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.

September 24, 1999 -- Vol. 3 Number 39

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Here is a biologist examining a culture of nerve
cells in a small dish. One set of nerve cells
examining another set of nerve cells. Not quite
a trivial scenario.
-- Anonymous

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

Contents of This Issue:

1. On the Migration of Planets
2. On the Future of Quantum Computing
3. Early Animal Evolution
4. The Evolution of Dinosaurs
5. Biology of Aging: Caloric Restriction and Gene Expression
6. Control of Infectious Diseases 1900-1999

In Focus: On the Quantum Principle

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

1. ON THE MIGRATION OF PLANETS
The "Solar System" is the collective name for the Sun and all the
bodies that orbit the Sun, including the 9 major planets and
their 61 known satellites, plus countless asteroids, comets, and
meteoroids. The farthest point of the orbit of Pluto from the Sun
(the "aphelion") is at 7.3 billion kilometers, and this marks the
outer limit of the known planetary system. But many *Kuiper belt
objects lie beyond this, and a number of long-period comets
apparently travel as much as half-way to the nearest star. With
the exception of the comets, all bodies of the Solar System orbit
the Sun in the same direction as the Earth, along orbits that lie
close to the plane of the Earth's orbit and the Sun's equator.
Most objects in the Solar System spin in the same direction as
their orbital motion, and this motion reflects the common origin
postulated for the Solar System -- the contraction of a rotating
cloud of interstellar gas and dust (the "Solar Nebula")
approximately 4.6 billion years ago. One important question
concerning the planetary orbits involves their stability: Once
the planets are formed, are their orbits relatively fixed or do
their orbits undergo significant changes during the history of
the system?
... ... Renu Malhotra (Lunar and Planetary Institute Houston, US)
presents a review of current research concerning the history of
Solar System planetary orbits, the author making the following
points:
     1) Until recently, most astronomers have generally presumed
that the observed distances of the planets from the Sun indicate
their origins in the Solar Nebula, and the orbital radii of the
planets have been used to infer the mass distribution within the
Solar Nebula. With this basic information, theorists have derived
constraints on the nature and timescales of planetary formation.
     2) It is widely accepted, however, that many of the smaller
bodies in the Solar System (asteroids, comets, and moons) have
altered their orbits during the past 4.5 billion years, some more
dramatically than others. For example, Earth's Moon is believed
to have formed within 30,000 kilometers of Earth, but it is now
at a distance of 384,000 kilometers. The Moon has apparently
receded by nearly 100,000 kilometers in the past billion years
because of *tidal forces exerted by Earth.
     3) Until recently, there was little data to support the idea
that the orbital configuration of the planets has altered
significantly  since their formation. But developments during the
past 5 years indicate that the planets may indeed have migrated
from their original orbits. The discovery of the Kuiper belt has
demonstrated that our Solar System does not end at Pluto.
Approximately 100,000 icy "minor planets", ranging between 100
and 1000 kilometers in diameter, and an even greater number of
smaller bodies, occupy a region extending from Neptune's to at
least twice that distance. The distribution of these objects
exhibits prominent non-random features that cannot be readily
explained by the current model of the Solar System.
     4) Although at this time other explanations cannot be ruled
out, the orbital distribution of Kuiper belt objects has been
interpreted to provide strong evidence of planetary migration.
The data suggest that Neptune was born approximately 3.3 billion
kilometers from the Sun and then moved approximately 1.2 billion
kilometers outward, an alteration almost 30 percent of its
present orbit. For Uranus, Saturn, and Jupiter, the magnitude of
migration was apparently smaller, perhaps 15, 10, and 2 percent
respectively. The estimates are less certain for these planets
because, unlike Neptune, they could not leave a direct imprint on
the Kuiper belt population.
     5) During the past 5 years, the search for and observations
of extrasolar planetary systems has yield some evidence
consistent with the idea of inward orbital migrations of large
planets, but the relationship between these extrasolar objects
and the large planets in our own system is not yet clear.
     6) The author concludes: "An elucidation of the relation
between the newly discovered extrasolar companions and the
planets in our Solar System awaits further theoretical and
observational developments. Nevertheless, one thing is certain:
the idea that planets can change their orbits dramatically is
here to stay."
-----------
Renu Malhotra: Migrating Planets.
(Scientific American September 1999)
QY: Renu Malhotra, Lunar and Planetary Institute, Houston TX US.
-----------
Text Notes:
... ... *Kuiper belt: In 1951 the astronomer Gerard P. Kuiper
(1905-1973) postulated the existence of a belt of objects beyond
the orbit of Pluto. Both the existence and nature of the objects
were matters of speculation for decades, until finally in 1992
Jewitt and Luu identified the first Kuiper object. The current
estimate is that as many as 10^(8) objects larger than 10
kilometers in diameter may exist in what is called the "Kuiper
belt", a disc that hugs the plane of the planetary system and
lies between 35 and 1000 *AU from the Sun. Observations to date 
have yielded some 55 trans-Neptune bodies with radii on the order
of 100 km or larger, and Pluto is considered by some astronomers
to be a member of this population.
... ... *AU: Astronomical Unit. 1 AU = the mean distance from the
Sun to the Earth = approximately 93 million miles, and exactly
149,597,870 kilometers.
... ... *tidal forces: In general, a "tidal force" is a force
arising in a system of one or more bodies as a result of
differential gravitation: different parts of the system
experience different accelerations, and this can result in the
production of tides and elongations of a body in the direction of
a nearby massive body.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 24Sep99
-------------------
Related Background:
ON MODELS FOR THE DEVELOPMENT OF SOLAR SYSTEMS
Recent discoveries of extrasolar giant planets are challenging
standard ideas about planet formation. Astronomers are now faced
with increasing numbers of apparently unusual planetary systems,
and simulation models are being developed to explain these giant
planets around Sun-like stars. ... ... Brett Gladman
(Observatoire de la Cote d'Azur, FR) presents a brief review of
present extrasolar planetary system simulation model research,
the author making the following points: 1) A bewildering variety
of extrasolar planetary systems are now known. The systems that
have been discovered are heavily biased by the methods used to
detect them, with the bias towards planets at least as large as
Jupiter and relatively near their stars, but the observations
have provided evidence of the apparent diversity of solar
systems. 2) Concerning the formation of these giant planets, one
general theoretical scheme involves the aggregation of kilometer-
size *planetesimals from the disk-like gas nebula surrounding a
young star. But the details are vague: the physics of these
processes is poorly known. We do not understand how planetesimals
form, and we do not understand the physical conditions
(temperature, mass, and density as a function of solar distance)
of the nebula. 3) Simulation models produce a wide variety of
final planetary systems. Some of these model systems have a few
widely spaced planets, others have many Uranus-sized planets
evenly spaced, while yet others have large planets closely packed
together... The variety found in these simulations may be due to
the fact that the range of physical parameters used in these
models (due largely to our ignorance) is far wider than the range
of parameters apparently present in protoplanetary nebulae.
Another cause of the variety of simulation results is that the
models involve a highly chaotic dynamical evolution of a small
number of planetary embryos, and this results in variable
locations and numbers of planets. Stable systems, for example,
have been found to range from 1 to 7 planets. Thus it is
unreasonable to demand that planet-formation theories produce our
own Solar System in detail. This is in contrast to the
"regularist" thinking of several decades ago, when it was popular
to postulate that most planetary systems would have a Jupiter
analogue just beyond the distance at which the temperature is low
enough so that icy solids condense and local accretion rates
increase. 4) The author states: "The near future holds the
promise of a doubling or tripling of the number of extraplanetary
systems known, with reasonable chances of detecting systems with
planets both smaller and further from their stars [than the giant
planets so far detected]."
-----------
[Editor's note: In addition to the related background material
below, other background material can be found in the SW Focus
Report "Astrophysics: Extrasolar Planets" available at URL
[http://scienceweek.com/swfr021.txt].]
-----------
Brett Gladman: Twenty-Eight ways to build a solar system.
(Science 10 Dec 98 396:513)
QY: Brett Gladman [gladman@obs-nice.fr]
-----------
Text Notes:
... ... *planetesimals: Planetesimals are bodies with dimensions
of 10^(-3) to 10^(3) meters that are believed to form planets by
a process of accretion. The term "accretion" refers to an
aggregation, an increase in the mass of a body by the addition of
smaller bodies that collide and adhere to it, provided the
relative velocities are low enough for coalescence. As the mass
of the agglomerate increases, so does the rate of accretion, and
this accretion process is believed to generally occur in the form
of a disk. A stellar accretion disk is a swarm of dust grains
that evolve into planetesimals and then planets.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 29Jan99
-------------------
Related Background:
ON THE ORIGIN OF THE SOLAR SYSTEM
During the past two centuries, astronomers have considered two
types of theories for the origin of our Solar System planets.
Catastrophic theories proposed that these planets formed from
some improbable cataclysm such as the collision of the sun and
another star, while gradualist theories proposed that the planets
formed naturally with the Sun. At the present time, as a result
of evidence accumulated during the past five decades, the
gradualist idea is the consensus idea, and nearly all astronomers
now believe that planets form naturally as a by-product of star
formation. ... ... John A. Wood presents an extensive review of
current ideas concerning the origin of the Solar System, and the
author makes the following points: 1) The current theory is that
the Sun and the planets were born from a rotating disk of cosmic
gas and dust (the "solar nebula"), and the flattened form of the
disk constrained the planets that formed from it to have orbits
lying in the same plane, or nearly so, the planets all moving in
the same direction in which the disk had turned. 2) The idea of a
solar nebula was first formulated in 1755 by *Immanuel Kant.
Although his treatment of the problem was only qualitative, its
precepts were remarkably similar to those considered fundamental
today, and at the present time, Kant's original idea is
considered to be correct: stars and their disks form in much the
same way he pictured, the formation resulting from the
gravitational collapse of huge volumes of thinly dispersed
interstellar gas and dust onto appropriate nuclei. 3) The present
view is that the solar nebula was hot near its center, tapering
off to a cold region, then a very cold region at its outermost
margins. Thus, the falloff of nebula temperature with
heliocentric distance defined 3 radial zones. The innermost zone
was too warm for water to condense as ice; objects forming in the
innermost zone consisted entirely of *silicate minerals and other
*refractory materials, and ultimately became the terrestrial
planets (Mercury, Venus, Earth, and Mars). The next zone of the
solar nebula was colder, water ice was stable, and a vast
blizzard of snowflakes gave rise to the much larger Jovian
planets (Jupiter, Saturn, Uranus, and Neptune). In the outermost
and thus coldest zone of the solar nebula, condensed matter was
also icy, but matter was too sparsely distributed to accrete into
sizable planets; instead matter remained dispersed in small icy
planetesimals -- comet nuclei -- in what is now called the
*Kuiper belt. Evidence suggests the planets assembled themselves
quickly: Although the process differed in detail from zone to
zone, virtually everything was in place within 10 million years,
by which time the solar nebula had largely dissipated. 4) Nearly
four centuries of telescopic observation, combined with four
decades of space exploration, have taught us this essential truth
about the Solar System: While the Sun and its planetary system
surely arose from one grand spiral of gas and dust in a flurry of
collective activity, the results are hardly a homogeneous set of
characterless orbiting entities. Instead this grand scheme of
formation has yielded amazing diversity in the properties of the
various objects in the Solar System.
-----------
John A. Wood (Smithsonian Astrophysical Observatory, US)
Forging the planets.
(Sky and Telescope January 99)
QY: John A. Wood, Smithsonian Astrophysical Observatory,
Cambridge, MA US.
-----------
Text Notes:
... ... *Immanuel Kant (1724-1804): Kant is best known as a
philosopher, but he first studied mathematics and physics, and
the year he obtained his doctorate degree (1755) he published his
physical view of the Universe in *General History of Nature and
Theory of the Heavens). In this treatise, Kant described the
solar nebula hypothesis of planet formation, suggested that our
own galaxy is a lens-shaped collection of stars and that other
such "island universes" exist, and suggested that *tidal friction
slows the rotation of the Earth. All three propositions are the
current view in astrophysics.
... ... *tidal friction: A force between the oceans of the Earth
and the ocean floors caused by the gravitational attraction of
the Moon.
... ... *silicate minerals: (silicates) The most important and
abundant group of rock-forming minerals.
... ... *refractory materials: (refractory minerals) Minerals
resistant to decomposition by heat, pressure, or chemical attack.
The term is most commonly applied to heat resistance.
... ... *Kuiper belt: See notes in main report.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 11Dec98
-------------------
Related Background:
A MODEL FOR THE MIGRATION OF MASSIVE PLANETS
Planetesimals are bodies with dimensions of 10^(-3) to 10^(3)
meters that are believed to form planets by a process of
accretion. The term "accretion" refers to an aggregation, an
increase in the mass of a body by the addition of smaller bodies
that  collide and adhere to it, provided the relative velocities
are low enough for coalescence. As the mass of the agglomerate
increases, so does the rate of accretion, and this accretion
process is believed to generally occur in the form of a disk.  A
stellar accretion disk is a swarm of dust grains that evolve into
planetesimals and then planets. There is now evidence of apparent
massive planets in close orbits around stars, but the formation
of such massive planets in close orbits is unexplained. One
possibility is that these massive planets were formed in a more
distant orbit and then migrated inward. ... ... Murray et al (4
authors at 2 installations, CA) now report a theoretical analysis
of the behavior of planets and planetesimals in a stellar disk.
The calculations predict that gravitational interactions and
collisions between planet and planetesimals, if total
planetesimal surface density exceeds a certain value, may drive
the planet inward a great distance. The authors suggest this
mechanism may explain the presence of Jupiter-mass objects in
small orbits around nearby stars.
QY: N. Murray, Univ. of Toronto, Dept. of Theoretical Astro-
physics, Toronto, ON M5S 3H8 CA.
(Science 2 Jan 98) (Science-Week 16 Jan 98)
-------------------
Related Background:
EVIDENCE OF A PROTOPLANETARY DISK AROUND A YOUNG STAR
The current nebula theory of planet formation proposes that
star-planet systems begin as a contracting cloud of gas and dust
that flattens into a rotating disk. The center of this cloud
becomes the star, and the planets eventually form in the disk of
the nebula. In the inner part of the nebula, the hottest part,
only high density minerals can form solid grains. The outer
regions are cooler, and in those regions icy materials of lower
density are formed. Planets grow from these solid materials,
beginning as dust grains, which grow by condensation and
accretion into planetesimals that range from a few centimeters to
a few kilometers in diameter. These planetesimals settle into a
thin plane around the star and accumulate into larger bodies, the
largest of which grow the fastest and eventually become
protoplanets. Once the star becomes a luminous object, the
remaining nebula is cleared as the star's radiation and the
stellar-wind (powerful streams of charged particles from the
star's surface) push the remnants out of the system. Thus ends
the phase of planet-building. As might be expected, the above
theory is also the current view of the history of our own solar
system. Since the details of disk formation, and the physical
properties of protoplanetary disks, can be modelled by
quantitative theory, the general idea is to investigate such
disks that are apparent around stars to test the theoretical
models. There is no way to do that with our own solar system,
because the protoplanetary disk is long gone. One needs young
stars. ... ... This week Vincent Mannings et al (California
Institute of Technology, CA US) report observations and analysis
of the apparent protoplanetary disk of a star only 6 million
years old, with a mass of 2.3 solar masses. The mass of the disk
is evidently greater than the minimum required to form a
planetary system like our own.
QY: V. Mannings [vgm@astro.caltech.edu]
(Nature 7 Aug 97) (Science-Week 15 Aug 97)
-------------------
Related Background:
A GRAVITATIONAL INSTABILITY MODEL FOR GIANT PLANET FORMATION
Until recently, the consensus theory for the formation of large
planets such as Jupiter was the core accretion model involving
the formation of cores of approximately 10 times Earth mass,
followed by rapid accretion of gas from the primitive solar
nebula. The problem with this model is that the time needed for
accretion (about 1 million years) is of the order of magnitude of
the time during which a young solar-type star's gas dissipates.
The other possible model is one involving a gravitational
instability mechanism in which the solar nebula breaks up into
giant gaseous protoplanets which then contract and collapse to
form giant planets. This model was in the past abandoned because
the extant data concerning the masses of Jupiter and the outer
planets seemed incompatible with the model. But there is now new
data concerning the masses of Jupiter and the outer planets, and
this week Alan P. Boss (Carnegie Institution of Washington, DC
US) reported a revisit to the gravitational instability model,
with computer solutions of the relevant equations of
hydrodynamics coupled with the Poisson equation in a spherical
coordinate system, such solutions providing evidence that the
formation of giant protoplanets in a gaseous nebula disk can
indeed occur. The old gravitational instability model has
therefore apparently been revived.
QY: Alan P. Boss [boss@dtm.ciw.edu]
(Science 20 Jun 97) (Science-Week 26 Jun 97)
-------------------
Related Background:
GIANT PLANET EVIDENCE CONFOUNDS SOLAR SYSTEM THEORISTS
Until recently, speculations and theories about planets orbiting
other stars than our sun have depended on our own solar system as
the guiding model. But during the past two years, astronomers
have been able to gather information about nine such planets, and
the evidence is apparently not in harmony with expectations. The
three variables that are evidently making trouble for theorists
are planet size, proximity to the parent star, and orbital
eccentricity. For example, the planet orbiting the star 51 Pegasi
is large enough to have about half the mass of Jupiter, but seems
to be orbiting the star at a radius of one-sixth the radius of
Mercury's to our sun. This is a puzzle, although there appears to
be still controversy about whether this planet is actually a
planet. Others of the discovered planets are apparently in highly
eccentric and unexplained orbits. So the theorists are busy
revising models for planet formation, establishment of orbits,
planetary orbital drift, and so on. The major difficulty is that
there are no direct observations of these discovered planets --
their existence is proposed to explain perturbations in the
behavior of their parent stars. Stephen Lubow of the Space
Telescope Science Institute (Baltimore MD US) says of the recent
observations: "It's been a revolution."
(Science 30 May 97) (Science-Week 5 Jun 97)


