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.

May 28, 1999 -- Vol. 3 Number 22

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Each answer begets a new question. To do science
day by day, year by year, is to sleep with puzzles.
-- Anonymous

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Contents of This Issue:

1. On National Security vs. the Universality of Science
2. A Major Sharp Controversy in Cosmology
3. On Modern Human Origins
4. Fluorescence Spectroscopy of Single Biomolecules
5. The Evolution of Hemoglobin
6. On G Protein Diseases

In Focus: A Small Closed Island

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1. ON NATIONAL SECURITY VS. THE UNIVERSALITY OF SCIENCE
Science is an activity that produces evidence concerning the
natural world, and with this evidence we build bridges, grow
crops, save our children from disease, and make weapons to kill
each other. That is the mix of it, and if the mix is an
interesting problem for sociologists and anthropologists, it is
also an ongoing crucial problem for governments and scientists.
How do we resolve the apparent conflict between national security
and the non-national enterprise of science?
... ... Irving A. Lurch (American Physical Society, US) presents
an editorial in the journal _Science_, the author making the
following points:
     1) The intellectual commerce that has propelled the
explosive growth of international science and technology over the
past 50 years is threatened. More than at any time since the
McCarthy era, the US government has barred entry of scientists
from certain nations and has prevented the travel of US
scientists to many of the same nations.
     2) Throughout the Cold War, there was much interaction
between Soviet and US scientists because it was understood that
such interactions reduced tensions, built confidence, and enabled
the development of workable schemes for arms control and weapons
reduction. The current attitude is apparently quite different.
     3) Because of Indian and Pakistani ambitions to be nuclear
powers, South Asian physicists and other scientists have recently
been prevented from attending international scientific
conferences in the US. At the same time, the US government has
announced that visas of already visiting South Asian physicists
will not be extended beyond the expiration dates. One result was
the threatened loss of a productive scientific collaboration by
US scientists in the Large Hadron Collider project at the
European Organization for Nuclear Research (CERN).
     4) In 1998, both the president of the American Chemical
Society and the society's administrator for international affairs
were denied permission to meet with their counterparts in the
Cuban Chemical Society. In 1997, five Cuban chemists from the
University of Havana were denied visas to attend an important
international meeting on quantum chemistry in the US because they
were declared "government employees", as are all university
professors in Cuba.
     5) In 1999, eight Department of Energy physicists from
Fermilab were denied permission to attend a high-energy physics
conference in India despite the scientific consensus that no
benefit could possibly accrue to the Indian weapons
establishment.
     6) The author concludes: "The variegated richness of science
is a product of its diversity. In the wake of World War II, the
world's scientific talent flocked to US and UK research
universities and laboratories, thereby vastly enriching science.
The efforts of government officials to slow this engine of
exchange under the disguise of preventing weapons technology
transfers threaten debilitating consequences for science here and
abroad."
-----------
Irving A. Lerch: The universality of science.
(Science 19 Mar 99 283:1847)
QY: [postmaster@aip.org]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 28May99
-------------------
Related Background:
US PHYSICISTS FORBIDDEN TO MEET IN INDIA
A controversy has apparently erupted in the physics community in
the US, resulting from the refusal of the US Department of Energy
to allow physicists at its national laboratories to travel to a
major particle physics conference in India during the week of 15
January. At least 7 physicists from the Fermi National
Accelerator Laboratory (Fermilab) and the Argonne National
Laboratory were apparently denied requests for travel to the 13th
Topical Conference on Hadron Collider Physics at the Tata
Institute for Fundamental Research in Mumbai (Bombay). John
Peoples, Director of Fermilab, said: "We never even did this with
the Russians at the worst part of the Cold War. This is a
precedent." Peoples also says that the US Department of Energy
ordered him in writing to remove the flag of India from the
United Nations-like display in front of the main building of
Fermilab. The Tata Institute, one of India's most prestigious
scientific institutes, was evidently placed on a list of
restricted sites because it conducts joint research with the
Bhabha Atomic Research Center, which is said to be "at the heart
of India's nuclear weapons program."
-----------
James Glanz: DOE blocks physicists from Indian meeting.
(Science 15 Jan 99 283:307)
QY: James Glanz 
-------------------
Summary by SCIENCE-WEEK  29Jan99
-------------------
Related Background:
NUCLEAR TEST EXPLOSIONS AND SCIENTISTS IN INDIA
G. Padmanaban, Director of the Indian Institute of Science
(Bangalore, IN), in a letter to the journal *Science*, comments
about the Indian science community and the recent nuclear test
explosions in India. The author makes the following points: 1)
The recent nuclear test explosions have created a "tremendous
euphoria" in India. The average Indian does not associate the
test with security concerns or power politics. "Right-thinking
Indians know that our priorities are such things as health,
education, and containment of population." 2) The author says
that India, despite having an ancient culture and a functioning
and stable large democracy, and being a hunting ground for
technically qualified people, has been persistently represented
in the US and the West as the home of poverty, filth, disease,
and backwardness. 3) The author says a feeling of alienation
permeates those segments of Indian society that have anything to
do with the West, and with the US in particular, and that the
general perception among Indian scientists in leading
institutions, most of whom are US-trained, is that they are being
discriminated against. Research papers sent to top international
journals from India seem to be reviewed with a bias. "Even if I
manage to publish one of my papers in one of the best journals,
it will seldom be quoted or have an impact, unless I have a US-
Western pedigree or a connection with an inner circle... Even if
I am invited to deliver a lecture at an international research
conference, I am made to feel like an outsider..." 4) The author
says India was denied a Cray computer for more than a decade, and
that Indian scientists "are appalled by how the US, which values
intellectual challenges and academic freedom, can have such a
discriminatory attitude toward a country struggling to develop
its science." 5) The author states: "India has many, many
problems, but we are tired of being depicted in the West as
having negative qualities. Given this treatment, one clutches at
any 'victory' that makes one feel like an entity to be counted.
It can be a win in cricket, a chess match, or a beauty contest,
or even a nuclear blast."
