|
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.
November 2, 2001 -- Vol. 5 Number 44
-----------------------------------------------
Science is not an intellectual computing-machine:
it is a slice of life.
-- Stephen Toulmin
-----------------------------------------------
=-=-=-=-=-=-=-=-=
Section 1
=-=-=-=-=-=-=-=-=
Contents of this Issue (Full reports in Section 2):
1. On Peer Review of Scientific Papers
2. Enzymes at Biological Interfaces
3. On LDL-Cholesterol and Coronary Heart Disease
4. Quorum-Sensing in Bacteria
5. Bacterial Contamination in US Swimming Pools
6. Molecular Fidelity in Biological Systems
7. Behavior Genetics
8. Genome-Phenome Diversity and Environmental Stress
9. Noble Gases in Meteorites
10. The Milky-Way Supermassive Black Hole
11. Physics in Archaeology
12. On the Deformation of Rocks
13. In Focus: On the Molecular Clock
14. SW Archive: A Critique of the Nobel Prize
15. Sources
=-=-=-=-=-=-=-=-=
Section 2
=-=-=-=-=-=-=-=-=
1. ON PEER REVIEW OF SCIENTIFIC PAPERS
Rex Dalton (NAT) discusses the current peer review system used by
scientific journals. Stories about abuses of the peer review
system are common. For example, some researchers complain of
manuscripts being stalled in review until similar findings emerge
in another journal, with questions raised whether any author of
the second paper was connected with the peer review of the first
paper. Other researchers are concerned about reviewers who are
consultants to companies and who could pass on information that
should remain confidential. But most journal editors and
researchers apparently agree that peer review is a mutually
beneficial system that provides effective quality control in
publication and grant awards. However, although instances of
abuse are considered to be rare, there is agreement that the
process is not without problems. The potential for abuse is
evidently greatest in fast-moving fields such as molecular
biology, in which it is sometimes possible to read a manuscript
and replicate the work in a matter of days. When problems arise,
the intense drive of individual scientists to further their
standing is most often to blame. But commercial pressures, and in
rare cases, political pressures, can also be involved. Many
reviewers admit to discussing papers or grant applications with
their colleagues, which increases the chance that someone might
abuse the privileged information. In general, despite the
problems caused by the peer review process, no serious
alternative has yet been proposed.
-----------
NAT 2001 413:102
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
MORE CRITICISM OF THE PEER REVIEW PROCESS
The peer review process connected to the publication of
scientific papers has its merits and its faults, and there has
perhaps never been a time when it was free from criticism. Of its
faults, there are two of most concern to working scientists: 1)
reviewers are usually chosen from among established scientists in
a field, all of whom know each other, which means that an
established author in a field will most likely have some of his
friends passing less than objective judgment on his work, more
favorable judgment than that accorded a newcomer to the field;
and, 2) established or not established, reviewers tend to miss
errors in the papers they review, do not read the papers
carefully, sometimes do not read them hardly, and only rarely
will a reviewer return a paper to an editor and claim not to be
qualified. Reviewers of scientific articles submitted to a
particular journal are usually chosen from that journal's
database of specialists, but there are no rules common to all
journals. At a recent Conference on Biomedical Peer Review held
in Prague (CZ), Christopher Martyn (Southampton University, UK)
presented the results of a study done in collaboration with the
British Medical Journal. A paper that had passed the peer review
process had 8 errors deliberately introduced into it, and the
paper was then sent for another review to 420 people from the
journal's database. Of the 221 reviewers who responded, none
identified all 8 mistakes, and few caught more than 2 or 3. This
was not simply a matter of inappropriate choice of reviewers,
since even those considered supremely qualified to review the
paper failed to catch the errors.
-----------
The Economist 1997 3 Oct
SW 1997 10 Oct
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
2. ENZYMES AT BIOLOGICAL INTERFACES
O.G. Berg et al (Uppsala University, SE) discuss enzymology at
interfaces. Biological tissues and cells have microscopically
fragmented aqueous compartments separated by vesiculated
membranes. Approximately one-half of the protein in cells is
estimated to be membrane associated, and many of the membrane
enzymes are operationally "interfacial enzymes" that access their
substrates directly from the lipid-water interface. In contrast,
the non-interfacial membrane-associated enzymes ("matrix
enzymes") access their substrates directly from the aqueous
phase. In a functional sense, the matrix enzymes are similar to
classical non-membrane soluble enzymes that also access their
substrates from the aqueous phase. In general, the observed
kinetics of soluble enzymes may depend on whether the enzyme or
its substrate is in thermodynamic partitioning equilibrium with
an extraneous interface. In addition, an involved interface may
also have an *allosteric effect on the intrinsic catalytic
parameters of both matrix enzymes and interfacial enzymes. A
large variety of enzymes participate in the metabolism of a
diverse group of nonpolar and *amphipathic solutes, including
phospholipids, dietary fats, sterols, eicosanoids, carotenoids,
and chlorophyll, and interfacial enzymes have evolved to deal
with the biophysical realities of molecular aggregates of
amphipathic and nonpolar substrates in aqueous dispersions. In
general, interfacial enzymes access water-insoluble substrates
partitioned in the interface, and the challenge of research in
the kinetics of interfacial enzymes derives from the fact that
biological interfaces are invariably microscopically dispersed.
-----------
CR 2001 101:2613
-----------
Notes:
... ... *allosteric effect: In general, an effect that arises
when the reaction of ligands with one site of any polyvalent
molecule affects the reaction of ligands at one or more other
sites as a result of conformational changes.
... ... *amphipathic: (amphiphilic) In general, an "amphipath" is
a substance whose molecules have an affinity for both aqueous and
nonaqueous media. The classic biologically relevant example is a
phospholipid; the classical chemical example is a soap
(detergent) molecule.
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. ON LDL-CHOLESTEROL AND CORONARY HEART DISEASE
J.L. Goldstein and M.S. Brown (University of Texas, US) discuss
low density lipoproteins and coronary heart disease. Low density
lipoprotein (LDL), the major cholesterol-carrying lipoprotein in
human plasma, is the offending agent in coronary heart disease,
which causes one-third of all deaths in the US. Originally, LDL
was implicated in heart disease through epidemiologic and
genetic observations in humans and animal models, and its
involvement has now been confirmed by the recent and repeated
demonstration that LDL-lowering drugs, called statins, reduce
heart attacks and prolong life. In general, LDLs are composed of
spherical particles with an average diameter of 22 nanometers.
The average LDL particle contains a hydrophobic core of
approximately 1500 molecules of cholesteryl ester surrounded by a
polar coat composed primarily of phospholipids and a 513-
kilodalton protein called apolipoprotein B-100. LDLs circulate in
human plasma with a mean life-span of 2.5 days. Important
questions for research are a) What determines the amount of LDL
in plasma? and b) Why do so many people have enough LDL to cause
heart attacks? In medicine, common problems are often solved by
studies of uncommon genetic diseases. In the case of LDL, answers
have emerged from unraveling the aberrant genes underlying four
rare genetic disorders that elevate plasma LDL and cause
premature heart attacks, with the final two molecular defects of
this quartet described only within the past year. Remarkably, all
four defects raise the amount of plasma LDL by impairing the
activity of liver (hepatic) LDL receptors that normally clear LDL
from plasma.