2. ON THE FUTURE OF QUANTUM COMPUTING
     The superposition principle in quantum mechanics derives
from the superposition principle in pure mathematics, which
states that for a linear homogenous differential equation, if
y(sub1)(x) and y(sub2)(x) are solutions, then so is y(sub1)(x) +
y(sub2)(x). In other words, for such a differential equation, the
sum of solutions is itself a solution. A corollary is that any
physical system which can be described by a linear homogeneous
differential equation (or a set of such equations) will obey the 
superposition principle.
     This principle produces various applications and
formulations in the physics of oscillating systems. In quantum
mechanics, where the time-independent Schrodinger equation is a
linear homogenous differential equation and systems are described
by oscillating probability amplitudes, the principle of
superposition results in the postulate that any state function of
a given quantum mechanical system corresponding to a given
observable (e.g., energy) can be expressed as a linear expansion
of the eigenstates of the system for the same observable, with
the term "eigenstate" referring to any one of the wave function
solutions (probability amplitude function solutions) to the
Schrodinger equation for the given boundary conditions.
     Another way to state the quantum mechanical principle of
superposition is as follows: If a physical state of a system can
be realized in a number of different but unknown distinct ways,
then the actual state of the system is a superposition for each
distinct way, and there is a distinct probability amplitude for
each way in which the physical state can be realized.
     This is essentially a restatement of Feynman's rule: The
probability amplitude of an event that can occur in two or more
indistinguishable ways is the sum of the probability amplitude
for each considered separately.
     And Feynman's rule, in turn, is an analog of Bayes' rule in
classical probability theory: The probability of an event which
can occur in two indistinguishable ways is the sum of the
probabilities for each way considered separately.
     The quantum mechanical principle of superposition is of
major importance in considerations of quantum computing,
particularly in connection with "decoherence". In this context,
the term "decoherence" refers to the observed destruction of the
superposition of pure quantum states, the destruction due to
interactions with uncontrolled or unknown physical effects (e.g.,
interactions with the environment of the system). It is currently
believed that quantum computers, which manipulate quantum states
rather than classical "bits", may someday be able to perform
tasks that would be inconceivable with conventional digital
technology.
... ... John Preskill (California Institute of Technology, US)
presents a review of current problems in the development of
quantum computers, the author making the following points:
     1) Formidable obstacles must be overcome before large-scale
quantum computers can become a reality. A major difficulty is
that quantum computers are highly susceptible to making errors.
The considerable theoretical power of a quantum computer derives
from its ability to process *coherent quantum states (i.e.,
quantum states obeying the principle of superposition), but the
coherence of such quantum states is very easily damaged by
uncontrolled interactions with the environment (decoherence). 
     2) The indivisible unit of classical information is the
"bit", which takes one of two possible values, 0 or 1. Any amount
of classical information can be expressed as a sequence of bits.
A classical computer executes a series of simple operations
("gates"), each of which acts upon a single bit or pair of bits.
By executing many gates in succession, the computer can evaluate
any *Boolean function of a set of input bits.
     3) Quantum information can also be reduced to elementary
units, called quantum bits or "qubits". A qubit is a two-level
quantum system (e.g., the spin of an electron). A quantum
computer executes a series of elementary quantum gates, each of
which is a *unitary transformation that acts on a single qubit or
pair of qubits. By executing many such gates in succession, the
quantum computer can apply a complicated unitary transformation
to a particular initial state of a set of qubits. Finally, the
qubits can be measured, the measurement outcome the final result
of a quantum computation.
     4) It was Richard Feynman (1982) who suggested that using a
quantum computer might enormously speed up finding solutions to
certain difficult computational problems. David Deutsch (1985),
developing the idea further, observed that a quantum computer can
invoke the equivalent of a massive parallelism by operating on a
coherent superposition of a vast number of classical states. In
fact, a single computation acting on just 300 qubits can achieve
the same effect as 2^(300) simultaneous computations acting on
classical bits, more than the number of atoms in the visible
Universe. It is not possible to build a conventional computer
with that many processors.
     5) There is, however, a problem of principle that is
potentially very serious for the future of quantum computers --
namely, decoherence. Unavoidable interactions with the
environment will cause the quantum information stored in a
quantum computer to decay, thus inducing errors in the
computation. Decoherence occurs very rapidly in complex quantum
systems, which is the reason we never observe macroscopic
superpositions. If quantum computers are ever to be capable of
solving difficult problems, a method must be found to control
decoherence and other potential sources of error.
     6) At present, quantum information technology remains in the
pioneering stage. It is currently possible to do experiments
involving a few qubits and a few quantum gates. For a quantum
computer to compete with a state-of-the-art classical computer,
we will need machines with hundreds or thousands of qubits
capable of performing millions or billions of operations. The
technology clearly has far to go before quantum computers can
assume their rightful place as the world's fastest machines. But
recent advances in the theory of quantum error correction suggest
there are no insurmountable obstacles, and quantum computers of
the 21st century may indeed unleash the vast computational power
woven into the fundamental laws of physics.
-----------
John Preskill: Battling decoherence: The fault-tolerant quantum
computer.
(Physics Today June 1999)
QY: John Preskill, Dept. of Theoretical Physics, California
Institute of Technology 818-395-6811.
-----------
Text Notes:
... ... *coherent quantum states: In order for a system to be
used to process and transfer information, the system must be
"coherent" in its parts. In quantum physics, coherence is a
matter of locking of phase differences between wave functions.
The wave functions of two or more particles are said to be
coherent if the phase difference between their wave functions
remains constant. So if new quantum electrodynamic information
processing devices are to be developed, methods must be found to
keep the quantum states of the parts of the system coherent long
enough for information to be processed and transferred from one
place to another. 
... ... *Boolean function: In general, a "Boolean function" is
any function assembled by the application of the operations AND,
OR, NOT to a set of variables and elements whose common domain is
a "Boolean algebra". The term "Boolean algebra" refers to a form
of symbolic logic devised by George Boole (1815-1864), such an
algebra providing a mathematical procedure for manipulating
logical relationships in symbolic form. In the realm of
computers, Boolean algebra is an important tool enabling the bits
0 and 1 to be related to logical functions of the computer.
... ... *unitary transformation: In this context, the term
"unitary transformation" refers to a linear operator whose
adjoint is equal to its inverse. The "adjoint" A* of an operator
A is an operator such that for all f and g in the domain of A:
(Af,g) = (f,A*g). If A* = A, then A is said to be self-adjoint.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 24Sep99
-------------------
Related Background:
ON QUANTUM COMPUTING WITH MOLECULES
In general, in quantum mechanics, the "superposition principle"
holds that any two quantum mechanical states can be combined in
infinitely many ways to form states that have characteristics
intermediate between those of the two that are combined.
Entanglement is unique to quantum mechanics, and involves a
relationship (a "superposition of states") between the possible
quantum states of two entities such that when the possible states
of one entity collapse to a single state as a result of suddenly
imposed boundary conditions, a similar and related collapse
occurs in the possible states of the entangled entity no matter
where or how far away the entangled entity is located. The idea
of quantum computing received a significant impetus in 1994 when
Peter W. Shor of ATT (US) proposed that quantum entanglement and
superposition could in principle be used to accomplish many
numerical tasks, in particular the factoring of large numbers,
much faster than the best classical calculator. Since the
security of many important encryption systems depends on the
difficulty of factoring large numbers, quantum computing suddenly
became of great practical importance, and Shor's algorithm
provoked computer scientists to learn about quantum mechanics,
and physicists to begin serious considerations of the
requirements of a quantum computer science. ... ... Gershenfeld
and Chuang (2 installations, US), review the theoretical bases
and current status of quantum computing, in particular their own
work applying nuclear magnetic resonance techniques. The authors
point out the following: 1) In classical computation, the state
of a bit (the fundamental unit of information) is specified by
one number, 0 or 1. An n-bit binary word in a typical computer is
thus described by string of n zeroes and ones. In contrast, in a
quantum computer, the qubit (the fundamental unit of information)
might be represented by an atom in one of two different states, 0
or 1, but unlike classical bits, qubits can exist simultaneously
as 0 or 1, with the probability for each state given by a
numerical coefficient. 2) A quantum computer promises to be
immensely powerful because it can be in multiple states at once
(superposition), and because it can act on all its possible
states simultaneously. Thus, a quantum computer could naturally
perform myriad operations in parallel, using only a single
processing unit. This is the essence of the idea of quantum
computing, although one must understand the expression here is
quite general. 3) The authors have investigated the construction
of a quantum computer based on the nuclear magnetic resonance
behavior of a simple molecular liquid [chloroform, CHCl(sub3)],
with the 2 possible quantum mechanical "spin" states of atoms as
the basic qubit states. Since chloroform is a simple molecule,
the fundamental limitation in this particular system is the small
number of qubits. The authors and other researchers are actively
working to increase the size of the basic molecule in
experimental quantum computing systems, and thus increase the
number of available qubits. 4) The authors conclude: "All along,
ordinary molecules have known how to do a remarkable kind of
computation. People were just not asking them the right
questions."
QY: Neil Gershenfeld, Massachusetts Institute of Technology 617-
253-1000.
(Scientific American June 1998) (Science-Week 12 Jun 98)
[Editor's note: Experimental details of the method and algorithm
used in the above mentioned NMR quantum computing technique were
recently presented by Chuang et al (5 authors 4 installations,
US) in Nature 14 May 1998 393:143] 
-------------------
Related Background:
A SILICON-BASED NUCLEAR SPIN QUANTUM COMPUTER
B.E. Kane (University of New South Wales, AU) presents an
analysis of quantum computing and a new scheme for implementing a
quantum mechanical computer. The author proposes: 1) Although the
concept of information underlying all modern computer technology
is essentially classical, "physicists know that nature obeys the
laws of quantum mechanics." The idea of a quantum computer has
been developed theoretically over several decades in order to
understand the capabilities and limitations of machines in which
information is treated quantum mechanically. 3) Logical
operations carried out on the qubits and their measurement to
determine the result of the computation must obey
quantum-mechanical laws. 4) Quantum computation can in principal
only occur in systems that are almost completely isolated from
their environment and which consequently must dissipate no energy
during the process of computation, conditions that are extra-
ordinarily difficult to fulfill in practice. The author presents
a scheme for implementing a quantum computer on an array of
nuclear spins located on donors in silicon. Logical operations
and measurements can in principle be performed independently and
in parallel on each spin in the array. Specific electronic
devices are described for the manipulation and measurement of
nuclear spins, and the author suggests that the development of a
silicon-based quantum computer can benefit from already existing
highly developed silicon technology.
QY: B.E. Kane [kane@newt.phys.unsw.edu.au]
(Nature 14 May 98 393:133) (Science-Week 12 Jun 98)