QY: G. Padmanaban 
(Science 10 Jul 98 281:175) (Science-Week 31 Jul 98)


2. A MAJOR SHARP CONTROVERSY IN COSMOLOGY
From the late 1940s to the late 1960s, astronomers had two rival
cosmological theories, the Steady State theory and the Big Bang
theory. The Steady State theory, introduced by Herman Bondi and
Thomas Gold in 1948, and later further developed by Fred Hoyle
and others, proposed that the Universe has always existed, that
it had no beginning, that it will continue forever, and that the
steady state average density of matter in the Universe is
maintained during cosmic expansion by the continuous creation of
new matter. The Steady State theory was abandoned by most
astronomers in the late 1960s, when it became accepted that the
then recently discovered *microwave background radiation was
evidence that a Big Bang, an effective initiation of the
Universe, had indeed occurred. In 1975, in fact, Fred Hoyle wrote
as follows: "The case against the steady-state model, resting
largely on the problem of the microwave background, although not
clear-cut, is strong enough to suggest that it may be more
profitable to consider alternative ways of coming to grips with
[cosmological data]." At that time, Hoyle also wrote: "We must be
on our guard against the ever-present tendency in astronomy to
imagine that nothing exists in the world except the things which
happen to be observable with present-day instruments. This point
of view has been repeatedly wrong, and doubtless will turn out to
be wrong again." [*Note #1].
... ... G. Burbridge et al (3 authors at 3 installations, US UK
IN), one of the authors Fred Hoyle, and the other two authors
also noted senior astrophysicists, now present a detailed review
of a revised Steady State theory (termed the "Quasi-Steady-State
Universe), the authors making the following points:
     1) The authors state that in science as they understand it,
one works from an initial situation, known from observation or
experiment, to a later situation that is also known. "That is the
way physical laws are tested. In the current popular form of
cosmology, by contrast, the physical laws are regarded as already
known and an explanation of the later situation is sought by
guessing at parameters appropriate to the initial state. We think
this approach does not merit the high esteem that cosmologists
commonly accord it." 
     2) The essential aspect of the Quasi-Steady-State model is a
proposed oscillating *cosmic scale factor (a measure of the size
of the Universe as a function of time), with a characteristic
oscillation time of 10^(11) years. The authors propose that in
our present epoch, we are almost half-way to the peak value for
the cosmic scale factor.
     3) Like the old Steady-State model, the new Quasi-Steady-
State model proposes the continuous creation of new matter in an
already existing Universe, instead of requiring the creation of
the entire Universe de novo in a Big Bang. The authors state they
regard the creation process as being triggered locally in what
they call "minicreation events", and that black holes are formed
in this process. The authors suggest that matter rotating about a
galactic center typically has an *angular momentum so large that
"it is difficult for us to see how a large quantity of matter in
a galaxy could come to be packed into the small scale of a black
hole, even when the black hole has a mass as large as 10^(10)
solar masses."
     4) The authors suggest their new theory, considering its
oscillatory aspects, can account for the currently observed
cosmic microwave background, and that "the ease with which the
complexities of the microwave background can be understood in the
quasi-steady-state cosmology is, in our opinion, a strong
indication that the theory is on the right track."
     5) Concerning so-called *active galactic nuclei, the authors
propose that not only gas, *relativistic particles, magnetic
flux, and radiation are being ejected, but also *quasars. The
authors suggest the observational evidence for this quasar
ejection is by now "extensive and overwhelming".
     6) Concerning quasars and observational astronomy in
general, the authors write: "Soon after quasars were first
discovered, it was suggested that many of them were much closer
to us than their surprisingly large *redshifts implied. The
circumstantial and observational evidence for this unorthodox
assertion was largely ignored... Halton Arp, the leading
spokesman for the radical proposition that high quasar redshifts
do not imply great distances, was eventually denied further
observing time to work in this field. He was forced to take early
retirement and leave Mount Wilson and Palomar Observatories. This
mistreatment had a chilling effect that is still being felt. The
tacit message was 'Don't ever find anything that conventional
theory cannot explain, and if you do, stop looking immediately.'
On modern facilities like the Hubble Space Telescope or the Keck
10-meter telescopes, no observing time is asked for or granted
for the further investigation of these issues."
     7) The authors conclude that much of current cosmology
consists of "ex post facto theoretical postulates that allow the
standard model makers to build what may well turn out to be a
make-believe universe."
... ... In a short commentary on the previous report, appearing
in the same issue of the journal, Andreas Albrecht (University of
California Davis, US) writes: "The authors... approach cosmology
with a set of prior prejudices that take them far afield from the
mainstream community of cosmologists. They hold on to views that,
I must say, look pretty unreasonable to most of us working in the
field. Nonetheless, I believe convergence will eventually be
possible... As extreme as the ideas of the quasi-steady-state
cosmology may appear to those of us more in the mainstream, we
freely admit that there are also domains of mainstream cosmology
that are far from being settled."
-----------
G. Burbridge et al: A different approach to cosmology.
(Physics Today April 1999)
QY: Geoffrey Burbridge, Univ. of Calif. San Diego 619-534-2230.
-----------
Andreas Albrecht: Reply to a "A different approach to cosmology".
(Physics Today April 1999)
QY: Andreas Albrecht, Univ. of California Davis 916-752-2971.
-----------
Text Notes:
... ... *microwave background radiation: The cosmic microwave
background is black-body radiation (the emission radiation of a
perfect absorber of radiation) at a present temperature of 2.73
degrees Kelvin, and has an almost equal intensity in all
directions in space. The deviations from isotropic intensity,
however, are of extreme importance in theoretical cosmology.
... ... *Note #1: The two quotes are from F. Hoyle: _Astronomy
and Cosmology, W.H. Freeman, San Francisco 1975, p.680.
... ... *cosmic scale factor: The cosmic scale factor S(t) is
related to the perhaps more familiar *Hubble constant H by
H = (dS/dt)/S.
... ... *Hubble constant: This constant defines the rate at
which the expansion velocity of the Universe changes with
distance. The notation is usually H(sub0).
... ... *angular momentum: In general, angular momentum is a
property of any rotating or revolving system, its value dependent
on the distribution of mass and velocity about the axis of
rotation or revolution.
... ... *active galactic nuclei: Central regions of galaxies in
which considerable energy is generated by processes other than
those operating in ordinary stars. Many astrophysicists believe
the energy may result from the accretion of material into a
massive black hole situated at the core of the galaxy.
... ... *relativistic particles: In general, a relativistic
particle is any particle whose velocity is close to the speed of
light.
