova Scotia, CA.
-----------
Text Notes:
... ... *ribosomal RNA (rRNA): See main report.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 5May00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
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: See main report.
... ... *intermediate metabolism: The sum of all metabolic
reactions between the uptake of nutrients and the excretion of
waste products.
... ... *lateral gene transfer: See previous report.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 3Jul98
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
BIO-TAXONOMY: EMERGENCE OF A SHARP PERSONAL CONTROVERSY
In a recent report (see related background material below) we
briefed a proposal by Ernst Mayr for a return to the *prokaryote-
eukaryote domain dichotomy from the present *archaea-eubacteria-
eukaryote domain trichotomy that has come to be used by many
biologists during the past decade. The details of the distinction
are provided in the report attached below, so we will not repeat
them. The controversy is of some interest in biology, as perhaps
a possible controversy concerning the present standard model
classification scheme of fundamental particles and forces in
physics would be to physicists. The domain trichotomy idea in
bio-taxonomy was first proposed in the 1980s by Carl Woese, who
like Ernst Mayr, is a member of the US National Academy of
Sciences. Writing in the same journal in which Mayr's proposal
appeared a few weeks ago, Woese now attempts to rebut Mayr's
ideas with an apparent singular vehemence, proposing that the
issue is more profound than that of merely assessing the utility
of a classification scheme. Woese writes: "If there were ever an
issue in biological classification that cannot be settled by
pedantry, it is this one." [Editor's note: This is not completely
gratuitous, since in his paper Mayr states, "Here it must be
remembered that Woese was not trained as a biologist and quite
naturally does not have an extensive familiarity with the
principles of classification."] And again from Woese: "To Mayr,
the issue is one of whether we should define two or three domains
and what the classificatory precedents or rules for deciding this
are. However, the *universal phylogenetic tree tells us that the
domains are unique among taxa and that their number and their
composition are not subject to classificatory fiat, but are
naturally defined." Woese's idea, apparently, is that the
trichotomous classification scheme is discovered rather than
constructed, which implies a significant problematic
philosophical subtext that is not amplified in his paper. In
summary, Woese makes the following points concerning his
position: 1) Mayr's article is not a taxonomic quibble but a "de
facto pronouncement on the nature of biology." A biological
classification is in effect an overarching evolutionary theory
that guides our thinking and experimentation, and it must be
structured to reflect evolutionary reality. 2) The prokaryote-
eukaryote dichotomy, which Mayr proposes to reinstitute, is a
failed taxonomic theory that was never recognized as theory and
therefore never tested in a timely fashion, with the consequence
that it has adversely affected the development of biology,
especially microbiology, in the latter half of this century. 3)
The scientifically perceived importance of a group of organisms
must reflect the natural importance of the group. 4) Microbial
diversity is far more than a listing of distinguishable microbial
species. We need to understand the quality of microbial
diversity, for it is the diversity that defines the biosphere of
this planet. 5) Evolution must be integrated into the fabric of
molecular biology... Any comprehensive understanding of a
biological entity, be it an organism or a molecule, necessarily
has an evolutionary component. Woese concludes: "The disagreement
between Dr. Mayr and myself is not actually about classification.
It concerns the nature of Biology itself. Dr. Mayr's biology
reflects the last billion years of evolution; mine, the first
three billion. His biology is centered on multicellular organisms
and their evolutions; mine on the *universal ancestor and its
immediate descendants. His is the biology of visual experience,
of direct observation. Mine cannot be directly seen or touched;
it is the biology of molecules, of genes and their inferred
histories. Evolution for Dr. Mayr is an "affair of phenotypes".
For me, evolution is primarily the evolutionary _process_, not
its outcomes. The science of biology is very different from these
two perspectives, and its future even more so." [Editor's note:
Ignoring the personalized undercurrents, the essential
controversy here is apparently between a classification system
based on utility criteria and observed similarities and
differences among entities (Mayr), and a classification scheme
based on theoretical and experimental molecular-genetic
relationships (Woese). The question of why there must be only one
classification scheme in use by working biologists is not
addressed by either Mayr or Woese.]
-----------
C.R. Woese (University of Illinois Urbana-Champaign)
Default taxonomy: Ernst Mayr's view of the microbial world.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11043)