3. EARLY ANIMAL EVOLUTION
The geological period known as the Cambrian is the time frame
from about 505 million years ago to 545 million years ago. Its
most outstanding aspect is the rather sudden appearance of
numerous invertebrate fossils, so numerous that some have termed
it an explosion of evolutionary processes. Many of the life forms
that existed during the Cambrian are long extinct, but their
fossils are numerous, and through their fossils the various
Cambrian species have been the subject of much study by
paleobiologists. The Cambrian explosion of life forms has been a
long-standing puzzle for paleobiologists, and at present there is
apparently no single generally accepted explanation. Among the
ideas proposed have been, 1) that the explosion of new forms
resulted from a sudden increase in atmospheric oxygen; 2) that
the explosion is only apparent, and the Precambrian, the period
previous to the Cambrian, lacks fossils because of heat and
pressure associated with important geological changes; 3) that
living forms evolved mostly in freshwater areas, and are
therefore absent in Precambrian sediments, which are primarily
marine; 4) that changes in the shape and extent of shorelines
produced by continental drift dramatically transformed climate
and environment; 5) that the previous evolution of DNA
recombination and regulatory genes culminated in and sparked the
diversity and anatomical complexity manifested in the explosion;
6) that an exponential increase of species could become
significant only after attaining a threshold value at the start
of the Cambrian; and 7) that once multicellular organisms
appeared, the intrinsic possibilities for variation increased
enormously with a resultant explosion of evolved forms.
Unfortunately, there is no evidence to suggest a selection of one
of these proposals, although some of them are less convincing
than others. And of course the truth may be that more than one
factor was involved. No matter the origin, the Cambrian explosion
is apparently accepted by most paleobiologists as a real
discontinuity, a period that saw the sudden emergence of dozens
of new orders and phyla, including sponges, *annelids,
*crustaceans, *hemichordates, *brachiopods, and *mollusks.
... ... A.H. Knoll and S.B. Carroll (2 installations, US) present
a review of recent fossil, phylogenetic, embryological, and
paleo-environmental discoveries that are provoking new ideas
about early animal evolution. The authors make the following
points:
     1) The debate about Cambrian evolution may be old, but only
in the past decade have the data necessary to weigh conflicting
hypotheses begun to emerge. The new information has come from a
broad range of disciplines that includes not only paleontology
and stratigraphy, but also geochemistry, molecular systematics,
and developmental genetics.
     2) It is becoming increasingly clear that understanding the
Cambrian explosion requires that considerations of the Cambrian
fauna and the environments that shaped it be complemented by new
perspectives on the late *Proterozoic world. To understand what
actually transpired during the Cambrian explosion, or what may
have enabled the Cambrian explosion, we must consider what
animals, what developmental and genetic mechanisms, and what
ecosystems were in place before it.
     3) We cannot yet claim to have solved the major questions of
early animal evolution. But we have reached a point where
pathways to understanding are becoming clearer. Testing
hypotheses concerning the identity, age, complexity, and
diversity of early animals and the environments in which they
lived has become an interdisciplinary exercise.
     4) We can see clearly now that intrinsic and extrinsic
hypotheses are not really alternative ways of explaining animal
diversification. There were certainly intrinsic catalysts of
early animal evolution. The assembly and regulatory
diversification of the genetic "toolkit" for animal development
undoubtedly underpin Proterozoic and Cambrian evolution. And the
evolution of complex appendages, organs, and sophisticated
nervous and musculo-skeletal structures must have facilitated
diversification. But extrinsic events also helped to shape early
animal evolution by altering environments in ways that doomed
some *clades and created opportunity for others.
     5) The authors conclude: "Discipline-bound intrinsic or
extrinsic explanations of early animal history fail not so much
because they are wrong as because they are incomplete. The
Cambrian explosion... is the historical product of the interplay
between genetic possibility and environmental opportunity,
amplified by ecological interactions to extend across all of
biology."
-----------
A.H. Knoll and S.B. Carroll: Early animal evolution: Emerging
views from comparative biology and geology.
(Science 25 Jun 99 284:2129)
QY: Andrew H. Knoll, Harvard University 617-495-1000.
-----------
Text Notes:
... ... *annelids: Soft-bodied, metamerically segmented coelomate
worms, e.g., earthworms. The term "coelomate" refers to the
possession of a body cavity.
... ... *crustaceans: A class of Arthropods, including shrimps,
crabs, water fleas, etc.
... ... *hemichordates: A group of marine invertebrates,
including the acorn worms.
... ... *brachiopods: Bivalve coelomate invertebrates that live
attached to the sea-bed (e.g., lamp shells).
... ... *mollusks: (Mollusca) A phylum of bilaterally symmetrical
unsegmented invertebrates. Includes aquatic bivalves such as
mussels and clams, terrestrial slugs and snails, octupi and
squids.
... ... *Proterozoic: The Proterozoic eon is the time-frame 2600
million years ago to 600 million years ago.
... ... *clades:  A "clade" is a cluster of taxa derived from a
single common ancestor.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 24Sep99
-------------------
Related Background:
A MOLECULAR DATING TEST OF THE CAMBRIAN EXPLOSION HYPOTHESIS
The early history of the *Metazoa, whether the Metazoa originated
as part of a *Cambrian "explosion" or with an extended
*Precambrian "phylogenetic fuse", remains controversial in
evolutionary biology. The Cambrian explosion hypothesis -- that
the phyla and even classes of the animal kingdom originated in a
rapid evolutionary radiation at the base of the Cambrian at 545
to 560 million years ago -- rests on the sudden appearance of a
diverse range of animals in the fossil record. Although recent
discoveries of *Ediacaran metazoans have extended the record of
sponges and bilateral animals to 570 million years ago, the
biological affinities of many Ediacaran organisms remains
controversial, and the earliest paleontological evidence of
metazoan life is no more than 600 million years ago. However, the
absence of earlier metazoan fossils could have been caused by
systematic biases in preservation that left the Precambrian
history of recognized phyla unrecorded in fossils. Molecular
studies have the potential to shed light on the origin of the
animal phyla by providing independent estimates of the divergence
times, but molecular studies have been criticized for failing to
account adequately for variations in rate of evolution.
... ... L. Bromham et al now present a study involving a method
of dating divergence times from molecular data (both
*mitochondrial DNA and nuclear DNA) which addresses the
criticisms of earlier studies, and which the authors state
provides more realistic but wider confidence intervals. The
authors report their data are not compatible with the Cambrian
explosion hypothesis as an explanation for the origin of metazoan
phyla, and they suggest their data provide additional support for
an extended period of Precambrian metazoan diversification. The
authors conclude: "Although we cannot provide precise estimates
of the origin of metazoan phyla, we can use our results to
confidently reject the Cambrian explosion hypothesis, which rests
on a literal interpretation of the fossil record and assumes that
special evolutionary phenomena, capable of producing profound
differentiation in a short period, operated in the Cambrian but
not before or since. By contrast, the Precambrian phylogenetic
fuse hypothesis assumes no more than we already know to be
reasonable: that lineages can diverge gradually over time and
that the fossil record contains gaps that can greatly reduce the
chances of finding fossils for certain periods or particular
types of organisms.
-----------
L. Bromham et al (3 installations, UK NZ)
Testing the Cambrian explosion hypothesis by using a molecular
dating technique.
(Proc. Natl. Acad. Sci. US 13 Oct 98 95:12386)
QY: Lindell Bromham [LBromham@zoology.uq.edu.au]
-----------
Text Notes:
... ... *Metazoa: In general, the term "metazoa" refers to all
multicellular animals. Among important distinguishing
characteristics of metazoa are cell differentiation and
intercellular communication. For certain multicellular colonial
entities such as sponges, some biologists prefer the term
"parazoa".
... ... *Cambrian "explosion": See notes in main report.
... ... *Precambrian "phylogenetic fuse": The term "fuse" here is
a metaphor for a proposed long series of precursor events leading
to the apparent "explosion" in the fossil record. The essential
question is whether the apparent explosion in the fossil record
was the result of relatively sudden changes in preservation
constraints (e.g., hard-body vs. soft-body forms), or whether a
set of special conditions (e.g., climate change or atmospheric
oxygen availability) provoked an actual rapid diversification of
forms.
... ... *Ediacaran metazoans: The term "Ediacaran" refers to an
assemblage (until recently the oldest) of soft-bodied marine
animals, the assemblage first discovered in the Ediacara Hills in
Australia.
... ... *mitochondrial DNA: Mitochondrial DNA (sometimes denoted
as mtDNA), found in the mitochondria of all eukaryotes, is
believed to evolve in parallel with nuclear DNA, but since sperm
lose their mitochondria, it is inherited only in the maternal
lineage in animals.
-------------------
Related Background:
EVOLUTION: 1 BILLION YR OLD FOSSILS OF TRIPLOBLASTIC ANIMALS
There are two contradictory views concerning the early history of
*metazoans. The "*Cambrian explosion" hypothesis is based on
Cambrian shell fossils and *Burgess-type exceptionally well-
preserved fossil deposits ("lagerstatten"). This hypothesis
suggests that animal phyla originated rather suddenly
approximately 580 million years ago during the *Proterozoic-
Phanerozoic transition. The alternative hypothesis (called "slow
burn") suggests that animals developed more slowly, first
appearing, according to some molecular analyses, more than 1
billion years ago. ... ... A. Seilacher et al now report data
from the Mesoproterozoic Chorhat Sandstone site in central India.
The authors report that certain *bedding plane features are