-----------
SCI 2001 292:1310
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4. QUORUM-SENSING IN BACTERIA
Y-H. Dong et al (National University of Singapore, SG) discuss
quorum-sensing in bacteria. Bacterial cells sense their
population density through a sophisticated cell-cell
communication system, and expressions of particular genes are
triggered when the population density reaches a certain
threshold. This type of gene regulation, which controls diverse
biological functions in bacteria including virulence, is known as
"quorum-sensing". Quorum-sensing signals, such as acyl-homoserine
lactones (AHLs), are the essential components of the
communication system. AHLs regulate virulence-gene expression in
a range of plant and animal (including human) bacterial
pathogens. AHL-producing tobacco plants restored the
pathogenicity of an AHL-negative mutant of Erwinia carotovora, a
major plant pathogen. Different bacterial species may produce
different AHLs, which vary in the length and substitution of the
acyl chain but contain the same homoserine lactone moiety. The
authors report a demonstration that an acyl-homoserine lactonase
(AHL-lactonase), a new enzyme from a Bacillus species,
inactivates AHL activity by hydrolyzing the lactone bond of AHLs.
Plants expressing AHL-lactonase quenched pathogen quorum-sensing
signaling and showed significantly enhanced resistance to E.
carotovora infection. The authors suggest their results highlight
a promising potential to use quorum-sensing signals as molecular
targets for disease control, thereby broadening current
approaches for prevention of bacterial infections.
-----------
NAT 2001 411:813
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
5. BACTERIAL CONTAMINATION IN US SWIMMING POOLS
The US Centers for Disease Control discusses the prevalence of
parasites in fecal material from chlorinated swimming pools in
the US. During the 1990s, reports of outbreaks of
gastrointestinal disease associated with the use of disinfected
recreational water (i.e., swimming and wading pools, water-parks,
fountains, hot tubs, and spas) gradually increased. During 1989
to 1998, approximately 10,000 cases of diarrheal illness were
associated with 32 recreational waterborne disease outbreaks in
disinfected water venues in the US. Ten outbreaks occurred during
1997-1998, the highest number of recreational water outbreaks
ever reported in a similar time-frame. Because diarrheal illness
is under-reported to public health authorities, the number of
outbreaks associated with recreational water use is probably
higher. Because swimming typically involves sharing water with
many other persons in a pool, the water contains various bodily
fluids, fecal matter, dirt, and debris that wash off bodies
during swimming activities. Fecal matter is regularly introduced
into the water when someone has a fecal accident through release
of formed stool or diarrhea into the water, or residual fecal
matter on the bodies of swimmers is washed into the pool. Fecal
contamination may be more likely to occur when there is a high
density of bathers, particularly diaper- and toddler-aged
children. Swallowing this fecally contaminated water is the
primary mode for transmission of enteric pathogens in
recreational water outbreaks. Although chlorine is an effective
disinfectant, it does not instantly kill all pathogens. In
addition, some pathogens, such as the parasite *Cryptosporidium,
are highly resistant to chlorine concentrations routinely used in
pools. Because of frequent fecal contamination, the inability of
chlorine disinfection to rapidly inactivate several pathogens,
and the common occurrence of accidental ingestion of pool water,
transmission of pathogens can occur even in well-maintained
pools.
-----------
MMWR 2001 50:410
JAMA 2001 285:2969
-----------
Notes:
... ... *Cryptosporidium: A genus of sporozoans that are common
opportunistic parasites of humans, and which flourish under
conditions of compromised immune function. Sporozoans are a large
class of parasitic protozoans that produce simple spores.
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
6. MOLECULAR FIDELITY IN BIOLOGICAL SYSTEMS
Miroslav Radman (University of Paris, FR) discusses molecular
fidelity in the evolution of biological systems. The apparent
perfection of organisms and the accuracy of biological processes
are still used in religious explanations of the origin of life,
but in real life it is survival, not fidelity, that is the
ultimate virtue. Because adaptability involves exploration of
genetic possibilities to fit ecological niches, molecular
infidelity and repetition are more likely to succeed than a
precise and non-repetitive process. Only a tiny fraction of
*antibodies produced will ever be useful; the rest can be
considered as mistakes. At least half of all human embryos fail
during development. During chromosome segregation from a mother
cell into two daughters, the polymerizing fibers (*microtubules)
do not know the exact location of the chromosomal target (the
*centromere) -- they shoot and miss until one hits. A precise
single shot would often miss a target of uncertain position,
whereas successive imprecise firing will eventually lead to a
hit. Selection at the level of molecules, cells, and organisms
may give an impression of designed perfection, but the structures
of life do not emerge by fully deterministic design. In the very
precise process of DNA replication, accuracy is achieved by using
a "proofreading" system to remove erroneously inserted
nucleotides, and then by quality-checking the synthesized DNA
using a "*mismatch-repair system" that removes virtually all
remaining mistakes. It would take too long to get it exactly
right in the first place. DNA replication is efficient and
therefore relatively imprecise, leaving mistakes to error-
correction enzymes that are themselves efficient because their
substrates are specific mistakes made by other enzymes.
-----------
NAT 2001 413:115
-----------
Notes:
... ... *antibodies: In general, an antibody is a protein
molecule produced by the immune system of vertebrate organisms,
the molecule designed to specifically interact with a particular
invading foreign entity called an antigen.
... ... *microtubules: Microtubules are part of the cytoskeleton
of biological cells, the quasi-rigid matrix that among other
things determines cell shape. The microtubules are 25 nanometers
in diameter, and composed of the protein tubulin. They occur in
regular arrays in cilia, flagella, the mitotic spindle, and in
the cytoplasm in general, and they contribute not only to cell
shape, but also to cell motility.
... ... *centromere: In cells with chromosomes, the
chromosomes are the physical structures into which DNA is
organized and on which genes are carried. The "centromere" is a
region of the chromosome to which traction fibers are attached
during replication.
... ... *mismatch-repair system: In this context, the term
"mismatch repair" refers to a system for the correction of errors
introduced during DNA replication when an incorrect nucleotide
base, which cannot form hydrogen bonds with the corresponding
base in the parent strand, is incorporated into the daughter
strand. Specific enzymes (excinucleases) recognize a pair of
non-hydrogen-bonded bases and cause a segment of the
polynucleotide chain to be excised, thereby removing the
mismatched bases. The resulting gap is then filled with correct
bases (by DNA polymerase 1) and the polymer spliced (by DNA
ligase).
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
7. BEHAVIOR GENETICS
Donald Pfaff (Rockefeller University, US) discusses behavior
genetics. The intellectual paths some scientists have followed
toward behavioral experimentation have traversed the physical
sciences, as well as biology and other academic territories.
Those who have studied physics may well be disposed to strive for
a universal lawfulness, expressed quantitatively, in the
demonstration of stimulus-response connections. This endeavor can
be difficult, because of the complexity of some stimuli and
certain behavioral responses, and because of the need to
recognize and control the relevant environmental variables. Even
more difficult is the delineation of causal relations between
particular genes and specific behaviors. The *pleiotropy of
individual genes and overlapping functions between genes are
fundamental problems. Our lack of understanding of mechanisms for
*penetrance of dominant *alleles makes it difficult to construct
meaningful gene dose/response relationships. Interpretations of
engineered gene removal (gene knockout) data can stumble over
unexpected compensations for the absent gene, effects of the
knockout on other gene products, altered endocrine and neuronal
feedback loops, and a lack of control over the temporal and
spatial impact of the genetic manipulation. Certainly the
behavioral aspects of functional genomics can fall prey to the
complexities of modifier genes and subtle environmental
variables. In addition, a familial pattern of behavior change can
be routed through non-genomic transmission, which may depend, for
example, on variations in maternal care. Nevertheless, when the
right level of neurobiological problem is identified -- simple
enough to be analyzable, while still embodying emergent
behavioral phenomena -- an interesting science of behavior
genetics comes forth, illustrated, for example, in the
delineation of causal relations between particular genes and
behavioral responses in the mouse.
-----------
PNAS 2001 98:5957
-----------
Notes:
... ... *pleiotropy: In general, the phenomenon in which a single
gene is responsible for a number of distinct and seemingly
unrelated phenotypic effects.
