ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy-makers.

July 21, 2000 -- Vol. 4 Number 29

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There is no national science just as there is
no national multiplication table; what is national
is no longer science.
-- Anton Chekhov (1860-1904)

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Contents of this Issue:

1. Evolutionary Biology:
Y Chromosome Evidence for an Early Common Human Ancestor
--------------------------------------------------------
A new study of the ancestry of human Y chromosomes reveals that 
the expected time to the most recent common ancestor of modern
humans is remarkably short, on the order of 50,000 years.
(Includes related background material.)

2. Medical Biology:
On the Immune System
--------------------
Nowhere is the idea of the human body as a colony of cells more
clear than in consideration of the cooperative interactions of
the various cells of the immune system functioning to protect the
entire organism. (Includes related background material.)

3. Science Policy:
On the Irresponsibility of "Politically Responsible" Science
------------------------------------------------------------
The call for politically responsible science, frequently heard
today, cannot solve the problem of how scientists can prevent
science from serving immoral and inhuman ends.
(Includes related background material.)

4. Chemistry:
Development and Applications of a Self-Associating Protein
----------------------------------------------------------
A single point mutation in the ligand-binding site of a human
immunosuppressant-binding protein converts the normally monomeric
protein into a ligand-reversible dimer.
(Includes related background material.)

5. Chemistry:
Selection of Optical Isomers by an Applied Magnetic Field
---------------------------------------------------------
Researchers report the first unequivocal use of a static magnetic
field to bias a chemical process in favor of one of left- or
right-handed enantiomers. (Includes related background material.)

6. Physics:
On the Nonessentiality of Theory in Physics
-------------------------------------------
A theoretical physicist argues that theoretical physics is
usually irrelevant and often a hindrance to new experimental
breakthroughs.

7. In Brief:
Bohr, Heisenberg, and Copenhagen -- Again.

8. In Focus: On Conditioned Reflexes

9. From the SW Archive:
An Interesting Case of Ant-Plant Mutualism
------------------------------------------
An intriguing mutualism between plants and ants in which "guard-
ants" are apparently signaled by the plant to stop guarding
during plant pollination periods.