biological and can be interpreted as the burrows of wormlike
undermat miners (i.e., *infaunal animals that excavated tunnels
underneath *microbial mats). The authors suggest these burrows
indicate that *triploblastic animals existed more than a billion
years ago. The authors further suggest their evidence indicates
that the diversification of animal designs proceeded very slowly
before the appearance of organisms with hard skeletons during the
Cambrian evolutionary explosion, and that the diversification
occurred before the ecological changes that accompanied that
explosion.
-----------
A. Seilacher et al (3 installations, DE IN US)
Triploblastic animals more than 1 billion years ago: Trace fossil
evidence from India.
(Science 2 Oct 98 282:80)
QY: Friedrich Pfluger, Yale University, 203-432-4771.
-----------
Text Notes:
... ... *metazoans: In general, the term "metazoa" refers to all
multicellular animals. Among important distinguishing
characteristics of metazoa are cell differentiation and
intercellular communication. For certain multicellular colonial
entities such as sponges, some biologists prefer the term
"parazoa".
... ... *Cambrian: Refers to the approximate general time-frame
500 to 600 million years ago (but often considered as 505 to 545
million years ago).
... ... *Burgess-type: The Burgess Shale fossil deposit site in
British Columbia (CA) is apparently a geological accident of
superb preservation, and one that has revealed to paleontologists
the limitations of their views of the varieties of life in the
*Cambrian period. All the fossils expected for the Cambrian are
found in the Burgess Shale, but studies have demonstrated in
addition a remarkable array of perfectly preserved soft-bodied
animals, including a variety of worms, *arthropods, sponges,
*brachiopods, and some bizarre forms seemingly unrelated to any
known groups. The consequence was a new appreciation among
paleontologists of the tremendous increase in metazoan diversity
that apparently occurred during the Cambrian period, and indeed
this increase is now considered one of the most important events
in the history of life on Earth. 
... ... *arthropods: The largest phylum in the Animal Kingdom in
terms of both number of taxa and biomass, but the taxonomy has
undergone revision, and it is now essentially an informal
classification. In general, the arthropods are characterized by a
tough chitinous protective covering (exoskeleton) flexible only
at the joints (e.g., insects).
... ... *brachiopods: A phylum of bivalve coelomate invertebrates
resembling bivalve molluscs. The term "bivalve" refers to the
presence of a hinged shell; the term "coelomate" refers to the
presence of a true body cavity.
... ... *Proterozoic-Phanerozoic transition: The Proterozoic eon
is the time-frame 2600 million years ago to 600 million years
ago. The Phanerozoic eon is the time-frame 600 million years ago
to the present. During the Phanerozoic, atmospheric oxygen
apparently increased by a factor of 10 to its present value.
... ... *bedding plane: A distinct surface separating two
strata, the bedding plane marking a break in the continuity of
sedimentation, a break that can be caused by a period of erosion
or a cessation of sediment supply.
... ... *infaunal: Refers to an organism that burrows into the
substrate.
... ... *microbial mats: A dense microbial layer. The authors
propose this served as a food source for wormlike animals
exploiting its decaying base.
... ... *triploblastic animals: These are animals with a body
organization derived from 3 germ layers (ectoderm, endoderm,
mesoderm). The category includes all metazoans except
*coelenterates, which are diploblastic.
... ... *coelenterates: A phylum of mostly marine multicellular
animals. (e.g., jellyfish).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 30Oct98
-------------------
Related Background:
DISCOVERY OF 3-DIMENSIONAL ALGAE AND ANIMAL EMBRYO FOSSILS
A phosphorite is a sedimentary rock composed chiefly of phosphate
minerals. The Proterozoic era (also called the Algonkian) is the
geologic time between the Archean and the Paleozoic, with the
Archean beginning about 3.9 billion years ago and involving the
first appearance of sedimentary rocks and the first primitive
organisms at the bottom of the oceans. In paleontology, the term
"radiation" refers to a diverging and diversifying spread of
animals or plants into new environments with a resultant
production of new evolutionary forms, and the Ediacaran radiation
refers to an assemblage (until now the oldest) of soft-bodied
marine animals, the assemblage first discovered in the Ediacara
Hills in Australia. The algae comprise a large mixed group of
photosynthetic and essentially single-celled plants, and are
considered ancestral to modern green plants. Thalli are primitive
types of plant bodies not differentiated into stems, leaves, and
roots; the term also refers to the gametophyte generation (the
phase of the plant life cycle producing reproductive cells) of
some ferns and lichens. The term "cleavage stages" refers to the
early stages of embryo formation when the egg cell rapidly
divides into smaller and smaller cells. The "Bilateria" are a
major division of the animal kingdom comprising all forms with
bilateral symmetry, and the term "bilaterians" refers to the
first such forms appearing after the emergence of protozoa. The
term "phylogeny" refers to the evolutionary history of an
organism or group of organisms. ... ... Xiao et al (3 authors at
2 installations, US CN) report the discovery of phosphorites of
the late Neoproterozoic (570 +- 20 million years ago) in the
Doushantuo Formation, southern China, an apparent exceptional
record of multicellular life from just before the Ediacaran
radiation of macroscopic animals. Abundant thalli with cellular
structures preserved in 3-dimensional detail show that late-
Proterozoic algae already possessed many of the anatomical and
reproductive features seen in modern marine flora. Embryos
preserved in early cleavage stages indicate the divergence of
lineages leading to bilaterians may have occurred well before
their macroscopic traces or body fossils appear in the geological
record. The authors suggest that discovery of these fossils shows
that the early evolution of multicellular organisms is amenable
to direct paleontological inquiry, and that paleontological
observations, together with insights from molecular phylogeny and
developmental genetics, can facilitate a modern integration of
phylogeny, development, and paleontology that extends deeply into
evolutionary history to address the early evolution of
multicellular life.
QY: Andrew H. Knoll, Botanical Museum, Harvard University,
617-495-1000
(Nature 5 Feb 98) (Science-Week 20 Feb 98)
-------------------
Related Background:
PRECAMBRIAN SPONGES WITH CELLULAR STRUCTURES
The sponges (Porifera) are a phylum of primitive multi-cellular
animals (Metazoa), always attached at one point to a substrate,
usually without a definite symmetry, and usually marine. The
sponge body is a loose aggregation of cells with little
intercellular coordination, but the cells are specialized into
various types with various functions important to the viability
of the entire organism. There is also in sponges an internal
"skeleton" of chalk, silica, or protein, and "calcareous sponges"
are sponges containing a relatively large amount of calcium
carbonate. In this report, "spicules" are the hard internal
structures in sponges composed primarily of silica or calcium
salts, and a "monoaxonal" spicule is a spicule having essentially
only one dimension (e.g., needle-like). The term "epidermis"
refers to the outermost layer of cells in any multicellular
organism; "porocytes" are tubular cells that constitute the walls
of certain sponges; "amoebocytes" are freely moving cells (sponge
cells in this context) within a metazoan tissue; "sclerocytes"
are cells involved in the formation of the sponge skeleton;
"spongocoel" refers to the branching internal cavity of a sponge,
the cavity having a connection in one place or another to the
external aqueous environment; "flagella" are long and thin
cellular organelles that protrude from the surfaces of cells and
are specialized to produce locomotion. The Cambrian period
extended from 545 to 505 million years ago, and was the time
during which many multicellular organisms first arose, and the
Vendian period is the Precambrian metazoan fossil period. The
term "Cambrian explosion" refers to the apparent relatively
sudden appearance of an enormous number of living forms during
the Cambrian period. ... ... Li et al (3 authors at 2
installations, TW CN) report the identification of sponge remains
in the Early Vendian Doushantuo phosphate deposit (cf. previous
report, this  issue) in south China. The skeletons consist of
siliceous monoaxonal spicules, with preserved soft tissues
including the epidermis, porocytes, amoebocytes, sclerocytes,
and spongocoel, and among thousands of metazoan embryos a sponge
larva having a shoe-shaped morphology and dense peripheral
flagella. The authors suggest the data indicate the calcareous
sponges may have an extended history in the Late Precambrian,
and that animals lived 40 to 50 million years before the
Cambrian explosion. They further suggest these Doushantuo rocks
provide a potentially inexhaustible resource for understanding
the early evolution of animal life.
QY: Chia-Wei Li, National Tsing Hua Univ., Hsinchu, Taiwan, China
(Science 6 Feb 98) (Science-Week 20 Feb 98)
-------------------
Related Background:
DISCOVERY OF LOWER CAMBRIAN FOSSILIZED METAZOAN EMBRYOS
... Until now, [Cambrian fossil] studies have been of the fossils
of mature organisms, fossils easily recognized in the Cambrian
strata with the naked eye or a hand lens. This week there is a
report by Stefan Bengtson and Yue Zhao (Swedish Museum of Natural
History, SE; Chinese Academy of Geological Sciences, CN) of
analysis of small globular fossils known as Olivooides and
Markuelia from basal Cambrian rocks in China and Siberia. They
show that these microscopic globular fossils contain developing
embryos of metazoans (multi-cellular organisms), the various
fossil embryos exhibiting all stages of development. The fossils
were apparently formed by phosphatization during the conversion
of sediment to limestone rock. In the laboratory, the limestone
rock was dissolved in 10% acetic acid to recover the phosphatized
fossils. The authors suggest this type of fossil formation may be
widespread and of great potential for paleobiologic research.
They also suggest that if metazoan embryos have been rare as
fossils, they may have merely been overlooked because of their
minute size and nondescript morphology.
QY: S. Bengtson, Dept. Paleozoology, Swed. Mus. of Nat. Hist.,
Box 50007, S-104 05 Stockholm SE
(Science 12 Sep) (Science-Week 26 Sep 97)