... ... *penetrance: In general, the proportion of individuals of
a specified genotype that show the expected phenotype under a
defined set of environmental conditions. For example, if all
individuals carrying a dominant mutant gene show the mutant
phenotype, the gene is said to show complete penetrance.
... ... *alleles: (allelomorph) In general, one of a series of
possible alternative forms of a given gene, differing in DNA
sequence and affecting the functioning of a single product (RNA
and/or protein).
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
ANIMAL BEHAVIOR: NONGENOMIC TRANSMISSION OF MATERNAL BEHAVIOR
The question of genetic vs. non-genetic determinants of behavior
is an area of controversy in several branches of science, and as
can be seen from the background material attached to this report,
discussion of the question is on occasion contentious. In humans,
individual differences in personality traits often appear to be
transmitted from parents to offspring, and a critical question
concerns the mode of transmission of such traits. Studies of
identical (monozygotic) and non-identical (dizygotic) twins have
provided some evidence for a genetic mechanism of transmission of
even complex personality traits. In contrast to genomic
transmission, parental behavior influences the development of
offspring and could therefore serve as a mechanism for a non-
genomic behavioral mode of transmission of traits. In rats, for
example, it has been known for nearly 50 years that variations in
maternal care are associated with the development of individual
differences in behavioral and endocrine responses to stress in
the offspring, and this species has served as an animal model in
many studies of the effects of variations in maternal care on the
behavior of offspring.
... ... D. Francis et al (4 authors at McGill University, CA)
now present cross-fostering studies examining the possibility
that variations in rat maternal care might be the mechanism for a
behavioral transmission of individual differences across multiple
generations. In the experimental and control protocols, no more
than 2 of 12 rat pups were fostered into or from any one litter.
The authors report their results provide evidence for 1) a causal
relationship between maternal behavior and stress reactivity in
the offspring; and 2) the transmission of such individual
differences in maternal behavior from one generation of females
to the next. In addition, the authors report that an
environmental manipulation imposed during early development that
alters maternal behavior can affect the pattern of transmission
in subsequent generations. The authors suggest that taken
together, these results indicate that variations in maternal care
can serve as the basis for a non-genomic behavioral transmission
of individual differences in stress reactivity across
generations. The authors conclude: "In humans, social, emotional,
and economic contexts influence the quality of the relationship
between parent and child and can show continuity across
generations. Our findings in rats may thus be relevant in
understanding the importance of early intervention programs in
humans."
-----------
SCI 1999 286:1155
SW 2000 25eb
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
GENETIC CONTROL OF SOCIAL ORGANIZATION IN ANTS
Biological evolution is marked by a number of major transitions,
one of which is the evolution of complex social behavior. Animal
social life can take a variety of forms, each distinguished by
features such as group size and the reproductive roles of group
members. One focus in evolutionary biology is to identify the
causes of social behavior and its conspicuous variation, and to
determine the extent to which social organization is under
genetic control. Such information is useful for reconstructing
pathways of animal social evolution. Current views on insect
social evolution stress the importance of ecological and
behavioral environments in molding what are largely plastic
social behaviors.
... ... K.G. Ross and L. Keller (2 installations, US CH) report
evidence that major variation in the social organization of fire
ant colonies is under simple genetic control, providing a
demonstration of an apparent strong genetic component to complex
social behavior. The authors report that a single genomic element
(the gene [Gp-9]) is responsible for the existence of two
distinct forms of social organization in the fire ant *Solenopsis
invicta. This genetic factor apparently influences the
reproductive *phenotypes and behavioral strategies of ant queens
and determines whether workers tolerate a single fertile queen or
multiple queens per colony. The authors suggest "these findings
reveal how a single genetic factor can have major effects on
complex social behavior and influence the nature of social
organization."
-----------
PNAS 1998 95:14232
-----------
Notes:
... ... *Solenopsis invicta: The fire ant S. invicta is an
introduced pest species in the southern US, the species existing
in two distinct social forms. The "monogyne" form features
colonies with a single fertile (egg-laying) queen, whereas the
"polygyne" form features colonies with multiple fertile queens.
The two social forms differ in other major aspects of their
reproductive biology.
... ... *phenotypes: The term "phenotype" refers to the total
appearance of an organism as determined by the interaction during
development between its genetic constitution (genotype) and the
environment.
-----------
SW 1999 15 Jan
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
ON HONEYBEE SOCIAL BEHAVIOR, GENES, AND THE ENVIRONMENT
The so-called social insects live in societies that rival human
societies in complexity and internal cohesion. Honey bees, for
example, apparently always follow 3 rules: a) they live in
colonies with overlapping generations; b) they care cooperatively
for offspring other than their own; and, c) they maintain a
reproductive division of labor. ... ... In a review of research
(much of it from the author's own laboratory) concerning the
genetic and environmental factors responsible for honey bee
behavior, Gene E. Robinson (University of Illinois Urbana-
Champaign, US) makes the following points: 1) Genes do not play
an exclusive role in regulating behavior: biologists have long
realized that behavior is influenced by genes, the environment,
and interactions between the two. 2) Genes never act alone. They
must operate in an environment where they code for proteins that
participate in many systems in an organism, with these systems in
turn influencing the expression of genes. Consequently,
biologists must take a broad approach in assessing the impact of
any gene. 3) The research group of the author uses the Western
honey bee, Apis mellifera. Honey bees pass through different life
stages as they age, and their behavioral responses to
environmental and social stimuli change in predictable ways.
Although worker bees go through a consistent path of behavioral
development, this path is not rigidly determined. Bees can
accelerate, retard, or even reverse their behavioral development
in response to changing environmental and colony conditions. 4)
Experimental evidence indicates that juvenile hormone, one of
the most important hormones influencing insect development, helps
time the pace of behavioral maturation in honey bees. The rate of
endocrine-mediated behavioral development is influenced by
inhibitory social interactions. Older bees inhibit the behavioral
development of younger bees: the rate of behavioral development
is negatively correlated with the proportion of older bees in a
colony. Inhibitory social interactions that influence the rate of
behavioral development involve chemical communication between
colony members. 5) Evidence from the laboratory of the author in
1993 indicated the so-called mushroom bodies in the bee brain are
involved in the behavioral changes occurring during maturation,
the volume of the bodies increasing, and the volume increase
associated with an increase in synapses with neurons from brain
regions devoted to sensory input. The author suggests this was
the first report of brain plasticity in an invertebrate. 6) The
author suggests that, in general, two-way interactions between
the nervous system and the genome contribute fundamentally to the
control of social behavior. Information about social conditions
that is acquired by the nervous system is likely to induce
changes in genomic function that in turn produce adaptive
modifications of the structure and function of the nervous
system. 7) The author proposes a new research initiative called
"sociogenomics", defined as a "wide-ranging approach to identify
genes that influence social behavior, determining the influence
of these genes on underlying neural and endocrine mechanisms, and
exploring the effects of the environment -- particularly the
social environment -- on gene action."
-----------
AS 1998 86:456
SW 11 Sep 98
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
IN FOCUS: ON SOCIOBIOLOGY
"Evolutionary theory itself has an appropriately zoocentric
core... But the zoocentric view can be extended too far into a
caricature often called the "nothing but" fallacy (humans are
"nothing but" animals). The simplistic accounts of human
sociobiology now flooding popular literature embody this
overextended version of zoocentrism. Sociobiology is not just any
statement that biology, genetics, and evolutionary theory have
something to do with human behavior. Sociobiology is a specific
theory about the nature of genetic and evolutionary input into
human behavior. It rests upon the view that natural selection is
a virtually omnipotent architect, constructing organisms part by
part as best solutions to problems of life in local environments.