QY: Carl R. Woese 
-----------
Text Notes:
... ... *prokaryote-eukaryote domain dichotomy: See report
attached below.
... ... *archaea-eubacteria-eukaryote domain trichotomy: See
reports attached below.
... ... *universal phylogenetic tree: Refers to the present
taxonomic-evolutionary classification scheme for all life on
Earth.
... ... *universal ancestor: Refers to the common ancestor from
which all life on Earth is considered to have derived.
-------------------
Summary & Notes by SCIENCE-WEEK  16Oct98
-------------------
Related Background:
BIO-TAXONOMY: A PROPOSAL FOR ONLY TWO EMPIRES
The physicist confronting bio-taxonomy for the first time may
experience bewilderment: there are in excess of 30 million
species of life forms, the classification system is far from
simple, the system has some historically based confusions, and
the system is frequently redefined. Perhaps only the organic
chemist can feel a full empathy here, since organic chemistry is
faced with the similar problem of classifying millions of organic
chemical entities. A fundamental consideration is that in the
context of such a diversity of objects, a self-consistent
classification scheme is of extreme importance. At the present
time, in biology, there is a significant controversy concerning
primary categories, and that is the subject of this report. Two
main groups of life forms have been recognized for some time,
prokaryotes and eukaryotes. Prokaryotes are cells without a cell
nucleus and other membrane-bound organelles, and eukaryotes are
cells with a cell nucleus and other membrane-bound organelles.
(Organisms composed of eukaryote cells are also called
"eukaryotes"). For example, all bacteria are prokaryotes; all
complex animals, plants, etc., are eukaryotes. Fifteen years ago,
C.R. Woese (University of Illinois Urbana-Champaign, US) proposed
that the prokaryotes actually consist of two main groups, the
eubacteria and the archaebacteria, and that the differences
between these two groups are as great as the differences between
prokaryotes and eukaryotes, and that as a consequence a
tripartite primary scheme should be used, the primary categories
(kingdoms or empires) consisting of Eubacteria, Archaebacteria,
and Eukaryotes. Woese's differentiation of eubacteria and
archaebacteria was based on *habitats, cell wall constituents,
genome organization, and various aspects of protein synthesis
biochemical machinery, and during the past decade most biologists
have apparently accepted his categorization scheme. ... ... Now
Ernst Mayr (1904- ), a prominent biologist, proposes a rejection
of the Woese categorization and a return to a scheme involving
only 2 primary categories (empires), the Prokaryotes and
Eukaryotes. Mayr makes the following points: 1) A classification
scheme is essentially an information storage and retrieval
system, permitting the location of an entity with a minimum of
effort and loss of time, the objective optimally achieved by
arranging entities in a hierarchy of classes, ranked by degree of
similarity. 2) Evidence indicates that the archaebacteria are so
much more similar to the eubacteria than to the eukaryotes, that
their removal from the prokaryotes is not justified. The
eukaryotes differ from the prokaryotes (including the
archaebacteria) not only by the possession of a nucleus and
*mitosis but also by individual protein-rich chromosomes,
*meiotic sexuality (including viable regular cell fusions),
cellular organelles, highly complex sets of regulatory genes, and
all those genes that permit biodiversity... When a biologist
speaks of eukaryotes, he or she has in mind palms, oaks, and
orchids; mice, bats, and whales; and hummingbirds, chickens, and
ostriches. And this world of highly evolved eukaryotes is simply
an entirely different world from the world of the two kinds of
bacteria, the Prokaryotes. 3) Ranking, in any scheme of
classification of items (living or not), is by necessity based on
degree of difference. The two kinds of bacteria, in the vast
majority of their characteristics, are exceedingly similar to
each other and fundamentally so different from the eukaryotes
that they have to be ranked as a single *taxon, the prokaryotes,
different from the only other taxon of this rank, the eukaryotes.
Mayr suggests that only a two-empire classification correctly
reflects this structure of the living world.
-----------
E. Mayr (Harvard University, US)
Two empires of three?
(Proc. Natl. Acad. Sci. US 18 Aug 98 95:9720)
QY: Ernst Mayr 
-----------
Text Notes:
... ... *habitats: Many species of archaebacteria live in hot
acidic conditions, growing best at temperatures approaching 100
degrees centigrade. Because of this, it has been suggested the
lineage is more ancient than eubacteria, arising during
primordial conditions on Earth.
... ... *mitosis: In this context, division of the cell nucleus.
... ... *meiotic sexuality: A reduction division process whereby
a nucleus divides by 2 divisions into 4 nuclei, each containing
half the original number of chromosomes.
... ... *taxon: The organisms comprising a particular taxonomic
entity.
-------------------
Summary & Notes by SCIENCE-WEEK  25Sep98
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