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1. EVOLUTIONARY BIOLOGY:
Y CHROMOSOME EVIDENCE FOR AN EARLY COMMON HUMAN ANCESTOR
     The main disciplines in the study of modern human origins
are human evolutionary genetics (especially evolutionary
molecular genetics), human paleontology (the study of human
fossils), archeology (especially the study of prehistoric human
cultures), and paleodemography (the study of prehistoric human
population distributions and migrations). Each discipline has its
own methods and specialist terminology, and there are areas of
both agreement and disagreement. The current consensus view
across all these disciplines is that modern humans originated in
Africa and spread to other continents, and that early modern
humans experienced an exponential population growth. Concerning
the time of the common origin of present humans, which is
presumed to be earlier than the emergence from Africa, the
estimates range from less than 50,000 years ago to approximately
150,000 years ago, with evidence from molecular genetics pointing
to a more recent common origin, and evidence from paleontology
indicating a more remote common origin.
     In this context, the term "polymorphism" refers to 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.
     The term "recombination", in this context, refers to the
occurrence of progeny with combinations of genes other than those
that occurred in the parents, the occurrence due to independent
assortment or "*crossing over".
     The Y chromosome is one of the two chromosomes that
determine sex in many animals, including humans, and it carries
mostly male-specific genes.
... ... R. Thomson et al (5 authors at 3 installations, US UK)
present a study of the ancestry of human Y chromosomes, the
authors making the following points:
     1) During the past 10 years, DNA polymorphisms have been
widely used to reconstruct human evolutionary history.
*Mitochondrial DNA originally was used for this purpose, because
the high mutation rate of mitochondrial DNA produced numerous
polymorphisms and the absence of recombination facilitated their
interpretation. In male lineages, the Y chromosome shares some of
these properties, e.g., uniparental inheritance and absence of
recombination (in the nonrecombining part), but until recently,
studies of the Y chromosome have been hampered by the scarcity of
DNA sequence polymorphisms.
     2) The authors analyzed a data set of DNA sequence variation
at three Y chromosome genes (SMCY, DBY, DFFRY) in a worldwide
sample of human Y chromosomes. Between 53 and 70 chromosomes were
fully screened for sequence variation at each locus by a high-
performance liquid chromatography method. The sum of the lengths
of the 3 genes is 64,120 base pairs. The authors used these data
to study the ancestral genealogy of human Y chromosomes, with a
particular focus on estimating the expected time to the most
recent common ancestor and the expected ages of certain mutations
with interesting geographic distributions.
     3) The geographic variation distribution was found similar
to that obtained for other gene loci, but the expected time to
the most recent common ancestor is remarkably short, on the order
of 50,000 years. Thus, although previous studies have noted that
Y chromosome variation shows extreme geographic structure, the
authors suggest that the spread of Y chromosomes out of Africa is
much more recent than previously believed. The authors also
suggest that their data indicate substantial population growth in
the effective number of human Y chromosomes.
     4) Commenting on this work, Jaume Bertranpetit (Universitat
Pompeu Fabra Barcelona, ES) states as follows: "Inferences from
molecules to populations are not straightforward, and there have
been recurrent worries [about] what was being analyzed, either
the genes or genomic regions on one hand, or the individuals,
populations, or species on the other. There have been worries
concerning the accuracy of our knowledge of genome dynamics,
worries concerning the ability and power to detect specific
processes and disentangle cases where more than one mechanism may
have produced similar genetic patterns, and worries concerning
the appropriateness of evolutionary models needed for the
inference. And finally, there have been worries from
anthropologists who do not perceive the interface between the
evolutionary biology of a species and that of tiny fragments of
DNA, usually in noncoding regions, worries surrounding a fast-
developing field, heir to classical population genetics, with
brilliant novelties but also eager to get headlines."
-----------
R. Thomson et al: Recent common ancestry of human Y chromosomes:
Evidence from DNA sequence data.
(Proc. Natl. Acad. Sci. US 20 Jun 00 97:7360)
QY: Marcus W. Feldman [marc@charles.stanford.edu]
-----------
Jaume Bertranpetit: Genome, diversity, and origins: The Y
chromosome as a storyteller.
(Proc. Natl. Acad. Sci. US 20 Jun 00 97:6927)
QY: Jaume Bertranpetit [jaume.betranpetit@cexs.upf.es]
-----------
Text Notes:
... ... *crossing over: In general, the exchange of genetic
material between homologous chromosomes.
... ... *Mitochondrial DNA: Mitochondria are double-membrane
enclosed organelles of cells, and they are involved in several
important biochemical  pathways, including electron transport and
oxidative metabolism. Various types of eukaryotic cells (cells
containing membrane-bound organelles such as a nucleus) may
contain from a few to several thousand mitochondria in each
individual cell. 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. (In
biology, "symbiosis" is an intimate and protracted association of
individuals of different species.) Mitochondria contain their own
genome, and mitochondrial DNA (denoted as mtDNA), found in the
mitochondria of all eukaryotes, is believed to evolve in parallel
with nuclear DNA, but since sperm mitochondria are apparently
quickly destroyed inside egg cells, mitochondrial DNA is
primarily inherited only in the maternal lineage in animals.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ANTHROPOLOGY: GENOMIC ANALYSIS OF HUMAN HISTORY
An important new trend in recent years has been a merging of the
research interests of molecular geneticists, anthropologists, and
historians. New tools of genomic analysis are beginning to shed
light on historical questions such as migrations of ancient
peoples, differences in migration patterns of males and females,
historical demography of cultures with ancient roots, patterns of
human genetic diversity, and so on. It is apparent that in
certain areas of the study of history, historical analysis is
undergoing a methodological transformation.
... ... K. Owens and M-C. King (University of Washington, US)
present a review of recent applications of genomic analysis to
history and anthropology, the authors making the following
points:
     1) Molecular genetics has begun to revolutionize the study
of human evolution. Analysis of human genomes now offers the
possibility of understanding movements and events of more recent
human history, and analysis of records written in human DNA can
complement historical analysis of records written by human
observers.
     2) Human migrations: Every present-day population retains
clues to its ancient roots, and common ancestries can be
confirmed and human migrations traced by comparing DNA
frequencies of present-day populations. Early migrations of
modern humans out of Africa have been traced by analysis of DNA
sequences; more recent human migrations have been followed
through genetic trails as well. An example is the application of
statistical analysis of classical *polymorphisms to the question
of ancient migrations within Europe. One important question
concerning migrations in general is whether males and females
migrate in the same ways. Genetic analysis of sequences of
*mitochondrial DNA (mtDNA) and *Y chromosome markers carried out
in the past few years suggest that the migration rates of males
and females have been dramatically different for much of human
history, with higher migration rates among females than among
males. When females relocate to the birthplaces of their spouses,
children are born close to the birthplaces of their fathers but
further from the birthplaces of their mothers. Most individual
females do not move far, but over hundreds of generations, the
genetic effects of their movements accumulate, leading to the
observed migration patterns.
     3) Genetic perspectives on cultural history: Genomic
analysis can reveal the historical demography of cultures with
ancient roots, and also indicate how current populations are
related to each other, including the extent and timing of their
contacts. An important historical question, for example, concerns
the movement of people and genes along ancient trade routes. The
Kazakh, Uighur, and Kirghiz populations of central Asia live
along the Silk Road, the trade route between Europe and Asia that
flourished between approximately 200 B.C. and 400 A.D. Analysis
of mitochondrial DNA sequences of these populations suggests that
they are descended from people moving from Europe to Asia and
vice versa more than 2000 years ago, albeit long after the early
human migrations out of Africa. Y chromosome variation in part
parallels language differences among these populations, whereas
mitochondrial DNA variation does not. Y chromosome data from
central Asia and from other regions of the world suggest that
genetic differences at linguistic boundaries are due primarily to
male rather than female isolation. Genetic evidence also supports
the oral tradition that the Lemba, who are now Bantu-speaking
people of southern Africa, derive from Jews who migrated from the
Middle East to Yemen 2700 years ago, and from Yemen to southern
Africa 2400 to 2000 years ago. More than 50 percent of Lemba Y
chromosomes carry *haplotypes that are common among Jewish
populations but absent in their African neighbors.
     5) Genetics, history, and race: Of importance is the fact
that genetic differences of populations from different continents
represent only approximately 10 percent of human genetic
diversity: no major genetic discontinuities across populations
have been observed. Most human genetic variation antedates the
migration of modern humans out of Africa. The possibility that
human history has been characterized by relatively homogeneous
genetic groups ("races"), distinguished by major biological
differences, is not consistent with genetic evidence. Variation
in traits, including skin color, popularly used to identify
"races", is likely due to straightforward mechanisms involving
limited numbers of genes with very specific physiological
effects. Of course prejudice does not require a rational basis,
let alone an evolutionary one, but the myth of major genetic
differences across "races" is nonetheless worth dismissing with
genetic evidence.
-----------
K. Owens and M-C. King: Genomic views of human history.
(Science 15 Oct 99 286:451)
QY: Kelly Owens, Univ. of Washington Seattle 206-543-8992.
-----------
Text Notes:
... ... *polymorphisms: See main report.
... ... *mitochondrial DNA (mtDNA): See main report.
... ... *Y chromosome markers: See main report.
... ... *haplotypes: (haploid genotypes) The term "haplotype"
refers to a particular combination of genes (specifically,
*alleles) in a defined region of a chromosome.
... ... *alleles: (allelomorph) An "allele" is one of two or more
forms of a given gene that control a particular characteristic,
with the alternative forms occupying corresponding loci on
homologous chromosomes. Different alleles usually produce
different characteristics in an organism, e.g., brown versus blue
eyes.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com 7Jan00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
PALEOLITHIC HUMAN POPULATION EXPANSION IN AFRICA
Human populations have undergone dramatic expansions in size, but
other than the growth associated with agriculture, the dates and
magnitudes of those expansions have never been resolved. Genetic
approaches to the study of human population expansions have
focused on variation at a single genetic locus, the "control
region" of *mitochondrial DNA. But in the study of demographic
history, single-locus investigations suffer from pronounced
statistical and biological limitations. The statistical problem
is that the conclusions rely on only one particular realization
of a gene genealogy, the "tree" determining the ancestral
relationships among a set of *alleles. The biological problem is
that there are a large number of functional genes in the
mitochondrion, and due to a complete linkage, a selective sweep
for any one of the genes may lead to a spurious signal of
expansion. ... ... Reich and Goldstein (University of Oxford, UK)
present two new statistical tests for population expansion, using
variation at a number of unlinked genetic markers to study the
demographic histories of natural populations. The authors report
that analysis of genetic variation in various aboriginal
populations throughout the world reveals highly significant
evidence for a major human population expansion in Africa, but no
evidence of expansion outside of Africa. The inferred African
expansion is estimated to have occurred between 49,000 and
640,000 years ago, certainly before the Neolithic expansions, and
probably before the splitting of African and non-African
populations. The authors suggest that in showing a significant
difference between African and non-African populations, their
analysis supports the unique role of Africa in human evolutionary
history. The authors also suggest that the missing signal in non-
African populations may be the result of a population bottleneck
associated with the emergence of these populations from Africa,
as postulated in the "Out of Africa" model of modern human
origins.
QY: David B. Goldstein [david.goldstein@zoo.ox.ac.uk]
(Proc. Natl. Acad. Sci. US 7 Jul 98 95:8119)
(Science-Week 7 Aug 98)
-------------------
Text Notes:
... ... *mitochondrial DNA: See notes to previous report.
... ... *alleles: See notes to previous report
-------------------
Related Background:
GENETIC TRACES OF ANCIENT DEMOGRAPHY
The term "haploid loci" refers to genome locations that derive
from only one parent... A "nonrecombining" part of a genome is a
part that does not vary when the entire genome is replicated
during reproduction. The Pleistocene is the geological time
period from about 2 million years ago to about the end of the
last glaciation about 10,000 years ago. Modern man is believed
to have evolved during the Pleistocene.
... ... Harpending et al (6 authors at 3 installations, US), in a
study of the demographic history of the human species as revealed
by patterns of gene differences, report that haploid loci like
mitochondrial DNA and the nonrecombining part of the Y chromosome
show a pattern indicating expansion from a population of only
several thousand during the late middle or early upper
Pleistocene. The authors suggest our ancestral population size
during nearly the whole Pleistocene was of the order of 10,000
breeding individuals, and that genetic evidence denies any
version of the multiregional model of modern human origins, and
implies instead that our ancestors were effectively a separate
species for most of the Pleistocene, a small population probably
occupying an area the size of Swaziland or Rhode Island rather
than a whole continent. The authors further suggest that
archeologists should find and identify this population.
QY: Henry C. Harpending [harpend@ibm.net]
(Proc. Natl. Acad. Sci. US 17 Feb 98) (Science-Week 20 Mar 98)
-------------------
Related Background:
Y CHROMOSOME EVIDENCE INDICATES AFRICAN ORIGINS OF MAN
The Y chromosome is one of the two chromosomes that determine sex
in many animals, including humans, and it carries mostly male-
specific genes. Genetic polymorphisms are individual functional
variations of specific genes or genetic markers that occur in a
population with a significant frequency, e.g., more than 1%.
... ... At a recent symposium on human evolution (Cold Spring
Harbor Laboratory, NY US), a consensus was apparently reached
that current studies of human Y chromosome polymorphisms indicate
that the major human migrations that occurred had their source in
Africa, and that a small number of present African populations,
the Ethiopians, Sudanese, and south African Khoisans, possess
markers that have been conserved since that time. The data are
considered to confirm the recent mitochondrial DNA studies which
also indicate Africa as the source of human migrations. Some
paleoanthropologists are calling the Y chromosome results an
"unquestionable major breakthrough".
(Science 31 Oct 97) (Science-Week 21 Nov 97)
For more information: http://scienceweek.com/swfr.htm