... ... *quasars: (quasi-stellar objects) Extremely luminous
sources radiating energy over the entire spectrum from x-rays to
radio waves, and which are apparently (according to standard
cosmology) the oldest and most distant objects in the universe.
... ... *redshifts: Redshift (symbol: z) is a lengthening of the
wavelengths of electromagnetic radiation from a source caused
either by the movement of the source (Doppler effect) or by the
expansion of the universe (cosmological redshift). Redshift is
defined as the change in wavelength of a particular spectral line
divided by the unshifted wavelength of that line. Large redshifts
imply large radial velocities (which imply large distances,
according to current cosmological theory), but at redshifts
greater than about 0.2 there is a relativistic divergence from a
linear relation. A redshift of 4.0 corresponds to an object
receding with a radial velocity 92% that of the velocity of
light. The largest astrophysical redshifts so far observed are of
the order of z = 4.9. The furthest galaxy on record is at a
redshift z=4.92), which implies a distance of approximately 13
billion light years.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 28May99
-------------------
Related Background:
ASTROPHYSICS: ON ACCELERATING COSMIC EXPANSION
The idea of cosmic expansion derives from the observation that
radiation from distant galaxies is *redshifted, and the consensus
is that the distance between clusters of galaxies is continuously
increasing, with all galaxies beyond the Local Group apparently
receding from us [*Note #1]. In other words, the Universe as a
whole is expanding, a phenomenon discovered by Edwin Hubble in
1929 but previously suggested by several theoretical cosmologists
(e.g., A. Friedmann [1922], G. Lemaitre [1927]). This expansion
is the observational basis of the *Big Bang theory. Essential to
the study of cosmic expansion is the accurate measurement of
intergalactic distances, and such measurement is dependent on the
use of "standard candles", astronomical objects whose intrinsic
brightness is known and whose distance can therefore be
calculated from apparent brightness. ... ... C.J. Hogan et al (3
authors at 3 installations, US CL) present a review of current
research on the temporal history of cosmic expansion, with
emphasis on recent work concerning the use of *type 1a supernovae
as standard candles. The authors make the following points: 1)
Until recently, the intrinsic brightness of all standard candles
used in observations has been found to be too variable, changing
with the evolution of the object or showing too much diversity
from one object to the other. However, during the past decade,
astrophysicists have been able to precisely determine the
intrinsic brightness of one kind of astronomical object, the type
1a supernova, and these objects have become the best calibrated
standard candles known to astronomers. Currently, observations of
type 1a supernovae are challenging decades of conventional ideas
concerning cosmic expansion. 2) Locating distant supernovae
involves taking images of the same part of the sky a few weeks
apart and searching for changes that might be exploding stars.
Because the digital light detectors can precisely count the
number of photons in each picture element, one makes a simple
subtraction of the first image from the second and looks for
significant differences from zero. With present equipment,
thousands of galaxies are checked in each image pair... After
supernovae candidates are located, the *Keck telescopes in
Hawaii, the largest optical instruments in the world, are pointed
at the objects, and critical observations establish whether or
not the objects discovered are in fact type 1a supernovae. The
observations are then used to gauge the intrinsic brightness of
the objects more exactly and to determine their redshifts... Two
teams have now studied a total of approximately 40 high redshift
supernovae, objects that erupted between 4 and 7 billion years
ago, when the universe was between one-half and two-thirds of its
present age. The results have been surprising: the supernovae are
fainter than expected. The difference is slight, the distant
supernovae on average only 25 percent dimmer than forecast, but
this result is enough to call long-standing cosmological theories
into question. The conclusion from the observations is that the
cosmic expansion is slowing less quickly than previously thought.
3) If the Universe is made of normal matter, gravity must
steadily slow the cosmic expansion. A reduced slowing, as
indicated by the supernovae measurements, implies that the
overall density of matter in the Universe is low... However, the
big surprise is that the observed supernovae are fainter than
predicted even for a nearly empty universe. Taken at face value,
the observations appear to require that expansion is actually
accelerating with time. This is consistent with the "vacuum
energy" embodied in Einstein's equations as the so-called
"*cosmological constant". Unlike ordinary forms of mass and
energy, the vacuum energy adds gravity that is repulsive and can
drive the Universe apart at ever increasing speeds. The authors
conclude: "Evidence for a strange form of energy imparting a
repulsive gravitational force is the most interesting result we
could have hoped for, yet it is so astonishing that we and others
remain suitably skeptical."
-----------
C.J. Hogan et al: Surveying space-time with supernovae.
(Scientific American January 1999)
QY: Craig J. Hogan, Univ. of Washington Seattle 206-543-8992.
-----------
Text Notes:
... ... *redshifted: See notes to previous report.
... ... *Note #1: In the expansion model, it is the space between
widely separated objects that is expanding. Neighboring objects,
such as close pairs of galaxies, do not move apart because their
mutual gravitational attraction exceeds the effect of the
cosmological expansion. However, the distance between two widely
separated galaxies, or clusters of galaxies, will increase as the
Universe expands.
... ... *Big Bang theory: The Big Bang theory is the general
cosmological model that proposes that all matter and radiation in
the universe originated in an explosion at a finite time in the
past.
... ... *type 1a supernovae: Type 1a supernovae are believed to
be *white dwarf stars that have accreted enough matter from
another star to be pushed over a mass threshold and into a
thermonuclear explosion.
... ... *white dwarf star: White dwarf stars are extremely dense
and compact stars that have undergone gravitational collapse.
They are the final stage in the evolution of low-mass stars after
they have lost their outer layers. White dwarf stars are about
the size of Earth, but with a mass about that of the Sun.
... ... *Keck telescopes: The Keck telescopes are a pair of twin
telescopes at the W. M. Keck Observatory on Mauna Kea, HI US,
each with 10 meter mirrors, the pair constructed 1992-1996. The
installation is managed by the University of California (US) and
the California Institute of Technology (US).
... ... *cosmological constant: A mathematical term introduced by
Einstein into the equations of general relativity, the purpose to
obtain a solution of the equations corresponding to a "static
universe". The term describes a pressure (if positive) or a
tension (if negative) which can cause the Universe to expand or
contract even in the absence of any matter ("vacuum energy").