4. THE EVOLUTION OF DINOSAURS
The Mesozoic Era is divided into the *Triassic, Jurassic, and
Cretaceous periods, with the entire Mesozoic occupying the time-
frame from approximately 230 million years ago to 70 million
years ago. Existing evidence indicates that during the Mesozoic
Era the reptiles diversified into many terrestrial habitats and
became the dominant vertebrate group. *Therapsid reptiles,
ancestors of the mammals, appear to have had temperature-
regulating mechanisms (i.e., to have been "endothermic") and may
have been the first endotherms. Special limb bones allowed the
*archosaur reptiles to become bipedal, increasing their speed and
size. Their descendants, the dinosaurs, *radiated into almost
every terrestrial habitat, and some became so enormous as to
approach theoretical terrestrial size limits. Some researchers
propose that on the basis of bone structure, posture, and
biogeographical distribution, the dinosaurs were endothermic, and
that endothermy, in combination with their size and other
favorable attributes, may have enabled dinosaurs to dominate all
other land vertebrates. At the end of the Cretaceous period
(which extended from approximately 145 million years ago to 70
million years ago), the dinosaurs, along with other large marine
reptiles and various other groups, became extinct, an extinction
whose cause has been the subject of considerable debate. Because
of their immense size and fierce appearance, the dinosaurs have
long captured the public imagination. The Mesozoic Era, the time
during which the dinosaurs thrived, has its own intriguing
peculiarities. Until well into the age of the dinosaurs there
were no birds and there was no grass, and no flowering plants
existed until the Mesozoic was half completed. The arrangement of
continents was quite different from that existing today, and
throughout much of the Mesozoic, the central part of the US was
apparently covered by an ocean.
... ... Paul C. Serano (University of Chicago, US) presents an
extensive review of current research concerning the evolution of
dinosaurs, the author making the following points:
     1) During the past 30 years, intensified paleontological
exploration has doubled the recorded diversity of dinosaurs and
extended their geographic range into polar regions. Exceptional
fossil preservation has revealed eggshell microstructure, nesting
patterns, and brooding posture among predators, and skin
structures such as downy filaments and feathers. Analysis of bone
microstructure and isotopic composition has shed light on
embryonic and post-hatching growth patterns and on the
thermophysiology of these animals. Footprint and track sites have
yielded new clues regarding posture, locomotion, and herding
among large-bodied herbivores. And the main lines of dinosaurian
descent have been charted, placing the new discoveries in
phylogenetic context.
     2) The most important impact of this enriched perspective on
dinosaurs may be its contribution to the study of large-scale
evolutionary patterns. What triggers or drives major replacements
in the history of life? How do novel and demanding functional
capabilities, such as powered flight, first evolve? And how does
the breakup of a supercontinent affect land-based life? The
critical evidence resides in the fossil record -- in the
structure, timing, and geography of evolutionary radiations such
as that of dinosaurs.
     3) The ascendancy of dinosaurs on land near the close of the
Triassic now appears to have been as accidental and opportunistic
as their demise and replacement by *therian mammals at the end of
the Cretaceous. The dinosaurian radiation, launched by 1-meter-
long bipeds, was slower in tempo and more restricted in adaptive
scope than that of therian mammals. A notable exception was the
evolution of birds from small-bodied predatory dinosaurs, which
involved a dramatic decrease in body size. Recurring phylogenetic
trends among dinosaurs include, to the contrary, an increase in
body size. There is no evidence for co-evolution between
predators and prey or between herbivores and flowering plants. As
the major land masses drifted apart, dinosaurian biogeography was
molded more by regional extinction and intercontinental dispersal
than by the breakup sequence of *Pangaea.
-----------
Paul C. Serano: The evolution of dinosaurs.
(Science 25 Jun 99 284:2137)
QY: Paul C. Serano, University of Chicago 773-702-8650.
-----------
Text Notes:
... ... *Triassic, Jurassic, and Cretaceous periods: The
approximate time-frames of these subdivisions of the Mesozoic Era
are as follows: Triassic 230-180 million years ago; Jurassic 180-
145 million years ago; Cretaceous 145-70 million years ago.
... ... *Therapsid reptiles: The therapsids were a group of
mammal-like reptiles that became extinct at the end of the
Triassic. The group contained both sluggish herbivores and active
carnivores, and it is believed that small Mesozoic therapsids
gave rise to the earliest mammals.
... ... *archosaur reptiles: (literally, "ruling reptiles") The
parent group of the dinosaurs. Birds are descendants; crocodiles
and alligators are living representatives.
... ... *radiated: In this context, the term "radiation" refers
to the spread of a group of biological entities into new
environments with consequent diversification.
... ... *therian mammals: The Theria is a subclass of mammals
containing those mammals that bear live young (as opposed to
mammals that lay eggs).
... ... *Pangaea: (Pangea) Some 375 million years ago, two large
supercontinent called Laurasia and Gondwana comprised most or all
of the present continental land masses, Laurasia in the north and
Gondwana in the south. These two supercontinents merged into the
single supercontinent Pangaea about 250 million years ago, and
subsequent fragmentation of Pangaea began about 180 million years
ago and the fragmentation eventually produced the continental
land masses we know today. During this fragmentation there
existed the second phase of Gondwana, incorporating what is now
South America, Africa, Antarctica, Australia, and India. This
historical picture, which is the present general consensus, is
the result of a large number of geological and paleobiological
studies. 
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 24Sep99