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2. MEDICAL BIOLOGY:
ON THE IMMUNE SYSTEM
Our environment is filled with a variety of infectious agents,
including bacteria, viruses, parasites, and fungi, and the
essential line of defense against these pathogenic invaders is
the "immune system". This system, an evolutionary development in
vertebrates, involves a complex set of dynamic interactions
between various specialized cells, the interactions mediated by
chemistry. An important component is an evolved genomic apparatus
that essentially provides for an "immune memory", which in
general is a capability of the immune system to modify and
enhance its responses based on its previous experience with
particular pathogens. Nowhere is the idea of the human body as a
colony of cells more clear than in consideration of the
cooperative interactions of the various cells of the immune
system functioning to protect the entire organism.
... ... P.J. Delves and I.M. Roitt (University College London,
UK) present an extensive 2-part review of current knowledge
concerning the human immune system, the authors making the
following points:
     1) In humans, there are two fundamentally different types of
responses to invading microbes: a) innate (natural) responses
that occur to the same extent however many times the infectious
agent is encountered; b) acquired (adaptive) responses that
improve after repeated exposure to a given infection.
     2) The innate immune response involves a) various
specialized "phagocytes" (neutrophils, monocytes, macrophages),
cells that "eat" pathogens; b) various cells (basophils, mast
cells, eosinophils) that release *inflammatory mediator
substances; c) *natural "killer" cells. The molecular components
of innate responses include a variety of identified proteins
(e.g., *complement, *cytokines).
     3) The acquired immune response involves the proliferation
of *antigen-specific *B and T cells, which occurs when the
surface receptors of these cells bind to antigen. Specialized
cells, called "antigen-presenting cells", display the antigen to
*lymphocytes and collaborate with them in the response to the
antigen. B cells secrete *immunoglobulins, the antigen-specific
*antibodies responsible for eliminating extracellular
microorganisms. T cells help B cells to make antibody and can
also eradicate intracellular pathogens by activating macrophages
and by killing virally infected host cells. In general, innate
and acquired responses usually work together to eliminate
pathogens.
     4) The various cells of the immune system develop from
*pluripotent stem cells in the fetal liver and in bone marrow and
then circulate throughout the extracellular fluid. B cells reach
maturity within the bone marrow, but T cells must travel to the
thymus gland to complete their development.
     5) Adaptive immune responses are generated in the *lymph
nodes, spleen, and *mucosa-associated lymphoid tissue, all of
which are called "secondary lymphoid tissues": a) In the spleen
and lymph nodes, the activation of lymphocytes by circulating
antigen occurs in distinctive B cell and T cell compartments of
lymphoid tissue. b) The mucosa-associated lymphoid tissues,
including the tonsils, adenoids, and *Peyer's patches, defend
mucosal surfaces. c) Diffuse collections of lymphoid cells are
present throughout the lung and *lamina propria of the intestinal
wall.
     6) To establish an infection, a pathogen must first overcome
numerous surface barriers, such as enzymes and mucus, that are
either directly antimicrobial or that inhibit attachment of the
microbe. Because neither the *keratinized surface of the skin nor
the mucus-lined body cavities are ideal habitats for most
organisms, microbes must breach the *ectoderm. Any organism that
breaks through this first barrier encounters the two further
levels of defense, the innate and acquired immune responses.
-----------
P.J. Delves and I.M. Roitt: The immune system.
(New England J. Med. 6 Jul 00 343:37)
(New England J. Med. 13 Jul 00 343:108)
QY: Peter J. Delves, Dept. of Immunology, University College
London, UK.
-----------
Text Notes:
... ... *inflammatory mediator substances: In general, an
"inflammatory change" is a response of tissues to irritation or
injury. The response involves a dynamic complex of cellular and
chemical reactions that occur in the affected blood vessels and
adjacent tissues.
... ... *natural "killer" cells: Cells of the innate immune
response that recognize and then kill abnormal cells such as
certain infected cells and tumor cells.
... ... *complement: A group of 9 interacting serum proteins,
mostly enzymes, which are activated during the immune response,
and which participate in bacterial lysis (destruction of bacteria
by disruption of cell membrane) and macrophage chemotaxis
(chemical attraction of macrophages, immune system amoeba-like
cells active in phagocytosis of bacteria and other particulates.)
... ... *cytokines: A cytokine is any substance that promotes
cell growth and cell division. Cytokines mediate many functions
of the immune system.
... ... *antigen: In general, an antigen is any entity that
provokes an immune response, and this includes, in certain
disease states, entities that are not "foreign" to the body.
... ... *B and T cells: (B and T lymphocytes) Lymphocytes (lymph
cells, lympho-leukocytes) are a type of leukocyte (white blood
cell) responsible for the immune response. In general, there are
two classes of lymphocytes: 1) the B-cells, when presented with a
foreign chemical entity (antigen), change into antibody producing
plasma cells; 2) the T-cells, which interact directly with
foreign invaders such as bacteria and viruses, and some types of
which assist B-cells in the B-cell response. The general
terminological differentiation between B-cells and T-cells is
based on where the cells mature: B-cells mature in (b)one marrow,
and T-cells mature in the (t)hymus gland.
... ... *lymphocytes: See above note.
... ... *immunoglobulins: (antibody): The immunoglobulins are a
large glycoprotein category that includes antibodies as a subset.
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 antigen.
... ... *antibodies: See above note.
... ... *pluripotent stem cells: In general, the term "stem"
cells refers to undifferentiated cells that upon differentiation
can give rise to various specialized cell lines such as blood
cells, skin cells, nerve cells, etc. Adult bone marrow, for
example, contains stem cells that are the precursors of the
various specialized types of blood cells. "Pluripotent stem
cells" are stem cells that have the capacity to differentiate
into various cell types.
... ... *lymph nodes: The lymphatic system is a complex network
for the distribution of lymph fluid (which is similar to blood
plasma -- blood without red cells). Lymph is collected by
drainage from the tissues throughout the body, flows in the
lymphatic vessels through the lymph nodes, and is eventually
added to the venous blood circulation. Lymph consists of a clear
liquid portion, varying numbers of white blood cells (chiefly
lymphocytes), and a few red blood cells. The lymph nodes are
small bodies located throughout the lymph system and varying in
diameter from 0.1 to 2.5 centimeters.
... ... *mucosa: In general, a multilayer tissue lining various
tubular structures in the body.
... ... *Peyer's patches: Aggregated lymphoid nodules of the
small intestine.
... ... *lamina propria: The layer of connective tissue
underlying the *epithelial layer of a mucosa. 
... ... *epithelial layer: In animals and humans, epithelial
cells compose the cell layers that form the interface between a
tissue and the external environment, for example, the cells of
the skin, the lining of the intestinal tract, and the lung airway
passages.
... ... *keratinized: Keratin is a protein which helps waterproof
and protect the skin and underlying tissues.
... ... *ectoderm: In the embryos of higher animals, there
occurs the transformation of a single-layer "blastula" into a
3-layered "gastrula" consisting of ectoderm (outermost layer),
mesoderm (middle layer), and endoderm (innermost layer)
surrounding a cavity with one opening. The 3 layers are called
the "germ layer", and these layers, via further cell
differentiation and proliferation, determine the development of
all the major body systems and organs.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON MODELS OF IMMUNE MEMORY
Higher vertebrates, including humans, have through evolution
developed an immune system that can selectively destroy or
inactivate foreign molecules and foreign cells (*antigens)
without harming the molecules or normal cells of the host. The
vertebrate immune system apparently retains a "memory" of each
antigen attack, allowing the immune system to respond more
efficiently the next time it encounters the same invader. One
group of immune system cells involved in this immune system
memory is a small fraction of the proliferating *B-lymphocyte
cell population, the fraction effectively set aside as a reserve
population of cells to be directed against a specific stimulating
antigen. Such cells, called "memory B cells", are
indistinguishable in appearance from other unstimulated
lymphocytes and like them do not secrete antibody. But if the
organism is exposed to the same antigen a second time, the
reserve population of antigen-specific memory cells quickly
proliferates and differentiates into antibody-secreting plasma
cells, thereby allowing what is called the "secondary response"
to a given antigen to occur more rapidly and produce more
antibody than the initial or "primary response". The
effectiveness of the secondary response is the apparent reason
why humans, for example, rarely contract such diseases as chicken
pox or mumps more than once. One of the central problems in
immunology is to provide a molecular explanation for immune
system memory (also called "immune memory). There has been much
debate concerning the relative contributions to immune memory of
processes such as the persistence of antigens, *cross-reactive
stimulation, *homeostasis, competition between different lineages
of lymphocytes, and the rate of cell turnover
... ... R. Antia et al (3 authors at 2 installations, US) present
several mathematical models designed to investigate the
contributions of the various processes to the longevity of immune
memory. The authors define immune memory as the maintenance of an
elevated population of antigen-specific cells, and they define
the longevity of immune memory as the rate of decline of the
population of antigen-specific memory cells. The models presented
by the authors incorporate a repertoire of immune cells, each
lineage with distinct antigenic specificities, the basic
equations describing the dynamics of individual lineages and the
total population of cells. The authors suggest their results
indicate that if homeostatic control regulates the total
population of memory cells, then immune memory will be long-lived
(half-life > 1 year). The authors also suggest that the longevity
of immune memory in this situation will be insensitive to the
relative rates of cross-reactive stimulation, the rate of
turnover of immune cells, and the functional form of the
mathematical term for the maintenance of homeostasis. Further,
the authors suggest their models predict that when the frequency
of antigenic stimulation from other infectious agents is very
high, the duration of immune memory is likely to be relatively
low: i.e., sufficiently frequent exposure to new pathogens will
result in a relatively high rate of decline of immune memory with
respect to a given pathogen.
-----------
R. Antia et al: Models of immune memory: On the role of cross-
reactive stimulation, competition, and homeostasis in maintaining
immune memory.
(Proc. Natl. Acad. Sci. US 8 Dec 98 95:14926)
QY: Rustom Antia [rantia@biology.emory.edu]
-----------
Editor's note: In addition to the background material below, see
the SW Focus Report "Immunology: Biological and Medical Aspects"
at URL [http://scienceweek.com/swfr037.htm]
-----------
Text Notes:
... ... *antigens: See main report.
... ... *B-lymphocyte cell: See main report.
... ... *cross-reactive stimulation: In general, in this context,
a "cross-reaction" is an immunological phenomenon in which an
antigen reacts with an antibody that has been raised (produced)
against a different antigen. The term "cross-reactive
stimulation" refers to the production of cross-reacting antibody
(or immune cell), i.e., an antibody (or immune cell) able to
react with an antigen that did not specifically stimulate its
original production.
... ... *homeostasis: The term "homeostasis" refers to a
physiological equilibrium necessary in general for the viability
of an organism, and in particular for the operation of many
cellular functions. Homeostatic mechanisms in biological systems
usually involve an element of negative feedback signaling. In
vertebrates, for example, when blood temperature is too high,
temperature receptors provoke a sequence of events involving many
pathways that ultimately results in a lowering of body temper-
ature. Similar homeostatic mechanisms operate at cellular levels.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 12Feb99
For more information: http://scienceweek.com/swfr.htm