When the expansion of the Universe was discovered, Einstein
apparently began to regard the introduction of this term as a
mistake, and he described the cosmological constant as the
"greatest mistake of my life". But the term has reappeared as the
proposed source of apparent accelerated cosmic expansion.
-------------------
Summary & Notes by SCIENCE-WEEK  22Jan99
-------------------
Related Background:
COSMOLOGY: THE END OF THE OLD MODEL UNIVERSE
Cosmologists are apparently expecting the near-future necessity
for profound conceptual alterations in their field. Peter Coles
(University of London, UK) presents a short review of the current
situation and makes the following points: 1) Observations only
recently made possible by improvements in astronomical
instrumentation have put theoretical models of the Universe under
intense pressure. The standard ideas of the 1980s about the shape
and history of the Universe have now been abandoned -- and
cosmologists are now taking seriously the possibility that the
Universe is pervaded by some sort of "vacuum energy" whose origin
is not at all understood. 2) The weakness of the Big Bang model
is that the numerical values of certain essential parameters in
the model (the Hubble constant, the density parameter, and, in
some versions, the cosmological constant) are not predicted by
theory, and thus the parameters must be inferred from
observations. 3) The Big Bang model does not deserve to be called
a "theory" unless and until it can explain how nonuniformities of
galaxies and clusters of galaxies came into being and evolved. 4)
The Cold Dark Matter model of structure formation, first proposed
in the 1980s, is in serious difficulty because the consequent
significant gravitational brake on expansion is not evident, and
in fact expansion may be accelerating. Current observations
coupled with current dynamical arguments all suggest a global
density of matter in the Universe less than the value required to
make the Universe recollapse. 5) The existence of a cosmological
constant (or vacuum energy) of the required size necessary to
make the basic cosmological models work is not at all explained
by current theories of the fundamental interactions of matter. 6)
There is every reason to be confident that the important issues
will soon be resolved, because a data explosion is about to
engulf cosmology, a new generation of galaxy surveys. The Sloan
Digital Sky Survey, for example, will encompass more than a
million galaxies. The cosmological community is bracing itself
for the arrival of these enormous new data sets and the new
insights they will surely bring. 7) It is possible that none of
the available models will fit all the new data. Coles concludes:
"For many of us, that is the most exciting possibility of all, as
we would have to move to stranger theories, perhaps not even
based on General Relativity."
QY: Peter Coles 
(Nature 25 Jun 98 393:741) (Science-Week 17 Jul 98)


3. ON MODERN HUMAN ORIGINS
The study of human origins, the field called paleoanthropology,
has intrinsic difficulties because of the relative scarcity of
data, but these difficulties are magnified enormously by the
simple fact that paleoanthropology, in essence, represents a
species attempting to reconstruct its own early history. As might
be expected, an objective reconstruction, one without biases and
preconceptions, is far from easy. The human group we call the
"Neanderthals" lived in much of Europe, part of Asia, and the
Middle East between 150,000 to probably less than 30,000 years
ago. Neanderthals were the first fossil humans to be discovered,
and they have long been the focus of anthropological
investigation. More bones of Neanderthals are known than for any
other human-related (hominine) fossil group, including 30 nearly
complete skeletons, so the preoccupation of the anthropology
community with the Neanderthals is perhaps understandable. One of
the important questions concerning the Neanderthals is what
happened to them? Hypotheses have shifted back and forth since
the first discovery in 1856 of Neanderthal bones, with two major
views. One view is that the Neanderthals were the direct
ancestors of modern Europeans. The other view regards the
Neanderthals as a side branch of human evolution, with extinction
as their fate. This latter view is apparently the majority view
in the paleoanthropology community.
... ... G.A. Clark (Arizona State University, US) presents a
review of current research controversies and methods concerning
the transition from early humans to modern humans that apparently
occurred during the period from 50,000 to 10,000 years ago
(Middle-Upper Paleolithic transition). A central question is
whether the transition occurred abruptly or gradually. The author
makes the following points:
     1) Insufficient data is only part of the reason the question
of human origins remains unresolved. Researchers in this area
come from various research traditions, and in each of these
traditions different assumptions about the remote human past
determine what is considered relevant data, which questions are
asked of the data, and how the data are interpreted. More data do
not remove the paradigmatic bias implicit within each research
tradition, and in consequence people from the different relevant
fields fail to communicate effectively.
     2) The disciplines that contribute to the field (archeology,
human paleontology, and molecular biology) tend to be discovery-
driven and focused on methodology. The result is a common absence
of concern for the logic of inference underlying claims of
knowledge. European archeological studies of modern human origins
are a particularly good example of such epistemological naivete.
These studies are based on a century-old typological systematics
that emphasizes retouched stone tools, coupled with a set of
biases and preconceptions concerning the relationships between
developments in tool-making and developments of cultures.
     3) On the surface, the voluminous literature produced by the
debate concerning modern human origins suggests an informed and
sophisticated interdisciplinary research in which data are
absorbed and digested, arguments assimilated, and methodologies
understood, compared, and evaluated. The author suggests "this is
a gross simplification of a much more complex reality."
     4) The author concludes: "We are, in effect, consumers of
one another's research conclusions, but we select among
alternative sets of research conclusions in accordance with our
biases and preconceptions. These biases and preconceptions must
be subjected to critical scrutiny. As long as there is no
explicit concern with the logic of inference -- how we know what
we think we know about the past -- there can be no consensus."
-----------
G.A. Clark: Highly visible, curiously intangible.
(Science 26 Mar 99 283:2029)
QY: G.A. Clark [gaclark@asu.edu]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 28May99
-------------------
Related Background:
HUMAN EVOLUTION: THE FATE OF THE NEANDERTHALS
The current consensus in paleoanthropology is that the
Neanderthals were an extinct side-line of human evolution.
European Neanderthals are thought to have diverged from the
lineage that gave rise to modern humans at least 500,000 years
ago. The current view is that approximately 30,000 to 40,000
years ago the Neanderthals were replaced by modern populations,
probably from an ultimately African source. A present debate
concerns how this population replacement occurred.
... ... Paul Mellars, in a short review of a recent conference
(28-30 Aug 1998, Gibraltar, UK) on the Neanderthals, makes the
following points: 1) The current consensus is that in the
southern part of the Spanish peninsula, roughly to the south of
the Ebro valley, the local Neanderthals survived for at least
5000 to 10,000 years after the arrival of modern populations in
the adjacent parts of northern Spain and the Mediterranean coast.
