ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

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

July 9, 1999 -- Vol. 3 Number 28

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One must show the greatest respect towards any thing
that increases exponentially, no matter how small.
-- Garrett Hardin

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Contents of This Issue:

1. Science, Evolution, and Contemporary America
2. Computer Science: Alan Turing
3. Carbon Nanotubes as Molecular Quantum Wires
4. Neurobiology: Complexity and the Nervous System 
5. Anthropology: Defining the Human Genus
6. Medical Biology: Pathogenesis of UV Induction of Melanomas

In Focus: On Function and Teleology in Biology

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1. SCIENCE, EVOLUTION, AND CONTEMPORARY AMERICA
Despite a flurry of media bugle blowing during the past several
years, a flurry purporting to demonstrate that religion and
science in the US are "merging", the reality is perhaps that any
such merging is a myth. A large and politically influential group
of Americans continues to refuse acceptance of the facts of
biological evolution on Earth provided by science, even if they
do accept, implicitly at least, the medical care, communication
systems, transportation systems, defense systems, etc. of the
technology produced by that same science. It is apparently not
yet understood that if biological and human evolution is denied,
all of science must be denied and the human species returns to
darkness -- to ignorance, hardship, and the decimation of infants
and children by disease. Stephen Jay Gould, paleobiologist and
current President of the American Association for the Advancement
of Science, confronts the issue in a recent editorial in the
journal _Science_, the author making the following points:
     1) The author poses the question: "What strange set of
historical circumstances, what odd disconnect between science and
society, can explain the paradox that organic evolution -- the
central operating concept of an entire discipline and one of the
firmest facts ever validated by science -- remains such a focus
of controversy, even of widespread disbelief, in contemporary
America?"
     2) Concerning the conflict, the author states: "Denigration
and disrespect will never win the minds (not to mention the
hearts) of these people. But the right combination of education
and humility might extend a hand of fellowship and eventually end
the embarrassing paradox of a technological nation entering a new
millennium with nearly half its people actively denying the
greatest biological discovery ever made."
     3) The author suggests three principles "to guide our
pastoral efforts": a) Evolution is true, and the truth can only
make us free. b) Evolution liberates the human spirit. c) For
sheer excitement, evolution, as an empirical reality, "beats any
myth of human origins by light-years. A genealogical nexus
stretching back nearly 4 billion years and now ranging from
bacteria in rocks several miles under the Earth's surface to the
tip of the highest redwood tree, to human footprints on the Moon.
Can any tale of Zeus or Wotan top this?"
     4) The author concludes: "Let us praise this evolutionary
nexus -- a far more stately mansion for the human soul than any
pretty or parochial comfort ever conjured by our swollen
neurology to obscure the source of our physical being, or to deny
the natural substrate for our separate and complementary
spiritual quest."
-----------
Stephen Jay Gould: Darwin's more stately mansion.
(Science 25 Jun 99 284:2087)
QY: Stephen Jay Gould, Dept. of Zoology, Harvard University 617-
495-1000.
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 9Jul99


2. COMPUTER SCIENCE: ALAN TURING
In 1936, the mathematician Alan M. Turing (1912-1954) proposed
consideration of an abstract computer that subsequently came to
be known as a "Turing machine". Essentially, the simplest Turing
machine system consists of a movable input tape, a black box (the
Turing machine) that reads the tape according to an internal
algorithm, and an output tape that records the output of the
black box. The machine originally considered by Turing was a bit
more complex, with a single input/output tape demarcated into
discrete small sections, and the machine capable of being in any
one of a set of states (determined by the algorithm or "Rule
Set") according to which section of the tape the machine happened
to be reading, and the output capable of moving the tape backward
or forward. As a mathematician, Turing's interest was to
determine the universe of problems capable of being solved by
such a machine, and his ideas have been of considerable influence
in both mathematical and engineering theories of computing
machines. Turing was also interested in several biological
problems, and to a number of mathematically inclined
biologists the Turing machine in its simplest form has been for
many decades an intriguing model for certain computational
processes in the nervous system. More recently, in molecular
biology, the Turing machine has been recognized as an analog of
the behavior of nucleic acid polymerases such as DNA polymerase
and RNA polymerase (enzymes which catalyze the formation of
nucleic acid polymers), which sequentially synthesize an output
polymer (output tape) according to the sequential reading of the
individual units of an input polymer (input tape). Also of
interest to neural systems researchers has been a little-known
paper by Turing on learning behavior of artificial neural
networks not published until 14 years after his death.
... ... B.J. Copeland and D. Proudfoot (University of Canterbury,
NZ) present a biographical essay on Alan Turing, the authors
making the following points:
     1) All current digital computers are essentially Turing
machines. Turing also pioneered the field of artificial
intelligence, proposing the widely debated "*Turing test" as a
method of determining whether a suitably programmed computer
exhibits "intelligence" (i.e., can "think"). During World War II,
as part of a British intelligence unit, Turing was instrumental
in breaking the German "Enigma" code, a feat that has been said
to have shortened the war by two years. At the end of his short
life, Turing was engaged in the earliest work on what would now
be called "artificial life", his research involving simulation of
the chemistry of biological growth.
     2) Throughout his career, Turing had no great interest in
publicizing his ideas, and as a consequence important aspects of
his work have been neglected or forgotten over the years. In
particular, few people are familiar with Turing's anticipation of
"connectionism" or neuron-like computing. Also neglected are his
groundbreaking theoretical concepts in the area of
"hypercomputation", a field devoted to the computational solution
of apparently intractable problems.
