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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.
February 23, 2001 -- Vol. 5 Number 8
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And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.
-- T.S. Eliot (1888-1965)
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Section 1
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Contents of this Issue (Full reports in Section 2):
1. PALEOENTOMOLOGY: A 90-MILLION-YEAR-OLD ANT FOSSIL
Given the near ubiquity of ants, particularly in regions either
inhabited by or familiar to humans, and their dramatic social
behavior, the ants have been an object of curiosity and study for
centuries. Discoveries of ants trapped and preserved in amber
have often yielded important clues to the evolution of this
fascinating group of insects. Researchers now report the
discovery of a worker ant preserved in amber for over 90 million
years, this fossil ant clearly assignable to a modern ant
subfamily that contains many familiar extant species. Combined
with other paleontological and phylogenetic information, this
unexpected fossil strongly indicates that the diversification of
many ant subfamilies occurred earlier and more rapidly than
previously suspected. It now appears that the ancestral ant
diverged during the Cretaceous period no earlier than 140 million
years ago, and more likely between 110 and 130 million years ago.
(Proc. Natl. Acad. Sci. US 19 Dec 00 97:14028)
2. NEUROBIOLOGY:
SPEECH-LIKE BRAIN ACTIVITY IN PROFOUNDLY DEAF PEOPLE
In a study using positron emission tomography with profoundly
deaf signers processing specific aspects of sign language,
researchers report observations of cerebral blood flow activity
in key brain sites widely assumed to be unimodal speech or sound
processing areas: the left inferior frontal cortex when signers
produced meaningful signs, and the planum temporale bilaterally
when the signers viewed signs or meaningless parts of signs
(sign-phonetic and syllabic units). Contrary to prevailing
wisdom, the planum temporale may not be exclusively dedicated to
processing speech sounds, but may be specialized for processing
more abstract properties essential to language that can engage
multiple modalities. The authors conclude that the human brain
can entertain multiple pathways for language expression and
reception, and that the cerebral specialization for language
functions is not exclusive to the mechanism for producing and
perceiving speech and sound.
(Proc. Natl. Acad. Sci. US 5 Dec 00 97:13961)
3. MEDICAL BIOLOGY:
ON CARCINOGENESIS IN NORMAL HUMAN MAMMARY EPITHELIAL CELLS
Cultured human fibroblasts undergo a limited number of cell
divisions before entering an irreversible arrest, called
"senescence". Researchers now report that human mammary
epithelial cells do not conform to this paradigm of senescence,
and that in contrast to fibroblasts, cultured human mammary
epithelial cells exhibit an initial growth phase that is followed
by a transient growth plateau, from which proliferative cells
emerge to undergo further population doublings (approximately 20
to 70) before entering a second growth plateau. The authors
report that the first growth plateau exhibits characteristics of
senescence but is not an insurmountable barrier to further
growth. Human mammary epithelial cells emerge from senescence,
exhibit eroding telomere nucleotide sequences, and ultimately
enter telomere-based crises to generate the types of chromosomal
abnormalities seen in the earliest lesions of breast cancer.
(Nature 1 Feb 01 409:633)
4. ASTROPHYSICS: NEW GIANT EXTRASOLAR PLANETS
An unusual extrasolar planetary system with massive planets has
been discovered. The star (HD168443) is located approximately 123
light-years away in the direction of the constellation Serpens.
Previous measurements (1999) indicated that HD168443 had at least
one planet. The latest data show that the original planet has a
mass of at least 7.5 Jupiter-masses, and an orbital period of 58
days, placing it closer to its star than Mercury is to our Sun.
The second object has an apparent mass of approximately 17
Jupiter-masses and orbits the star with a period of 4.8 years at
a distance of 3 astronomical units, corresponding to the distance
to the Sun of the asteroid belt in our Solar System. The larger
of the planets is massive enough to be called a brown dwarf star,
and there is currently no explanation of how such a planetary
system could be formed. (Science 25 Jan 01 409:462)
5. GEOCHEMISTRY: ON RIVER CARBON AND THE CARBON CYCLE
Dissolved organic carbon in the oceans is one of the largest
reservoirs in the global carbon cycle, this reservoir comparable
in size to all of the carbon in terrestrial plants, or to all of
the carbon in form of carbon dioxide in the atmosphere. Although
rivers are the main source of most organic constituents of sea
water, dating methods indicate that ocean organic carbon is
several thousand years old, rather than "fresh" organic carbon
expected from river supply. Now an analysis of organic materials
in four rivers that feed the Atlantic Ocean indicates that
organic carbon in these rivers is also up to several thousand
years old. This is in sharp contrast with the general belief that
most of the organic carbon in rivers should be relatively
"fresh". (Nature 25 Jan 01 409:466)
6. HISTORY OF PHYSICS:
MILLIKAN'S OIL DROPS, ELECTRON CHARGE, AND COOKED DATA
During the first decade of the 20th century, a race was on to
determine the exact magnitude of the charge of the electron. An
improved exact measurement of electron charge was made by Robert
A. Millikan (1868-1953) and his assistants in 1910-1912 using oil
droplets, for which Millikan received the Nobel Prize in Physics
in 1923. His reputation established, Millikan quickly became one
of the most important scientists in the US. Recently, however,
Millikan has been sharply criticized for effectively swindling a
graduate student, Harvey Fletcher, out of credit for the oil-drop
experiments, and even for "cooking" the data used in his
[Millikan's] classic paper reporting the experiments. A new
defense of Millikan is presented by a member of the physics
community. (American Scientist Jan/Feb 2001 89:54)
7. IN FOCUS: ON QUANTUM MECHANICS, REALITY, AND HIDDEN VARIABLES
8. FROM THE SCIENCEWEEK ARCHIVE:
MOLECULAR BIOLOGY: ON THE PHYLOGENY OF INNATE IMMUNITY
=-=-=-=-=-=-=-=-=
Section 2
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1. PALEOENTOMOLOGY: A 90-MILLION-YEAR-OLD ANT FOSSIL
The phylum of living arthropods contains 4 subphyla:
Chelicerata (which includes horseshoe crabs, scorpions, spiders,
ticks, mites, etc.); Crustacea (which includes crabs, lobsters,
shrimp, barnacles, etc.); Uniramia (which includes centipedes,
millipedes, etc.); insects (which includes flies, beetles, bugs,
bees, wasps, ants, locusts, etc.).
Insects (hexapods) have a body with a distinct head, thorax,
and abdomen. The head bears one pair of antennae and paired
mouthparts, the thorax bears 3 pairs of legs and frequently
either one or two pairs of wings, and the abdomen bears no legs
but other appendages may be present. Fossil insects have been
dated from the *Devonian period onward. 750,000 different insect
species have been recognized, and it is believed that at least
that many different species are still unrecognized.
Of the insects, the order Hymenoptera comprises the 3rd
largest group, with more than 110,000 species of ants, bees,
wasps, etc., such insects abundant in most habitats (except in
the polar regions), and particularly abundant in tropical and
subtropical regions. Collectively, the Hymenoptera are important
as pollinators of wild and cultivated flowering plants, as
parasites of destructive insects, and as producers of honey. The
Hymenoptera also includes the best known of the "social insects"
-- the ants, and some species of bees and wasps. Most species of
Hymenoptera, however, are solitary in habit.
In this context, the term "metamorphosis" refers to a
process in which an animal undergoes a relatively rapid change
from a pre-adult form (larval form) to an adult form. The process
is under hormonal control, and is most notable in the life
histories of the majority of insects and in the amphibia. In
general, however, insect and amphibian metamorphosis are
qualitatively quite different: whereas amphibian metamorphosis is
characterized by the remodeling of existing tissues, insect
metamorphosis often involves the destruction of larval tissues
and their replacement by an entirely different population of
cells. The Hymenoptera are characterized by 4 distinct and
completed stages of metamorphosis: egg, larva, pupa, adult. Sex
is determined by whether an egg is fertilized: unfertilized eggs
develop into males; fertilized eggs develop into females. It is
believed that the first Hympenoptera appeared approximately 150
to 225 million years ago.
In this context, the term "eusociality" refers to certain
"colonial" insects (e.g., ants) which exhibit cooperative brood
care, an overlap between generations, and reproductive castes.
The eusocial insects include various species of termites, bees,
ants, and wasps. (Termites are of the order Isoptera.)
In this context, the term "amber" refers to a fossil tree
resin that has achieved a stable state through loss of volatile
constituents and chemical change after burial in the ground. Once
solidified, amber is almost indestructible, and fossil organisms
trapped and preserved in amber have been of great importance in
paleontology. What is often preserved in amber is an entire
insect, its morphology intact in a transparent solid whose origin
may date more than 50 or 60 million years ago.
Given the near ubiquity of ants, particularly in regions
either inhabited by or familiar to humans, and their dramatic
social behavior, the ants have been an object of curiosity and
study for centuries. Discoveries of ants trapped and preserved in
amber have often yielded important clues to the evolution of this
fascinating group of insects.
... ... Ted R. Schultz (Smithsonian Institution, US) presents a
commentary on a recent discovery of a 90-million-year-old ant
preserved in amber (D. Grimaldi and D. Agosti: Proc. Natl. Acad.
Sci. US 5 Dec 00 97:13678), the author (Schultz) making the
following points:
1) The author points out that ants are arguably the greatest
success story in the history of terrestrial multicellular animals
(terrestrial metazoa). On average, ants monopolize 15 to 20
percent of the terrestrial animal biomass, and in tropical
regions, where ants are especially abundant, they monopolize 25
percent or more of the animal biomass. However, ants were not
always so successful. They do not appear in the fossil record
until the mid-Cretaceous period, and for more than the first half
of their apparent history -- i.e., for more than 60 to 80 million
years -- ants occupied a relatively modest position in the
terrestrial biosphere. An understanding of the factors, both
ecological and historical, that contributed to the rise of the
ants, requires a picture of the stepwise evolution of the major
ant lineages.
2) Ants represent the family Formicidae in the Insect order
Hymenoptera. All ants are eusocial, living in colonies in which a
wingless neuter daughter caste cooperates to raise subsequent
generations of their mother queen's offspring. Like all of its
descendants, the evolutionary ancestral ant was almost certainly
eusocial, with colonies consisting of small bands of "hunter-
gatherers" living in simple temporary nests in the soil. From
this modest beginning arose the current diversity of the family
Formicidae, now numbering over 9500 described species and an
estimated 3000 to 9000 additional species as yet unknown.