It fragments organisms into "traits", explains their existence as
a set of best solutions, and argues that each trait is a product
of natural selection operating "for" the form or behavior in
question. Applied to humans, it must view _specific_ behaviors
(not just general potentials) as adaptations built by natural
selection and rooted in genetic determinants, for natural
selection is a theory of genetic change. Thus, we are presented
with unproved and unprovable speculations about the adaptive and
genetic basis of specific human behaviors: why some (or all)
people are aggressive, xenophobic, religious, acquisitive, or
homosexual. Zoocentrism is the primary fallacy of human
sociobiology, for this view of human behavior rests on the
argument that if the actions of "lower" animals with simple
nervous systems arise as genetic products of natural selection,
then human behavior should have a similar basis."
-----------
Stephen Jay Gould: _Hen's Teeth and Horse's Toes_
(W.W. Norton, New York 1983, p.243)
SW 14 May 99
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
IN FOCUS: ON THE EVOLUTION OF HUMAN BEHAVIOR
"The uniqueness of Man is not a matter of his structure. His body
and its functions are in general very similar to those of other
mammals -- that is why medicine can study in animals the
functions of, say, kidneys, of the heart, of eye and ear, even
the basic functions of the nerve cells, and extrapolate with
confidence. The uniqueness of Man is agreed to be a matter of
behavior. If it is to be reduced to structural characters, it is
the brain that is unique, that functions in a unique way. There
are of course links with other structural characteristics, but
attempts (made in the past) to reduce Man's behavioral uniqueness
to, say, the possession of hands, or to his upright posture, have
not been very convincing -- they have been too simplistic, too
one-sided. The way the biologist approaches this problem is based
on his knowledge of the fact of evolution. No informed person can
doubt any more that Man has evolved, slowly and very gradually,
from ancestors which were far more similar to other mammals than
Man is now. This means that everything Man is and does now must
have evolved, through a long series of minute evolutionary steps,
from what his animal ancestors were and did. Man has diverged
very gradually from monkey or ape-like stock to what he is now,
just as modern closely related animal species have diverged from
common stock... It has often been pointed out that Man, himself a
product of evolution of a type similar to that which has created
all other animal forms, namely adaptive hereditary change, has
now embarked on a new type of evolution, which Huxley calls
'psycho-social evolution'. I prefer the term 'cultural
evolution'. It is based on _accumulated_ transfer, by tradition,
from one generation to the next, of knowledge (or _phenotypic_)
behavior changes, i.e., changes acquired through individual
experience. Our culture is very different from that of Cro-Magnon
Man, but generally we may not have changed much -- most of our
modern attributes are due to the accumulation of transferred
knowledge. We differ from animals not merely in the extent of
what we can ourselves learn, but in the progressive (and steadily
accelerating) accumulation of experience through the
generations."
-----------
Niko Tinbergen: _The Animal in its World_
(George Allen & Unwin, London 1972)
-----------
[Editor's note: Nikolaas Tinbergen (1907-1988) was awarded the
Nobel Prize in Physiology and Medicine in 1973, and is considered
one of the founders of ethology, the objective study of animal
behavior. Although researchers who approach human behavior in
terms of the evolution of genes (e.g., sociobiologists) often
cite Tinbergen as one of their intellectual sources, the above
quoted passage illustrates that Tinbergen's view of human
behavior was otherwise: Tinbergen approached human behavior
primarily in terms of the evolution of culture, rather than in
terms of the evolution of genes. (The quoted passage is from a
lecture given by Tinbergen at Oxford University, 27 October
1964.)]
-----------
(SW 2000 29 Sep
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
8. GENOME-PHENOME DIVERSITY AND ENVIRONMENTAL STRESS
Eviatar Nevo (University of Haifa, IL) discusses the evolution of
diversity under environmental stress. The enigma of genotypic-
phenotypic diversity and biodiversity evolution of genes,
genomes, *phenomes, and *biomes has been a central problem in
evolutionary biology and has been explored using modern molecular
techniques. Genotypic and phenotypic diversity has been found in
all species at the protein, DNA, and organismal levels. Genome-
phenome organization in nature is non-random, heavily structured,
and correlated with abiotic and environmental diversity and
stress. Deciphering the origin and maintenance of genetic
diversity are aided via investigations focusing on the interface
between ecology and genomics. Critical tests and strong
inferences in nature of abiotic and biotic factors include
transplant experiments at microscales and macroscales to unravel
genome organization and fitness in contrasting and changing
environments and to relate genomics to phenomics. DNA
*polymorphisms and the noncoding genome largely mirror protein
(*isoenzyme) polymorphisms, are subjected to natural selection,
and can be used to highlight genome structure and evolution. The
focus of evolutionary biology is the organism-environment
interaction involving genomes, phenomes, and biomes across the
tree of life, and the noncoding and regulatory genome should
become a central target in understanding evolution. The author
reviews the last 25 years of research in ecological genomics at
the University of Haifa.
-----------
PNAS 2001 98:6233
-----------
Notes:
... ... *phenomes: In general, the whole of the phenotypic
characteristics of an organism. In this context, the term
"phenotype" refers to the specific individuality of an organism
as determined by the interaction between its genetic constitution
(genotype) and the environment.
... ... *biomes: In general, a "biome" is a major terrestrial,
climatically controlled, regional ecological complex or set of
ecosystems possessing characteristic vegetation, and among which
there is exchange of water, nutrients, and biotic components.
Examples are a tropical rain forest, a coral reef, a grassland.
... ... *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.
... ... *isoenzyme: (isozyme) In general, any one of the multiple
forms of an enzyme arising from a genetically determined
difference in primary structure. Any one of a group of enzyme
proteins with similar catalytic properties but separable by
suitable methods, e.g., electrophoresis. If different enzyme
proteins derive from a common gene, the term "multiple forms"
rather than "isoenzymes" should be used.
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
EVOLUTIONARY BIOLOGY: HOW DO NEW SPECIES ARISE?
In biology, the term "species" has had a history filled with
controversy, since the term essentially involves categorizations
of living systems, and such categorizations can range from the
subjective to the objective, but with objective categorizations
heavily dependent on extant knowledge of biological systems. Both
present and past biological systems show an extreme diversity of
form and function, and thus far no single definition of the term
"species" has been accepted as universally useful. The current
general view among biologists is to consider a species to be a
group of organisms that resemble each other and that are
generally able to interbreed and produce fertile offspring. This
is the so-called "biological species concept", derived from
Georges Buffon (1707-1788) and others, the concept defining a
species as a sexually interbreeding or potentially interbreeding
group of individuals normally separated from other species by the
absence of genetic exchange, i.e., by "reproductive isolation".
In contrast to this is the "evolutionary species concept",
championed by George Gaylord Simpson (1902-1984), an influential
paleontologist who proposed the idea that species be defined in
terms of differences that are not dependent on sexual isolation
but rather on their evolutionary isolation, of which sexual
isolation is only one aspect. In Simpson's words: "An
evolutionary species is a lineage (an ancestor-dependent sequence
of populations) evolving separately from others and with its own
unitary evolutionary role and tendencies." Neither concept of
species can be universally applied to all biological systems.
Some organisms, for example, exhibit asexual reproduction, which
makes irrelevant the idea of reproductive isolation as defining
speciation. Similarly, the application of the evolutionary
species concept depends on extensive knowledge of lineages, and
detailed lineages are not always apparent.
Concerning both concepts, a natural and important question
is, How do species arise? What is the mechanism of "speciation"?
In the context of this report, this question is posed within the
framework of the biological species concept.
In this context, an important idea is that of "natural
selection" (selection by natural circumstances, as opposed to
selection ["artificial selection"] by human intervention). The
theory of natural selection asserts that the genetic composition
of an evolutionary lineage will change through time by non-random
transmission of genes from one parental generation to the next, a
non-randomness ("selection") due solely to the fact that not all
gene combinations are equally suited to a given environment, and
that consequently individuals differ in their biological fitness.