-----------
B.J. Copeland and D. Proudfoot: Alan Turing's forgotten ideas in
computer science.
(Scientific American April 1999)
B.J. Copeland, Dept. of Philosophy, University of Canterbury, NZ.
-----------
Text Notes:
... ... *Turing test: The Turing test is essentially a protocol
for distinguishing between real (human) thought and simulated
(computer) thought. A classic statement of the Turing test is as
follows: One room contains a person and another room contains a
machine. An interrogator in a third room asks questions of both
in an attempt to identify them. When the interrogator cannot
distinguish between them by questioning, the machine can be said
to possess human-like intelligence. [Editor's note: There are
aspects of the test as thus stated which are ill-defined. For
example, there is no operational definition of "intelligence".
Secondly, in terms of procedure, the test is perhaps more useful
when amended as follows: If a determined questioner can find no
question that can enable absolute identification of the machine,
then it can be concluded that, in the frame of reference of the
questioner, the analytical processes of the machine are at least
qualitatively equivalent to the analytical processes of the
human.]
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 9Jul99
-------------------
Related Background:
ON COMPUTING WITH DNA
... ... Leonard M. Adleman (University of Southern California,
US) presents an essay on a computing ensemble involving DNA, the
ensemble based on the author's recognition of the Turing machine
as an analog of DNA polymerase, and the ensemble applied to the
solution of a mathematical problem known as the "Hamiltonian Path
Problem". As a mathematician and computer scientist, Adleman's
objective is the demonstration that his DNA ensemble can perform
as a powerful computer and solve a posed mathematical problem.
The author considers the following as the tools of a potential
DNA computing system: *Watson-Crick pairing, *polymerases,
*ligases, *nucleases, *gel electrophoresis, DNA synthesis, and
the *polymerase chain reaction. The author presents the
Hamiltonian Path Problem as follows: Given a graph with directed
edges and a specified start vertex and end vertex, one says there
is a Hamiltonian path if and only if there is a path that starts
at the start vertex, ends at the end vertex, and passes through
each remaining vertex exactly once. The Hamiltonian Path Problem
is to decide for any given graph with specified start and end
vertices whether a Hamiltonian path exists or not. The specific
problem chosen by the author involves a 7-vertex graph. Each
vertex is identified by a specific assigned sequence of nucleic
acid bases, and using the repertoire of biochemical tools
indicated above (and an added auxiliary separation technique),
the author demonstrates that this particular problem is easily
solved. Considering molecular computers, the author points out
their advantages: 1) The possibility of extremely dense
information storage. "For example, one gram of DNA, which when
dry would occupy a volume of approximately one cubic centimeter,
can store as much information as approximately 10^(9) CDs." 2)
The possibility for enormous parallelism. In the author's
problem, approximately 10^(14) connection paths were
simultaneously concatenated in about 1 second. 3) Extraordinary
energy efficiency. In principle, 1 joule is sufficient for
approximately 2 x 10^(19) DNA ligation operations. The author
suggests that his experiment "can be viewed as a manifestation of
an emerging new area of science made possible by our rapidly
developing ability to control the molecular world."
QY: Leonard M. Adleman, Univ. of Southern California 213-740-2311
(Scientific American August 1998) (Science-Week 31 Jul 98)
-------------------
Related Background:
... ... *Watson-Crick pairing: Also known as complementary base
pairing. This refers to the specific chemical affinities between
specific base pairs in a nucleic acid: adenine always pairs with
thymine, and guanine always pairs with cytosine. In pairing
between DNA and RNA, the uracil of RNA always pairs with adenine.
Complementary base pairing is not only responsible for the DNA
double helix, but it is also essential for various in vitro
techniques such as PCR (*polymerase chain reaction).
... ... *polymerases: Refers to any enzyme that directs the
synthesis of a polymer by linking individual monomers. Examples
in biological systems are DNA polymerase and RNA polymerase.
... ... *ligases: Ligases are enzymes that catalyze the stitching
together of polymer fragments. DNA ligase, for example, catalyzes
phosphodiester bond formation between two DNA fragments, and this
enzyme is involved in normal DNA replication, repair of damaged
chromosomes, and various in vitro techniques in genetic
engineering that involve linking DNA fragments.
... ... *nucleases: Refers to any enzyme that acts on nucleic
acids, e.g., DNase, RNase, endonuclease, etc.
... ... *gel electrophoresis: In general, electrophoresis is a
laboratory technique used to separate macromolecules on the basis
of electric charge and size, the technique involving application
of an electric field to a population of macromolecules dispersing
according to their electric mobilities. In gel electrophoresis,
the porous medium through which the macromolecules move is a gel.
... ... *polymerase chain reaction (PCR): A technique for
isolating and amplifying any specifically desired DNA sequence.
The reaction is facilitated by a heat-stable DNA polymerase
(e.g., Taq, which is obtained from a thermophilic bacterium) that
can withstand the many cycles of heating and cooling involved in
the technique. PCR is considered by many molecular biologists to
be the most important technical advance in molecular biology in
the second half of the 20th century. The inventor of the
technique, Kary Mullis, received the Nobel Prize in Chemistry in
1993 for his discovery. 