3) At present, ants occupy keystone positions in most
terrestrial environments, serving as major conduits of energy and
organic material. Ants, for example, are important turners of the
soil, matching or exceeding the activity of earthworms in this
role. Ants are among the leading predators of invertebrates in
most ecosystems, and in the *Neotropics they are the leading
herbivores as well, with leaf-cutter ants taking more than 15
percent of the fresh vegetation and feeding it to a *symbiotic
fungus, which the ants in turn eat. Interactions with ants have
shaped the evolution of diverse organisms to an astonishing
degree. Ants participate in symbioses (*facultative or obligate)
with over 465 plant species in over 52 families, with thousands
of arthropod species, and with as yet unknown numbers of fungi
and microorganisms. In addition, because of their complex colony-
level behaviors, ants serve as model organisms for the highly
visible disciplines of behavioral ecology and sociobiology,
particularly in studies focused on the dynamics of kin selection,
intra-colony conflicts of interest, caste differentiation, and
division of labor [*Note #1].
4) Grimaldi and Agosti (2000) now report the remarkable
discovery of a worker ant preserved in amber for over 90 million
years, this fossil ant clearly assignable to a modern ant
subfamily that contains many familiar extant species, including
*carpenter ants [*Note #2]. Combined with other paleontological
and phylogenetic information, this unexpected fossil strongly
indicates that the diversification of many ant subfamilies
occurred earlier and more rapidly than previously suspected. It
now appears that the ancestral ant diverged during the
*Cretaceous period no earlier than 140 million years ago, and
more likely between 110 and 130 million years ago.
-----------
Ted R. Schultz: In search of ant ancestors.
(Proc. Natl. Acad. Sci. US 19 Dec 00 97:14028)
QY: Ted R. Schultz: schultz@onyx.si.edu
-----------
Text Notes:
... ... *Devonian period: The term "Devonian" refers to the
time-frame 400 to 360 million years ago.
... ... *Neotropics: (Neogea) One of the biogeographical realms
into which the Earth is divided according to the distribution of
animal life (fauna). The Neotropic region includes South America,
the West Indies, and Central America from the Mexican plateau
south.
... ... *symbiotic: In biology, "symbiosis" is an intimate and
protracted association of individuals of different species
... ... *facultative or obligate [symbioses]: In this context,
the term "facultative" refers to the ability to live under varied
conditions: a facultative symbiosis is a symbiosis that is not
necessary for survival of either species. In contrast, an
"obligate symbiosis" is one which is necessary for one or both
species.
... ... *Note #1: Although the common conception is that an ant
"colony" has a single queen, the various ant species exhibit a
tremendous diversity of social organization. A supercolony of
ants in northern Japan contains an estimated 300 million
individuals, including a million queens, in 45,000 interconnected
nests spread over 2.7 square kilometers.
... ... *carpenter ants: In general, ants that gnaw galleries in
dead or decaying wood.
... ... *Note #2: The ant-containing amber reported by Grimaldi
and Agosti was discovered in the Raritan Formation in Sayreville,
Middlesex, New Jersey (US).
... ... *Cretaceous period: The approximate time-frame 146
million years ago to 65 million years ago.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 23Feb01
For more information: http://scienceweek.com/swfr.htm
-------------------
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 ) 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."
-----------
K.G. Ross and L. Keller: Genetic control of social organization
in an ant.
(Proc. Natl. Acad. Sci. US 24 Nov 98 95:14232)
QY: Kenneth G. Ross: kenross@arches.uga.edu
-----------
Text 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.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 15Jan99
For more information: http://scienceweek.com/swfr.htm
-------------------
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."
QY: Gene E. Robinson: Dept. of Entomology, Univ. of Illinois
Urbana-Champaign 217-333-3090.
(American Scientist Sep/Oct 1998 86:456)
(Science-Week 11 Sep 98)
-------------------
Related Background:
THE EVOLUTION OF AGRICULTURE IN ANTS
Fungus farming by ants of the tribe Attini apparently originated
in the early *Tertiary period and thus predates human agriculture
by approximately 50 million years. During its extensive
evolutionary history, this *symbiosis between "attine" ant
farmers and their fungal *cultivars has acquired an astonishing
complexity involving, among other things, secretion of antibiotic
"herbicides" to control weed molds and elaborate manuring regimes
that maximize fungal harvests. Of the over 200 known extant
attine ant species, all are *obligate fungus farmers. Cultivars
are propagated vegetatively as *clones within nests, and between
parent and offspring nests. In the few studied cases, the
foundress ant queen carries in her mouth a pellet of fungus from
the origin nest that she uses to start her own garden. This mode
of propagation has suggested the long-standing hypothesis that
the fungi of attine ants are ancient clones that have strictly
coevolved with their hosts. ... ... U.G. Mueller et al now report
an analysis of the evolutionary history of this ant-fungi
symbiosis as revealed in phylogenetic and population-genetic
patterns of 553 cultivars isolated from the gardens of relatively
primitive fungus-growing ants. The authors report these patterns
suggest that fungus-growing ants succeeded at domesticating
multiple cultivars, that the ants are capable of switching to
novel cultivars, that single ant species farm a diversity of
cultivars, and that cultivars are shared occasionally between
distantly related ant species, probably by lateral transfer
between ant colonies.
-----------
U.G. Mueller et al (3 authors at 3 installations, PA US)
The evolution of agriculture in ants.
(Science 25 Sep 98 281:2034)
QY: Ted R. Schultz: schultz@onyx.si.edu
-----------
Text Notes:
... ... *Tertiary period: A geological period comprising the
time-frame 70 million to 3 million years ago.
... ... *symbiosis: In biology, symbiosis is an intimate and
protracted association of individuals of different species.
Mutualism is a type of symbiosis in which both participants
receive benefits from the association.
... ... *cultivars: In general, a variety of plant produced by
selective breeding, i.e., a distinct subspecies that does not
occur naturally in the wild.
... ... *obligate: In this context, refers to an essentiality for
survival. Thus, "obligate fungus farmers" here denotes ants for
which fungus farming is essential for ant survival.
... ... *clones: In general, cloning is a reproduction of
individual organisms asexually, as in propagating a plant through
stem or leaf cuttings, or the production of a population of
organisms by successive replications from a single organism. A
"clone" is an organism or group of organisms so produced.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 30Oct98
For more information: http://scienceweek.com/swfr.htm
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2. NEUROBIOLOGY:
SPEECH-LIKE BRAIN ACTIVITY IN PROFOUNDLY DEAF PEOPLE
One of the most remarkable and important features of human
cognition is the ability to associate arbitrary symbols with
specific meanings in order to report thoughts and emotions -- the
production of "language". Studies of patients with damage to
specific regions of the *cerebral cortex have demonstrated that
the linguistic abilities of the human brain are located in
several specialized areas of the cortex in the temporal and
frontal lobes. In most people, these major language functions are
located in the left hemisphere. Despite this left-sided
predominance, the emotional (affective) content of language is
governed largely by the right hemisphere. In addition, the
cortical areas specialized for language may not be concerned
solely with words: studies of congenitally deaf individuals have
suggested that the brain areas devoted to signed language are the
same as those that organize spoken and heard communication. Such
regions are therefore apparently specialized for symbolic
representation and communication rather than for spoken language
as such. To date, however, no study has directly demonstrated
that the specific left hemisphere sites observed in the
processing of specific linguistic functions in speech are also
the same for signed language.
... ... L.A. Petitto et al (6 authors at McGill University, CA)
present a study of cerebral activity associated with the
processing of signed languages, the authors making the following
points:
1) The authors point out that the existence of naturally
evolved signed languages of deaf people provides a powerful
research opportunity to explore the underlying neural basis for
language organization in the human brain. Signed and spoken
languages possess identical levels of linguistic organization
(for example, phonology, morphology, syntax, semantics), but
signed languages use hands and vision, whose neural substrates
are distinct from the substrates associated with talking and
hearing. If the functional neuroanatomy of human spoken language
is determined exclusively by the production and perception of
speech and sound, then signed and spoken languages may exhibit
different patterns of cerebral organization.
2) Studies of profoundly deaf babies acquiring signed
languages have found that they babble with their hands with the
same phonetic and syllabic linguistic organization as hearing
babies babble vocally, and that profoundly deaf babies acquire
signed languages on the same maturational time table as hearing
babies acquire spoken languages. This suggests that common brain
mechanisms may govern the acquisition of signed and spoken
languages despite radical modality differences.
3) In a study using *positron emission tomography with
profoundly deaf signers processing specific aspects of sign
language, the authors report observations of cerebral blood flow
activity in key brain sites widely assumed to be unimodal speech
or sound processing areas: the left inferior frontal cortex when
signers produced meaningful signs, and the *planum temporale
bilaterally when the signers viewed signs or meaningless parts of
signs (sign-phonetic and syllabic units). Contrary to prevailing
wisdom, the planum temporale may not be exclusively dedicated to
processing speech sounds, but may be specialized for processing
more abstract properties essential to language that can engage
multiple modalities.
4) The authors hypothesize that the neural tissue involved
in language processing may not be prespecified exclusively by
sensory modality (such as sound), but may involve polymodal
neural tissue that has evolved unique sensitivity to aspects of
the patterning of natural language. Such neural specialization
for aspects of language patterning appears to be neurally
unmodifiable in so far as languages with radically different
sensory modalities such as speech and sign are processed at
similar brain sites, while at the same time, the neural pathways
for expressing and perceiving natural language appear to be
neurally highly modifiable.
5) The authors conclude: "What is certain... is that the
human brain can entertain multiple pathways for language
expression and reception, and that the cerebral specialization
for language functions is not exclusive to the mechanism for
producing and perceiving speech and sound."
-----------
L.A. Petitto et al: Speech-like cerebral activity in profoundly
deaf people processing signed languages: Implications for the
neural basis of human language.
(Proc. Natl. Acad. Sci. US 5 Dec 00 97:13961)
QY: Laura Ann Petitto: petitto@hebb.psych. mcgill.ca
-----------
Text Notes:
... ... *cerebral cortex: (cortex) The cerebral cortex is a thin
surface layering of nerve cells of the brain, the region only
several millimeters thick but covering all of the brain surface.
This is the part of the central nervous system most intimately
involved with the so-called "higher faculties", although the
cortex operates in concert with other parts of the brain. The
structure is primitive in lower mammals, and is found
progressively more pronounced and with greater surface area in
primates and man.