2) The most likely explanation for the prolonged coexistence of
these two populations lies in the ecological differences between
the northern and southern parts of the Iberian peninsula. 3)
Studies of Neanderthal skeletal remains reinforce the conclusion
that the Neanderthals were a divergent lineage that probably made
no contribution to the evolution of anatomically modern humans.
This is consistent with the DNA evidence that the two lineages
separated at least 500,000 years ago, and even longer divergence
times are favored by some researchers. 4) The impression at the
end of the conference was that the Neanderthals were really quite
different from humans -- well adapted to survive in the harsh
glacial environments of Europe, but with distinct anatomical and
behavioral patterns different from their modern human successors.
The author concludes: "The eagerness of some scientists to claim
close kinship with the Neanderthals could come close to denying
that human evolution actually took place."
-----------
Paul Mellars (University of Cambridge, UK)
The fate of the Neanderthals.
(Nature 8 Oct 98 395:539)
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 6Nov98
-------------------
Related Background:
FIRST ANALYSIS OF DNA FROM A NEANDERTHAL BONE
About 10 kilometers east of Dusseldorf in Germany, in the valley
of the Dussel, there is a little town called Neander. One hundred
and forty-one years ago, in the summer of 1856, some workmen
broke into a cave to get at the limestone inside and discovered a
set of ancient bones. Most of the bones were smashed to bits by
the workmen, but some of the bones, including part of the skull,
survived, and the skeleton was soon recognized by anthropologists
as belonging to an ancient race of men who came to be known as
the Neanderthals. A Neanderthal fossil had actually been
discovered some years earlier in Gibraltar, but not recognized as
such. Neanderthal-like fossils have also been found in France,
Spain, Italy, Yugoslavia, Iraq, China, Java, and Israel. For more
than a century, one of the central questions in paleoanthropology
has been whether modern man evolved from this race -- or was the
Neanderthal a separate branch that became extinct? Until
recently, the primary laboratory method of investigation of such
a question was analysis of the morphology of bone fragments. This
week, the field of paleoanthropology has apparently crossed an
important watershed, as M. Krings et al (University of Munich,
DE; Pennsylvania State University, US) report the first analysis
of DNA from an extinct human, in this case DNA extracted from the
actual Neanderthal skeleton found near Dusseldorf in 1856. The
key to the investigation was the analysis of mitochondrial rather
than nuclear DNA. Mitochondrial DNA is usually present in
concentrations two or three orders of magnitude greater than
nuclear DNA, and they were able to find enough of it still intact
to amplify with the PCR technique and piece together a total DNA
sequence of 379 base pairs. Comparison of this sequence with
contemporary human sequences leads to the conclusion that
Neanderthal and modern man are separate evolutionary lines, and
that the latter did not evolve from the former. The work will
have to be replicated with other Neanderthal fossils, but most
paleoanthropologists are excited by the results and expect them
to be confirmed. The technology of evolutionary paleoanthropology
has evidently now progressed from caliper measurements of bones
to measurements of bone DNA fragments.
(Cell 11 July) (Science-Week 18 Jul 97)


4. FLUORESCENCE SPECTROSCOPY OF SINGLE BIOMOLECULES
The term "luminescence" refers to the emission of light by a
substance for any reason other than a rise in its temperature. In
general, atoms of substances emit photons of electromagnetic
energy when they return to the ground state after having been in
an excited state. The causes of excitation and the temporal
characteristics of the luminescence are various, and various
types of luminescence are thus defined. In general, if
luminescence persists for more than 10 nanoseconds after the
exiting cause is removed, it is called "phosphorescence"; if the
persistence of luminescence is less than 10 nanoseconds, it is
called "fluorescence". The term "fluorescence energy transfer"
(also called "fluorescence resonance energy transfer") refers to
energy transfer between two fluorophores (chemical groups or
molecules capable of fluorescence). If the two fluorophores are
attached to a molecule at different positions, observations of
fluorescence energy transfer between them can be used to
determine the distance between the two attachment positions.
... ... Shimon Weiss (Lawrence Berkeley National Laboratory, US)
presents a review of the fluorescence spectroscopy of
fluorophores attached to biological macromolecules at specific
sites, the author making the following points:
     1) Recent advances in single-molecule detection and single-
molecule spectroscopy at room temperature by laser-induced
fluorescence are making possible new methods for the study of
individual macromolecules in biological systems under
physiological conditions. These tools relate conformational
states, conformational dynamics, and activity of single
biological molecules to physical observables, without the
relationships masked by ensemble averaging.
     2) Single-molecule methods are also suited to study
fluctuating systems under equilibrium conditions and to measure
time trajectories and reaction pathways of individual members in
a non-equilibrated system. In particular, these methods can
measure intermediates and follow time-dependent pathways of
chemical reactions that are difficult or impossible to
synchronize at the ensemble level.
     3) Although fluorescence spectroscopy of single biological
molecules is now a research tool in many laboratories, major
improvements are needed in dye chemistry, in the chemistry of
molecular complexes, and in instrumentation and methodologies.
     4) The author suggests that in the near future fluorescence
single-molecule detection and single-molecule spectroscopy will
probably be used not only in cutting-edge biological research,
but also in the biotechnology and analytical chemistry
industries.
-----------
Shimon Weiss: Fluorescence spectroscopy of single biomolecules.
(Science 12 Mar 99 283:1676)
QY: Shimon Weiss [sweiss@lbl.gov]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 28May99
-------------------
Related Background:
EVIDENCE THAT DNA IS A POOR ELECTRON CONDUCTOR
In general, electron transfer is the passage of an electron from
one constituent of a system to another. In recent years, there
have been two views of electron transfer through the DNA double
helix, with one view holding the electron conduction properties
of DNA are that of an insulator and no greater than that of a
protein, and the other view holding that the DNA double helix can
transfer electrons along its length freely enough to make the
double helix an electrical conductor...
... ... Tanaka and Fukui now report determination of
the rate of electron transfer through a DNA system modified to
include the insertion of a fluorescing electron acceptor (9-
amino-5-chloro-2-methoxymeridine). The electron donor guanine was
placed at varying distances from the dye moiety, the system
irradiated, and the resulting fluorescence spectra measured to
calculate the rates of electron transfer from the fluorescence
quantum yields. The electron transfer rate was found to be
comparable to that of proteins, and the authors suggest that DNA-
base stacking does not form a special mediator for the fast
electron transfer process
QY: Kazuyoshi Tanaka, Kyoto Univ., JP.