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 31Jul98


3. CARBON NANOTUBES AS MOLECULAR QUANTUM WIRES
Fullerenes are large molecules composed entirely of carbon, with
the chemical formula C(n), where n is any even number from 32 to
over 100. They apparently have the structure of a hollow
spheroidal cage with a surface network of carbon atoms connected
in hexagonal and pentagonal rings. Carbon nanotubes are similar
to fullerenes, except their shape is tubular. They were first
discovered by Sumio Iijima (NEC Laboratories, JP) in 1991, they
come in both multi-wall and single-wall versions, and they
have diameters of the order of 10 to 30 nanometers. There have
been rapid developments in understanding the chemistry and
physics of carbon nanotubes, and there is much excitement in both
the chemistry and physics communities concerning possible
applications of these unique structures. ... ... Cees Dekker
(Delft University of Technology, NL) presents and extensive
review of recent experiment research in the physics of carbon
nanotubes, the author making the following points:
     1) Research on the physical properties of carbon nanotubes
accelerated after 1995, when R. Smalley et al discovered a laser
ablation technique that made possible the production of single-
wall nanotubes at yields up to 80 percent instead of the few
percent yields of early experiments.
     2) The conductive properties of nanotubes depend drastically
on both the diameter and the *chirality of the hexagonal carbon
lattice along the tube. A slight change in the winding of
hexagons along the tube can transform the tube from a metal into
a *large-gap semiconductor. Approximately two-thirds of tubes are
semiconducting and one-third are metallic.
     3) Carbon nanotubes exhibit unique quantum wire properties
that derive from the nanometer diameters of the tubes in
combination with the special electronic structure of graphite.
The electron wavelength around the circumference of a nanotube is
quantized due to periodic boundary conditions: only a discrete
number of wavelengths can fit around the tube. Along the tube the
electrons are not confined, but the quantization of
circumferential modes results in a splitting of electronic states
into one-dimensional sub-bands with band onsets at relatively
widely separated different energies.
     4) A recent development in the field is the renewed interest
in multi-wall carbon nanotubes, which have a much larger diameter
(e.g., 20 nanometers). This size allows, for example, *Aharonov-
Bohm studies, in which the nanotube resistance is modulated by a
magnetic field along the tube axis.
     5) Experimental evidence indicates that carbon nanotubes
exhibit *ballistic electron transport, even at room temperature.
As a result, no heat is dissipated in the tubes, and very high
current densities can be obtained without destroying the tube.
The author reports his laboratory has obtained extraordinary
current densities up to 10^(9) amperes per square centimeter
(many orders of magnitude larger than the fusing current density
for a regular copper wire) through an individual single-wall
nanotube between two electrodes at room temperature.
     6) In conclusion, the author suggests that the future for
nanotubes appears very promising. These structures are extremely
versatile. They can be functionalized at their ends and along
their bodies, filled with superconducting or magnetic metals,
coated on the outside, and joined together seamlessly. There
appears to be no material in the world that is as strong,
conducting, inert, etc. -- all at the same time. The rapid
progress in nanotube research is largely driven by this unique
combination of properties.
-----------
Cees Dekker: Carbon nanotubes as molecular quantum wires.
(Physics Today May 1999)
QY: Cees Dekker [dekker@qt.tn.tudelft.nl]
-----------
Text Notes:
... ... *chirality: In general, chirality is a property of
certain asymmetric systems such that the mirror images of the
system cannot be superimposed one on the other while facing in
the same direction.
... ... *large-gap semiconductor: In this context, a "band" is a
closely spaced group of energy levels in atoms, in particular a
range of energies that electrons can have in a solid. Each band
represents a large number of allowed quantum states. The
outermost electrons of the atoms form the "valence band" of the
solid. In order for electrons to move through a solid, there must
exist empty quantum states with the same energy, and this can
occur only in an unfilled band, the "conduction band". In
general, so-called "metals" are good conductors because the
partly filled conduction band overlaps with a filled valence
band, and vacant energy states in the conduction band are thus
readily available to electrons. In "insulators", the conduction
band and valence band are separated by a wide forbidden band, and
electrons do not have enough energy to jump from one band to
another. In intrinsic "semiconductors", the forbidden gap is
narrow, and at normal temperatures some electrons at the top of
the valence band can move by thermal agitation into the
conduction band. In a so-called "doped" semiconductor, the doping
impurities essentially create one or more thin separate
conduction bands in the forbidden band. Concerning the term
"large-gap semiconductor", in this context, the "gap" refers to
the gap between energy bands, i.e., from the upper boundary of
the valence band to the lower boundary of the conduction band.
Thus, a "large-gap semiconductor" is a semiconductor whose band
distribution properties (i.e., its conduction characteristic) are
closer to that of an insulator than to that of a metal. In
general, many of the technological applications of the various
types of semiconductor systems depend on the ability of the
system to exhibit a reversible and relatively discontinuous
switching from one conduction characteristic to another in
response to a controllable input.
... ... *Aharonov-Bohm studies: In quantum mechanics, the
Aharonov-Bohm effect occurs when a beam of electrons, split into
two beams that travel in opposite directions around a region
containing a magnetic flux, are then recombined with the result
that the intensity of the recombined electron beam oscillates
periodically as the enclosed magnetic field is varied.