In contrast to natural selection is "genetic drift", which
refers to a statistically significant change in population gene
frequencies resulting not from selection, emigration or
immigration, but from causes operating randomly with respect to
the fitnesses of the genes concerned. For example, external
events suddenly impacting a population can result in an abrupt
shift in gene frequencies in that population.
In this context, the term "genetic revolution" refers to the
emergence of new species by a process involving drastic changes
-- changes in many genes, as opposed to the emergence of new
species by a process involving changes in only a few genes.
The term "founder event" refers to the "founder effect", the
principle that when a small sample of a large population
establishes itself as a newly isolated entity, its gene pool
carries only a fraction of the genetic diversity represented in
the parental population, and the evolutionary fates of the
parental and derived populations are thus likely to diverge.
The term "gene flow" refers to the exchange of genes between
different populations of the same species produced by population
migrants, the process usually resulting in simultaneous changes
in gene frequencies at many loci in the recipient gene pool.
A "premating (prezygotic) isolation mechanism" is any factor
that tends to reduce or prevent interbreeding between members of
genetically divergent populations or species, with the factor
functioning before fertilization occurs: e.g., ecological,
temporal, ethological, and other isolating factors. A "postmating
(postzygotic) isolation mechanism is any factor that similarly
reduces or prevents interbreeding, but with the factor
functioning after fertilization has occurred: e.g., hybrid
inviability, hybrid sterility, hybrid breakdown.
In this context, the term "ecological selection" refers to
natural selection dependent on the relationships between
organisms plus the relationships between organisms and their
surroundings (ecological factors), and the term "ecological
speciation" refers to an ecologically forced emergence of new
species.
At Lower Nahal Oren, Mount Carmel, Israel is a geologic
formation that has come to be known in the evolutionary biology
community as "Evolution Canyon". The opposite slopes of this
canyon, separated by only 100 meters at the bottom and 400 meters
at the top, manifest dramatic biotic contrasts because of the
higher (as much as 600 percent more) solar radiation on the
south-facing slope than on the north-facing slope. The south-
facing slope is warmer, drier, microclimatically more
fluctuating, and less predictable than the north-facing slope.
Previous studies have demonstrated a strong Evolution Canyon
interslope differentiation of the fruit fly Drosophila for a
complex of adaptive traits. These traits include changes in
viability and longevity caused by short-term and lifetime
temperature treatments, changes in fly weight because of
desiccation/starvation treatments at different temperatures,
different levels in the variation of fluctuating asymmetry,
different rates of mutation and *recombination, and changes in
habitat choice (preferred locus temperature for deposition of
eggs [oviposition temperature]). This remarkable differentiation
has evolved despite the small interslope distance (a few hundred
meters), a distance well within the dispersal capability of
Drosophila species. So far, there have been approximately 80
publications resulting from studies in Evolution Canyon, nearly
all studies showing adaptive divergence to the microscale climate
differences in the canyon.
... ... Christopher J. Schneider (Boston University, US) presents
a commentary on some recent work on Drosophila in Evolution
Canyon (A. Korol et al: Proc. Nat. Acad. Sci. US 97:12637 2000),
the author (Schneider) making the following points:
1) The author points out that one of the most persistent
questions in evolutionary biology is, How do new species arise?
As with many simple questions, there is no simple answer, only
complex answers to a number of interrelated questions: How do
sexually reproducing organisms become reproductively isolated?
How do environment and ecological interactions influence the
formation of new species? Are the processes of local adaptation
and the evolution of reproductive isolation the same (i.e., both
resulting from the accumulation of small adaptive genetic
changes), or are the genetic changes leading to reproductive
isolation fundamentally different (i.e., large and rapid genetic
changes such as chromosomal rearrangements, genetic revolutions,
or founder events)? Is the disruption of gene flow necessary?
What are the relative roles of chance events (e.g., genetic
drift) and natural selection in speciation?
2) The author (Schneider) suggests the short answer to all
of the above questions is that reproductive divergence can evolve
in a number of ways: Both drift and selection can be important,
depending on the number, degree of interaction, and magnitude of
effect of genes involved in reproductive isolation; depending on
the relationship between genes controlling reproductive
compatibility and *phenotypic characters that may be under
ecological selection; and depending on the historical effective
population size of the diverging populations.
3) Korol et al report highly significant mate choice by
Drosophila flies from different slopes of Evolution Canyon, with
preference for sexual partners originating from the same slope.
No preferences were found when the sexual partners belonged to
different *isofemale lines from the same slope.
4) Schneider suggests that the report by Korol et al
demonstrates significant premating reproductive divergence
between Drosophila melanogaster populations adapted to distinct,
but closely adjacent, habitats in Evolution Canyon. Korol et al
suggest that reproductive isolation has evolved _in situ_ as a
result of adaptive divergence in response to the contrasting
environments of north- and south-facing slopes in Evolution
Canyon, despite the fact that the populations are within easy
"cruising range" of each other. Korol et al suggest that the
divergence of Drosophila occupying distinct habitats in Evolution
Canyon represents an early stage in ecological speciation in
which divergent natural selection drives the accumulation of
genetic differences among populations, resulting in reproductive
isolation.
-----------
PNAS 2000 97:12398
-----------
Notes:
... ... *recombination: In general, integration of DNA fragments
into a particular site in a genome.
... ... *phenotypic characters: In general, the term "phenotype"
refers to the total appearance of an organism as determined by
the interaction during development between its genetic
constitution (genotype) and the environment.
... ... *isofemale lines: In general, a genetic lineage derived
from a single inseminated female.
-----------
SW 2001 5 Jan
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
9. NOBLE GASES IN METEORITES
Typhoon Lee (Academia Sinica, TW) discusses new evidence
concerning the origin of the Solar System. The 5 noble gases --
helium, neon, krypton, argon, and xenon -- neither react with
other elements to form solids nor condense easily. Although they
are abundant in the Universe, the strong preference of the noble
gases is to remain gaseous and thus their concentrations in rocks
are very low -- which is why they are called "rare gases". Now
R. Okazaki et al (2001) report surprisingly high concentrations
of noble gases in the silicate beads found in a primitive
meteorite (Yamato 791790). The most primitive, but also the most
common, meteorites are the "chondrites", so called because they
contain "chondrules", which are silicate spherules solidified
from melt droplets formed by a mysterious heating event early in
the history of the Solar System. The discovery of large amounts
of volatile noble gases in these chondrules is unexpected because
it is widely believed either that the gases never existed in the
material that formed the chondrules or, if they were present,
that the noble gases were driven out by the mysterious heating
event. Although noble gases have not yet been found in chondrules
in any other meteorites, this discovery may lead to new insights
into the processes that formed our Solar System. Concerning the
question of how noble gases get into meteorites, one possibility
is the bombardment of meteorite precursors by noble gases in the
solar wind. This is the consensus explanation for the presence of
noble gases in samples from the surface of the Moon.
-----------
NAT 2001 412:783,795
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
10. THE MILKY-WAY SUPERMASSIVE BLACK HOLE
Fulvio Melia (University of Arizona, US) discusses the apparent
supermassive *black hole at the center of the Milky Way. The
center of our Galaxy lies behind a dusty cloud of gas and a
clustering of stars in the constellation Sagittarius. The closest
object to the actual center, discovered in 1974, is a bright
compact source of radio waves known as Sagittarius A*.