(Angew. Chem. Int. Ed. 37:158 1998) (Chem. & Eng. News 9 Feb 98)
(Science-Week 20 Feb 98)


5. THE EVOLUTION OF HEMOGLOBIN
Heme is an iron-containing porphyrin acting as the prosthetic
group of several biological pigments, including hemoglobin,
*myoglobin, and several *cytochromes. Hemoglobin is the chief
transport protein involved in carrying oxygen within red blood
cells (erythrocytes). The heme *prosthetic group is similar in a
variety of hemoglobins, but the globular *apoenzyme has
fluctuated considerably in the course of evolution. Hemoglobin is
a tetrameric molecule, consisting of two pairs of nonidentical
polypeptides associated in a quaternary structure, each of the 4
heme groups containing an iron atom that binds oxygen reversibly.
The molecule occurs intracellularly in vertebrate erythrocytes,
but in invertebrates hemoglobin is usually found in simple
solution in the blood. It is also found in certain *nitrogen-
fixating plants. A variety of hemoglobin types are especially
evident in mammals, and in some cases specific polypeptide chains
are different for the fetus than for the adult. The molecule
produces a red color when oxygenated and a bluish-red color when
deoxygenated. The ability of the hemoglobin molecule to pick up
and unload oxygen depends on its shape in solution, and this
shape varies *allosterically with local pH, which in turn is a
function of the partial pressure of blood carbon dioxide. Carbon
dioxide combines with hemoglobin at its amino groups. Carbon
monoxide (CO) is highly poisonous because it binds to hemoglobin
irreversibly, causing suffocation at the cellular level. Human
hemoglobin consists of 574 amino acids, and has a globular shape
with a diameter of approximately 6 nanometers. The hemoglobin
concentration in normal human erythrocytes is extremely high: in
the erythrocyte, the hemoglobin molecules are only 1 nanometer
apart, but they apparently can rotate and flow past one another
without hindrance. ... ... Ross Hardison (Pennsylvania State
University, US) presents a review of current research concerning
the molecular biology and evolution of hemoglobin, the author
making the following points concerning the evolution of the
molecule:
     1) The 3-dimensional structure of hemoglobin -- its shape,
folds, pockets, and surfaces -- have been well conserved over the
evolutionary history of the protein. But some of the most rapid
and dramatic changes in hemoglobin proteins have occurred in the
ways these molecules are regulated -- the when and how of their
manufacture inside the cell.
     2) The active core of hemoglobin, the porphyrin ring, which
is responsible for the basic chemistry of the molecule in which
it is located, eventually came to be embedded, via evolution, in
larger organic structures. The structure of these organic
molecules imparts to the molecule its specific function,
determining, for example, whether that basic chemistry was used
in connection with respiratory reaction chains, oxygen transport,
or oxygen sequestration. Thus, structural changes in these
organic molecules have been translated into functional changes.
     3) Structurally similar molecules can become further
differentiated functionally by being expressed at different times
in the development of an organism, as is the case for fetal and
adult *globins, or under different circumstances, such as the
scarcity or abundance of oxygen. These distinctions are not
attributable to differences in the overall structures of the
proteins themselves, but to the differences in *expression
profiles achieved through differences in regulatory segments of
genes. It has become apparent that in many cases regulatory
regions of genes are changing more rapidly via evolution than are
the structures of proteins themselves.
     4) This idea is relatively new in the study of molecular
evolution, which has concentrated on comparisons between protein
structures to determine evolutionary relationships between
species. But molecular evolutionists are beginning to recognize
the value of looking at relations between regulatory regions.
-----------
Ross Hardison: The evolution of hemoglobin.
(American Scientist Mar-Apr 1999 87:126)
QY: Ross Hardison [rch@psu.edu]
-----------
Text Notes:
... ... *myoglobin: Myoglobin is a hemoglobin-like protein
complex found in the muscle tissue of vertebrates and in some
invertebrates. The molecule has only one polypeptide chain
associated with a heme group, but it performs essentially the
same function as hemoglobin, that of reversibly binding oxygen.
It has a higher oxygen affinity than hemoglobin, releasing oxygen
only when the blood oxygen supply becomes limiting, thus serving
as an extra oxygen storage system in muscles.
... ... *cytochromes: The cytochromes are a system of electron-
transfer proteins with iron- or copper-porphyrin as a prosthetic
group. They are found in both animal and plant cells.
... ... *prosthetic group: In this context, a non-protein group
firmly attached to a protein to form a functional complex (a
"conjugated protein").
... ... *apoenzyme: In general, this refers to the protein
component of an enzyme-cofactor complex (holoenzyme). The
apoenzyme is usually catalytically inactive by itself.
... ... *nitrogen-fixating plants: In general, the incorporation
of atmospheric nitrogen to form nitrogenous organic compounds.
... ... *allosterically: In general, an "allosteric" molecule is
a molecule whose 3-dimensional conformation alters in response to
a change in its environment, the alteration resulting in a change
in molecular function. So, for example, the hemoglobin molecule
is allosteric under different blood pH values.
... ... *globins: The term "globin" refers to the globular
protein that complexes with the heme group in oxygen-carrying
proteins such as hemoglobin and myoglobin. (This term must be
distinguished from "globulins", which refers to a class of
globular proteins of importance in the immune system).