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3. SCIENCE POLICY:
ON THE IRRESPONSIBILITY OF "POLITICALLY RESPONSIBLE" SCIENCE
Since science, in the words of J.R. Oppenheimer (1904-1967)
brings "power over the world", and since politics is more or less
devoted to the wielding of such power, one can reasonably expect
an implicit or explicit bond between science and politics to
always pervade their respective histories. How is the individual
scientist to deal with this dangerous dance of science and
politics, a dance which is more a passionate tango than a
minuet? This question is not easily answered.
... ... Ute Deichmann (Institute for Genetics Cologne, DE),
presents an essay on the dangers of "politically responsible"
science, the author making the following points:
     1) Disillusionment concerning the contributions of eminent
scientists to the Nazi Regime (1933-1945) led many to question
the notion of a pure and universal science, to reject this as a
myth, and instead to redefine science as a socially organized
political enterprise. Proponents of this view argue that science
must be politically responsible, directed towards socially
acceptable goals, and assessed according to its long-range
consequences.
     2) But this call for politically responsible science does
not guarantee an ethical stance. For example, environmentalists
attempted in the 1980s to create a "political ecology", but the
intellectual origins of their criticisms of "causal reductionist"
science lie in the 1920s, when German ecologists proclaimed
ecology as a path to "a view of the world, in which everything is
related to everything else, everything directly or indirectly
affects everything else." The ecologist Karl Friederichs became a
leading Nazi ecologist, and he and his colleagues created and
spread the view of biology as an eminent political science aimed
at serving "the benefit of the people (Volk)" and of ecology as
the "doctrine of blood and soil".
     2) Eugenics, or race hygiene, is another example of
scientists claiming to act in a politically responsible manner,
with the idea that to avert long-range threats to the gene pool
it is necessary to institute compulsory sterilization of
"genetically unfit" people. These attempts to create a
politically responsible biology ended disastrously. The author
states: "If we criticize reductionist science for having
contributed to the technical and military power of the Nazis, we
have to acknowledge that 'politically responsible' biologists
provided for their ideological and political power."
     3) The author suggests there is a scientific level outside
politics, ethics, and applications. It is not the quest for
knowledge that was responsible for the Nazi atrocities, but the
fact that scientists did not pay due regard to normal ethical
principles. The author states: "Nazi moral standards were not
imposed on scientists. On the contrary, for whatever reason --
opportunism, conviction, promotion, or power -- scientists lent
their support to ranking human beings as valuable, inferior or
worthless, hence providing the ideological basis of the Nazi
state."
     4) For example, Otmar von Verschuer, the director of the
Kaiser Wilhelm Institute for Anthropology, collaborated with
Josef Mengele in Auschwitz, and Verschauer's acceptance of organs
and blood from deliberately infected concentration-camp inmates
is considered by many as the most infamous crime in which
geneticists have participated, and a clear transgression of the
limits of science.
     5) The author concludes: "The example of Nazi Germany shows
that 'politically responsible' science endowed with power can
have disastrous consequences for innocent people and for science
itself. The call for politically responsible science, frequently
heard today, cannot solve the problem of how scientists can
prevent science from serving immoral, inhuman ends."
-----------
Ute Deichmann: An unholy alliance.
(Nature 15 Jun 00 405:739)
QY: Ute Deichmann, Institute fur Genetik, Weyertal 121, D 50931,
Koln, DE.
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 21Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON THE FIFTIETH ANNIVERSARY OF THE NUREMBERG CODE
This past August was the 50th anniversary of the formulation of
the Nuremberg Code, which occurred during the so-called Nazi
Doctors Trial held in Nuremberg DE immediately after the Second
World War, and which included 23 defendants, all but 3 of whom
were physicians accused of murder and torture in the conduct of
medical experiments on concentration camp inmates. Of the 23
defendants, 16 were found guilty, and of the guilty 7 were
sentenced to death by hanging, 5 were sentenced to life
imprisonment, 2 to imprisonment for 25 years, 1 to imprisonment
for 15 years, 1 to imprisonment for 10 years. The executions were
carried out at the Landsberg prison, DE. In a recent review of
the Nuremberg Code, Evelyne Shuster (Veterans Affairs Medical
Center, Philadelphia US) describes the important role physicians
had in the prosecution of the Nazi doctors and in the formulation
of the Nuremberg Code, and she summarizes how medical researchers
have used the code over the past 5 decades. The author emphasizes
that perhaps the most important aspect of the code is the
centrality of informed consent of human subjects in experiments.
The editors of the journal in which the review appears have
recently criticized US research authorities for unethical
protocols in connection with HIV research in undeveloped
countries, protocols using placebo controls involving patients
with diagnosed medical conditions who could have been helped by
the drugs that were tested.
QY: E. Shuster, VA Medical Center, Philadelphia, PA 19104 US)
(New England J. Med. 13 Nov 97) (Science-Week 21 Nov 97)
For more information: http://scienceweek.com/swfr.htm