... ... *positron emission tomography: (PET) Positron emission
tomography is a technique for producing cross-sectional images of
the body after ingestion and systemic distribution of safely
metabolized positron-emitting agents. The images are essentially
functional or metabolic, since the ingested agents are
metabolized in various tissues. Fluoro-deoxyglucose and
H(sub2)O(sup15) are common agents used for cerebral applications,
and in cerebral applications of central importance to the
technique is the fact that changes in the cellular activity of
the brains of normal, awake humans and unanesthetized laboratory
animals are invariably accompanied by changes in local blood flow
and also changes in oxygen consumption.
... ... *planum temporale: A superior aspect of the temporal
lobe. In the 1960s, a region here was discovered to be
significantly larger on the left side in approximately two-thirds
of human subjects studied postmortem. A similar difference has
been described in higher apes but not in other primates.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 23Feb01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
LANGUAGE GRAMMAR PROPOSED TO HAVE EVOLVED BY NATURAL SELECTION
Language is considered a quintessentially human trait, and
attempts to shed light on the evolution of human language have
come from diverse areas including studies of primate social
behavior, the diversity of existing human languages, the
development of language in children, the genetic and anatomical
correlates of language competence, and theoretical studies of
cultural evolution, learning, and lexicon formation. One major
question is whether human language is a product of evolution or a
side-effect of a large and complex brain evolved for non-
linguistic purposes. M.A. Nowak and D.C. Krakauer (UK) now
provide an approach to language evolution based on evolutionary
game theory, the authors exploring the ways in which
protolanguage can evolve in a nonlinguistic society and how
specific signals can become associated with specific objects. The
authors argue that grammar originated as a simplified rule system
that evolved by natural selection to reduce mistakes in
communication, and they suggest their theory provides a
systematic approach for thinking about the origin and evolution
of human language. (Proc. Natl. Acad. Sci. US 6 Jul 99)
(ScienceWeek Bulletin 14 Jul 99)
-------------------
Related Background:
ON THE GESTURAL ORIGINS OF HUMAN LANGUAGE
A view currently held by many anthropologists and linguistics
researchers is that the remarkable flexibility of human language
is achieved at least in part through the human invention of
grammar, a recursive set of rules that allows the generation of
sentences of any desired complexity. The linguist Noam Chomsky
has attributed this to a unique human endowment termed "universal
grammar", with Chomsky suggesting that all human languages are
variants of this fundamental endowment.
... ... Michael C. Corballis (University of Auckland, NZ)
presents a review of current ideas concerning the origins of
human language, with emphasis on a scenario involving gestural
antecedents. The author makes the following points:
1) There is little doubt that the great apes (orang-utan,
gorilla, chimpanzee) (and perhaps other species such as dolphins)
can use symbols to represent actions and objects in the real
world, but these animals lack nearly all the other ingredients of
true language.
2) Since the common ancestor of human beings and chimpanzees
lived approximately 5 million years ago, it is a reasonable
inference that grammatical language must have evolved in the
hominid line (i.e., the line of human primates) at some point
following the split from the line that led to the modern
chimpanzee. There has been much disagreement as to when this
might have happened.
3) One major view holds that it is impossible to conceive of
grammar as having been formed incrementally; grammar therefore
must have evolved as a single catastrophic event, probably late
in hominid evolution. But many researchers hold a contrary view,
that language evolved gradually, shaped by natural selection, and
that the cognitive prerequisites of language are already present
in the great apes and antedated the split of our hominid
ancestors from the chimpanzee line, probably by several million
years.
4) The author suggests that at least a partial
reconciliation of these alternative perspectives may be that
language emerged not from vocalization, but from manual gestures,
and switched to a vocal mode relatively recently in hominid
evolution, perhaps with the emergence of Homo sapiens. This is an
old idea, apparently first suggested by Condillac in the 17th
century, but argument in its favor has continued to grow.
5) The author points out that there are countless different
sign languages invented by deaf people all over the world, and
there is little doubt that these are genuine languages with fully
developed grammars. The spontaneous emergence of sign languages
among deaf communities everywhere confirms that gestural
communication is as natural to the human condition as is spoken
language. Indeed, children exposed from an early age only to sign
language go through the same basic stages of acquisition as
children learning to speak, including a stage when they "babble"
silently in sign.
6) The authors proposes the following speculative scenario
concerning the historical development of human language:
... ... a) 6 or 7 million years ago: Simple gestures first
anticipated more complex forms of communication, shortly after
the human line diverged from the great apes. At this stage
vocalizations served only as emotional cries and alarm calls.
... ... b) Approximately 5 million years ago: With the advent of
bipedalism, a more sophisticated form of gesturing involving hand
signals may have evolved among the early hominids now labelled as
"Australopithecus".
... ... c) Approximately 2 million years ago: In association with
the increasing brain size of the genus Homo, hand gestures became
fully syntactic (i.e., with syntax; with ordered arrangements),
but vocalizations also became prominent.
... ... d) 100,000 years ago: Homo sapiens switched to speech as
its primary means of communication, with gestures now playing a
secondary role.
... ... e) Modern times: The development of telecommunication now
permits the routine use of spoken language in the complete
absence of hand gestures, but even so, many people find
themselves gesturing when they speak on the telephone.
7) Concerning the question of what it was that enabled our
species to prevail over other large-brained hominids, the author
concludes: "Perhaps the most plausible answer is that they
prevailed because of superior technology. But that technology
might have resulted, not from an increase in brain size or
intelligence, but from a switch from manual to vocal language
that allowed them to use their hands for the manufacture of tools
and weapons and their voices for instruction."
-----------
Michael C. Corballis: The gestural origins of language.
(American Scientist Mar-Apr 1999 87:138
QY: Michael C. Corballis: m.corballis@auckland.ac.nz
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 4Jun99
-------------------
Related Background:
HYPOGLOSSAL CANAL SIZE AND HOMINID SPEECH
The mammalian *hypoglossal canal transmits the *nerve that
supplies the *motor innervation to the tongue. Hypoglossal canal
size has been used to date the origin of human-like speech
capabilities to at least 400,000 years ago, and to assign modern
human vocal abilities to *Neandertals. These conclusions are
based on the hypothesis that the size of the hypoglossal canal is
indicative of speech capabilities.
... ... D. DeGusta et al (3 authors at 2 installations, US) now
present the results of a study to test the hypothesis that
hypoglossal canal size is indicative of speech. The authors
report they measured the following: a) the hypoglossal canals of
75 nonhuman primates and 104 modern humans; b) the hypoglossal
canal in specimens of the early *hominid *taxa *Australopithecus
afarensis and *Australopithecus boisei; c) both the nerve and
canal diameter and estimated nerve axon number in a sample of
human cadavers. The authors report the following results: a) Many
nonhuman primate specimens have hypoglossal canals that are
absolutely and relatively within the size range of modern humans.
b) The hypoglossal canals of Australopithecus afarensis,
Australopithecus boisei, and *Australopithecus africanus are also
within the modern human size range. c) The size of the
hypoglossal nerve and the number of axons it contains do not
appear to be significantly correlated with the size of the
hypoglossal canal. The authors conclude: "The size of the
hypoglossal canal is not a reliable indicator of speech.
Therefore the timing of the origin of human language and the
speech capabilities of Neandertals remain open questions." [*Note
#1].
-----------
Editor's note: The authors present this report essentially as a
refutation of a paper by R.F. Kay et al, a summary of which
appears in the background material below. Also, for more
generally related material, see the SW Focus Report
"Anthropology: Human Evolution" at URL
[http://scienceweek.com/swfr017.htm].
-----------
D. DeGusta et al: Hypoglossal canal size and hominid speech.
(Proc. Natl. Acad. Sci. US 16 Feb 99 96:1800)
QY: David DeGusta: degusta@uclink.berkeley.edu
-----------
Text Notes:
... ... *hypoglossal canal: This canal, at the level of the
brainstem, is a passageway through bone for the XII cranial
nerve, the nerve bundle that innervates the tongue.
... ... *nerve: In general, the term "nerve" refers to a bundle
of nerve axons (nerve fibers; neuron axons), the nerve usually
visible to the naked eye. Nerves can contain large number of
individual axons: the optic nerve in humans, for example,
contains approximately 1 million nerve fibers. The hypoglossal
nerve, the cranial nerve of relevance in this report, contains
mostly nerve axons whose cell bodies are in the hypoglossal
nucleus in the brainstem (efferent fibers carrying information to
activate the muscles of the tongue), and perhaps some axons
carrying information from sensory receptors in the tongue to the
central nervous system (afferent fibers).
... ... *motor innervation: This refers to the anatomical
connections of nerve fibers to muscle cells, the electrical
activity of the nerve axons resulting in the activation of the
muscle cells.
... ... *Neandertals: (Neanderthals) About 10 kilometers east of
Dusseldorf in Germany, in the valley of the Dussel, there is a
little town called Neander. One hundred and forty-one years ago,
in the summer of 1856, some workmen broke into a cave to get at
the limestone inside and discovered a set of ancient bones. Most
of the bones were smashed to bits by the workmen, but some of the
bones, including part of the skull, survived, and the skeleton
was soon recognized by anthropologists as belonging to an ancient
race of men who came to be known as the Neanderthals. A
Neanderthal fossil had actually been discovered some years
earlier in Gibraltar, but not recognized as such. Neanderthal-
like fossils have also been found in France, Spain, Italy,
Yugoslavia, Iraq, China, Java, and Israel. For more than a
century, one of the central questions in paleoanthropology has
been whether modern man evolved from this race.
... ... *hominid: The term "hominid" refers to any primate in the
human family (Hominidae) of which Homo sapiens (modern man) is
the only living specimen.
... ... *taxa: In general, a grouping defined in terms of shared
similar characters.
... ... *Australopithecus afarensis: The first record of human
footprints, of hominids walking upright, was discovered at
Laetoli in East Africa, and has been dated at 3.6 million years
ago. This ancestor, Australopithecus afarensis, probably weighed
25 to 50 kilograms (60 to 120 lbs.) as an adult.
... ... *Australopithecus boisei: Discovered by Mary Leakey in
the Olduvai Gorge in Tanzania, this fossil has been dated at 1.75
million years ago.
... ... *Australopithecus africanus: Apparently derived from
Australopithecus afarensis were several species, including
Australopithecus africanus, a species which is believed to have
appeared approximately 3 million years ago.
... ... *Note #1: Although the focus in this report is on the
role of the neural innervation of the tongue in human speech, it
must be emphasized that the organization of information and motor
output necessary for speech apparently occurs concomitantly in
several localized region of the cerebral cortex, and the
evolution of these regions of the brain most likely played a
significant role in the appearance of speech in humans.