... ... *ballistic electron transport: (ballistic transport) In
this context, the term refers to the passage of electrons through
a semiconductor whose length is less than the mean free path of
electrons in the semiconductor, with the result that most of the
electrons pass through the semiconductor without scattering.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 9Jul99
-------------------
Related Background:
A SINGLE-WALL CARBON NANOTUBE ROOM-TEMPERATURE TRANSISTOR
... The use of individual molecules as functional electronic
devices was first proposed by Aviram and Ratner in 1974. Since
then, molecular electronics has attracted much interest,
particularly because it could lead to conceptually new
miniaturization strategies in the electronics and computer
industry. But the realization of single-molecule devices has
remained a challenge, largely owing to difficulties in achieving
electrical contact to individual molecules. Recent advances in
nanotechnology, however, have resulted in electrical measurements
on single nano-scale molecules. ... ... Tans et al (3 authors at
Delft University of Technology, NL) report the fabrication of a
field-effect transistor -- a 3-terminal switching device -- that
consists of one semiconducting single-wall carbon nanotube
connected to 2 metal electrodes. By applying a voltage to a gate
electrode, the nanotube can be switched from a conducting to an
insulating state. The device operates at room temperature,
thereby meeting an important requirement for potential practical
applications. Electrical measurements on the nanotube transistor
indicate that its operation characteristics can be qualitatively
described by the semi-classical band-bending models currently
used for traditional semiconductor devices, an unexpected result.
The authors suggest the fabrication of this 3-terminal switching
device at the level of a single molecule represents an important
step towards molecular electronics.
QY: Cees Dekker (dekker@qt.tn.tudelft.nl)
(Nature 7 May 98 393:49) (Science-Week 29 May 98)
-------------------
Related Background:
ELASTICITY, STRENGTH, AND TOUGHNESS OF NANO-STRUCTURES
There has been much excitement in recent years concerning the
possible applications of so-called "nano-structures". Carbon
nanotubes are similar to fullerenes, except their shape is
tubular. They were first discovered by Sumio Iijima (NEC
Laboratories, JP) in 1991, they come in both multi-walled and
single-walled versions, and they have diameters of the order of
10 to 30 nanometers. They may be the strongest materials ever
produced, and depending on their geometry, their electrical
behavior can be that of a metal, a semiconductor, or an
insulator. Nanorods are similar to nanotubes, except they are
solid rather than hollow. Atomic force microscopy is a method of
mapping surface atomic structure by measuring the force acting on
the tip of a sharply pointed probe as it is moved over the
surface. Eric W. Wong et al (Harvard University, US) have now
used atomic force microscopy to determine the mechanical
properties of individual structurally isolated silicon carbide
nanorods and multi-wall carbon nanotubes pinned at one end. The
authors found carbon nanotubes to have particularly high energy-
absorbing capability, and they suggest that both nanorods and
nanotubes should have great potential in mechanical applications.
QY: Charles M. Lieber 
(Science 26 Sep 97) (Science-Week 17 Oct 97)
-------------------
Related Background:
CONDUCTIVITY ENHANCEMENT IN METAL-DOPED CARBON NANOTUBES
As we have indicated in earlier reports, carbon nanotubes are
graphite-like sheets of hexagonally bonded carbon rolled up into
tubes of nanometer dimensions. They can now be synthesized as
single-walled or multi-walled tubes with specific diameters, and
the chemists who work with these molecular structures believe
they will eventually revolutionize a number of technologies. This
week R. S. Lee et al (University of Pennsylvania US; Rice
University, Houston TX) report that doping of single-walled
carbon nanotubes with bromine and potassium produces what are
essentially synthetic metals. In a second paper by an associated
group, A. M Rao et al (various installations in US, JP) report
that examination of metal-doped nanotube bundles using Raman
scattering indicates charge transfer mechanisms are responsible
for the metal-like behavior. R. E. Smalley (Rice University, TX),
who received the Nobel Prize in Chemistry for his work with
fullerenes (spherical carbon structures related to the nanotubes)
is associated with both groups, and one of the authors of both
papers. Now that nanotube synthesis is apparently maturing, we
can expect a flood of new reports on their electrical properties
under various conditions.
(Nature 17 Jul 97) (Science-Week 25 Jul 97)


4. NEUROBIOLOGY: COMPLEXITY AND THE NERVOUS SYSTEM 
If there is any biological tissue which has consistently been
termed "complex", it is certainly the nervous system,
particularly the brains of the higher mammals, and most
particularly the brain of the human species. Of course, from one
perspective this is a bit of human self-aggrandizement, since a
lump of dirt contains more fundamental particles than the human
brain contains neurons, and considering only electrons, the
electron wave function interconnections in that lump of dirt can
be viewed to be at least as "complex" as the interconnections in
the human brain. So the use of the term "complexity" as
qualitatively applied to natural systems is perhaps a question
of perspective and what one wishes to achieve by the use of that
term. Concerning the human brain, the relation between its
apparent "complexity" and what we call "mind" or "consciousness"
continues to be elusive, and indeed a case can be made that
perhaps in this domain we are not even asking the right
questions.
... ... C. Koch and G. Laurent (California Institute of
Technology, US) present an essay on the "complexity" of the
nervous system, the authors making the following points:
     1) The brain has a function -- to protect the individual (or
its kin) in its particular ecosystem and to ensure the
propagation of its genome -- and that possession of a function is
"the most relevant difference from other large physical systems
such as galaxies and their tens to hundreds of billions of
stars."
     2) The authors propose that "everything biological must be
considered within an evolutionary framework." The brains that
exist today are the result of 0.6 to 1.2 billion years of
*metazoan evolution, and this vast span of time has allowed for a
very large number of adaptive steps between our stem ancestors
and today's animal cohort. These iterative elaborations can
perhaps be related to certain ideas of "logical depth" in
complexity theory.