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

4. CHEMISTRY:
DEVELOPMENT AND APPLICATIONS OF A SELF-ASSOCIATING PROTEIN
Many intracellular biological processes are mediated by inducible
protein-protein interactions, and methods that allow such
processes to be arbitrarily manipulated can be powerful tools for
understanding and controlling cellular activities. The use of
chemical dimerization inducers ("dimerizers") has proved to be a
particularly versatile approach: cells are engineered to express
a bifunctional-bipartite ("chimeric") protein comprising a
"signaling" domain (a domain that when activated initiates
intracellular signaling) fused to a drug-binding domain, the
protein such that treatment with bivalent ligands crosslinks the
protein and initiates signaling. This strategy has been used to
create genes for a variety of inducible signaling proteins that
are activated by oligomerization. Dimerizers can also be used to
regulate *gene transcription through the controlled association
of chimeric DNA-binding and activation domains. In general, these
approaches allow protein function to be dissected inside cells or
whole organisms, and the approaches also have apparent
therapeutic promise as a means for bringing cell and gene
therapies under small-molecule control.
... ... C.T. Rollins et al (12 authors at 2 installations, US UK)
now report they have discovered that a single point mutation in
the ligand-binding site of a human *immunosuppressant-binding
protein (FKBP) converts the normally monomeric protein into a
ligand-reversible dimer, and that various studies of this protein
indicate that the mutant protein forms discrete homodimers that
can be completely dissociated within minutes by addition of
monomeric synthetic ligands. The authors suggest these unexpected
properties form the basis for a "reverse dimerization" regulatory
system involving mutant *fusion proteins in which association is
the ground state and addition of ligand abolishes interactions.
The authors report they have used this strategy to rapidly and
reversibly aggregate fusion proteins in different cellular
compartments, and to provide an "off switch" for transcription.
The authors suggest reiterated mutant domains should be generally
useful as conditional aggregation domains to control
intracellular events where rapid reversible dissociation of
interactions is required. The authors also suggest their results
indicate that dimerization is a latent property of this
particular protein (FKBP): analysis of the crystal structure of
this protein reveals a remarkably complementary interaction
between monomer binding sites, with only subtle changes in side-
chain disposition accounting for the dramatic change in
*quaternary structure.
-----------
C.T. Rollins et al: A ligand-reversible dimerization system for
controlling protein-protein interactions.
(Proc. Natl. Acad. Sci. US 20 Jun 00 97:7096)
QY: Tim Clackson [clackson@ariad.com]
-----------
Text Notes:
... ... *gene transcription: In this context, the term
"transcription" refers to the process by which genetic
information in DNA is converted into RNA. Subsequently, the
information in RNA is "translated" into the amino-acid sequence
that constitutes a protein. 
... ... *immunosuppressant: In general, a chemical agent that
causes suppression of the immune response to antigens. The
particular immunosuppressant involved in this report is known as
"FK506", and FKBP is the acronym for "FK506-binding protein".
... ... *fusion proteins: In general, a protein that results from
the fusion of two genes.
... ... *quaternary structure: The "quaternary structure" of
proteins is characterized by the interaction of 2 or more
individual polypeptides (often via disulfide bonds), the result a
larger functional molecule.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ANALYSIS OF INTRACELLULAR SIGNALING MECHANISMS
In multicellular organisms, chemical messengers of various types
are important entities in the communication between cells
necessary for the function and viability of cells, tissues, and
the organism itself. These messengers usually interact with the
surfaces of cells, particularly with specific receptors on cell
surfaces. Such an interaction is called an "extracellular
signal", and what happens next is a cascade of internal signal
events that effectively transmit the external signal from the
cell membrane to one or more places inside the cell, especially
to the cell nucleus. This sequence in internal signal events
apparently involves specific protein-protein and protein-
phospholipid interactions, with the interactions mediated by
protein domains (regions) of tertiary structure (higher order
configuration) that have evidently been conserved through
evolution. The details of these biochemical interactions are
becoming apparent, at least in some types of somatic cells, so
that molecular biologists are now characterizing the involved
proteins as anchoring (docking) proteins, adaptor proteins,
scaffold proteins, and so on, according to the role played by the
particular protein in the spatial location and translocation and
signal events that eventually produce important reactive or
regulatory responses of the cell. Pawson and Scott (2
installations, CA US), in a review of how extracellular signals
are relayed from the plasma membrane to specific intracellular
sites, discuss the role of scaffold, anchoring, and adaptor
proteins that contribute to signal transduction by recruiting
active enzymes into signaling networks or by placing enzymes
close to their substrates. The authors suggest that the challenge
ahead is to understand both the physiological functions and
regulation of such signaling networks.
QY: Tony Pawson, S. Lunenfeld Res. Inst., Toronto, ON M5G 1X5 CA.
(Science 19 Dec 97) (Science-Week 9 Jan 98)
For more information: http://scienceweek.com/swfr.htm