Essentially, the hypoglossal nerve merely transmits information
originating in the brain, and both the origin and transmission of
this information must be considered in any analysis of the
evolution of human speech. Unfortunately, the brain is soft
tissue and is not preserved in fossils; what we have is bone, and
the data provided by bone and relevant archeological entities.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 16Apr99
-------------------
Related Background:
ORIGIN OF HUMAN VOCAL BEHAVIOR: AN ANATOMICAL CONSIDERATION
It can be argued that language is the most important behavioral
attribute that distinguishes humans from other animals, and one
of the important problems in anthropology and human evolution is
to demarcate as narrowly as possible the time frame during which
language in humans first appeared. Such demarcations have been
based on either apparent anatomical correlates (e.g., bone and
soft tissue analysis) or apparent archeological correlates (e.g.,
analysis of apparent symbolic behavior), with no firm specific
consensus among specialists. One of the important anatomical
features related to language is the nerve supply controlling the
muscles of the tongue. The mammalian hypoglossal canal is a bony
canal that contains the trunk of nerve fibers that constitute
this nerve supply. This canal is absolutely and relatively larger
in modern humans than it is in the African apes. ... ... Kay et
al (3 authors at Duke University, US) report a study of the
cross-sectional areas of hypoglossal canals in adult skulls of
contemporary humans, African apes, and several key fossil
hominids. They propose that hypoglossal canal size in fossil
hominids may provide an indication of the motor coordination of
the tongue and reflect the evolution of speech and language. What
they report is that the hypoglossal canals of gracile
Australopithecus, and possibly Homo habilis, fall within the
range of extant African apes, and are significantly smaller than
those of modern Homo. The canals of Neanderthals and an early
"modern" Homo sapiens (Skhul 5), as well as of African and
European middle Pleistocene Homo (Kabwe and Swanscombe), fall
within the range of contemporary Homo and are significantly
larger than those of Pan troglodytes (a chimpanzee species). In
summary, the authors suggest these anatomical findings indicate
the vocal capabilities of Neanderthals were the same as those of
humans today. The authors further suggest that the vocal
abilities of Australopithecus were not advanced significantly
over those of chimpanzees, whereas those of Homo may have been
essentially modern by at least 400,000 years ago, which is
consistent with the evidence for accelerated encephalization
rates in middle Pleistocene Homo. The authors conclude: "Thus,
human vocal abilities may have appeared much earlier in time than
the first archeological evidence for symbolic behavior."
QY: Richard F. Kay: Rich.Kay@baa.mc.duke.edu
(Proc. Natl. Acad. Sci. US 28 Apr 98 95:5417)
(Science-Week 19 Jun 98)
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
3. MEDICAL BIOLOGY:
ON CARCINOGENESIS IN NORMAL HUMAN MAMMARY EPITHELIAL CELLS
Breast cancer is a disease characterized by the growth of
malignant cells in the mammary glands, with women approximately
100 times more likely than men to develop the disease. Most
cancers in the female breasts occur shortly before, during, or
after menopause, with 75 percent of all cases diagnosed after age
50. At present, it is estimated that more than 10 percent of all
women in the US will develop breast cancer at some point in their
lives. The etiology of breast cancer is for the most part
unknown, but both environmental and genetic factors are
considered to be involved. A family history of breast cancer
increases the risk, and specific mutations (inherited or
acquired) in a number of genes have been linked to the disease.
Prolonged exposure to the hormone estrogen evidently favors the
disease.
Somatic cells are all cells other than germline cells such
as egg cells and sperm cells, and the term "cellular replicative
senescence" refers to the observation that somatic cells, in
contrast to germline cells, can proliferate (divide) only a fixed
number of times, the actual number dependent on the organism from
which the somatic cells derive. In this report, the term
"senescence" refers to cellular replicative senescence.
"Telomeres" are regions at the ends of chromosomes, the
regions consisting of repeats of particular nucleotide sequences,
and with each somatic cell division a small part of the telomere
is ordinarily lost. What has been observed is that in germline
cells the lengths of telomeres are maintained constant by repair,
while in somatic cells this repair does not occur, and this
difference has led to the idea that the finite proliferative
capacity of somatic cells is related to the ultimate depletion of
telomere lengths. Another apparent consequence of telomere
reduction or damage is an increased incidence of chromosome
abnormalities in dividing cells, such aberrations expected to
result in specific genome aberrations.
"Fibroblasts" are a type of connective tissue cell,
secreting structural proteins such as collagen, the proteins
forming a matrix in which the fibroblasts become embedded. These
cells can be easily obtained from various tissues, and they can
be easily cultured outside the body.
In animals, "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. Epithelial cells also form
the inner linings of glandular ducts.
In general, the term "mesenchymal tissue" refers to
connective tissue. Fibroblasts are standard components of
mesenchymal tissue.
"Isogenic cells" are cells of the same organ of the same
individual. In this report, isogenic human breast epithelial
cells and human breast fibroblasts were obtained from disease-
free patients undergoing breast reduction (reduction
mammoplasty).
... ... S.R. Romanov et al (6 authors at 2 installations, US)
present a report on senescence of cultured mammary cells, the
authors making the following points:
1) The authors point out that cultured human fibroblasts
undergo a limited number of cell divisions before entering an
irreversible arrest, called "senescence". The authors report that
human mammary epithelial cells do not conform to this paradigm of
senescence, and that in contrast to fibroblasts, cultured human
mammary epithelial cells exhibit an initial growth phase that is
followed by a transient growth plateau (termed "selection"), from
which proliferative cells emerge to undergo further population
doublings (approximately 20 to 70) before entering a second
growth plateau (previously termed "senescence"). The authors
report that the first growth plateau exhibits characteristics of
senescence but is not an insurmountable barrier to further
growth. Human mammary epithelial cells emerge from senescence,
exhibit eroding telomere nucleotide sequences, and ultimately
enter telomere-based crises to generate the types of chromosomal
abnormalities seen in the earliest lesions of breast cancer.
2) The authors suggest their experiments have several
important implications:
... ... a) These results challenge traditional views of how and
when cells acquire genomic changes in cancer, the data providing
a cell-intrinsic mechanism that early in the neoplastic process
generates several simultaneous genetic changes without obligatory
exposure to physical, viral, or chemical mutagenic agents.
... ... b) Although post-selection-phase human mammary epithelial
cells have commonly been regarded as normal, the observations of
the authors refute this assumption. These cells do not express
the *regulatory protein p16, they lack proper *checkpoint
control, and they do not maintain genomic integrity.
... ... c) The authors suggest their findings redefine a high-
frequency spontaneous event that occurs in human mammary
epithelial cells, the findings demonstrating that the first
replicative plateau ("selection") is actually senescence. Human
mammary epithelial cells spontaneously emerge from senescence,
whereas isogenic fibroblasts do not. Should these epithelial
cells arise in vivo (a proposal consistent with preliminary
observations), they would provide generative material for human
carcinogenesis. Therefore, the observation of the authors that
human mammary epithelial cell proliferation beyond senescence
leads to telomeric dysfunction, coupled with previous reported
observations that telomeric dysfunction leads to carcinogenesis
in mice, might explain the early steps in carcinogenesis.
3) The authors conclude: "Given that irreversible senescence
and tight control of genomic stability are believed to be
important barriers for the development of cancerous lesions, our
observations also suggest that there is a much higher risk of
neoplastic transformation originating in mammary epithelial
tissue than in mesenchymal tissue, a prediction consistent with
extensive epidemiological studies."
-----------
S.R. Romanov et al: Normal human mammary epithelial cells
spontaneously escape senescence and acquire genomic changes.
(Nature 1 Feb 01 409:633)
QY: Thea D. Tlsty: ttlsty@itsa.ucsf.edu
-----------
Text Notes:
... ... *regulatory protein p16: The protein p16 inhibits cyclin-
dependent kinases and is evidently inactivated in many different
tumors. In general, a "kinase" is any enzyme involved in
the transfer of a phosphate group. The cyclins are a group of
proteins involved in the regulation of cell-division.
... ... *checkpoint control: Studies have identified genes that
sense damaged DNA and cause the arrest of the cell cycle, which
allows time for the molecular defect to be repaired. These genes
operate at several specific "checkpoints" in the cell cycle as a
means of ensuring genomic integrity before DNA is synthesized.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 23Feb01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
CELL BIOLOGY: TELOMERES AND THE FATE OF BIOLOGICAL CELLS
A major distinction between bacteria (prokaryotes) and
higher organisms consisting of cells with a nucleus (eukaryotes)
is the arrangement of the genome: in general, genomes are
circular in prokaryotes, whereas in eukaryotes genomes are
collections of linear molecules called "chromosomes". Although a
linear architecture has its benefits, it also presents certain
specific problems. For example, the free ends of DNA molecules
are unstable: they degrade chemically and undergo recombination
much more often than their circular counterparts. Another problem
is that DNA polymerase, the enzyme responsible for replicating
the nuclear genome during cell proliferation, has difficulty
copying the very ends of DNA molecules, so that without special
precautions the end molecular sequences of DNA tend to be lost in
the copies. To solve this problem, eukaryotic cells cap their
chromosomes at both ends with specialized structures (specific
DNA sequences) called "telomeres". Since telomeres are not
replicated by DNA polymerase, and since because of the nature of
the replication process telomeres will shorten at each cell
division, an enzyme called "telomerase" exists to maintain the
telomeres. Telomerase adds telomere sequences onto each
chromosome at each cell division.
Most mammalian non-germ cell tissues (somatic tissues) lack
telomerase, so it has been proposed that telomere shortening
could be a "clock" that eventually stops cells from further
divisions. When, for example, human *fibroblasts are cultured,
they can divide only a certain number of times, their telomeres
shortening with each division. But if these cells are made to
express telomerase, they can continue dividing indefinitely.
There is no correlation, however, between telomere length
and the life span of an animal (e.g., humans have much shorter
telomeres than mice), nor is there a correlation between human
telomere length and the age of an individual. Telomerase-
deficient mice do not show profound aging defects. But studies of
normal human and nonhuman cells that are naturally immortal
(e.g., germ cells) have demonstrated that the telomeres of such
cells appear to be stable with time. There is thus the suggestion
that telomerase activity is generally absent in normal mortal
cells, which as a consequence experience replicative telomere
shortening, while telomerase activity in immortal cells exists.
In addition, telomerase activity is also generally found in
cancer cells.