Approximately 10 million stars swarm within a light year of its
position, the closest three or four of which swing past it at
incredible speeds up to 5 million kilometers per hour. The
central mass required to keep these stars in their high velocity
orbits (only 7 light days away from the Galactic center) is equal
to 2.6 million solar masses, which suggests that the dark force
powering Sagittarius A* is a black hole -- an object so dense
that gravity prevents everything, even light, from escaping. All
this matter appears to be concentrated at the Galactic Center in
a region no larger than our Solar System, and probably smaller
than the region within the orbit of Mars around the Sun. If the
Galactic Center is indeed a black hole, then all its matter must
be contained within its "*event horizon". However, the orbits
traced by the stars closest to Sagittarius A* are approximately
30,000 times larger than the event horizon predicted for a black
hole of 2.6 million solar masses, which means explanations other
than a black hole are possible. Now F.K. Baganoff et al (2001)
report the rare detection of an x-ray emission flare occurring
just outside the calculated event horizon of the suspected
Galactic Center supermassive black hole, and this is considered
an important confirmation of the black hole's existence.
-----------
NAT 2001 413: 25,45
-----------
Notes:
... ... *black hole: If the terminal stages of star death leave
a remnant star mass greater than 3 solar-masses, the ultimate
gravitational collapse will produce a black hole, a relativistic
singularity. A black hole is a localized region of space from
which neither matter nor radiation can escape. The "trapping"
occurs because the requisite escape velocity, which can be
calculated from the relevant equations, exceeds the velocity of
light and is therefore unattainable.
... ... *event horizon: Space and time essentially have no
meaning in a black hole. The boundary of the black hole is called
the "event horizon", because any event within the boundary is
invisible outside, the invisibility resulting from the fact that
no radiation can escape to be detected. The radius of the black
hole depends upon how much matter has fallen into the region; it
is called the "Schwarzschild radius", and it is usually a few
kilometers. However, massive black holes are possible and are
thought to be the source of quasars and also the centers of
certain galaxies. Our own galaxy is believed to have a massive
black hole at its center.
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
ON SUPERMASSIVE BLACK HOLES
The death of supermassive stars must result in collapse,
since no known force can resist gravity in such stars once their
nuclear energy sources are exhausted. For the most massive stars,
the result of this inevitable collapse is the "*black hole", at
the present time the most exotic astronomical object in the
Universe. Although existence of black holes is predictable from
Einstein's theory of general relativity, the possibility of
something like a black hole exists even within the Newtonian
theory of gravity, if one considers the Newtonian escape velocity
for supermassive objects: when the mass of an object is so great
that the velocity required to escape the object exceeds the speed
of light, the object turns "black", since no light can escape.
In recent years, astrophysicists have come to distinguish
ordinary black holes and supermassive black holes, and these
latter objects, of unknown origin, now reign as the supreme
cosmic exotica.
... ... John Kormandy (University of Texas Austin, US) presents
an account of supermassive black hole research presented at the 6
June 2000 meeting of the American Astronomical Society, the
author making the following points:
1) Black holes 10^(6) to 10^(9.5) times as massive as the
Sun were first invoked in the 1960s to explain the enormous
energy output of *active galactic nuclei (AGN) such as *quasars.
These supermassive black holes are in contrast to ordinary black
holes, which have masses of only a few solar masses and which are
well known to form when massive stars die.
2) The origin of supermassive black holes is unknown, and
their existence long remained a hypothesis. By the mid-1980s,
however, black hole "engines" had become part of the theoretical
framework for understanding the activity of active galactic
nuclei, but evidence for their existence was still lacking. In
the 1990s, much effort was made to look for dynamical evidence of
dark objects in galactic nuclei, and that evidence is now strong.
In two objects, our Galaxy and the galaxy NGC 4258, the evident
dark mass must live inside such a small radius that plausible
alternatives to a supermassive black hole can be excluded.
3) The author points out that although until recently
supermassive black holes were studied to understand the
spectacular but restricted phenomena of active galactic nuclei,
the situation is changing rapidly. Surveys with the Hubble Space
Telescope are finding evidence of supermassive black holes in
every galaxy that has an *elliptical-galaxy-like central "bulge"
component. These observations strengthen hints from ground-based
spectroscopy that supermassive black holes are standard features
of galaxy bulges. The observations indicate that supermassive
black hole growth and galaxy formation are closely linked, and
these results have profoundly changed the view of supermassive
black holes: they are more than just exotica needed to explain
rare active galactic nuclei: "Supermassive black holes are
becoming an integral part of our understanding of galaxy
formation."
-----------
SCI 2000 289:1484
-----------
Notes:
... ... *black hole: See main report notes.
... ... *active galactic nuclei (AGN): Some galaxies are known to
have very "active" central regions from which enormous amounts of
energy are emitted each second. These "active galactic nuclei"
are probably powered by accretion of matter into a supermassive
black hole of 10^(6) to 10^(9) solar-masses.
... ... *quasars: (quasi-stellar object). An extremely luminous
source radiating energy over the entire spectrum from x-rays to
radio waves. Quasars are apparently the oldest and most distant
objects in the universe.
... ... *elliptical-galaxy: These are galaxies that have no
disc component, the shape varying from almost circular to narrow
ellipses. The stars within elliptical galaxies are predominantly
old stars. Elliptical galaxies display the greatest variation in
mass, ranging down to extreme dwarfs (approximately 10^(6) solar-
masses.
-----------
SW 2000 29 Sep
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
ON THE BLACK HOLE AT THE CENTER OF OUR GALAXY
Recent observations have led to the conclusion that at the center
of many galaxies there is an object producing effects
characteristic of a supermassive *black hole. Alexei V.
Filippenko (University of California Berkeley, US) reviews
current research on black holes, the author making the following
points concerning the apparent massive black hole at the center
of our own Galaxy:
1) Some galaxies are known to have very "active" central
regions from which enormous amounts of energy are emitted each
second. These "active galactic nuclei" are probably powered by
accretion of matter into a supermassive black hole of 10^(6) to
10^(9) solar-masses. The center of our own Galaxy exhibits mild
activity, especially at radio wavelengths: so-called "nonthermal
radiation" characteristic of high-energy electrons spiraling in
magnetic fields is emitted by a compact object at the Galactic
center known as *Sagittarius A*. Does the center harbor a
supermassive black hole? One approach is to determine whether
stars in the central region are moving very rapidly, as would be
expected if a large mass were present. During the past 5 years,
two teams have obtained high-resolution images of our Galactic
center, each team on several occasions, so that temporal changes
in the positions of stars could be detected. The observations
were conducted at infrared wavelengths, which penetrate the gas
and dust between Earth and the Galactic center (a distance of
approximately 25,000 light years) much more readily than optical
light. In summary, the data are in excellent agreement with the
conclusion that the gravitational potential of the central region
of our Galaxy is dominated by a single object. The derived mass
of this object is (2.6 +- 0.2) x 10^(6) solar-masses, and the
mass density within a radius of 0.05 light-years is at least 6 x
10^(9) solar-masses per cubic light-year, effectively eliminating
all possibilities other than a black hole.
2) Although our Galaxy provides the most convincing case for
the existence of supermassive black holes, observations of the
centers of a few other galaxies bolster the conclusion. For
example, very precise measurements of the galaxy NGC 4258 reveal
a central compact object with a derived mass 3.6 x 10^(7) solar-
masses. On somewhat larger scales, spectra obtained with the
Hubble Space Telescope show gas and stars rapidly moving in a
manner consistent with the presence of a supermassive black hole.
The most massive existing case, that of the giant elliptical
galaxy M87, is approximately 3 x 10^(9) solar-masses. Moreover,
x-ray observations of some active galactic nuclei reveal emission
from a hot disk of gas apparently very close to a black hole,
since extreme relativistic effects are detected. In general, it
now seems that a supermassive black hole is found in nearly every
large galaxy amenable to such observations.