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

5. CHEMISTRY:
SELECTION OF OPTICAL ISOMERS BY AN APPLIED MAGNETIC FIELD
     One of the great puzzles of biology is the homochirality of
most amino acids and sugars present in biological systems. In
general, chirality is a property of certain asymmetric objects
such that the object and its mirror image cannot be superimposed
one on the other while both objects are restricted to the same
plane (e.g., a left- and right-handed glove). In chemistry,
chiral molecules are optically active, a phase of each form
rotating the plane of incident polarized light. The two possible
forms are called "optical isomers", and each form is called an
"enantiomer". An equal mixture of the two forms is called a
"racemic mixture". Homochirality is the preference of a process
or system for a single optical isomer in a pair of isomers.
Optically active substances are termed "dextrorotatory" (the D-
form; the + form) or "levorotatory" (the L- form; the - form)
according to whether the plane of polarization of the incident
polarized light is rotated to the right or to the left with
respect to the direction of incidence of the light. The great
puzzle in biology is that nearly all amino acids in biological
systems are of the L- form, while nearly all sugars are of the D-
form. The question is how did this arise? Is the basis
terrestrial or extraterrestrial?
... ... G.L. Rikken and E. Raupach (Grenoble High Magnetic Field
Laboratory, FR) now report the first unequivocal use of a static
magnetic field to bias a chemical process in favor of one of
left- or right-handed enantiomers. The authors make the following
points:
     1) Reactions can proceed enantio-selectively if chiral
reactants or catalysts are involved, or if some external chiral
influence is present. But since chiral reactants and catalysts
themselves require an enantioselective production process,
efforts to understand the homochirality of life have focused on
external chiral influences. One such external influence is
circularly polarized light, which can influence the chirality of
photochemical reaction products. [See related background material
below.]
     2) Because both natural optical activity, which occurs
exclusively in media lacking mirror symmetry, and magnetic
optical activity, which can occur in all media and is induced by
longitudinal magnetic fields, cause polarization rotation of
light, many researchers in the past have investigated the
possibility of magnetically induced enantio-selectivity in
chemical reactions. So far, however, no convincing demonstrations
of such an effect have been found.
     3) The authors report they have demonstrated experimentally
that magnetochiral anisotropy -- an effect linking chirality and
magnetism -- can give rise to an enantiomeric excess in a
photochemical reaction driven by unpolarized light in a parallel
magnetic field, and that this suggests this effect may have
played a role in the origin of the homochirality of life.
     4) The experiment reported by the authors involved the use
of the chiral Cr(III)tris-oxalato complex. which is unstable in
solution and spontaneously dissociates and re-associates, with
equal concentrations of right- and left-handed enantiomers at
equilibrium. Dissociation in this system is accelerated by the
absorption of light. The authors demonstrate that in the presence
of an unpolarized laser beam traveling parallel to a static
magnetic field, a small excess of one enantiomer is produced and
maintained, and that on reversing the magnetic field, an equal
concentration of the mirror-image enantiomer results.
     5) The authors conclude: "Clearly, the question of the
origin of the homochirality of life is far from answered. Our
results can only suggest that magnetochiral anisotropy merits
consideration in this discussion. They do, however, show
convincingly that photochemistry with unpolarized light in a
magnetic field is in principle enantio-selective."
... ... In a commentary on this work, Laurence D. Barron
(University of Glasgow, UK) points out that the quest for the
reported effect began in 1846 when Michael Faraday (1791-1867)
made the plane of polarization of a linearly polarized light beam
rotate by applying a magnetic field parallel to the beam. This
discovery was of fundamental importance because it demonstrated
conclusively the intimate connection between electromagnetism and
light. But the discovery also became a source of confusion to
many scientists who failed to appreciate the distinction between
Faraday's magnetic optical rotation and the natural optical
rotation discovered three decades earlier by D. Arago (1786-1853)
and J. Biot (1774-1862) in certain crystals and fluids. Such
natural optical activity is due to the handedness within the
microstructure of the crystals and fluids, as A. Fresnel (1788-
1827) later showed. 
-----------
G.L. Rikken and E. Raupach: Enantioselective magnetochiral
photochemistry.
(Nature 22 Jun 00 405:932)
QY: G.L. Rikken [rikken@polycnrs-gre.fr]
-----------
Laurence D. Barron: Chirality, magnetism, and light.
(Nature 22 Jun 00 405:895)
QY: Laurence D. Barron [laurence@chem.gla.ac.uk]
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 21Jul00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
POLARIZED STARLIGHT AND AMINO ACID HOMOCHIRALITY
... Stuart Clark (University of Hertfordshire, UK) presents a
review of recent astronomical observations that suggest a
solution to the puzzle of biological homochirality, the author
making the following points:
     1) The author suggests that the nature of the starlight
present when the Earth first formed may be responsible for the
asymmetry of the amino acids now found in all living systems. In
general, the idea is that bombardment of comets, large and small,
brought water, gases, and a number of other volatile compounds to
Earth billions of years ago, and the rain of this material from
space may have seeded the young planet with a preponderance of L-
amino acids.
     2) The author points out that the decades old controversy
concerning the *Murchison meteorite was finally settled in 1997
when it was confirmed that L-alanine is twice as abundant in the
meteorite as its optical isomer, that L-glutamic acid is 3 times
as abundant. The previous ambiguities that had caused some
researchers to consider the amino acids in the meteorite in
racemic mixture are now resolved, and the author suggests that
the asymmetries in the meteorite make it almost certain that the
Solar System formed with an excess of amino acids (see background
material below).
     3) The author delineates some of the observational evidence
concerning circularly polarized infrared starlight associated
with certain young stars (see background material below).
Circularly polarized ultraviolet light is of special significance
in this context, since if a racemic mixture is subjected to
circularly polarized ultraviolet light, under the proper
conditions, one of the isomers can be preferentially destroyed
(asymmetric photolysis) (see background material below).
Theoretical work suggests that dust grains associated with stars
can indeed generate circularly polarized radiation at both
visible and ultraviolet wavelengths, as well as in the infrared
part of the spectrum. The general idea is that circularly
polarized light forms when initially unpolarized or plane
polarized starlight is scattered by a group of spinning dust
particles oriented by a local magnetic field.
     4) The author suggests that planets forming around stars in
regions bathed in ultraviolet light with high circular
polarization will naturally incorporate amino acids with
enantiomeric excesses of one sort or the other, and that the same
probably held true for Earth approximately 5 billion years ago.
The author suggests that one consequence of this hypothesis is
that if carbon-based life exists on extrasolar planets, a
biochemistry based on D- amino acids could well be the rule.
-----------
Stuart Clark: Polarized starlight and the handedness of life.
(American Scientist Jul/Aug 99 87:336)
QY: Stuart Clark [sclark@star.herts.ac.uk]
-----------
Text Notes:
... ... *Murchison meteorite: A *carbonaceous chondrite that fell
in 1969 near Murchison, Australia. Analysis of the interior of
the meteorite revealed evidence of amino acids. 
... ... *carbonaceous chondrite: "Stony" meteorites (aerolites)
are meteorites formed solely of rock-forming silicates, and
chondrites are a type of stony meteorite consisting of an
agglomeration of millimeter-sized globules (chondrules) that are
thought to be unchanged since the original condensation out of
the nebula from which the Sun and Solar System formed. A
carbonaceous chondrite is a chondritic meteorite that contains a
relatively large amount of carbon, with a resultant dark
appearance.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 20Aug99
-------------------
Related Background:
STELLAR CIRCULAR POLARIZATION AND BIOMOLECULAR HOMOCHIRALITY
Electromagnetic radiation involves the propagation of both
electric and magnetic forces, and at each point in a light beam,
there is a component electric field and a component magnetic
field, both of which oscillate in all directions perpendicular to
each other and to the direction in which the beam is propagated.
In plane-polarized light, the component electric field oscillates
as in ordinary light except that the direction of oscillation is
contained within a plane. Likewise, in plane-polarized light, the
component magnetic field oscillates within a plane, the planes in
question being perpendicular. Circularly polarized light has a
component electric field that varies in direction but not in
magnitude, so that the field traverses a spiral path in either a
clockwise or counterclockwise direction. In the laboratory, high
levels of *enantiomeric excess in *racemic substances can be
produced by asymmetric photolysis by circularly polarized light. 
Biological molecules exhibit extensive *homochirality (e.g.,
living systems use almost exclusively L-amino acids and D-
sugars), and this has been a puzzle since its discovery in the
19th century. It has been suggested that homochirality may be a
prerequisite for the origin of life, and a number of processes
have been proposed that may have produced enantiomeric excess in
prebiotic organic molecules, including the action of circular
polarization from the daylight sky, but these effects are
considered too small to account for homochirality. Another view
is that the origin of homochirality is extraterrestrial, and
apparent support for this view has been provided by the recent
discovery of an excess of L-amino acids in the *Murchison
meteorite. ... ... Bailey et al (8 authors at 4 installations, AU
UK FR JP) now report strong infrared circular polarization
resulting from dust scattering in *reflection nebula in an Orion
star formation region (OMC-1), and the authors suggest that
circular polarization at shorter wavelengths might have been
important in inducing chiral asymmetry in interstellar organic
molecules that could be subsequently delivered to the early Earth
by comets, interplanetary dust particles, or meteors. The authors
suggest this could account for the excess of L-amino acids found
in the Murchison meteorite, and could explain the origin of the
homochirality of biological molecules. The authors conclude:
"Whether a very high enantiomeric excess is a prerequisite for
the origin of life, or a very small effect is amplified in the
process, the ultimate source [of the excess] is likely to be of
extraterrestrial origin."
-----------
QY: Jeremy Bailey, Anglo-Australian Observatory, PO Box 296,
Epping, New South Wales 2121, AU.
(Science 31 Jul 98 281:672) (Science-Week 21 Aug 98)
-------------------
Related Background:
... ... *enantiomeric: See main report.
... ... *racemic: See main report.
... ... *homochirality: See main report.
... ... *Murchison meteorite: This meteorite, which fell near
Murchison AU in 1969, contains 8 amino acids and the nucleotide
bases adenine, guanine, and uracil.
... ... *reflection nebula: A bright cloud of interstellar gas
and dust that lies in the vicinity of a star or stellar group,
with the starlight scattered in all directions by the dust
grains, and the scattered light visible because of the high
density of the dust.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 28Aug98
For more information: http://scienceweek.com/swfr.htm