     3) Brain complexity is reflected in the complexity of its
structural makeup. At the most elementary level, *voltage- and
neurotransmitter-gated ionic channels of all types are found
throughout the animal kingdom. The genome of the worm
Caenorhabditis elegans contains sequences for 80 different types
of potassium-selective ion channels, 90 ligand-gated receptors,
and approximately 1000 *G protein-linked *receptors. "The
combinatorial possibilities are staggering for a nervous system
with only 302 neurons."
     4) The authors suggest that it is important to recognize the
differences between brains and computers. Individual transistors
are homogeneous and nonadaptive. The interconnectivity of
transistor gates is very low: in the central processing unit of
any microprocessor, one gate is connected, on average, to two or
three others. This pales in comparison to interneuronal
convergence and divergence ratios, often in the tens of
thousands.
     5) The authors conclude: "A positive correlation between
complexity, as measured across large neuronal ensembles over a
fraction of a second or longer, and consciousness is not
implausible. Alternatively, it is at this time equally plausible
that consciousness arises out of a novel feature of certain types
of brains, some cellular or circuit property with a unique
molecular, anatomical, or physiological signature. Only time will
tell if and how the mind arises out of "complex" brains.
-----------
C. Koch and G. Laurent: Complexity and the nervous system.
(Science 2 Apr 99 284:96)
QY: Christof Koch [koch@klab.caltech.edu]
-----------
Text Notes:
... ... *metazoan: In general, the term "metazoa" refers to all
multicellular animals. Among important distinguishing
characteristics of metazoa are cell differentiation and
intercellular communication. For certain multicellular colonial
entities such as sponges, some biologists prefer the term
"parazoa".
... ... *voltage- and neurotransmitter-gated ionic channels: Ion
channels are protein channels in cell membranes that allow
ions to pass from the extracellular solution to the intracellular
solution and vice versa. Most ion channels are selective,
allowing only certain ions to pass, and an individual cell has
ion channels with various ion selectivities. The selectivity of
an ion channel can be "gated", the channel effectively opened or
closed, and ion channels are said to "voltage-gated" or "ligand-
gated", depending on how the change in selectivity is provoked.
"Neurotransmitters" are chemical substances released at the
terminals of nerve axons in response to the propagation of an
impulse to the end of that axon. The neurotransmitter substance
diffuses into the synapse (the junction between the presynaptic
nerve ending and the postsynaptic neuron), and at the membrane of
the postsynaptic neuron the transmitter substance interacts with
a molecular "receptor". Depending on the type of receptor, the
result may be an excitatory or an inhibitory effect on the
postsynaptic nerve cell. A "neurotransmitter-gated ionic channel"
is a ligand-gated channel.
... ... *G protein: G-proteins are a family of signal-coupling
proteins that act as intermediaries between activated surface
cell receptors and internal cellular systems, for example, the
transduction of hormonal ("first messenger") signals from the
cell surface to the cell interior. The G-protein is apparently
embedded in the cell membrane with parts exposed on the outside
surface and inside surface. The outside moiety is activated by
the "first messenger", and the inside moiety activates the
"second messenger", which interacts with some intracellular
molecular system. The G-protein thus acts as a trans-membrane
signal transducer.
... ... *receptors: In this context, the term "receptor" refers
to membrane-bound protein complexes interacting with specific
ligands.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 9Jul99
-------------------
Related Background:
PROPOSED COGNITIVE IMPLICATIONS OF EINSTEIN'S BRAIN
In an OpEd page commentary on the recent publication of an
anatomical study by Witelson et al of the preserved and sectioned
brain of Albert Einstein, cognitive scientist Steven Pinker
(Massachusetts Institute of Technology, US) writes as follows:
"The elegant study... is consistent with the themes of modern
cognitive neuroscience. Every aspect of thought and emotion is
rooted in brain structure and function, including many
psychological disorders and presumably, genius. The study
confirms that the brain is a modular system comprising multiple
intelligences, mostly nonverbal." But although the brain may
indeed be a modular system in its function, most neuroscientists
would agree that this particular study "confirms" nothing except
certain apparently unusual details of the gross surface foldings
of one small region of Einstein's brain, and that in fact the
study found no significant histological differences, or
differences in size or weight, between Einstein's brain and other
brains. Important histological or cytological differences might
be there, but they have not yet been identified. The title of
Pinker's commentary was "His Brain Measured Up: Einstein still
solving scientific mysteries." Unfortunately, not any more. And
one might conjecture that this sort of pop science exaggeration
by someone with an authoritative academic title will only add to
the public confusion concerning the relation between the brain
and behavior. (New York Times 24 Jun 99) (SW Bulletin 25 Jun 99)
-------------------
Related Background:
HUMAN NEUROCOGNITIVE ARCHITECTURE: A PLASTICITY MODEL
In human neurobiology, the term "cognition" refers to
intellectual functions that include perceiving, remembering,
imagining, conceiving, understanding, judging, and reasoning. And
one of the central problems of human neurobiology is to
understand the neurological substrates for all of these aspects,
and also to understand the evolution of these aspects where such
evolution can be delineated. In other words, from a neurological
standpoint, the questions in this context are how does the mind
work and how did it get that way? From any research perspective,
that is what is called a tall order. One view, proposed by
evolutionary psychologists, is based on the presumption that the
demands on *hunter-gatherer life during the *Pleistocene epoch
generated a vast array of evolutionary cognitive adaptations that
determine current human cognition and behavior. But many
neurobiologists disagree with this approach, and instead focus on
the intrinsic *plasticity of the human brain, and in particular
on the intrinsic plasticity of the human neocortex, an intrinsic
plasticity manifested during individual development -- a response
to the individual's physical and psychological environment. These
two approaches are in essence restatements of the classical
nature vs. nurture controversy, but the classical character of
the question does not make the question less important. ... ...