5. BIOLOGY OF AGING: CALORIC RESTRICTION AND GENE EXPRESSION
Most multicellular organisms exhibit a progressive and
irreversible physiological decline that characterizes what is
called "senescence" -- the aging process. The molecular basis of
this process is unknown, but various mechanisms have been
postulated, including: a) cumulative damage to DNA leading to
genome instability; b) biochemical pathway alterations that lead
to changes in *gene expression patterns; c) *telomere shortening
in replicative cells; d) oxidative damage to critical
macromolecules by reactive oxygen species; and e) nonenzymatic
*glycation of proteins. Experimental genetic manipulation of the
aging process in multicellular organisms has been achieved in the
fruit fly Drosophila through the overexpression of certain
enzymes, and in the nematode worm C. elegans through alterations
in the *insulin receptor pathway, and in both organisms through
the experimental selection of stress-resistant mutants. In
mammals, however, the only intervention that appears to slow the
intrinsic rate of aging is caloric restriction. Most studies of
caloric restriction in mammals have involved laboratory rodents
subjected to a long-term 25 to 50 percent reduction in caloric
intake without essential nutrient deficiency, and the result in
these rodents is a delayed onset of age-associated pathological
and physiological changes and an extension of maximum lifespan.
Various mechanisms have been postulated to explain this result,
including increased DNA repair capacity, altered gene expression,
depressed metabolic rate, and reduced oxidative stress.
... ... C-K. Lee et al (4 authors at University of Wisconsin, US)
now present a study to examine the molecular events associated
with aging in mammals, with experiments involving analysis of the
aging process in *skeletal muscle of mice. The authors report
that the use of high-density *oligonucleotide arrays representing
6347 genes (5 to 10 percent of the mouse genome) revealed that
aging resulted in a differential gene expression pattern
indicative of a marked stress response and lower expression of
metabolic and biosynthetic genes. Most alterations were either
completely or partially prevented by caloric restriction.
*Transcriptional patterns of calorie-restricted animals suggest
that caloric restriction retards the aging process by causing a
metabolic shift toward increased protein turnover and decreased
macromolecular damage. The authors state: "The data presented
here provide the first global assessment of the aging process in
mammals at the molecular level and underscore the utility of
large-scale parallel gene expression analysis in the study of
complex biological phenomena."
-----------
C-K. Lee et al: Gene expression profile of aging and its
retardation by caloric restriction.
(Science 27 Aug 99 285:1390)
QY: Tomas A. Prolla [taprolla@facstaff.wisc.edu]
-----------
Text Notes:
... ... *gene expression patterns: This refers to the profile of
genes in a genome that are actually operating (i.e., undergoing
expression) at any point in time. In a mammal, for example, a
liver cell is a liver cell because of a particular profile of
expressed genes, and what that liver cell is doing at any point
in time is determined by variations of that profile. It is the
operating patterns (gene expression patterns) of the genome that
are the paramount determinants of the behavior of cells.
... ... *telomere: Telomeres are defined ends of chromosomes
that contain specific repeated DNA sequences. They are essential
for normal chromosome replication, and since their length
shortens a bit with each replication, they are believed to be
involved in the aging of the cell.
... ... *glycation of proteins: "Glycation" is the post-
translational (i.e., after protein synthesis) modification of a
protein by the covalent attachment of a sugar residue, the
modification resulting from a spontaneous amino-carbonyl reaction
("Maillard reaction"). Glycation of various proteins has recently
been implicated in the etiology of various diseases such as the
development of Alzheimer's-type pathologies (e.g., dementias).
... ... *insulin receptor pathway: Insulin is a polypeptide
chemical messenger (hormone) comprising 51 amino acids in two
chains linked by disulphide bridges. The insulin receptor is a
specific membrane protein derived from an intracellular precursor
and transported from specialized intracellular structures to the
cell surface.
... ... *skeletal muscle: In general, the term "skeletal muscle"
refers to striated muscle fibers (singly or in a collection)
attached at one or both ends of a part of the body skeleton.
"Striated muscle" is muscle usually associated with voluntary
motion, the adjective "striated" arising from the microscopically
visible cross striations which occur in the fibers as a result of
regular overlapping of thick and thin muscle fiber filaments
(myofilaments). In general, such fibers are specialized for rapid
contraction and relaxation.
... ... *oligonucleotide arrays: The essential idea concerning
the use of "arrays" in determining gene expression patterns
involves the fact that for every gene (DNA sequence) undergoing
expression there exists in the cytoplasm a specific RNA whose
nucleotide sequence is a result of transcription of that gene
(see next note on "transcriptional patterns"). There exists now a
technique for profiling the large variety of RNAs that can be
extracted from tissue, the technique depending on highly ordered
arrays of large numbers of oligonucleotide probes (essentially
pieces of DNA) in a parallel format, with specific DNA-RNA
interactions producing localized fluorescences, and the array of
fluorescences providing a profile of detectable RNAs. A
determination of the profile of existing RNA sequences implies
the profile of the DNA sequences (genes) that are being naturally
expressed in the genome, and if one knows which genes are
involved with which functions in that particular cell or
organism, one has obtained a profile of existing functions. The
use of such arrays of nucleotide probes (sometimes called micro-
arrays or "chips") is now highly automated ("robotic"), and the
technique can be used to determine the expression profile of
thousands of genes in an ensemble of cells.
... ... *Transcriptional patterns: "Transcription" is the process
by which genetic information in DNA is converted into RNA.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 24Sep99
-------------------
Related Background:
AGING, LIFESPAN, AND SENESCENCE
Our knowledge of the basis of senescence of cells, tissues, and
organisms (including humans) has entered a new phase in recent
decades because of the new vistas opened by molecular biology.
Model systems have started to provide insights, and one important
approach has been the identification of genes that determine the
lifespan of an organism. The very existence of genes that when
mutated can extend lifespan suggests to many researchers that one
or a few processes may be critical in aging, and that a slowing
of these processes may slow aging itself. ... ... In a short
review of current research in the molecular biology of aging and
lifespan, L. Guarente et al make the following points: 1) In the
budding yeast Saccharomyces cerevisiae, aging results from the
asymmetry of cell division, which produces a large mother cell
and a small daughter cell arising from the bud. Much of the
macromolecular composition of the daughter cell is newly
synthesized, whereas the composition of the mother cell grows
older with each cell division. It has been shown that mother
cells of this yeast species divide a relatively fixed number of
times, and exhibit a slowing of the cell cycle, cell enlargement,
and sterility. Analysis of *ribosomal DNA in old cells reveals an
accumulation of *extrachromosomal ribosomal DNA of discrete
sizes, apparently representing a cumulative fragmentation of
chromosomal ribosomal DNA. The authors suggest it will be of
great interest to assess the generality of this process as an
aging mechanism. 2) In *Caenorhabditis elegans (a *nematode worm;
see notes), the *neurosecretory system regulates whether animals
enter the reproductive life cycle or arrest development at a
primitive *diapause stage. Developmental arrest is apparently
induced by a *pheromone and involves behavioral and morphological
changes in many tissues of the animal, with the lifespan becoming
4 to 8 times longer than that of the normal 3-week lifespan of
fully developed animals. Declines in pheromone concentration
induce recovery to reproductive adults with normal metabolism and
lifespan. Genes that regulate the function of the C. elegans
diapause and the neuroendocrine aging pathway have been
identified, and at least one of these genes codes for an
*insulin-like receptor apparently involved in metabolism. The
authors suggest that if the association of longevity and diapause
is general, it is possible that *polymorphisms in the human
insulin receptor-signaling pathway genes and related gene
*homologues may underlie genetic variation in human longevity. 3)
In plants, there is a large range of lifespans in the various
plant kingdoms. Certain tree species live for well over a
century, whereas other plants complete their life cycle in a few
weeks. The "yellowing" of leaves is often referred to in the
plant literature as leaf senescence or the "senescence syndrome"
-- referring to the process by which nutrients are mobilized from
the dying leaf to other parts of the plant to support their
growth. The senescence syndrome is characterized by distinct
cellular and molecular changes, with the chloroplast the first
part of the cell to undergo disassembly (producing the
"yellowing"). In many plant species, certain hormones can either
enhance or delay senescence. Although the genes that are
expressed during the plant senescence syndrome (as well as ways
to manipulate such senescence) have been identified, much remains
to be done to understand the molecular basis of aging in plants.
For example, nothing is known about the signal transduction
pathways that lead to altered gene expression during senescence,
or how plant hormones such as *cytokinin influence senescence.
But there are now many tools to explore this process. The authors
conclude: "It remains to be seen whether common mechanisms link
the aging process in diverse organisms."
-----------
L. Guarente et al (3 authors at 3 installations, US)
Aging, lifespan, and senescence.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11034)
QY: Leonard Guarente, Mass. Inst. of Technology 617-253-1000.
-----------
Text Notes:
... ... *ribosomal DNA: 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 term "ribosomal DNA" refers to the gene
or genes that code for the RNA in ribosomes. In other words, the
term "ribosomal DNA" does not refer to any DNA in ribosomes
(there is no DNA in ribosomes).
... ... *extrachromosomal: In general, this refers to anything
outside of chromosomes, and in this case to DNA fragments
unincorporated into chromosomal DNA.
... ... *Caenorhabditis elegans: This is a small (1 mm) nematode
worm. It is transparent, hermaphroditic, free-living, and found
in soil. It has a relatively small genome (approximately 19,000
genes), and only a few types of cells in its body. It has a 16-hr
embryogenesis that can be achieved in a petri dish, and is thus
highly suitable for the study of developmental and behavioral
genetics.
... ... *nematode: An abundant and ubiquitous phylum of
unsegmented roundworms.
... ... *neurosecretory system: In general, all neural systems
contain both neurons that themselves secrete chemical messengers
and neurons that signal special secretory cells to secrete
chemical messengers. A neurosecretory pathway is a delineated
signaling system that involves such a resultant secretion.
... ... *diapause: In general, this refers to any programmed
period of suspended development in invertebrates. 
... ... *pheromone: In general, a chemical substance which, when
released into an animal's surroundings, influences the
development or behavior of other individuals of the same species.
... ... *insulin: A protein hormone that promotes uptake by body
cells of free glucose and/or amino acids, depending on target
cell type.
... ... *polymorphisms: A genetic polymorphism is a naturally
occurring variation in the normal nucleotide sequence of the
genome within individuals in a population. Variations are denoted
as polymorphisms only if they cannot be accounted for by
recurrent mutation and occur with a frequency of at least about 1
percent.
... ... *homologues: In general, the term "homologous" means
having the same structure. But the term has special uses in
genetics and evolution biology.
... ... *cytokinin: A group of plant growth substances. They are
chemically identified as derivatives of the purine base adenine.
They stimulate cell division and determine the course of
differentiation. They work synergistically with other plant
hormones called "auxins".
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 6Nov98
-------------------
Related Background:
A POSSIBLE LINK BETWEEN AGING AND GLUCOSE METABOLISM
Insulin is a vital hormone involved in glucose metabolism, and
uncovering the details of the molecular biology of insulin and
its pathways is the focus of much research. Koutaru D. Kimura et
al (Massachusetts General Hospital and Harvard Medical School,
US) report an insulin-receptor-like gene in the small transparent
worm C. elegans that apparently regulates longevity of the
organism. Evidently poor nutritive conditions cause the worm to
halt normal reproductive development and enter a resting state,
and this process is controlled by a family of genes. Mutations in
these genes can cause the resting state to be abnormally provoked
with a resultant increase in the longevity of the organism. The
similarity between the C. elegans insulin receptor and the human
insulin receptor is apparently causing excitement among
researchers specializing in the molecular biology of glucose
metabolism.
QY: Gary Ruvkun [ruvkun@opal.mgh.harvard.edu]
(Science 15 August) (Science-Week 29 Aug 97)