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

6. PHYSICS:
ON THE NONESSENTIALITY OF THEORY IN PHYSICS
In modern physics, the historical roles of experiment and theory
and their interactions are often the focus of intense partisan
debate, so it is interesting to be confronted with the views of a
senior theoretical physicist who proposes that theory, despite
what most theorists proclaim, is far from the prime mover of
physics.
... ... Harry J. Lipkin (Weizmann Institute of Science, IL)
presents a letter on the subject, the author making the following
points:
     1) The author suggests that real physics is an experimental
science that progresses from one experimental breakthrough to
another, and that in physics theorists are often irrelevant and
sometimes actually hinder progress by sitting on committees and
opposing the experiments that lead to new breakthroughs.
     2) The author suggests that the main breakthroughs in
physics since 1950 can be characterized as "who-ordered-that?"
effects, named after the famous remark by I.I. Rabi concerning
the discovery and existence of the particle that came to be
called the "*muon". The physics of the 1950s consisted of one
experimental discovery after another of who-ordered-that
particles, with no theoretical predictions beforehand and no
theoretical understanding afterward. By the 1960s, enough of such
particles had been discovered so that Murray Gell-Mann and Yuval
Ne'eman could arrange them in a table "without any understanding
of who ordered what." The subsequent Gell-Mann-Zweig *quark model
provided an explanation, but this model was strongly rejected by
members of a theoretical establishment who were still fiddling
with irrelevancies.
     3) The next dramatic who-ordered-that experiment was
*charge-parity violation in 1965, which is still being debated by
theorists after 35 years. During this time, the theoretical
establishment was again confounded by the discovery of *scaling
in electron scattering, and a satisfactory after-the-fact
explanation by several young theorists was again resisted by the
theoretical establishment.
     4) In 1974, in what is sometimes called the "November
Revolution", the *J/psi particle was discovered by experiments
that theorists had insisted were completely useless and a waste
of valuable accelerator time and budget. "Of course, as soon as
the discovery was confirmed, a chorus of theorists claimed they
had predicted the existence of this hidden *charm particle." The
author states: "The November Revolution would have occurred
without theorists. It might even have occurred earlier if
theorists had not been around at accelerator program committees."
     5) The discovery of two kinds of *neutrinos was also
motivated not by theorists but by experimenters who noticed the
possibility of creating a neutrino beam in an accelerator, and
who actually did it -- without help from theorists.
     6) Eventually, after experimental data had been accumulated
so that the theorists could begin to make sense of them, the
*Standard Model came into existence. But the Standard Model did
not result from great theoretical or philosophical visions: it
arose from a succession of who-ordered-that and other pioneering
experiments that defied the theorists until there were enough
data to enable an after-the-fact analysis that would lead the
theorists in the right direction.
     7) The author states: "I have no patience with social
scientists, historians, and philosophers who insist that the
'scientific method' is doing experiments to check somebody's
theory. The best physics I have known was done by experimenters
who ignored theorists completely and used their own intuitions to
explore new domains where no one had looked before. No theorists
had told them where and how to look."
     8) The author suggests that the important questions to be
asked by social scientists, historians, and philosophers concern
the experimenters in physics: What guides their explorations? How
do they choose where to look? How do they know when to persevere
despite continuous failure to find anything new? How do they know
when to drop an unproductive line and move on, rather than
obstinately pursue a dead end?
-----------
Editor's note: As is evident, Lipkin's comments focus on the
history of particle physics during the past five decades. In
other areas of physics, the separate roles of theory and
experiment are perhaps less easy to assess. And in still other
areas of physics, where predictions associated with new
theoretical approaches have indeed produced new experimental
breakthroughs, the balance can be said to be on the other side.
In any case, it should be emphasized that Lipkin's main point is
not that theory in physics is useless, but that theory is not a
_necessary_ provocation for breakthrough experiments. Lipkin's
letter will no doubt produce rejoinders from theorists, more
thrust and parry in an ongoing debate. Meanwhile, nature knows
nothing of any disputes between theorists and experimenters, such
disputes remaining human secrets.
-----------
Harry J. Lipkin: Who ordered theorists?
(Physics Today July 2000)
QY: Harry J. Lipkin [harry.lipkin@weizmann.ac.il]
-----------
Text Notes:
... ... *muon: A negatively charged particle with a mass
approximately 207 times that of the electron. The muon has a mean
lifetime of 2.2 microseconds, and decays into an electron,
*neutrino, and *antineutrino (see *neutrinos below).
... ... *quark: See "charmed quark" below.
... ... *charge-parity violation: (charge conjugation-parity
violation) Charge parity is a characteristic quantity
(eigenvalue) of a "charge conjugation operation", which in
general is an operation that changes every particle into its
antiparticle. In general, in such an operation, the laws of
motion are left unchanged (the principle of charge conjugation
conservation), but this principle is apparently violated by the
weak interactions.
... ... *weak interactions: (weak forces) The weak force, one of
the four fundamental forces, occurs between leptons (particles
without internal structure, e.g., electrons, neutrinos) and
hadrons (particles with internal structure, e.g., neutrons and
protons); the weak force is responsible for radioactivity and for
the interconversion of neutrons and protons in stars.
... ... *scaling in electron scattering: In this context, the
term "scaling" refers to a type of behavior occurring when high-
energy electrons are directed at protons to reveal the existence
of proton constituents. In this context, the term "scattering"
refers to the change in direction of a particle resulting from
collision with another particle.
... ... *J/psi particle: (psi = psi meson) This particle was
discovered independently by Burton Richter and Sheldon Ting, and
they shared the Nobel Prize in Physics 1976 for their discovery.
The discovery of this particle, the main event in the "November
Revolution", electrified the physics community because it was
discovered apparently independently and simultaneously, and
because it was the first example of a particle formed from a
"*charmed quark", the quark whose existence had actually been
postulated by Sheldon Glashow 10 years earlier.
... ... *charmed quark: A quark is a hypothetical fundamental
particle, having charges whose magnitudes are one-third or
two-thirds of the electron charge, and from which the elementary
particles may in theory be constructed. Along with fractional
electric charge, quarks also have "flavor" in 6 varieties (up,
down, charm, strange, top, and bottom), and "color" (red, yellow,
or blue). Thus, the "charmed quark" is one of the 6 known types
of quark. In the theory of quarks, "charm" is a *quantum number.
... ... *quantum number: In quantum mechanics, certain properties
of a physical system often can take only discrete values (the
properties are "quantized"), and the various possible values are
called "quantum numbers".
... ... *charm particle: (J/psi particle) See notes above.
... ... *neutrinos: Neutrinos are fundamental particles with zero
charge, possibly zero mass, and an angular momentum factor (spin)
of 1/2. Various natural processes produce neutrinos: stellar
nuclear reactions, reactions occurring during supernova
explosions, cosmic ray collisions with matter, etc.
... ... *Standard Model: In particle physics, the Standard Model
is a theoretical framework whose basic idea is that all the
visible matter in the universe can be described in terms of the
elementary particles *leptons and quarks and the forces acting
between them.
... ... *leptons: A class of elementary particles. Although they
are affected by electromagnetic and gravitational forces, apart
from that they are involved only with weak interactions, acted
upon by weak forces but not by *strong forces, as opposed to
quarks, which are acted upon by strong forces but not by weak
forces. One further difference between leptons and quarks is that
leptons can be isolated as single particles, whereas quarks
apparently cannot. The leptons include the electron, the muon,
the tau, and their associated neutrinos. The mass of the tau is
approximately 3484 times the mass of the electron; the mass of
the muon is intermediate.
... ... *strong forces: According to the Standard Model, the
fundamental forces comprise the gravitational force, the
electromagnetic force, the nuclear strong force, and the nuclear
weak force. The strong force is approximately 100 times stronger
than the electromagnetic interaction and in general is the force
responsible for the stability of the atomic nucleus.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 21Jul00
For more information: http://scienceweek.com/swfr.htm