5. PLANT BIOLOGY:
ON PHOTOSYNTHESIS
     Photosynthesis is one of the more important biological
processes on Earth, providing nearly all the oxygen we breathe,
providing (either directly or indirectly) all the food we eat,
and providing the most important net input of energy into the
biosphere.
     From the standpoint of chemistry, photosynthesis can be
defined as the reductive carboxylation of organic substrates
carried on by chlorophyll-containing biological cells capable of
using light as their energy source. Fully oxidized carbon atoms
in the form of carbon dioxide are covalently linked ("fixed") to
organic acceptor molecules and are subsequently reduced and
rearranged into sugars and other organic molecules, with light
energy used to drive the fixation and provide the reducing power.
     Many differences exist among photosynthetic organisms with
respect to the components and organization of the photosynthetic
apparatus and the end products of photosynthetic energy
transduction. For example, the photosynthetic apparatus of
oxygen-evolving organisms (*eukaryotic plants and
*cyanobacteria), contains two different photosynthetic systems,
whereas nonoxygenic photosynthesis in the *purple photosynthetic
bacteria involves only one system. Nevertheless, there are a
number of features and principles associated with photosynthetic
energy transduction that are common to all organisms:
     a) The process is always associated with membranes
(*thylakoids in oxygen-evolving organisms; *chromatophore
membranes in photosynthetic bacteria).
     b) The process always involves multi-unit protein complexes.
Initially, light energy must be captured and transferred to a
photochemical reaction center, where it can be used to drive a
reduction-oxidation (redox) reaction. This occurs in complexes,
each complex containing a light-harvesting cluster of chlorophyll
molecules ("antenna complex"; "antenna system") and a
photochemical reaction center. The chemical redox energy
resulting from the photochemical reaction at the reaction center
can then drive a series of redox reactions, commonly termed
"electron transport" reactions, which result in spatial
separation of oxidized and reduced chemical species, and which
provide a source of chemical energy in the form of reducing
equivalents. Coupled with electron transport is the pumping of
protons across the membrane, and the free energy stored in the
resulting electrochemical potential difference of protons across
the membrane is used by an enzyme (ATP synthetase) to
phosphorylate adenosine diphosphate (ADP) and provide *adenosine
triphosphate (ATP) for the cell.
... ... R.J. Cogdell et al (3 authors at University of Glasgow,
UK) present a review of current research on photosynthetic light
harvesting in purple bacteria, the authors making the following
points:
     1) The past few years have seen remarkable progress in our
understanding of the very early light reactions in
photosynthesis, and a large part of this research involves the
study of the photosynthetic purple bacteria. These anaerobic
prokaryotes have proved to be excellent model organisms in which
to investigate the basic mechanisms of the primary light
reactions of photosynthesis.
     2) The light-absorbing pigments in purple-bacteria
photosynthesis, mainly bacteriochlorophyll-a and carotenoids, are
contained within two types of integral membrane pigment-protein
complexes: light-harvesting complexes and reaction centers. Solar
energy is absorbed by the light-harvesting components before
being rapidly and efficiently transferred to the reaction
centers. These reaction centers "trap" this light energy and
convert it into chemical energy via a series of transmembrane
redox reactions which initiate photosynthetic electron transport
and lead to proton pumping and ATP synthesis.
     3) Photosynthesis can occur in the absence of a light-
harvesting system, but only in very bright sunlight. The antenna
system associated with a reaction center increases the effective