6. CONTROL OF INFECTIOUS DISEASES 1900-1999
The first US civilian whose life was saved by penicillin died in
June 1999 at the age of 90 years. The story is as follows: In
March 1942, a 33-year-old woman was hospitalized for a month with
a life-threatening streptococcal infection at a New Haven,
Connecticut hospital. She was delirious, and her temperature
reached almost 107 degrees fahrenheit (41 degrees centigrade).
Treatments with sulfa drugs, blood transfusions, and surgery had
no effect. As a last resort, her doctors injected her with a
minuscule amount of an obscure experimental drug called
penicillin. Her hospital chart, now at the Smithsonian
Institution, indicates a sharp overnight drop in temperature, and
apparently by the next day she was no longer delirious. The woman
survived to marry, raise a family, and meet Alexander Fleming
(1881-1955), the scientist who discovered penicillin [*Note #1].
In 1945, Fleming was awarded the Nobel Prize for Physiology and
Medicine, along with Ernst Chain and Howard Florey, who helped
develop penicillin into a widely available medical product.
... ... The US Centers for Disease Control and Prevention, in a
recent review of the control of infectious diseases in the 20th
century, makes the following points:
     1) Deaths from infectious diseases have declined markedly in
the US during the 20th century. This decline contributed to a
sharp drop in infant and child mortality, and to the 29.2-year
increase in life expectancy.
     2) In 1900, 30.4 percent of all deaths occurred among
children less than 5 years of age; in 1997, deaths in this group
were only 1.4 percent of the total.
     3) In 1900, the 3 leading causes of death were a) pneumonia,
b) tuberculosis, c) diarrhea and inflammation of the intestinal
tract (enteritis). These 3 causes, together with diphtheria,
caused one-third of all deaths. Of these deaths, 40 percent were
among children less than 5 years of age. In 1997, heart disease
and cancers accounted for 54.7 percent of all deaths, with 4.5
percent attributable to pneumonia, influenza, and human immune
deficiency virus (HIV) infection.
     4) Despite this overall progress, one of the most
devastating epidemics in human history occurred during the 20th
century: the 1918 influenza epidemic that resulted in 20 million
deaths, including 500,000 in the US, in less than 1 year -- more
than have died in as short a time during any war or famine in the
world. HIV infection, first recognized in 1981, has caused a
pandemic that is still in progress, affecting 33 million people
and causing an estimated 13.9 million deaths. These epidemics
illustrate the volatility of infectious diseases death rates and
unpredictability of disease emergence.
-----------
CDC Morbidity and Mortality Weekly Report: Control of Infectious
Diseases, 1900-1999.
(MMWR 1999 48:621) (J. Amer. Med. Assoc. 15 Sep 99 282:1029)
QY: National Center for Environmental Health, Centers for Disease
Control and Prevention, Atlanta, GA 30333 US.
-----------
Text Notes:
... ... *Note #1: The story of Fleming's discovery of penicillin
is a classic tale of serendipity. In 1928, shortly after he was
appointed professor of bacteriology at the University of London,
Fleming left a culture of staphylococcus germs uncovered for some
days. He was finished working with the culture, and he was about
to discard the culture dish when he noticed that several specks
of mold had fallen into it, and that around every mold speck the
bacterial colony had dissolved away for a short distance. The
clear space surrounding each speck indicated that bacteria had
died and no new growth had invaded the area. The physicist John
Tyndall (1820-1893), who among other things did much research
with ordinary dust, had briefly noted a similar observation 50
years earlier. Fleming isolated the mold and eventually
identified it as Penicillium notatum, a mold closely related to
the common variety often found growing on stale bread. Fleming
decided that the mold liberated some compound that inhibited
bacterial growth, and he labelled the substance "penicillin". In
a lecture many years later, Fleming spoke of his accidental
discovery of penicillin: "I have been trying to point out that in
our lives chance may have an astonishing influence and, if I may
offer advice to the young laboratory worker, it would be this --
never to neglect an extraordinary appearance or happening. It may
be -- usually is, in fact -- a false alarm that leads to nothing,
but it may on the other hand be the clue provided by fate to lead
you to some important advance."
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 24Sep99