... ... Elizabeth H. Blackburn (University of California San
Francisco, US) now presents a new model of telomere function, the
author making the following points:
1) The author points out that recent work in several
biological systems has revealed a more complex relationship than
previously realized between telomere length and cell
proliferative capacity. The author proposes a new way to link
telomeres to cellular senescence, with the central concept that
the telomere is a dynamic nucleoprotein complex that can switch
stochastically between two states: capped and uncapped. "Capping"
is functionally defined as preserving the physical integrity of
the telomere, allowing cell division to proceed. But regulated
"uncapping" occurs normally in dividing cells, with the crucial
property that a functional telomere then has a high probability
that it will switch back to a capped state. Left uncorrected too
long, the uncapped state elicits *cell-cycle arrest or other
responses. The author states: "Crucially, this probabilistic
model identifies telomere capping status, as opposed to telomere
length alone, as the important property relevant to telomere
function." [Editor's note: "telomere capping" should be
distinguished from "chromosome capping": chromosome capping
involves capping of the ends of the chromosome by telomeres;
telomere capping involves capping of the telomere by an apparent
protein capping complex.]
2) The author suggests that quantitative examinations, on a
cell by cell basis, of normal human and mouse somatic cells in
culture have demonstrated that these cells exist in two states:
a) cells that are in the cell-cycle; and b) cells that have
exited the cell-cycle. Even from the very beginning of *tissue
culture passaging, cells are stochastically dropping out of the
cycling population. They do so with ever-increasing frequency
until the population as a whole ceases to double. Notably, even
late in the passaging, any cells still in the cycling state are
cycling as fast as those early in the passaging. Thus, the only
difference between early and late passages is the frequency of
cycling versus non-cycling cells; those cycling cells that are
"old" by virtue of their passage number are not significantly
different from the cycling cells early in the passaging.
3) The author concludes: "Increasingly, investigations into
a variety of biological processes point to the view that
stochastic stabilization of one of two functionally different
physical states can underlie many seemingly deterministic
phenomena in biology. The stochastic behavior of telomeres and
cells provide another example of this."
-----------
Elizabeth H. Blackburn: Telomere states and cell fates.
(Nature 2 Nov 00 408:53)
QY: Elizabeth H. Blackburn: telomer@itsa.ucsf.edu
-----------
Text Notes:
... ... *fibroblasts: See main report.
... ... *cell-cycle arrest: In this context, the term "cell
cycle" refers to the entire life history of a single cell from
mitosis to mitosis, including the sequence of intervening phases
(stages).
... ... *tissue culture passaging: In this context, the term
"passage" refers to a replication of cells in culture, with each
passage referring to a single replication.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 19Jan01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
TELOMERASE ACTIVITY AND IMMORTAL CELLS
Tumors arise as the end product of a multistep process involving
successive rounds of mutation, selection, and *clonal expansion.
One obstacle to the completion of tumor development may be the
limited number of replication cycles apparently allowed normal
human cells. In vitro, normal human cells exhibit a limited
replicative potential, eventually succumbing to "senescence".
Premalignant cell populations evolving in vivo may exhaust this
apparent allotment of doublings before the population progresses
to a malignancy, and when that happens such progression to a
malignancy will only occur if the "replication clock" is
disrupted by the cells acquiring replicative immortality.
Telomeres are defined ends of chromosomes that contain specific
repeated DNA sequences. They are apparently essential for normal
chromosome replication, and since their length shortens a bit
with each replication, they are believed to be involved in the
aging of the cell. Telomerase is an enzyme that repairs damage to
telomeres, and it is thought by some that cancerous cells may
have mutant telomerase, the mutant enzyme conferring immortality
on the cancer cell. In addition to cell "senescence", there is a
phenomenon called "crisis" (proliferative crisis), which
essentially involves the following: Certain viral or biochemical
interventions in human cell cultures can overcome cell
senescence, typically by causing 20 to 30 extra population
doublings, but at the end of this extended lifespan, there is a
decline and death of the culture in 4 to 6 weeks, which has been
termed "crisis" (proliferative crisis). Cell culture crisis has
been proposed to be the result of telomeric shortening.
... ... C.M. Counter et al (8 authors at 4 installations, US CA)
now report that ectopic expression (i.e., "abnormal" expression)
of the telomerase catalytic subunit (human telomerase *reverse
transcriptase) and subsequent activation of telomerase can allow
post-senescent cells to proliferate beyond crisis. The authors
also report that alteration of the *carboxyl terminus of human
telomerase reverse transcriptase does not affect telomerase
enzymatic activity but does impede the ability of this enzyme to
maintain telomeres, and cells expressing this mutant enzyme fail
to undergo immortalization. The authors state: "Our results
formally demonstrate that acquisition of human telomerase reverse
transcriptase expression is sufficient to immortalize human cells
and [thus our results] validate the role of telomerase in
rescuing cells from crisis."
-----------
C.M. Counter et al: Dissociation among in vitro telomerase
activity, telomere maintenance, and cellular immortalization.
(Proc. Natl. Acad. Sci. US 8 Dec 98 95:14723)
QY: Robert A. Weinberg: weinberg@wi.mit.edu
-----------
Text Notes:
... ... *clonal expansion: In this context, the term "clonal
expansion" refers to the replicative production of a population
of cells from a single originating parent cell.
... ... *reverse transcriptase: Transcription is the process by
which genetic information in DNA is converted into RNA, and
*reverse transcription, involving the enzyme reverse
transcriptase, is the synthesis of complementary DNA from an RNA
template. (Note: The terminological convention in biochemistry is
to identify an enzyme by use of the suffix "-ase")
... ... *carboxyl terminus: In general, since all proteins (and
all enzymes are proteins) are linear polymers consisting of amino
acid subunits connected by peptide bonds, one terminus of the
linear polymer is a carboxyl residue and the other terminus is an
amino residue.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 29Jan99
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
4. ASTROPHYSICS: NEW GIANT EXTRASOLAR PLANETS
In 1995, astronomers reported the first tentative evidence
of planets orbiting stars outside our Solar System, and since
then astronomers have detected perturbations in the motions of
dozens of nearby stars, these perturbations presumably due to the
gravity of planets. Currently, the identification and study of
extrasolar planets depends for the most part on indirect methods
such as those involving the measurement of perturbations of the
observed brightness or motions of their parent stars.
One emerging problem is the classification of a number of
giant extrasolar planets: Are they planets or brown dwarf stars?
Brown dwarf stars are formed by the contraction of a lump of gas
with a mass too small for nuclear reactions to begin in the core.
Such a star has a relatively short-lived luminosity
(approximately 100 million years) as the result of conversion of
gravitational energy to radiation. The surface temperature of a
brown dwarf is below 2500 degrees kelvin. As recently as 1994,
brown dwarfs were "theoretical" stars, with no brown dwarfs
considered to be unambiguously identified; at present, a number
of stars have been recognized as brown dwarfs. In addition to the
problem of classifying apparently supermassive extrasolar giant
planets, there is the even more important problem of explaining
their origin (see related background material below).
... ... Alan P. Bass (Carnegie Institution of Washington, US)
presents a commentary on new evidence reported at a recent
meeting (American Astronomical Society San Diego, US 7-11 January
2001) by Geoff Marcy (University of California Berkeley, US) and
Paul Butler (Carnegie Institution of Washington, US). Bass makes
the following points:
1) Marcy and Butler have discovered approximately two-thirds
of the 50-plus extrasolar planets known to date. The newest
objects are in orbit around a Sun-like star known as HD168443,
the star located approximately 123 light-years away in the
direction of the constellation Serpens. Previous measurements
(1999) indicated that HD168443 had at least one planet. The
latest data show that the original planet has a mass of at least
7.5 Jupiter-masses, and an orbital period of 58 days, placing it
closer to its star than Mercury is to our Sun (approximately 0.3
astronomical units). The second object has an apparent mass of
approximately 17 Jupiter-masses and orbits the star with a period
of 4.8 years at a distance of 3 astronomical units, corresponding
to the distance to the Sun of the asteroid belt in our Solar
System. Both objects have non-circular (eccentric) orbits, as do
nearly all the known extrasolar planets orbiting at these
distances.
2) Bass points out that HD168443 and its two giant planets
form a 3-body system with the larger of the planets massive
enough to be called a brown dwarf star. "Beyond simple
classification, there is the looming question of how a system
like HD168443 might be created." Bass concludes: "Theorists have
their work cut out to explain HD168443's unexpected companions.
The planet hunters, meanwhile, are discovering bizarre solar
systems at an alarming rate."
-----------
Alan P. Bass: Giant giants or dwarf dwarfs?
(Science 25 Jan 01 409:462)
QY: Alan P. Bass: bass@dtm.ciw.edu
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 23Feb01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ASTROPHYSICS: ON EXTRASOLAR PLANETS
... The ideal method would be direct imaging of extrasolar
planets, and this would considerably enhance the possibilities
for understanding their nature. A major problem in direct imaging
of extrasolar planets is that the bright light from the parent
star (more particularly, its diffracted halo in the imaging
apparatus) can easily overwhelm nearby faint light sources such
as orbiting planets.
... ... J.J. Lissauer et al (3 authors at 3 installations, US JP)
present a review of current research on extrasolar planets, the
authors making the following points:
1) The authors point out that more than two dozen extrasolar
planets have been detected during the 1990s by observations of
the wobble that results from their gravitational tugs on the
stars to which they are bound. These extrasolar planets
demonstrate the large diversity of planetary systems, and current
research aims at detecting an even greater variety of extrasolar
planetary systems, and also aims at systematically explaining the
origins of extrasolar planets and the origin of our Solar System.
2) Several research groups have successfully pursued an
indirect method of detecting extrasolar planets, the method
making use of Newton's Second Law, i.e., "for every action, there
is an equal and opposite reaction." Thus, it is stellar wobble
that betrays the existence of an invisible orbiting planet. The
greater the wobble, the more massive the planet, and the time to
complete one wobble cycle is the orbital period of the planet.
The Doppler effect has been used to detect these small stellar
movements: As a star travels toward the observer, the light waves
are shortened toward the blue; conversely, as a star moves away
from Earth, the wavelengths are lengthened toward the red. These
Doppler shifts are extremely small. In our Solar System, the Sun
wobbles by only 12.5 meters per second because of the presence of
Jupiter; Saturn induces variations of 2.7 meters per second on a
longer time scale, and the effect of other planets is
substantially less. A reliable detection of this wobble requires
precision of 3 meters per second, which is equivalent to
detecting changes in the wavelengths of starlight by 1 part in
10^(8). The periodic wobble of a star, analyzed with Newton's
laws, provides the planet's orbital period, the orbital distance,
and the mass of the planet multiplied by the unknown parameter
sin(i), where (i) is the inclination of the planet's orbital
plane to the line of sight.