cross-sectional area available for photon capture, and this
allows the reaction centers to be supplied with sufficient solar
energy to drive photosynthesis even on dull days. The combination
of light-harvesting complexes with a reaction center is the
"photosynthetic unit". In purple bacteria, the size of this unit
varies with the light intensity at which the bacteria are grown.
In very bright light, the purple-bacteria photosynthetic unit can
be as small as 30 bacteriochlorophyll-a molecules per reaction
center, while at low light intensity the unit can be as large as
several hundred such molecules per reaction center.
-----------
R.J. Cogdell et al: Photosynthetic light harvesting.
(The Biochemist, June 2000)
QY: Richard J. Cogdell [r.cogdell@bio.gla.ac.uk]
-----------
Text Notes:
... ... *eukaryotic plants: In general, plants whose cells
contain nuclei and other intracellular membrane-bound organelles.
(Cells without nuclei are "prokaryote" cells.)
... ... *cyanobacteria: A phylum of bacteria characterized by
blue-green (cyan) photosynthetic pigments, abundant in a variety
of habitats, particularly in fresh water and soil. Cyanobacteria
are responsible for generating a large portion of the free oxygen
in the Earth's atmosphere. They apparently produced stromatolite
limestone deposits, as well as the bulk of modern petroleum
deposits. (Stromatolites are laminated calcareous microbial
fossil deposits formed principally by cyanobacteria and algae.)
... ... *purple photosynthetic bacteria: Specifically, any of the
various photosynthetic bacteria that contain bacteriochlorophyll,
and are thus distinguished by purplish or reddish-brown pigments.
(But the term "purple bacteria" is sometimes used as a synonym
for the phylum Proteobacteria, a general category comprising a
large number of diverse forms.)
... ... *thylakoids: A sac-like vesicle containing the
photosynthetic pigments in photosynthetic organisms. In
prokaryotes, the thylakoids are of various shapes and are
attached to the plasma membrane; in eukaryotes, the thylakoids
are flattened and located in chloroplasts; in the chloroplasts of
higher plants, the thylakoids form dense stacks called "grana".
Isolated thylakoids preparations can carry out photosynthetic
electron transport and associated phosphorylation.
... ... *chromatophore membranes: In this context, the term
"chromatophore" refers, in general, to any of the particles,
isolated from photosynthetic organisms, that contain
photosynthetic pigments.
... ... *adenosine triphosphate (ATP): ATP is the most important
chemical energy source in all living cells, intimately involved
in various cell functions and cell metabolism, and an entity in
numerous cyclic chemical pathways involved in the synthesis of
various cell components.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 28Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
PURPLE BACTERIA, QUANTUM PHYSICS, AND PHOTOSYNTHESIS
Purple bacteria are a type of photosynthetic bacteria in which
the photosynthesis apparatus is apparently derived from the
plasma membrane. They are large organisms, about 0.5 microns in
diameter, and several microns in length, and the molecular basis
of the photosynthesis process in these bacteria has been
intensively investigated by molecular biologists. Physicists are
also interested in these organisms as examples of efficient
electron transfer systems. Recently, Xiche Hu and Klaus Schulten
(University of Illinois Urbana-Champaign, US) reviewed the
present structural model of the light harvesting system of purple
bacteria. The authors suggest the physical principles governing
the light harvesting and electron transfer processes of bacteria,
processes that have been selected and optimized over billions of
years of evolution, may one day be applied to the engineering of
solar cells.
-----------
QY: K. Schulten, Univ. Illinois Urbana-Champaign 217-333-3645.
(Physics Today August 1997) (Science-Week 10 Oct 97)
For more information: http://scienceweek.com/swfr.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