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

IN FOCUS: ON THE QUANTUM PRINCIPLE
"What is the stuff of creation? Is all reality simply matter in
motion or something else entirely, a complex concert of
vibrations in a primordial field? Is the world we see but a gross
simplification of an underlying cosmic chaos, or is there a
fundamental simplicity and harmony at its heart? Is what we see
and experience the unfolding of a single simple rule repeated
over and over again at every level of physical reality, or are
there endless rules each with its own domain of application? Just
what is the world made of, and can we know it? These are ancient
questions, inevitable as the fact of our own consciousness. As
this century draws to a close we think we know the answers to
some. Quantum theory is our most fundamental and successful
description of what there is. Yet the view of reality it presents
is so bizarre and so at variance with common sense, that after
almost a century we are still debating just what it means. The
quantum principle appears to apply to all reality, yet we still
cannot agree on how the world we see can be derived from a
principle at once so simple and so perplexing. The quantum
principle is this: physical reality is irreducibly random, but
random in a way we could never have expected. Reality exhibits a
randomness so constrained, by an as yet undiscovered principle,
that the odds with which it deals confound anyone who studies it.
The fact of this randomness is deeply shocking and acknowledged
as such by the originators of the theory."
-----------
Gerard J. Milburn: _The Feynman Processor: Quantum Entanglement
and the Computing Revolution_.
(Helix Books, Reading MA 1998, p.1)
[Gerald L. Milburn is Professor of Theoretical Physics at the
University of Queensland, AU]


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