3) After a century of hopeful but dubious claims, evidence
for planets around other stars finally appears robust. Surveys of
normal stars indicate that 5 percent of such stars harbor
planetary companions having masses 0.5 to 8 times that of
Jupiter, and orbital periods of a few years or less. Within that
mass range, low-mass planets are more common. To date, 28
extrasolar planet candidates are known. Their orbits are either
very small or quite elliptical, both properties being different
from those of planets within our Solar System.
4) The authors conclude: "Extrapolating from the small and
biased sample of planets that have been detected to a model of
the variety of planetary systems that may be present elsewhere in
the Galaxy is a daunting challenge surely fraught with pitfalls.
Detailed predictions are almost certain to be erroneous. However,
the substantial progress made over the past few decades toward
understanding the origins and dynamical stability of planetary
systems makes it possible to assess hypothesized common
attributes and scaling relations of planetary systems in a
quantitative manner."
-----------
J.J. Lissauer et al: Extrasolar planets.
(Proc. Natl. Acad. Sci. US 7 Nov 00 97:12405)
QY: J.J. Lissauer: lissauer@ringside.arc.nasa.gov
-------------------
Summary by SCIENCE-WEEK http://scienceweek.com 15Dec00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
... ... A.C. Cameron et al (4 authors at 2 installations, UK) now
report detection and measurement of starlight reflected from an
extrasolar planet, the authors making the following points:
1) In the 4 years following the discovery (by M. Mayor and
D. Queloz [1995]) of a planet orbiting the star 51 Pegasi,
approximately 20 other planets have been detected through their
influence on the radial velocities of lines in the spectra of
their parent stars. The orbital motion of the planet can be
detected by perturbations of the motion of the parent star
("reflex motion"), and these perturbations can be measured using
high-precision spectroscopy. This indirect technique cannot
investigate the radius or composition of the planet, and can
place only a lower limit on the mass of the planet.
2) The authors report the probable detection of *Doppler-
shifted starlight reflected from the planet known to orbit tau-
Bootis with a period of just 3.3 days. The authors find that the
*orbital inclination of the planet is approximately 29 degrees,
from which the authors infer that the mass is approximately 8
times that of Jupiter, and that the planet has the size and
reflectivity expected for a "*gas-giant planet".
3) The authors point out that if this is indeed a giant
planet, with a Jupiter size and *albedo, the scattered starlight
will be 10,000 to 20,000 times fainter than the parent star even
under the most favorable planet-illumination conditions.
4) The authors conclude: "Our candidate detection of
starlight scattered from the atmosphere of an extrasolar planet
strengthens the case for the existence of the giant, close-
orbiting planets whose presence has so far been inferred only
indirectly from the reflex motions of their parent stars... The
close-orbiting planets of other systems, including both 51 Pegasi
and the nu-Andromedae triple-planet system, should be amenable to
similar studies in the near future."
-----------
A.C. Cameron: Probable detection of starlight reflected from the
giant planet orbiting tau-Bootis.
(Nature 16 Dec 99 402:751)
QY: Andrew Collier Cameron: andrew.cameron@st-and.ac.uk
-----------
Text Notes:
... ... *Doppler-shifted starlight: In general, the term "Doppler
shift" refers to the change in wavelength of electromagnetic
radiation as a result of relative movement between the source and
the observer.
... ... *orbital inclination: In general, the angle between the
orbital plane of a body and a reference plane centered on the
object about which the body is revolving. In this context, the
orbital inclination of the planet is not directly measured, but
is implied by a "best-fitting" orbital velocity.
... ... *gas-giant planet: In general, a planet of much larger
mass and diameter than the Earth, and which consists mostly of
gas. In our own Solar System, Jupiter, Saturn, Uranus, and
Neptune are gas-giant planets.
... ... *albedo: In this context, the fraction of total starlight
falling on a planet that is reflected from it. In general, the
albedo is equal to the amount of light reflected divided by the
amount of light received.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Feb00
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
GIANT PLANETS VS. BROWN DWARFS
Filipe D. Santos (Centro de Fisica da Universidade de Lisboa, PT)
presents a short review of current ideas concerning giant
extrasolar planets and *brown dwarf stars. The author makes the
following points: 1) The recent discoveries of planets orbiting
nearby Sun-like stars have revealed that planetary systems can be
surprisingly diverse. The initial discovery in 1995 of the planet
around the star 51 Pegasi was a surprise because it is apparently
a planet with mass about that of Jupiter (at least 0.44 Jupiter-
mass) and an orbital period of only 4.2 days, which implies that
the planet is 20 times closer to its star than Earth is to the
sun. 2) Seven additional planets around solar-type stars have
since been discovered, with Jupiter-mass values ranging from 0.44
to 6.84. 3) Two critical questions are, a) Where should we set
the dividing line that distinguishes massive planets from brown
dwarfs? and, b) What are the mechanisms leading to the formation
of massive planets and brown dwarfs? 4) Brown dwarfs are expected
to have masses smaller than the hydrogen-burning limit of
approximately 0.075 solar-mass (approximately 75 Jupiter-mass),
but probably larger than the deuterium-burning limit of 0.013
solar-mass (approximately 13 Jupiter-mass). 5) Like the companion
massive planets mentioned, several companion brown dwarfs to
solar-type stars have also been identified. One method of
investigating brown dwarfs involves *astrometric measurements,
and in all cases of brown dwarfs investigated by the astrometric
method, the masses are above or very close to the hydrogen-
burning limit. The extant data thus suggest that the distribution
of mass of brown dwarfs does not extend to masses as small as
giant planets. Also, the new measurements indicate that brown
dwarfs orbiting solar-type stars are very rare. 6) The discovery
of Jupiter-mass planets with orbits very close to their stars
poses a considerable problem, because it is difficult to
understand how such planets could form in place. (Five known
Jupiter-mass planets have orbital radii smaller than the distance
from Mercury to the Sun.) The suggestion has been made that these
planets formed at larger distances and migrated inward, but the
proposed migration mechanisms are not yet empirically
distinguishable. The author concludes: "Clearly the discovery of
planetary systems outside our solar system has opened a Pandora's
box of startling phenomena and new questions."
QY: Filipe D. Santos: fdsantos@milkyway.cii.fc.ul.pt
(Science 17 Jul 98 281:359) (ScienceWeek 31 Jul 98)
-------------------
Related Background:
... ... *brown dwarf stars: See main report.
... ... *astrometric measurements: This method of detection
infers the presence of a companion to a star by measuring the
position of the star as it orbits the center of mass of the
entire system. From the orbital inclination, the real mass of the
companion can be derived.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 31Jul98
For more information: http://scienceweek.com/swfr.htm
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
5. GEOCHEMISTRY: ON RIVER CARBON AND THE CARBON CYCLE
In its most general outline, the term "carbon cycle", in
geochemistry and Earth science, refers to the movement of carbon
from an atmospheric inorganic state to a biospheric organic state
and then back to an atmospheric inorganic state. In detail, there
are several pathways from biospheric organic carbon to
atmospheric inorganic carbon, one of which, of great importance,
is the movement of organic carbon into the hydrosphere,
principally via rivers that empty into oceans, with oceanic
dissolved organic carbon a reservoir for movement of organic
carbon to an atmospheric inorganic state. Concerning the transfer
of dissolved organic carbon from rivers to oceans, there are
puzzles that have not yet been solved.
... ... Wolfgang Ludwig (University of Perpignon, FR) presents a
commentary on new data concerning river carbon (P.A. Raymond and
J.E. Bauer: Nature 25 Jan 01 409:497), the author (Ludwig) making
the following points:
1) The author points out that dissolved organic carbon in
the oceans is one of the largest reservoirs in the global carbon
cycle, this reservoir comparable in size to all of the carbon in
terrestrial plants, or to all of the carbon in form of carbon
dioxide in the atmosphere. The input of terrestrial organic
carbon from rivers, the main source of most constituents of sea
water, could fill the oceanic reservoir in only a few thousand
years, which (according to radiocarbon dating) is apparently the
average age of oceanic organic carbon. But although there ought
to be a great amount of terrestrial-derived organic carbon in the
oceans, geochemical studies indicate there is apparently very
little, and the fate of river-transported carbon ("riverine
carbon") once it enters the oceans is unclear.
2) Almost all of the organic carbon on Earth is created via
photosynthesis, whether on land or in water, but on land the
process produces characteristic markers, so that terrestrial
carbon should be traceable after it has entered the oceans. For
example, many land plants synthesize certain compounds, such as
*lignin or *tannin, which are absent in marine *phytoplankton. In
principle, therefore, detecting these biomarkers in the oceans
can reveal if carbon had a terrestrial origin. The other widely
used method involves measuring the ratio between the two stable
carbon isotopes, C-13 and C-12, in the bulk organic matter. Most
land plants produce carbon that is more depleted in C-13 than
carbon produced by marine phytoplankton, which results in higher
isotopic ratios in marine than in terrestrial carbon.
3) Raymond and Bauer (2001) now present an analysis of
organic materials in four rivers (Amazon [BR], Hudson [New York,
US], (York [Virginia, US], Parker [Massachusetts, US] by
radiocarbon dating (carbon-14, carbon-13 measurements), and they
report the organic carbon in these rivers is up to several
thousand years old [*Note #1]. This is in sharp contrast with the
general belief that most of the organic carbon in rivers should
be relatively "fresh". The particulate organic carbon (i.e., the
fraction retained on a filter) was especially old (C-14-
depleted). From these results, and laboratory evidence that
suggests selective degradation of young (C-14-rich) dissolved
organic carbon over the residence times of river and coastal
waters, Raymond and Bauer conclude that pre-aging and degradation
may alter significantly the structure, distribution, and
quantities of terrestrial organic matter before its delivery to
the oceans. The implication is that the absence of riverine
carbon in the oceans is only apparent and due to the fact that we
have not been able to distinguish riverine carbon from marine-
generated carbon.
-----------
Wolfgang Ludwig: The age of river carbon.