3) The author concludes: "In the last decade of the 20th
century, black holes have moved firmly from the arena of science
fiction to that of science fact. Their existence in some *binary
star systems, and at the centers of massive galaxies, is nearly
irrefutable. They provide marvelous laboratories in which the
strong-field predictions of Einstein's general theory of
relativity can be tested."
-----------
PNAS 1999 96:9993
-----------
Notes:
... ... *black hole: See notes in main report.
... ... *Sagittarius A*: Sagittarius A is a prominent radio
source in the constellation Sagittarius, coincident with or close
to the center of our Galaxy. It is a highly complex region
consisting of a central core approximately 50 light-years in
diameter. Sagittarius A* is a compact component at the heart of
the central core of Sagittarius A. Sagittarius A* is an intense
source of radio waves, and is apparently unique in our Galaxy:
while everything else in our Galaxy is on the move as they follow
their orbits, Sagittarius A* is absolutely stationary and must
therefore lie exactly at the Galaxy's center. Many astronomers,
in fact, use Sagittarius A* as the "Greenwich Meridian" of the
Galaxy.
... ... *binary star systems: Binary stars are a pair of stars
revolving around a common center of mass under the influence of
their mutual gravitational attraction, and apparently the
majority of stars in the Universe are binaries and not singlets.
In some cases the binary system is resolvable into two
components, and in other cases the presence of a second star is
inferred by perturbations in the motion or emitted radiation of
the first star. If the binaries are close enough, they may share
stellar material, and this results in a particular kind of
stellar evolution. In the black hole-binary systems mentioned in
this report, matter transfers from a relatively normal star
(known as the "secondary star") to a dark compact object (the
"primary"). Recent comparisons of x-ray and optical brightness
suggest that in many cases the dark primary in such a binary
system is a black hole.
-----------
SW 1999 15 Oct
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
11. PHYSICS IN ARCHAEOLOGY
Ervan G. Garrison (University of Georgia, US) discusses the use
of physical techniques in archaeology. The field of traditional
archaeology has not easily accepted science, and archaeologists
have only gradually accepted physics as a tool. The only physical
discovery to truly revolutionize archaeology has been radiocarbon
dating, with Willard F. Libby (1908-1980) winning a Nobel Prize
in 1960 for development of the technique. Radioisotopes have
characteristic decay probabilities, commonly expressed as "half-
lives", which render them more or less useful in dating the
objects that contain them. Carbon-14, for example, has a
relatively short half-life of 5730 years. In the first
archaeological demonstration of radiocarbon dating, Libby
determined the age of wooden items found in an Egyptian pharaoh's
tomb. With the discovery of increasingly ancient fossils, the
date of the earliest human horizons has moved steadily backward
to the *Pliocene-Pleistocene boundary 5 million years ago -- well
beyond the 50,000-year limit of radiocarbon dating. Breaching
that limit was a knotty problem until the late 1940s, when Alfred
Nier confirmed Carl Friedrich von Weizaecker's prediction that
argon-40, a decay product of potassium-40, would accumulate in
volcanic minerals such as micas, feldspars, and hornblendes. When
lava spews out of a volcano, argon gas trapped within the lava is
forced out. But potassium, in a naturally occurring mixture of
radioactive potassium-40 and non-radioactive potassium-39,
remains. Potassium-40 decays into argon-40, which then starts to
accumulate as potassium-40 decay continues. With a half-life of
4.1 billion years, argon is ideal for dating ancient humans.
Measuring the amount of accumulated argon in a rock yields the
age of the rock, as well as that of any fossils found in the same
stratum.
-----------
PT 2001 October
-----------
Notes:
... ... *Pliocene-Pleistocene: The Pliocene epoch is the time-
frame 5.4 million years ago to 1.64 million years ago. The
Pleistocene epoch is the time-frame 1.64 million years ago to
10,000 years ago.
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
-------------------
Related Background:
IN FOCUS: ON RADIOCARBON DATING
"Radiocarbon dating depends on a chain of natural events, some
having taken place in deep space long ago. The sequence begins in
various parts of the Galaxy, where charged particles are
accelerated to immense velocities, forming what are known as
cosmic rays. A fraction of these particles eventually rain down
on the Earth and strike molecules of atmospheric gas, producing
neutrons. Some of these neutrons in turn react with nitrogen,
(sup14)N, to form (sup14)C, which quickly combines with oxygen to
form molecules of radioactive carbon dioxide [(sup14)CO(sub2)].
By the time the radioactive carbon dioxide reaches the Earth's
surface, it has mixed fully with normal carbon dioxide and
accounts for about one molecule in 10^(12). The vast majority of
this (sup14)C eventually enters the oceans. But 1 or 2 percent
goes into the terrestrial biosphere, because plants absorb carbon
from carbon dioxide in the air during photosynthesis. Thus
vegetation, and the animals that feed on it, are tagged with
(sup14)C. Living things maintain a (sup14)C content that is about
equal to the atmospheric concentration because the carbon atoms
that undergo radioactive decay within their bodies are
continually replaced [*Note #1]. But once an organism dies and
its metabolic processes cease, the amount of (sup14)C begins to
diminish. The rate of decline is measured by the (sup14)C half-
life, about 5730 years." [*Note #2]
-----------
R.E. Taylor: AS 2000 88:60
-----------
Text Notes:
... ... *Note #1: Carbon-14 decays by beta emission back to
nitrogen-14. Beta emission (beta-decay) is a type of interaction
in which an unstable atomic nucleus changes into a nucleus of the
same mass number but different proton number. In general, the
change involves the conversion of a neutron into a proton with
the emission of an electron plus energy or a positron plus
energy. The electrons or positrons emitted are called "beta
particles". (Positrons are electron antiparticles; they have the
same mass as the electron, but are of opposite charge.) Carbon-14
to nitrogen-14 decay involves the emission of an electron plus
energy, another fundamental particle (electron antineutrino)
accounting for the energy released.
... ... *Note #2: The accelerator mass spectrometry dating method
makes use of smaller quantities of material than required for
conventional radiocarbon dating and extends the radiocarbon
dating range to beyond 50,000 years from the approximately 0 to
25,000 years for conventional radiocarbon dating. The technique
of accelerator mass spectroscopy involves the combination of a
mass spectrometer and an accelerator to measure the concentration
of rare isotopes such as carbon-14 at levels lower than parts per
trillion. An accelerator mass spectrometer can be used to count
the carbon-14 atoms from only a milligram sample of carbon,
whereas the conventional radiocarbon dating method would require
as much as a gram of the same material to achieve the same
resolution by counting current beta particle emission.
-----------
SW 2000 3 Mar
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
12. ON THE DEFORMATION OF ROCKS
Steven Wojtal (Oberlin College, US) discusses rock deformation.
The deformation of rock generates individual macroscopic
structures such as fractures, faults, and folds, as well as
mappable patterns of structures that indicate the relative motion
of *tectonic plates. Deformation also produces distinctive
features that pervade rocks at mesoscopic and microscopic scales.
These *fabrics are defined by distorted *sedimentary or *igneous
features or by preferred orientations of mineral grains or
reshaped rock fragments. Over the past 50 years, geologists have
developed increasingly precise 3-dimensional characterizations of
rock structures and fabrics in different geologic settings.
During the same interval, geologists have used a growing body of
experimental data, better mathematical descriptions of
displacement and velocity fields associated with rock structures,
and theoretical analyses of the mechanics of deformable materials
to interpret structures and fabrics and, in some cases, to
determine the dynamics of rock deformation. Among the many
techniques in modern structural geology, the mathematical
approach of continuum mechanics is the thread that weaves
together studies of processes at different spatial and temporal
scales: from individual mineral grains to regional deformation to
tectonic plates, and from instantaneous displacements like
earthquake slip to movements taking millions of years.