6. MEDICAL BIOLOGY:
ENVIRONMENT VS. HEREDITY IN THE CAUSATION OF CANCER
     There is considerable public confusion concerning the origin
of cancer. What we call "cancer" is essentially a set of diseases
of genes (see related background material below), but most
cancers are not inherited: the gene damage responsible for most
cancers is apparently produced by environmental factors affecting
the genetic information that controls replication of ordinary
tissue cells. In other words, the damaged gene (or genes)
responsible for a cancer is usually not inherited; most often the
damage is produced (or occurs spontaneously) during the life of
the individual.
     Certain types of cancer are indeed apparently familial,
determined primarily by hereditary factors, but most types of
cancer are non-familial ("sporadic"), with an unclear
contribution of hereditary factors to the response of the
individual to environmental factors. In general, studies of twins
make it possible to estimate the overall contribution of
inherited genes to the development of cancer, and such studies
form the basis of current views of the heritability of various
cancers.
... ... P. Lichtenstein et al (9 authors at 7 installations, SE
DK FI) now report a study of data on 44,788 pairs of twins listed
in the Swedish, Danish, and Finnish twin-registries, the purpose
of the study to assess the risks of cancer at 28 anatomical sites
for the twins of persons with cancer. Statistical modeling was
used to estimate the relative importance of heritable and
environmental factors in causing cancer at 11 of those sites. The
authors conclude as follows: "We conclude that the overwhelming
contributor to the causation of cancer in the population of twins
that we studied was the environment. For some of the forms of
cancer, in which a shared environment is important, it may be
possible to find clues in studies of childhood environment or
long-lasting family habits. The relatively large heritability
proportions for cancers at some sites, despite the wide
confidence intervals, suggest major gaps in our understanding of
hereditable cancer. Even for cancers for which there is
statistically significant evidence of a heritable component, most
pairs of twins were discordant for the cancer -- indicating that,
on the population level, the increase in the risk of cancer even
among close relatives of affected persons is generally moderate."
-----------
P. Lichtenstein et al: Environmental and heritable factors in the
causation of cancer.
(New England J. Med. 13 Jul 00 343:78)
QY: Paul Lichtenstein [paul.lichtenstein@mep.ki.se]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 28Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON GENETICS AND HUMAN CANCERS
The current consensus is that cancer results from the
accumulation of mutations in the genes that directly control the
birth and death of biological cells. But the mechanisms through
which these mutations are generated are the subject of continuing
debate and much research. It has been argued that an underlying
genetic instability is absolutely essential for the generation of
the multiple mutations that underlie cancer. On the other hand,
it has also been suggested that normal rates of mutation, coupled
with waves of *clonal expansion, are sufficient for the cancer
process to occur in humans. ... ... C. Lengauer et al (Johns
Hopkins University, US) present a review of observations
concerning the stability of the genome of human cancer cells, the
authors making the following points:
... 1) Numerous genetic alterations that affect growth-
controlling genes have been identified in neoplastic cells over
the past 15 years, and these observations provide persuasive
evidence for the genetic basis of human cancer. The alterations
can be divided into 4 major categories:
... ... a) Subtle sequence changes: These changes involve
nucleotide base substitutions or deletions or insertions of a few
nucleotides in the genome, and unlike the alterations described
below, they cannot be detected via cytogenetic analysis. Such
mutations, for example, occur in over 80 percent of pancreatic
cancers.
... ... b) Alterations in chromosome number: Such alterations
involve losses or gains of whole chromosomes. Such changes are
found in nearly all major human tumor types.
... ... c) Chromosome translocations: These alterations can be
detected cytogenetically as fusions of different chromosomes or
of normally non-contiguous segments of a single chromosome. At
the molecular level, such translocations produce fusions between
two different genes, endowing the fused genetic entity with
tumorigenic properties. Such translocations are known to occur in
the *chronic myelogenous leukemias.
... ... d) Gene amplifications: These are seen at the cytogenetic
level as homogeneously stained regions, and at the molecular
level they involve multiple copies of a gene. An example of gene
amplification occurs in advanced *neuroblastomas.
... 2) All 4 of the alterations described above occur commonly in
specific tumor types but are rarely or never observed in normal
cells. However, the existence of genetic alterations in a tumor,
even when frequent, does not mean that the tumor is genetically
unstable. By definition, instability is a matter of rate, and the
existence of a mutation provides no information about the rate of
its occurrence. The higher prevalence of mutations in tumor cells
compared with normal cells still requires explanation.
... The authors conclude: "One can argue persuasively that all
chemotherapeutic compounds used at present are more toxic to
cancer cells than to normal cells only and specifically because
of the defective *checkpoints that occur in cancer cells. This
line of reasoning suggests that, although instability may be
essential for neoplasia to develop, it may also prove to be its
Achilles' heel when the tumor is attacked by the right agents.
Further research to define the molecular and physiological bases
of instability may, therefore, yield entirely new approaches to
treating common forms of cancer."
-----------
C. Lengauer et al: Genetic instabilities in human cancers.
(Nature 17 Dec 98 396:643)
QY: Christoph Lengauer [lengauer@jhmi.edu]
-----------
Text Notes:
... ... *clonal expansion: In this context, this refers to the
expansion of a population of cells all deriving from a single
mutated cell.
... ... *chronic myelogenous leukemias: (granulocytic leukemias)
These leukemias are characterized by an uncontrolled
proliferation of myelopoietic cells (blood cells derived from
bone marrow).
... ... *neuroblastomas: Neuroblastomas are malignant neoplasms
characterized by only slightly differentiated immature nerve
cells of embryonic type.
... ... *checkpoints: In this context, the term "checkpoint"
refers to a point in the eukaryotic cell division cycle where the
cycle can be halted until conditions are suitable for the cell to
proceed to the next stage. (eukaryotic = containing membrane-
bound organelles such as a nucleus.)
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 26Mar99
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ENVIRONMENTAL RISKS AND CANCER
In the study of cancer, many oncologists emphasize the
interaction of genetics and environment, pointing out that
genetic factors acting alone are believed to explain only about
5% of all cancer, with the remainder attributable to extrinsic
environmental factors that act in conjunction with both genetic
and acquired susceptibility. Environmental factors such as
carcinogenic industrial pollutants thus interact with individual
susceptibilities due to ethnicity, gender, health status,
nutrition, age, and various genetic polymorphisms. Frederica P.
Perera (Columbia University, US), in a review of genetic
susceptibility to environmental carcinogenic factors, emphasizes
that most cancer results from the interaction of genetics and the
environment, with new molecular evidence indicating that specific
human groups characterized by predisposing genetic traits
(including those associated with ethnicity and gender) may have
heightened risk from certain exposures. The author suggests that
more research will allow future environmental regulatory policies
to explicitly account for individual variation in susceptibility
to environmental carcinogens.
QY: F. Perera 
(Science 7 Nov 97) (Science-Week 5 Dec 97)