(Nature 25 Jan 01 409:466)
QY: Wolfgang Ludwig: ludwig@univ-perp.fr
-----------
Text Notes:
... ... *Note #1: Carbon-14 dating depends on the decay of
carbon-14 to nitrogen. Carbon-14 is continually formed in nature
by the interaction of neutrons with nitrogen-14 in the Earth's
atmosphere, the required neutrons produced by cosmic rays
interacting with the atmosphere. The carbon-14 from this reaction
is converted to carbon dioxide by reaction with atmospheric
oxygen and mixed and uniformly distributed with the atmospheric
carbon dioxide containing stable carbon-12. Since living
organisms use atmospheric carbon dioxide either directly or
indirectly, their systems contain the constant ratio of carbon-12
to carbon-14 that exists in the atmosphere. Death of an organism
terminates the equilibrium process: no fresh carbon dioxide is
added to the dead substance, and the carbon-14 present in the
dead substance decays with a half-life of 5730 years, while
carbon-12 in the dead substance remains what it was at death.
Measurement of the carbon-14 activity at a given time thus allows
calculation of the time elapsed after the death of the organism.
... ... *lignin: A complex organic polymer and major component of
wood.
... ... *tannin: A complex astringent substance occurring widely
in plants, particularly in leaves, unripe fruits, and tree bark.
... ... *phytoplankton: Small, usually microscopic, aquatic
plants capable of photosynthesis; e.g., unicellular algae.
Phytoplankton and plankton are not equivalent. The term
"plankton" is a general designation for various drifting
microscopic aquatic organisms in the upper regions of the oceans,
both photosynthetic and non-photosynthetic.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 23Feb01
For more information: http://scienceweek.com/swfr.htm
-------------------
Related Background:
ON THE CHEMISTRY AND BIOLOGY OF THE OCEANS
The combination of vast areas of liquid water on its surface
together with a high concentration of free molecular oxygen in
its atmosphere is unique to Earth in this solar system.
Calculations based on *ultraviolet absorption cross sections
indicate that whereas direct photolysis of water could have
produced small amounts of O(sub2), almost all of the gas was
produced by biological systems through the photobiologically
catalyzed oxidation of the liquid. ... ... Falkowski et al (3
authors at 3 installations, US DE) review the controls and
feedbacks between oceanic *phytoplankton and geochemical
processes with an emphasis on factors that cause a deviation from
the steady state. The authors make the following points: 1)
Changes in oceanic primary production, linked to changes in the
network of global biogeochemical cycles, have profoundly
influenced the geochemistry of Earth for over 3 billion years. 2)
In the contemporary ocean, photosynthetic *carbon fixation by
marine phytoplankton leads to the formation of approximately 45
gigatons of organic carbon per year, of which 16 gigatons are
exported to the ocean interior. 3) Changes in the magnitude of
total and export production can strongly influence atmospheric
CO(sub2) levels (and hence climate) on geological time scales, as
well as set upper bounds for sustainable fisheries harvest. 4)
Because the average turnover time of phytoplankton carbon in the
ocean is on the order of a week or less, total and export
production are extremely sensitive to external forcing, and
consequently are seldom in steady state. 5) Elucidating the
biogeochemical controls and feedbacks on primary production is
essential to understanding how oceanic biota responded to and
affected natural climate variability in the geological past, and
to understanding how oceanic biota will respond in the coming
decades to changes influenced by human activities.
QY: Paul G. Falkowski
(Science 10 Jul 98 281:200) (Science-Week 31 Jul 98)
-------------------
Related Background:
... ... *ultraviolet absorption cross sections: The ratios of the
amount of energy removed from incident UV by absorption to the
total energy of incident UV. In other words, in this context, a
measure of how much energy is (was) actually available for direct
photolysis of liquid water.
... ... *phytoplankton: See main report.
... ... *carbon fixation: Refers to the process of converting the
carbon in a substance into a form usable by an organism. For
example, the conversion of the carbon in CO(sub2) into organic
carbon (the carbon in organic compounds).
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 31Jul98
For more information: http://scienceweek.com/swfr.htm
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6. HISTORY OF PHYSICS:
MILLIKAN'S OIL DROPS, ELECTRON CHARGE, AND COOKED DATA
Joseph John Thomson (1856-1940) is often credited by the
media with discovering the electron, but evidence that cathode
rays consist of negatively charged particles was first
demonstrated by William Crookes (1832-1919), and Jean-Baptiste
Perrin (1870-1942), and others, who showed the rays could be
deflected by a magnetic field and charge a body upon which they
fell. The problem was that no one could deflect the rays with an
electric field, and if the rays consisted of negatively charged
particles, that should certainly occur. Thomson's contribution,
which he made in 1897 and which was indeed essential, was to
demonstrate that under the proper experimental conditions of
lower gas pressure, cathode rays can also be deflected by an
applied electric field. Photographs of Thomson usually show him
in his middle age, but he was all of 28 when he succeeded Lord
Rayleigh as professor and head of the Cambridge Cavendish
Laboratory, and 31 years old when he confirmed the demonstration
of the existence of the electron in 1897 and calculated its
approximate mass.
What was known exactly was the ratio of charge to mass of
the electron, and it was thus important to determine the
magnitude of the charge carried by the "corpuscles" (only later
called "electrons"). John S. Townsend (1868-1957), one of
Thomson's research students, was assigned the task of determining
the charge. Townsend used clouds of ionized water vapor: By
observing the rate of fall of the cloud and applying *Stokes' law
for the free fall of spheres through a viscous medium, Townsend
was able to determine the size of the droplets; from a
measurement of the total amount of water in the cloud, he then
calculated the number of droplets contained in the cloud; having
also measured the total charge on the cloud, he was able to
calculate the charge on a single ion as 3 x 10^(-10)
electrostatic units (esu). A later measurement by Thomson
produced the value 6.5 x 10^(-10) esu. (The present established
value is 4.803 x 10^(-10) esu or 1.602 x 10^(-19) coulombs.)
The inexactness of the water-cloud method was due primarily
to evaporation of the water droplets during the experiment (which
changed their volumes), and a more exact measurement of electron
charge was made by Robert A. Millikan (1868-1953) and his
assistants in 1910-1912 using oil droplets, for which Millikan
received the Nobel Prize in Physics in 1923. Millikan reported
4.774 x 10^(-10) esu as the value of the electron charge. One
problem with the analysis of the oil-drop experimental data, a
problem well-recognized by Millikan, is that Stokes' law requires
a continuous medium, and the oil droplets in the experiment are
small enough so that an assumption of a continuous medium is not
completely justified. Millikan arbitrarily added a correction
term to the Stokes' equation and devoted great effort to
estimating the magnitude of this correction.
Millikan obtained his PhD at Columbia University in 1895,
and was on the faculty of the University of Chicago from 1896 to
1921, and at the California Institute of Technology from 1921 to
1945. At Caltech, Millikan had much responsibility for university
policy, and many consider him the "patron saint" of the
California Institute of Technology.
Recently, however, Millikan has been sharply criticized for
effectively swindling a graduate student, Harvey Fletcher, out of
credit for the oil-drop experiments, and even for "cooking" the
data used in his [Millikan's] classic paper reporting the
experiments.
... ... David Goodstein (California Institute of Technology, US)
presents an essay in defense of Robert A. Millikan, the author
(Goodstein) making the following points:
1) At about 1910, Millikan assigned a new graduate student,
Harvey Fletcher (?-1982), the task of devising a way to use
mercury or glycerin or oil, instead of water, in droplet
experiments to establish the charge of the electron. Fletcher
immediately set up a crude apparatus involving minute droplets of
watch oil, the droplets created by an ordinary perfume atomizer.
Through the eyepiece, Brownian motion caused by the impacts of
unseen air molecules on the oil droplets could be observed and
measured. Within a few years, Fletcher and Millikan, working with
this basic apparatus, had an accurate value of the electron
charge and a determination of the product (N)(e), where (N) is
Avogadro's number and (e) is the electron charge, the product
derived from the observations of Brownian motion. Thus, two
separate research papers from this work were possible. The
academic rules of that time allowed Fletcher to use a published
paper as his PhD thesis, but only if he were the sole author.
Evidently, Millikan, who was then 40 years old and had not yet
made a mark in physics, approached Fletcher with a "deal":
Fletcher would be sole author on the Brownian motion paper (which
was less important), and Millikan would be sole author on the
electron-charge paper. Goodstein states: "No doubt Millikan
understood that the measurement of [electron charge] would
establish his reputation, and he wanted full credit. Fletcher
understood this too, and he was somewhat disappointed, but
Millikan had been his protector and champion throughout his
graduate career, so he had little choice but to accept." This
manipulation by Millikan first became widely known only in the
early 1980s.
2) Concerning mishandling of data by Millikan, the view is
widespread that Millikan "cooked" the data (i.e., retained only
those results that fit his conclusions and discarded other
results) for his important 1913 paper amplifying the electron-
charge measurements with the oil-drop technique. It was
essentially this paper that led directly to the Nobel Prize.
Goodstein states: "He published the results of measurements on
just 58 drops, whereas the notebooks reveal that he studied some
175 drops... And to make matters worse, he lied about it.
Millikan's 1913 paper contains the following explicit assertion:
'It is to be remarked, too, that this is not a selected group of
drops, but represents all the drops experimented upon during 60
consecutive days. during which time the apparatus was taken down
several times and set up anew." But having made a detailed
examination of Millikan's notebooks and the published 1913 paper,
Goodstein concludes that, albeit not explicitly, Millikan
implicitly indicates in the 1913 paper that measurements on only
58 drops were presented because measurements on 117 drops were
considered incomplete, the drops too small (too subject to
Brownian motion) or too large (falling too rapidly for velocity
to be measured), etc. Goodstein states: "What scientist familiar
with the vagaries of cutting-edge experimental work would fault
Millikan for picking out what he considered to be his most
dependable measurements in order to arrive at the most accurate
possible result?"
[EDITOR'S NOTE: Admitting the "vagaries of cutting-edge
experimental work", and admitting that in this case the final
numerical results would probably _not_ have changed had all the
measurements been included, we still strongly disagree with the
assessment by Goodstein. We believe that what Millikan should
have done was publish _all_ his data, then explicitly discuss in
his paper the reasons for discarding data on 117 out of 175
drops. What Millikan did instead was essentially conceal his
selection of only 58 drops by using ambiguous language, and thus
he truly "cooked" the data for publication.]
3) Goodstein concludes: "Like anyone, [Millikan] had his
strengths and his flaws. He wasn't generous enough to put his
student's interests ahead of his own at a critical point in his
career. In describing the results of his oil-drop experiment, he
let himself get carried away a bit in demonstrating the
correctness of his empirical correction to Stokes' law... But
Robert Andrews Millikan was not a villain. And he certainly did
not commit scientific fraud in his seminal work on the charge of
the electron."