P. La Cerra and R. Bingham present a critique of the evolutionary
psychology approach to the understanding of cognitive processes
and offer an alternative model which they propose is more in
agreement with the current evidence in neurobiology. The authors
make the following points: 1) An extensive literature underscores
the enormous functional plasticity of the *neocortex, a
distinguishing characteristic of mammals. This evidence supports
the position that cortical representational features are
systematically constructed by the dynamic interaction between
environmentally derived neural activity and intrinsic neural
growth mechanisms. 2) The information-processing capacities of
the neocortex are largely constructed in response to the problem
domains confronting the individual throughout development, and
these constructions remain modifiable throughout the life
history. 3) This neurobiological account of the ongoing
construction of the human neurocognitive architecture contrasts
sharply with the account of evolutionary psychologists, who
conceive of the mind as a confederation of information-processing
adaptations, each of which evolved in response to a problem posed
by Pleistocene selection pressures. 4) Numerous methodological
problems and theoretical flaws call the validity of the
evolutionary psychological paradigm into question... Evolutionary
psychologists have suggested that investigation of the neural
correlates of behavior is not mandatory for the study of
cognitive adaptations. This failure to reconcile theoretical
claims with neurobiological data has veiled from evolutionary
analyses the functional organization of the information-
processing circuits that comprise the human neurocognitive
architecture. 5) The authors propose that the problems faced by
ancestral *hominids and their mammalian predecessors would have
required an adaptively flexible online information-processing
system, and would have driven the evolution of a functionally
plastic neural substrate, the neocortex, rather than a
confederation of evolutionary prespecified social cognitive
adaptations. 6) The authors propose that human cognitive
processes result from the activation of constructed cortical
representational networks, which reflect probabilistic
relationships between sensory inputs, behavioral responses, and
adaptive outcomes. The construction of these networks throughout
development, and their modification throughout experience, are
mediated by subcortical circuits that are responsive to the life
history regulatory system. The authors conclude: "The model we
have outlined emphasizes individual differences as the product of
an evolved self-adapting system, a neurocognitive architecture
that is unique by design." In summary, the La Cerra and Bingham
idea is essentially that human neurocognitive systems (the
neurocognitive "architecture") are "constructed" during
individual development and experience, rather than inherited as
preformed circuits (structures) selected by evolutionary
pressures during and before the Pleistocene epoch. The authors
term their approach "constructivist".
-----------
P. La Cerra and R. Bingham (Calif. Inst. of Tech., US)
The adaptive nature of the human neurocognitive architecture: An
alternative model.
(Proc. Natl. Acad. Sci. US 15 Sep 98 95:11290)
QY: Roger Bingham [bingham@bbb.caltech.edu]
-----------
Text Notes:
... ... *hunter-gatherer life: The consensus among
paleoanthropologists is that sometime between the beginning of
*hominid bipedalism (the "hominini") and the appearance of Homo
sapiens, perhaps about 2 to 3 million years ago, there occurred a
divergence from essential ape-like behavior and the emergence of
a hunter-gatherer existence, the hunting of animals and the
gathering of plants, both for food.
... ... *hominids: In general, any primate in the human family.
... ... *Pleistocene epoch: A geological epoch with the time-
frame 2.5 million years ago to 11,000 years ago. This was the
epoch of rapid hominid evolution, and the appearance of cattle
and the modern horse.
... ... *plasticity: In neurobiology, the term "plasticity" is
the name given to the capacity of neural tissue to adjust to
change. One variant of this concerns the dependence of the
"wiring" of the nervous system on its input. Another variant
concerns the degree to which one region can under certain
conditions assume the function of another region. Plasticity does
not occur everywhere in the nervous system, but it is often
evident in the cerebral cortex of the brain, the cortex being the
thin layer of cells apparently responsible for higher analysis of
sensory input, language, ideation, and other so-called higher
functions lumped together in the category "cognitive processes".
... ... *neocortex: The most recently evolved part of the
cerebral cortex.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 23Oct98


5. ANTHROPOLOGY: DEFINING THE HUMAN GENUS
Taxonomy is the field in biology devoted to the classification of
living organisms, and the term "taxon" is used to indicate the
members of any particular group in the classification scheme:
class, family, genus, etc [*Note #1]. The general problem is how
to incorporate information about evolutionary history and
adaptation into taxonomic classification schemes, with the
problem exemplified by attempts to define our own genus, Homo.
The definition of the genus Homo has always been somewhat
contentious, not least because it is tied, implicitly or
explicitly, to the state of "being human". A series of anatomical
characteristics is found to be apparently unique in Homo -- for
example, an increase in cranial vault height and cranial
thickness, reduced lower facial prognathism (i.e., reduced
projection of the jaw), and in dentition reduction in the size of
the premolars and molars and the length of the molar row -- but
what has always been emphasized by taxonomic definitions is the
size of the Homo brain as revealed by the size of the cranium.
According to the classical scheme, to be Homo is to be a large-
brained *hominine (the apparent human-related fossil group), a
hominine presumably more technologically accomplished than the
ancestor group, the *Australopithecines. At the present time, as
is evident in this report, the taxonomic categorizations related
to the human genus are far from fixed. ... ... B. Wood and M.