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

7. FOCUS REPORT: ON COSMIC HEAT DEATH
"There is no question as to the way in which energy runs down in
[the astronomical Universe]. It is first liberated in the hot
interior of a star in the form of quanta of extremely short
wavelength and excessively high energy. As this radiant energy
struggles out to the star's surface, it continually adjusts
itself, through repeated absorption and re-emission, to the
temperature of that part of the star through which it is passing.
As longer wavelengths are associated with lower temperatures...,
the wavelength of the radiation is continually lengthened; a few
energetic quanta are being transformed into numerous feeble
quanta. Once these are free in space, they travel onward
unchanged until they meet dust particles, stray atoms, free
electrons, or some other forms of interstellar matter. Except in
the highly improbable event of this matter being at higher
temperature than the surfaces of stars, these encounters still
further increase the wavelength of the radiation, and the final
result of innumerable encounters is radiation of very great
wavelength. The quanta have increased enormously in numbers, but
have paid for their increase by a corresponding decrease in
individual strength. In all probability, the original very
energetic quanta had their source in the annihilation of protons
and electrons, so that the main process of the Universe consists
in the energy of exceedingly high availability which is bottled
up in electrons and protons being transformed into heat energy at
the lowest level of availability."
-----------
James H. Jeans: _The Universe Around Us_
(Cambridge University Press, Cambridge UK 1929)
-----------
James H. Jeans (Sir James Jeans) (1872-1946) was a mathematical
physicist noted for his work on the kinetic theory of gases, the
forms of energy radiation, giant and dwarf stars, the nature of
spiral nebulae, and the origin of the Cosmos. Jeans was a
professor of mathematics at Princeton University (US) 1905-1909,
then lecturer at Cambridge University (UK) 1910-1912. After the
age of 40, Jeans had no academic affiliation, devoting himself to
private research and writing. He was knighted in the UK in 1928.
His _Dynamical Theory of Gases_ (1904), which became a standard
text, was written at the age of 32 while convalescing from an
illness. His knowledge and love of music was considerable, and he
became director of the UK Royal Academy of Music in 1931.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