-----------
SCI 2001 293:1597
-----------
Notes:
... ... *tectonic plates: The term "lithosphere" refers to the
outer layer of the Earth, comprising the crust and upper mantle,
and extending to a depth of 50 to 70 kilometers. The traditional
view of tectonics (changes in the structure of the Earth's crust)
is that the lithosphere consists of a strong brittle layer
overlying a weak ductile layer. "Plate tectonics" is the current
consensus theory that the Earth's lithosphere is broken into
fairly rigid plates, seven or eight major plates and many smaller
plates, and that convection within the underlying less rigid
"asthenosphere" causes the plates (and the associated continents
and crust) to move relative to each other.
... ... *fabrics: In this context, the term "fabric" refers to
the pervasive features of a rock.
... ... *sedimentary: Sedimentary rocks are rocks formed by the
hardening of accumulated particles (sediments) that were
transported by agents such as wind and water.
... ... *igneous: Igneous rocks are rocks that have congealed
from a molten mass (magma) derived from the Earth's crust.
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
13. IN FOCUS: ON THE MOLECULAR CLOCK
"The molecular clock hypothesis states that for all evolutionary
lineages there is a relatively constant rate of evolutionary
change over time. More specifically, rather than there being a
'global' universal rate for all molecules and evolutionary
lineages, each molecule, DNA or protein, has a specific rate of
evolution. If most mutations are neutral or almost neutral in
their selective effects, and if this rate of mutation has not
changed over time, then the rate of evolution of a particular
molecule should be nearly constant over time, permitting us to
estimate the age of evolutionary lineages. However, some lineages
have been documented to have, for various reasons, faster rates
of evolution than other lineages (e.g., rodents vs. primates).
However, leaving this and other caveats aside, if molecules
evolve at a constant rate they can be used as 'time keepers' to
calculate 'lineage-specific' divergence times and to estimate the
age of the nearest common ancestor of two species. To use the
molecular clock in such a way requires the calibration of its
'ticking rate'. This can be done through several means such as
the fossil record (keeping in mind that the first occurrence of a
fossil is always a minimum estimate for the age of this lineage)
or through major vicarious events such as plate tectonics. Once
the homologous gene (A) has been sequence in, for example, two
species, and the rate of evolution in this gene is known through
prior calibration (let's say 2 percent per million years), then
knowing the percent difference in the DNA sequence of gene (A)
between these two species permits the calculation of the age of
their last common ancestor. In this example, if species (1) and
(2) differed by 10 percent in their DNA sequence of gene (A),
then the common ancestor of these two species would be expected
to have lived around 2.5 million years ago. It would have taken
these two lineages this long to both diverge at a rate of 2
percent per million years to accumulate 10 percent difference in
gene (A)."
-----------
Ernst Mayr: _What Evolution Is_
(Basic Books, New York 2001, p.198)
http://www.amazon.com/exec/obidos/ASIN/0465044255/scienceweek
[Editor's note: Born in 1904 and obviously still at work, Ernst
Mayr, to many biologists, is a scientific heirloom on its way to
becoming a legend. From 1953 until his "retirement" in 1975, he
was Agassiz Professor of Zoology at Harvard University.]
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
14. SW ARCHIVE: A CRITIQUE OF THE NOBEL PRIZE
There are supreme awards in nearly all the branches of science,
but none of them have acquired the popular interest of the Nobel
prizes, and certainly no science prizes except the Nobel prizes
have had even a remotely comparable portrayal in melodrama.
... ... Elizabeth Crawford (Universite Louis Pasteur, FR), a
sociologist and historian of science, presents a critique of the
Nobel prizes and the Nobel prize system, the author making the
following points:
1) Nobel intended his prizes to encourage promising young
scientists, so it would no doubt be a surprise for him to see the
prizes become the standards for the highest achievements of
modern science.
2) The notion that the Nobel prizes parallel the history of
modern science ignores the fact that the awards cover only a
small part of modern science, neglecting a number of important
fields such as technology, astronomy, meteorology, and
psychiatry. Thomas Edison, the Wright brothers, the
astrophysicists G.E. Hale and Arthur Eddington, the meteorologist
Vilhelm Bjerknes, Sigmund Freud -- all did not receive a Nobel
prize. Before the 1920s, even theoretical physics and theoretical
chemistry were neglected, and Arnold Sommerfeld, G.N. Lewis,
Ludwig Boltzmann, Josiah Willard Gibbs, Oliver Heaviside, and
Henri Poincare also did not receive a Nobel prize.
3) The manner in which attention has focused on the prize
winners -- never on the candidates -- is one reason for the
extraordinary success of the prizes. Another reason is the
wholesale acceptance of the justification provided by the prize
awarders for the choices. Major eligible discoveries have indeed
received prizes, but for the most part, the awarders of the prize
"have been engaged in the rather humdrum business of choosing
among works produced by what Kuhn called 'normal' science."
4) From the beginning, secrecy has been at the heart of the
Nobel system, the statutes of the Nobel Foundation adopted in
1901 stipulating that no part of the prize deliberations could be
made public, nor could a prize decision be appealed. But in 1974
the statutes of the Nobel Foundation were changed to authorize
the four institutions that award Nobel prizes to permit access to
archival documents at least 50 years old for purposes of
historical research.
5) Myths are necessary for the cohesion of institutions and
groups, and the myth of the Nobel laureate as the lone discoverer
may appear to be one that preserves some of the innocence of
science in an age of multimillion dollar research projects and
research teams involving hundreds of collaborators. But the
winner-take-all mentality masks the realities of doing science in
the 20th century.
6) It is important to bear in mind that prize winners are
chosen from a large pool of worthy candidates, and that the
choices are conditioned not only by the predilections of the
Swedish prize awarders but also by their ties to international
networks that so far have centered almost exclusively in Europe
and North America, allowing for few prize winners residing in
Russia, India, and Japan, and none in China.
-----------
SCI 1998 282:1256
SW 1998 27 Nov
-----------
SCIENCE-WEEK 2 Nov 2001 http://scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
15. SOURCES:
------------
AS: American Scientist; CEN: Chemical & Engineering News;
CR: Chemical Reviews; GD: Genes & Development;
GR: Genome Research; JACS: J. Amer. Chemical Society;
JAMA: J. Amer. Medical Association; JCE: J. Chem. Education;
MMWR: CDC Morbidity and Mortality Weekly Report; NAT: Nature;
NATM: Nature Medicine; NEJM: New England J. Medicine;
NS: New Scientist; NYT: New York Times; NYR: New York Review;
PNAS: Proceedings of the National Academy of Sciences;
PRL: Physical Review Letters; PT: Physics Today; PRAX: PRAXIS;
SA: Scientific American; SCI: Science; SW: ScienceWeek;
TS: The Scientist.
In the text, the affiliation following the names of authors is
the affiliation of the lead author.
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
NOTICES
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
CHANGE OF EMAIL ADDRESS:
If at any time you need to change the Email address at which you
receive SW, please send the information to:
request@scienceweek.com
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
SCIENCE-WEEK SUBSCRIPTIONS:
Complete subscription information is available at:
http://scienceweek.com/subinfo.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
We welcome comments, suggestions, and criticisms from our
subscribers. Public letters relevant to any report are also
welcome. Editorial contact: editors@scienceweek.com
Editor/Publisher: Dan Agin
Managing Editor: Claire Haller
Associate Editor: Joan Oliner
Copyright (c) 1997-2001 SCIENCE-WEEK/Spectrum Press Inc.
All Rights Reserved
US Library of Congress ISSN 1529-1472
---------------------------------------------
ScienceWeek is published by Spectrum Press Inc.,
3023 N. Clark Street #109, Chicago, 60657-5205 IL, USA.
---------------------------------------------
-----end file
|