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7. IN BRIEF:
BOHR, HEISENBERG, AND COPENHAGEN -- AGAIN.
In the ScienceWeek issue of 19 May 2000 (4:20), we presented an
account of several responses to the new play _Copenhagen_ by
Michael Frayn, a theatrical work dealing with the September 1941
meeting of the physicists Niels Bohr and Werner Heisenberg in
Copenhagen, Denmark. Discussion of the play and the personalities
involved continues in various places, and now the journal Physics
Today presents 3 articles on the Copenhagen meeting, Niels Bohr,
and Werner Heisenberg. These articles offer further details and
should be noted by anyone interested in the subject.
----------
David C. Cassidy: A historical perspective on _Copenhagen_.
Hans A. Bethe: The German uranium project.
Gerald Holton: Werner Heisenberg and Albert Einstein.
-----
(Physics Today July 2000)
-------------------
SCIENCE-WEEK http://scienceweek.com 21Jul00

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8. IN FOCUS: ON CONDITIONED REFLEXES
"If food or some rejectable substance finds its way into the
mouth, a secretion of saliva is produced. The purpose of this
secretion is in the case of food to alter it chemically, in the
case of a rejectable substance to dilute and wash it out of the
mouth. This is an example of a reflex due to the physical and
chemical properties of a substance when it comes into contact
with the mucous membranes of the mouth and tongue. But, in
addition to this, a similar reflex secretion is evoked when these
substances are placed at a distance from the dog and the receptor
organs affected are only those of smell and sight. Even the
vessel from which the food has been given is sufficient to evoke
an alimentary reflex complete in all its details, and, further,
the secretion may be provoked even by the sight of the person who
brought the vessel, or by the sound of his footsteps. All these
innumerable stimuli falling upon the several finely
discriminating distance receptors lose their power forever as
soon as the [cerebral] hemispheres are taken from the animal, and
only those which have a direct effect on the mouth and tongue
still retain their power. The great advantage to the organism of
a capacity to react to the former stimuli is evident, for it is
in virtue of their action that food finding its way into the
mouth immediately encounters plenty of moistening saliva, and
rejectable substances, often nocuous to the mucous membrane, find
a layer of protective saliva already in the mouth, which rapidly
dilutes and washes them out. Even greater is their importance
when they evoke the motor component of the complex reflex of
nutrition, i.e., when they act as stimuli to the reflex of
seeking food."
-----------
I.P. Pavlov: _Conditioned Reflexes: An Investigation of the
Physiological Activity of the Cerebral Cortex_
(Foreign Languages Publishing House, Moscow 1924)
-----------
Ivan Petrovich Pavlov (1849-1936) received the Nobel Prize in
Physiology and Medicine in 1904 for his work on conditioned
reflexes. The classical Pavlovian reflex involves a previously
neutral stimulus (e.g., the sound of a bell) becoming a
"conditioned stimulus" when presented together with an
"unconditioned stimulus" (e.g., food). As an unconditioned
stimulus, food produces a reflex secretion of saliva. After
conditioning, the conditioned stimulus (e.g., the sound of the
bell) elicits the physiological response (e.g., secretion of
saliva) previously elicited only by the unconditioned stimulus.
The secretion of saliva following the sound of the bell is then
called a "conditioned reflex". A complete understanding of the
neural interconnections and dynamics of such a simple
experimental situation is still one of the central problems of
neurobiology.
-------------------
SCIENCE-WEEK http://scienceweek.com 21Jul00

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9. FROM THE SW ARCHIVE:
AN INTERESTING CASE OF ANT-PLANT MUTUALISM
In biology, symbiosis is an intimate and protracted association
of individuals of different species, and mutualism is a type of
symbiosis in which both participants receive benefits from the
association. An intriguing mutualism is that between ants and
Acacia trees. In East Africa, one finds Acacia trees that are
"ant-guarded": the ants live on the trees inside modified thorns
(pseudogalls), patrol the branches, and attack any insect or
vertebrate herbivore, thus protecting the plant, but also
preserving the plant for the use of the ant. But this plant
requires cross-pollination by visiting insects in order to
reproduce, and what one observes is that during the pollination
periods the ant-guards essentially remain in the guard-house and
cross-pollination by visiting insects proceeds without
difficulty. Which of course provokes the question of what are the
signals involved in this delicate bit of cooperative maneuvering?
This week P.G. Willmer and G.N. Stone (University of St. Andrews,
UK; Oxford University, UK) report that during the pollination
period, the young Acacia flowers apparently release a volatile
chemical that deters the ant-guards. The ants thus patrol before
and after pollination, but not during the pollination period
itself.
(Nature 10 July 97) (Science-Week 18 Jul 97)

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