Collard (2 installations, US UK) present an extensive review of
the taxonomic situation concerning the genus Homo, the authors
making the following points:
     1) The authors suggest that recent data, fresh
interpretations of the existing evidence, and the limitations of
the paleoanthropological record invalidate existing criteria for
allocating fossil species to Homo.
     2) The authors suggest that regardless of any formal
definitions, in current practice fossil hominin species are
assigned to Homo on the basis of one or more out of 4 criteria:
a) absolute brain size at least 600 cubic centimeters; b)
possession of language as inferred from *endocranial casts; c)
possession of a modern human-like precision grip involving a
well-developed and opposable thumb (pollex); d) the ability to
manufacture stone tools. The authors state: "It is now evident,
however, that none of these criteria is satisfactory."
     3) The authors present a revised definition for the genus
Homo based on criteria considered verifiable and conclude that
two species, *Homo habilis and *Homo rudolfensis, do not belong
in the genus. The authors suggest the earliest taxon to satisfy
the criteria is *Homo ergaster, or early African *Homo erectus,
which currently appears in the fossil record at about 1.9 million
years ago.
     4) The authors suggest that a fossil species should be
included in Homo only if the following can be demonstrated:
... ... a) the species is more closely related to H. sapiens than
it is to the australopiths;
... ... b) the species has an estimated body mass more similar to
that of H. sapiens than to that of the australopiths;
... ... c) the species has reconstructed body proportions that
match those of H. sapiens more closely than those of the
australopiths;
... ... d) the species has a *postcranial skeleton whose
functional morphology is consistent with modern human-like
obligate bipedalism and limited facility for climbing;
... ... e) the species is equipped with teeth and jaws that are
more similar in terms of relative size to those of modern humans
than to those of the australopiths;
... ... f) the species shows evidence for a modern human-like
extended period of childhood growth and development.
     5) The authors conclude by suggesting that the adoption of
the above criteria would mean the genus Homo would have both
phylogenetic and adaptive significance. "Researchers can then
explore whether this adaptive shift in hominin evolution
corresponds with changes in climate, analogous evolutionary
changes in other large mammal groups, particular innovations in
the hominin cultural record, substantial expansions in geographic
range, or changes in ecological tolerance as reflected in
reconstructions of hominin habitats."
-----------
B. Wood and M. Collard: The human genus.
(Science 2 Apr 99 284:65)
QY: Bernard Wood [bwood@gwu.edu]
-----------
Text Notes:
... ... *Note #1: The conventional hierarchy of classification in
biology is Kingdom, Phylum, Class, Order, Family, Genus, and
Species. In the literature, organisms are usually referred to by
genus and species in binomial nomenclature, with the genus
capitalized. Human beings are genus Homo, species sapiens,
binomially Homo sapiens. The convention in binomial nomenclature
is to initialize the genus; thus: H. sapiens.
... ... *hominine: The terms hominine, hominin, hominoid,
hominid, are not interchangeable, but their classification
criteria are variously in a state of flux. In general, the
hominoids are a primate superfamily, the hominid family comprises
the great apes within the hominoid superfamily, the hominini are
a "tribe" within the hominids characterized by a number of
features including bipedalism, and the hominini are further
partitioned into the genera Homo and Australopithecus. Concerning
research in human evolution, most paleoanthropologists agree that
what is important is to achieve an understanding of the
evolutionary transitions and transformations, and any
classification scheme must be secondary to this objective. In
other words, in this context, classification must ultimately
reflect phylogeny (the actual evolutionary relationships), and as
knowledge of phylogeny changes, so must the extant classification
schemes.
... ... *Australopithecines: Members of the now extinct genus
Australopithecus, believed to exist between 4.4 and 1 million
years ago, and believed to be precursors of the genus Homo. All
australopithecines are apparently characterized by an ape-like
form, rather than the human-like form of the Homo genus.
... ... *endocranial casts: In general, an "endocast" (steinkern)
is any fossil formed after dissolution of an interior molding
substance. An "endocranial cast" is an endocast involving the
cranium. The interior of the endocast can often reveal details
concerning the absent soft interior substance (in this case, the
brain).
... ... *Homo habilis: In 1964, an early fossil hominin (1.9 to
1.6 million years before the present) was found in Olduvai,
Tanzania, the brain apparently intermediate in size between the
earliest known Homo fossil *Homo erectus and the Australopithecus
group. This new fossil was denoted as a new species by its
discoverers and named Homo habilis. The original set of H.
habilis fossils included a relatively complete hand, its
structure apparently compatible with an ability to make and use
tools. (Homo habilis literally means "handy-man") Considerable
controversy in the paleoanthropology community concerning H.
habilis has continued from 1964 until the present.
... ... *Homo rudolfensis: The original H. habilis species has
more recently been divided into H. habilis and H. rudolfensis,
after a fossil of the latter group was discovered in 1993 and
related to an earlier find in 1967, both dating at approximately
2.4 million years ago. One view is that Homo habilis/rudolfensis
evolved in Africa approximately 2 million years ago and quickly
expanded into Asia to become *Homo erectus/ergaster.
... ... *Homo ergaster: H. ergaster and *H. erectus are the two
immediate precursors of H. sapiens, with H. ergaster believed to
have originated in Africa and to have given rise to H. erectus in
Asia. But as with other hominid fossil groups, precise
evolutionary sequences and geographical loci continue to be
debated.