8. FROM THE SW ARCHIVE: 
MARIETTA BLAU: THE DESTRUCTION OF A CAREER IN PHYSICS
A nuclear emulsion is a photographic emulsion specifically
designed to register individual tracks of ionizing particles. The
emulsion technique, so important in the early history of 20th
century particle physics, was developed in the 1930s primarily by
Marietta Blau (1894-1969), an Austrian physicist. Blau was a
Jew, and she was forced to flee her laboratory when the Nazis
occupied Austria in 1938. The other people in the laboratory,
including Blau's assistant, the physicist Hertha Wambacher, were
in fact Nazis themselves, and they immediately assumed control of
the laboratory and may have ordered the seizure of Blau's
notebooks, which were confiscated as she exited Germany from
Hamburg. Although the chemists and physicists of the nuclear
emulsion group who remained in Germany and Austria for the most
part continued their work and after the war moved into important
professorships in those countries, Marietta Blau, the prime
force in the early development of nuclear emulsion technology,
wandered from country to country as a lost experimental physicist
without a laboratory. She died poor and unemployed 20 years after
the war ended. Peter Galison, a physicist and historian of
science, recently published a book entitled IMAGE AND LOGIC: A
Material Culture of Microphysics (University of Chicago Press,
1997), and in a recent issue of the journal Physics Today he
presents an excerpt from that book that details the Blau story.
He says, "the fate of Marietta Blau signifies what it meant to be
a woman, a Jew, and a solitary physicist fleeing the convulsing
world of Nazi Austria."
-----------
(Physics Today November 97) (Science-Week 21 Nov 97)

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
NOTICES  
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 

CHANGE OF EMAIL ADDRESS:
If at any time you need to change the Email address at which you
receive SW, please send the information to:
request@scienceweek.com

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 

SCIENCE-WEEK SUBSCRIPTIONS:
Subscriptions to ScienceWeek cost as little as US$15 a year.
Complete subscription information is available at:
http://scienceweek.com/subinfo.htm

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

The first issue of SCIENCE-WEEK appeared May 1, 1997, and it has
been published regularly each week since that date. SW is
designed to cross existing conceptual and linguistic barriers
between the scientific disciplines. In general, the biology is
written for physicists and chemists, and the physics and
chemistry are written for biologists, with an attempt to retain
some exactitude in the particular science involved in the news.
These are the aims. Undoubtedly, we are not always successful,
and for that we apologize. In any case, what we hope is that our
readers are reading out of their fields more than in their
fields, since that is the essence of this publication.

We welcome comments, suggestions, and criticisms from our
subscribers. Public letters relevant to any report are also
welcome. Editorial contact: [editors@scienceweek.com].

Editor/Publisher: Dan Agin
Managing Editor: Claire Haller
Associate Editor: Joan Oliner

Copyright (c) 1997-2000 SCIENCE-WEEK/Spectrum Press Inc.
All Rights Reserved

---------------------------------------------
This publication is protected by U.S. and International Copyright
Laws, and no display, transmission, or duplication in any medium,
including BBS, Internet Email, website duplication, fax, or print
is permitted without the explicit consent of the holder of the
copyright. SCIENCE-WEEK is published by Spectrum Press Inc.,
3023 N. Clark Street #109, Chicago, 60657-5205 IL, USA.
---------------------------------------------
-----end file