... ... *expression profiles: The "expression profile" of a
genome or a group of genes in a genome refers to the set of genes
that have been "switched on" to express their proteins. Various
types of cells have different expression profiles, and within a
single type of cell, the expression profile may change during the
life history of the cell.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 28May99
-------------------
Related Background:
MICE WITHOUT MYOGLOBIN
Heme is an iron-containing porphyrin associated with several
physiologically important pigments and proteins. Organisms as
diverse as *annelid worms, molluscs, flowering plants, and
*protochordates express cytoplasmic hemoproteins (tissue
hemoglobins) that reversibly bind oxygen, presumably to
facilitate oxygen transfer to sites of use. In vertebrates, only
cardiac muscle cells and certain *mitochondria-rich skeletal
muscle fibers express the hemoprotein myoglobin, a monomeric
protein distantly related to the oxygen-binding hemoglobin of
blood cells. Myoglobin concentrations in skeletal muscles are
increased in mammals adapted for deep-sea diving or life at high
altitude, or in response to sustained muscle contractions. In
general, myoglobin readily binds oxygen but gives up its oxygen
only during periods of intense mitochondrial activity (i.e.,
intense muscle activity). Muscle fibers involved in sustained
intensive activity (e.g., the flight muscles of insects, cardiac
muscle, certain skeletal muscles) usually contain high
concentrations of mitochondria (as much as 50 percent of total
cell volume) and also high concentrations of myoglobin that give
these muscle a red color ("red muscle"). ... ... D.J. Garry et al
now report that mice without myoglobin, the mice produced by
*gene-knockout genetic engineering, are fertile and exhibit
normal exercise capacity and a normal *ventilatory response to
low oxygen levels (hypoxia). Heart and soleus muscles from these
animals are depigmented, but function normally in standard assays
of muscle performance. The authors suggest these data indicate
that myoglobin is not required to meet the metabolic needs of
pregnancy or exercise in a terrestrial mammal, which raises new
questions about oxygen transport and metabolic regulation in
working muscles.
-----------
D.J. Garry et al (8 authors at 2 installations, US)
Mice without myoglobin.
(Nature 29 Oct 98 395:905)
QY: R. Sanders Williams 
-----------
Text Notes:
... ... *annelid worms: A phylum of segmented worms with a true
body cavity, and with well-developed circulatory and nervous
systems.
... ... *protochordates: In general, the chordates possess a
notochord, a flexible rod (present only in vertebrate embryos)
that supports the nerve cord. Protochordates are an invertebrate
chordate subphylum.
... ... *mitochondria: 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 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 (i.e., cells containing membrane-bound
organelles such as a nucleus). In biology, "symbiosis" is an
intimate and protracted association of individuals of different
species.
... ... *gene-knockout genetic engineering: One approach widely-
used to test the importance of a particular protein is the
genetic manipulation of animals such as mice or fruit flies to
produce a "knockout" of a selected protein. By a technique known
as "homologous recombination", it is possible to replace the
normal gene for a selected mouse protein by a nonfunctional
mutant gene. Such mutant animals can then be bred to produce
strains of mice that lack the functional protein.
... ... *ventilatory response: In the context of this report, the
"ventilatory response" is measured as the increase in respiration
rate as a function of reduced oxygen in the ambient air supplied
to the animal.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 4Dec98
-------------------
Related Background:
ON THE RESPIRATORY FUNCTION OF HEMOGLOBIN
Hemoglobin is the respiratory protein of erythrocytes (red blood
cells), carrying oxygen from the lungs to peripheral tissues and
participating in the reverse transport of carbon dioxide. In
normal human erythrocytes, hemoglobin concentration is extremely
high (340 grams/liter), and corresponds to a 5.2 mM solution,
assuming a molecular mass of 65K grams/mole. The oxyhemoglobin
dissociation curve is a measured sigmoid-shaped quantitative
relation between oxygen saturation or content of hemoglobin and
the oxygen tension at equilibrium, and its parameters have been
intensively investigate for more than 50 years and related to
various aspects of respiratory physiology. At the present time, a
central interest is to understand the molecular mechanisms
producing conformational changes in hemoglobin and how these
changes relate to the binding of oxygen and the regulation of
respiration. ... ... C. Hsia (Univ. Texas Southwestern Medical
Center, US), in a review of the respiratory function of
hemoglobin, discusses the regulation of oxygen transport via the
oxyhemoglobin dissociation curve, and how physiologically induced
variation of oxyhemoglobin dissociation is regulated to support
the highest rate of oxygen transport in both health and disease.
QY: Connie C.W. Hsia, Univ. of Texas SW Med. Sch. 214-648-2670.
(New England J. Med. 22 Jan 98) (Science-Week 30 Jan 98)


6. ON G PROTEIN DISEASES
One of the important achievements of molecular biology during the
past four decades has been the identification of the molecular
entities and processes involved in a number of major event
sequences in biological cells. At the molecular level, an event
sequences is essentially a cascade of chemical reactions -- event
A leading to event B leading to event C and so on -- and such
sequences are evidently of paramount importance for the viability
and functions of biological cells. The cell membrane is the
boundary between the cell and its exterior, and in this membrane
reside a variety of membrane proteins, some of which act as
receptors for ligands, the ligands chemical entities in the
external environment of the cell that act as triggers ("first
messengers") to initiate event sequences inside the cell. The
simplest paradigm involves the interaction of a ligand with a
receptor membrane protein, and the subsequent release of a
"second messenger" inside the cell (e.g., cyclic AMP, i.e.,
adenosine 3,5-monophosphate), the second messenger triggering
further steps in an event sequence that may result in a variety
of specific cellular consequences. During the past several
decades, it has become apparent that a family of proteins called
"G proteins" have an important involvement in the steps between
receptor activation and the release of the second messenger, the
G proteins involved with a large variety of receptors and the G
proteins themselves existing in a large variety of types. In
general, what a G protein does is act as a control intermediary
between a membrane receptor protein and a nearby membrane second-
messenger-releasing protein (*adenylyl cyclase). The G proteins
are widely distributed but evidently unique to *eukaryotic cells,
and they are apparently involved in the responses produced by
functionally different numerous receptor types, including photon
receptors in the visual system, ion channels in nerve and muscle
cells, and hormone receptors in all types of cells. The "G"
derives from the fact that G proteins are guanine-nucleotide-
binding proteins (e.g., binding guanosine 5'-triphosphate (GTP)).
These proteins are evidently lipid-anchored to the cell membrane
at its inner (cytoplasmic) surface. Each G protein consists of 3
subunits, and there are apparently 27 different genes involved in
the encoding of these 3 polypeptides subunits, the genetic array
producing a spectrum of possible G protein subtypes. As might be
expected, there is evidence that either genetic or pathogen-
provoked dysfunctions in the chemistry of G proteins can produce
various important diseases related to first messenger-to-second
messenger signal dynamics.
... ... Z. Farfel et al (3 authors at 3 installations, IL US JP)
present a detailed review of the biochemistry and medical biology
of known G protein diseases, the authors making the following
points:
     1) At the present time, the known G protein diseases are for
the most part confined to a set of rare endocrine disorders.