-----------
David Goodstein: In defense of Robert Andrews Millikan.
(American Scientist Jan/Feb 2001 89:54)
QY: dg@caltech.edu
-----------
Text Notes:
... ... *Stokes' law: This law, discovered by George Stokes
(1819-1903), predicts the frictional force (F) on a spherical
ball moving through a viscous medium, with F given by 6ărnv,
where (r) is the radius of the ball, (n) is the viscosity of the
medium, and (v) is the velocity of the ball. For a falling ball,
the force (F) equals the gravitational force on the sphere, less
any upthrust.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 23Feb01
For more information: http://scienceweek.com/swfr.htm
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7. IN FOCUS: ON QUANTUM MECHANICS, REALITY, AND HIDDEN VARIABLES
"The formalism of the quantum theory leads to results that agree
with experiment with great accuracy and covers an extremely wide
range of phenomena. As yet there are no experimental indications
of any domain in which it might break down. Nevertheless, there
still remain a number of basic questions concerning its
fundamental significance which are obscure and confused... All
that is clear about the quantum theory is that it contains an
algorithm for computing the probabilities of experimental
results. But it gives no physical account of individual quantum
processes. Indeed, without the measuring instruments in which the
predicted results appear, the equations of the quantum theory
would be just pure mathematics that would have no physical
meaning at all. And thus quantum theory merely gives us
(generally statistical) knowledge of how our instruments will
function. And from this we can make inferences that contribute to
our knowledge, for example, of how to carry out various technical
processes. That is to say, it seems, as indeed Bohr and
Heisenberg have implied, that quantum theory is concerned only
with our _knowledge_ of reality and especially of how to predict
and control the behavior of this reality, at least as far as this
may be possible. Or to put it in more philosophical terms, it may
be said that quantum theory is primarily directed towards
_epistemology_, which is the study that focuses on the question
of how we obtain our knowledge (and possibly on what we can do
with it). It follows from this that quantum mechanics can say
little or nothing about reality itself. In philosophical
terminology, it does not give what can be called an _ontology_
for a quantum system."
-----------
D. Bohm and B.J. Hiley: _The Undivided Universe: An ontological
interpretation of quantum theory_
(Routledge, London 1993, p.1)
-----------
[Editor's note: US-born physicist David Bohm (1917-1992) worked
on the development of the atomic bomb under J. Robert Oppenheimer
(1904-1967). Bohm joined the Princeton University physics faculty
in 1947, and shortly afterward ran into political difficulties
when he was called to testify before the House Un-American
Activities Committee, pleaded the Fifth Amendment and refused to
give evidence against his colleagues. He was cited for contempt
and threatened with prison. When his Princeton contract expired
in 1951, Bohm found himself unemployable in the US, and on the
advice of Oppenheimer, Bohm left the US. He worked at Sao Paulo
University (BR) (1951-1955) and Haifa University (IL) (1955-
1957). He then settled in the UK, and in 1961 he was appointed
Professor of Theoretical Physics at Burbeck College London, where
he served until his retirement in 1983. In 1959, Bohm and his
student Yakir Aharanov discovered the Aharanov-Bohm effect, in
which the motions of charged particles can be affected by
magnetic fields even if the particles never enter the regions in
which those fields are confined. Throughout his career, Bohm was
concerned with the foundations of quantum theory, and he is best
known as one of the proponents of "hidden variable theory". Many
physicists, including Einstein (1879-1955), did not and have not
accepted the basic indeterminacy of particle behavior postulated
by quantum mechanics. In quantum mechanics, for example,
considering radioactive decay, quantum theory proposes that
although one nucleus decays and another does not, the two nuclei
were previously in an identical state: the decay is a completely
random process, and which nucleus decays is indeterminate.
Einstein, Bohm, de Broglie (1892-1987), and others rejected the
idea that such nuclei were initially in an identical state, and
instead postulated the existence of some other property,
presently unknown, that differs for the two nuclei. This type of
unknown property is termed a "hidden variable". If such variables
existed, they would return determinacy to physics.]
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8. FROM THE SCIENCEWEEK ARCHIVE:
MOLECULAR BIOLOGY: ON THE PHYLOGENY OF INNATE IMMUNITY
All biological organisms are subject to invasive attack by
microbial pathogens, and the survivability of biological
organisms depends on the activation of various protective
mechanisms (immune responses) when a microbial invasion occurs.
In biology, the "immunity" of organisms to infection by various
pathogens is functionally characterized into 2 types: The term
"innate immunity" refers to non-specific antimicrobial systems of
response (e.g., phagocytosis: engulfment and digestion of
microbes by "killer" cells) that are innate and not intrinsically
affected by prior contact with the infectious agent; the term
"adaptive immunity" refers to immune responses which involve an
enhanced ability to respond to specific molecular *antigens
presented by the invading pathogenic entity, the enhancement
dependent on prior contact with the same pathogen. In addition,
the concept of innate immunity generally refers to the first-line
host defense that serves to limit infection in the early hours
after exposure to microorganisms. Recent data have highlighted
similarities between pathogen recognition, signaling pathways,
and *effector mechanisms of innate immunity in both the fruit fly
Drosophila and in mammals, pointing to a common ancestry of these
defenses. In addition to its role in the early phase of defense,
innate immunity in mammals appears to play a key role in
stimulating the subsequent *clonal response of adaptive immunity.
... ... J.A. Hoffmann et al (4 authors at 4 installations, FR DE
US) present an extensive review of innate immunity in Drosophila,
the essential characteristics of mammalian innate immunity, and
the links between innate and adaptive immunity. The authors make
the following points:
1) The fruit fly Drosophila is particularly resistant to
microbial infections, and 3 mechanisms contribute to this
resistance: a) phagocytosis of invading microorganisms by blood
cells; b) *proteolytic cascades leading to localized blood
clotting, *melanin formation, and *opsonization; c) transient
synthesis of potent antimicrobial peptides. These reactions all
take place within a short period after pathogenic injury.
2) Drosophila is capable of discriminating between classes
of invading microorganisms, for instance, between bacteria and
fungi, and of responding by preferentially producing peptides
that target destruction of the recognized pathogen.
3) A key feature of innate immunity in mammals is the
ability to rapidly limit the infectious challenge. This is based
on the capacity to discriminate species self from infectious
nonself. Microbes display molecular arrays or patterns that are
apparently recognized by pattern recognition molecules or
receptors, and these patterns are evidently shared among groups
of pathogens, e.g.: lipopolysaccharides of *gram-negative
bacteria; lipotechoic acids of *gram-positive bacteria; mannans
of *yeast; double-stranded RNA of viruses. To limit infection,
the mammalian host uses a wide variety of pattern recognition
molecules, including *complement, *collectins, and a battery of
antimicrobial peptides that act together with effector cells to
combat the infectious challenge.
4) The adaptive immune system apparently appeared
approximately 450 million years ago when a *transposon that
carried the forerunners of certain *recombinase-activating genes
was inserted into the germ-line of early jawed vertebrates. The
ability to mount an adaptive immune response allowed organisms to
"remember" the pathogens they had already encountered, and
natural selection made the adaptive immune response a virtually
universal characteristic of vertebrates. But the innate immune
system was not discarded, and indeed the innate immune system has
been coopted in vertebrates to serve a second function, that of
stimulating and orienting the primary adaptive immune response by
controlling the expression of "*costimulatory molecules".
5) Concerning innate immunity, it is a provocative thought
that innate immunity in both plants and animals may have evolved
from common ancestral modules that have been used to protect
against infection for more than 1 billion years of evolution.
-----------
J.A. Hoffmann et al: Phylogenetic perspectives in innate
immunity.
(Science 21 May 99 284: 1313)
QY: Jules A. Hoffmann [jhoff@ibmc.u-strasbg.fr]
-----------
Text Notes:
... ... *antigens: In general, any chemical entity that activates
an immune response, especially an entity originating outside the
body. Antibodies are specific proteins synthesized by the immune
system which interact with specific antigens.
... ... *effector mechanisms: In this context, an "effector
mechanism" is any process which is part of the response of the
biological system to microbial invasion.
... ... *clonal response: In this context, the term "clonal
response" refers to an immune system effector mechanism involving
proliferation of a single line of cells producing a single
antibody to a single specific antigen.
... ... *proteolytic cascades: In general, "proteolysis" is the
enzyme-catalyzed degradation of protein by hydrolysis of one or
more peptide bonds. A "proteolytic cascade" is a sequence of
proteolytic reactions involving a series of enzymes, with each
reaction serving to activate the next reaction in the sequence.
... ... *melanin: A dark brown pigment product of tyrosine
metabolism, usually bound to proteins.
... ... *opsonization: (opsonification) Opsonin is a blood
protein that when combined with microorganisms or other
particulate matter renders them more susceptible to phagocytosis.
The term "opsonization" refers to the coating of microorganisms
or other particulate matter with opsonin.
... ... *gram-negative/gram positive bacteria: Most bacteria can
be classified into two types, depending on the chemistry of their
outer coat, which chemistry determines whether a bacterium will
admit certain dyes into the interior. The classification,
according to the differential staining technique, is
gram-negative vs. gram-positive, named after the bacteriologist
H.C. Gram (1853-1938). Gram-positive bacteria take up a crystal
violet stain and turn purple, while gram-negative bacteria
exclude the crystal violet and counterstain instead with stains
such as safranin, eosin red, or brilliant green. As might be
expected, since the technique differentiates the outer coats of
bacteria, some antibiotics are effective against one type and not
the other type, and vice versa.
... ... *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.)
... ... *collectins: A family of plasma lectins (a group of
antibody-like proteins which agglutinate cells and particulates).
... ... *transposon: A transposon is a limited DNA sequence that
under the proper dynamic conditions can effectively translocate
from one DNA system to another, either in the same cell, or
between cells, or between cells of different organisms of the
same or different species, and remain functional.
... ... *recombinase: In general, an enzyme that plays a specific
role in recombining DNA sequences into genes that encode for
antibodies.
... ... *costimulatory molecules: An alternative name for the
interleukins, a heterogeneous group of *cytokines that act as
signaling molecules between different populations of immune
system white blood cells (leukocytes).
... ... *cytokines: A cytokine is any substance that promotes
cell growth and cell division. As a promoter of cell growth and
division, a cytokine acts as a messenger to cells, and the
transmission of the message requires a binding of the cytokine
molecule to a cytokine-specific receptor on the cell surface.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 23Jul99
For more information: http://scienceweek.com/swfr.htm
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