However, a recent study suggests that mutations in G proteins can
also lead to *essential hypertension, and if this is true,
hypertension may be one of several common disorders caused by
defects in this ubiquitous family of signaling molecules.
     2) Mutations that alter G protein activation may cause
disorders characterized by either insufficient or excessive
transmission of signals. Deficient transmission of signals --
loss of function -- results from mutations that impair the
ability of the G protein to become activated by hormone
receptors. Increased transmission of signals --  gain of function
-- results from mutations that mimic or augment the activation of
receptors. In addition, toxins secreted by infectious pathogens
can alter G protein function with pathological consequences
(known infectious G protein diseases: *cholera, *pertussis).
     3) The authors categorizes 3 types of G protein pathologies:
... ... a) Defective signal termination -- signal excessive:
cholera, *adenomas of *pituitary and *thyroid, adenomas of
*adrenals and ovaries, *McCune-Albright syndrome.
... ... b) Absent or inactive G protein subunit (the G-alpha
subunit) -- signal deficient: *pseudohypoparathyroidism (types 1a
and 1b), *night blindness.
... ... c) Abnormal signal initiation -- signal inadequate or
excessive: pertussis, pseudohypoparathyroidism type 1a,
*testotoxicosis with pseudohypoparathyroidism type 1a, essential
hypertension.
     4) The authors conclude: "Because G proteins play key parts
in regulation, genetic analysis is likely to reveal additional
mutations in G proteins that cause disease in humans. Some of
these mutations will cause rare diseases... but they will
nonetheless teach us lessons about basic regulatory mechanisms.
In other cases... balanced polymorphisms may be found to
contribute to... common chronic disorders."
-----------
Z. Farfel et al: The expanding spectrum of G protein diseases.
(New England J. Med. 1 Apr 99 340:1012) 
QY: Taro Iiri [tiiri-tky@umin.ac.jp]
-----------
Text Notes:
... ... *adenylyl cyclase: (adenylate cyclase) This enzyme
catalyzes the production of cyclic AMP from ATP. Adenosine
triphosphate (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 components. One of
the reaction products of ATP is cyclic AMP, which acts as an
intracellular hormone responding to signals from extracellular
hormones (i.e., an intracellular chemical messenger: thus the
name "second messenger").
... ... *eukaryotic cells: Biological cells with internal
membrane-bound organelles such as a nucleus.
... ... *essential hypertension: Hypertension is high blood
pressure, and "essential hypertension" is high blood pressure
without known cause.
... ... *cholera: An acute epidemic infectious disease caused by
the bacterium Vibrio cholerae and now occurring primarily in
Asia. A soluble toxin produced by the bacterium in the intestinal
tract activates the adenylate cyclase of the intestinal mucosa
(the mucous tissue lining the interior of the intestine), and
this causes active secretion of fluid into the intestine, which
in turn produces extreme diarrhea, loss of the fluid,
dehydration, and collapse. Historically, the term "cholera" was
applied to any of a variety of gastrointestinal diseases.
... ... *pertussis: (whooping cough) A common infectious disease
caused by the bacterium Bordetella pertussis, the organisms
living in the upper respiratory tract. The infection causes a
paroxysmal cough that can persist for weeks and which may
complicated by secondary infection and death. The principal toxin
of B. pertussis is an enzyme that chemically modifies G proteins
with the effect of markedly reducing the response of G proteins
to receptor activation.
... ... *adenomas: An adenoma is an ordinarily benign neoplasm in
which tumor cells form glands or glandular-like structures.
... ... *pituitary: (pituitary gland; hypophysis cerebri) A small
gland at the base of the brain. The pituitary supplies a number
of hormones that control various physiological processes
... ... *thyroid: (thyroid gland) An organ at the front of the
neck, the gland releases the hormone thyroxin directly into the
blood. The thyroid is essentially controlled by the pituitary
gland release of thyrotropic hormone. The thyroid gland is
essential for normal body growth in infancy and childhood, and in
adulthood is an important part of the general control system that
regulates systemic metabolic rates.
... ... *adrenals: (adrenal glands) An adrenal gland is located
on the top of each kidney. Various parts of the adrenals secrete
various hormones: corticosteroids, androgens, epinephrine, and
norepinephrine.
... ... *McCune-Albright syndrome: A fibrous dysplasia (a
dysplasia is any abnormal tissue development) producing brown
patches of skin pigmentation, endocrine dysfunction, and
precocious puberty in girls.
... ... *pseudohypoparathyroidism: This is apparently caused by
genetic loss of one of the subunits of a G protein. The clinical
features resemble those of hypoparathyroidism, but result from
inherited resistance of target tissues to parathyroid hormone
rather than to lack of the hormone. Parathyroid hormone, secreted
by the parathyroid glands attached to the thyroid gland, acts to
control calcium ion level in body tissues.
... ... *night blindness: (nyctalopia) Decreased ability to see
in reduced illumination. Seen in patients with impaired retinal
rod function, and often associated with vitamin A deficiency.
... ... *testotoxicosis: Autonomous production of testosterone, 
resulting in precocious puberty in boys.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 28May99


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
IN FOCUS: A SMALL CLOSED ISLAND
"There are many lessons for us in the history of life on Earth.
We share, with all living beings, a common ancestry. Over
geological time, our ancestors, together with the ancestors of
the creatures that exist or have existed, have created complex
communities of life. These communities have been built over
millions of years, as interdependent webs of activity. Some of
these communities have disappeared. If there is too much
perturbation of a system, the web of life may partly fail, only
to be rebuilt again over millions of years by other organisms.
The changes that we have made in the past few centuries equal the
greatest in the geological record: we are challenging the
stability of the system that has given birth to us. Today we live
on a planet with no frontier. We are the first generation of
humanity to encounter not boundless nature but a small closed
island. Our future, surely, is to attempt to sustain what is left
of our heritage, the life of our planet. If we can achieve that,
we may then go beyond into space, to carry life there. If we
fail, we may go the way of the dinosaurs. Whatever we do, we
cannot deny our ability and sink back to stasis, for in stasis we
die."

-- E.G. Nisbet: _Living Earth_
   (HarperCollins, London 1991, p.225)


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