... ... *Homo erectus: First discovered by Eugene Dubois in 1891
in Indonesia, this fossil group is currently viewed as the
closest precursor to H. sapiens. Formerly called "Anthropithecus
erectus" and "Pithecanthropus erectus". Pithecanthropus erectus
and Sinanthropus erectus ("Peking man", discovered in 1927) were
in 1951 subsumed under the single category Homo erectus, which
was then recognized as a widespread species exhibiting
significant geographical variation.
... ... *postcranial skeleton: In general, this refers to the
skeleton behind the cranium in a quadruped and below the cranium
in a biped.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 9Jul99
-------------------
Related Background:
EVIDENCE FOR HUMAN WATERCRAFT 800,000 YEARS AGO
The term "fission-track dating" refers to a method of dating
geological specimens by counting the radiation-damage tracks
produced by spontaneous fission of uranium impurities in minerals
and glasses, and in this report zircon grains were used as the
dating material to date stone tools. The islands of Wallacea are
located between Southeast Asia and Australia, east of Java and
Bali, and investigations of extant animal species and animal
fossils on the Wallacean island of Flores indicate this island
was not land-connected to ancient Southeast Asia (called Sunda)
during approximately the past 1 million years, or perhaps even
before that. Homo erectus is considered the second species of the
human genus Homo to evolve. H. erectus used fire and stone tools,
appeared in Africa about 1.7 million years ago, and evidently
migrated throughout Eurasia. The species disappeared from Africa
approximately 500,000 years ago, and from Asia about 250,000
years ago. The Pleistocene is the geological time period from
about 2 million years ago to about the end of the last glaciation
about 10,000 years ago. Modern man is believed to have evolved
during the Pleistocene. ... ... Morwood et al (3 authors at 3
installations, AU ID) report zircon fission-track dating of
material from two fossil sites on the Wallacean island of Flores,
the fossil sites now and at the time of the dated material
reachable only by water crossings from Southeast Asia. The data
indicate that Homo erectus in this region, in the period 800,000
to 900,000 years ago, was capable of repeated water crossings
using watercraft. The authors suggest this evidence, combined
with the geographical radiation of Homo erectus in the Early
Pleistocene and other recent discoveries, indicates the cognitive
capabilities of this species may be due for reappraisal.
QY: M.J. Morwood (mmorwood@metz.une.edu.au)
EMAIL
(Nature 12 Mar 98) (Science-Week 27 Mar 98)


6. MEDICAL BIOLOGY: PATHOGENESIS OF UV INDUCTION OF MELANOMAS
Skin cancers, predominantly *basal-cell and *squamous-cell
*carcinomas, have accounted for an estimated 40 percent of all
cancers in the US in recent years, and the frequency of these
cancers has been increasing. The most common fatal skin cancer is
*melanoma, and this has also increased, indeed by a factor of
approximately 15 in the past 60 years. In 1997, more than 40,000
new cases of melanoma were diagnosed in the US, with more than
7200 fatalities. ... ... B.A. Gilchrest et al (Boston University,
US) present an extensive review of current research concerning
the pathogenesis of melanoma induced by UV radiation, the authors
making the following points:
     1) The factors underlying the rapid increase in the
incidence of skin cancer are incompletely understood, but
increased total exposure to the Sun, and in the case of melanoma,
altered patterns of exposure, are strongly implicated.
     2) The risk of melanoma is higher in fair-skinned people,
especially those with blond or red hair who sunburn and freckle
easily, than in people with darker complexions. The incidence of
melanoma among whites is inversely related to the latitude of
residence, with the world's highest incidence in Australia, a
subtropical country with a largely Celtic population. Conversely,
melanomas are uncommon in darker-skinned people.
     3) The epidemiologic evidence implicating solar exposure in
the causation of melanoma is supported by biologic evidence that
damage caused by ultraviolet radiation, particularly damage to
DNA, plays a central part in the pathogenesis of these tumors.
     4) Age plays a major part in vulnerability to
photocarcinogenesis. Aging (the passage of time) provides more
opportunities for the initiation of tumor formation (the
induction of mutations by exposure to UV radiation) and for the
promotion of tumor formation (the reparative cell proliferation
after exposure to UV radiation or after other skin injury). There
is an age-associated decrease in the capacity to repair DNA, and
a consequent increase in the rate of mutations of DNA. Moreover,
the rate of removal of UV-radiation-induced DNA photoproducts
from UV-irradiated skin decreases with age, especially during the
first two decades of life.
     5) There has been considerable research addressing the
relative contributions of UV-B wavelengths (290-320 nm) and UV-A
wavelengths (320-400 nm) to photocarcinogenesis, particularly to
the development of melanoma. UV-B radiation is overwhelmingly
responsible for the formation of the principle DNA lesions,
cyclobutane pyrimidine dimers and pyrimidine (6-4) pyrimidone
photoproducts, whose incorrect repair leads to mutations.
However, UV-A radiation is far more abundant in sunlight than UV-
B radiation, and UV-A radiation causes oxidative DNA damage that
is also potentially mutagenic. UV-A radiation is also believed to
contribute substantially to immunosuppression, thus preventing
immunologic rejection of nascent UV-induced skin cancers.
     6) Unlike the more common skin cancers, which are associated
with total cumulative exposure to UV radiation, melanomas are
associated with intense intermittent exposure. Thus, basal-cell
and squamous-cell carcinomas occur most commonly in maximally
solar-exposed areas of the body (e.g., face, back of hands,
forearms, and in persons with almost daily and substantial
lifetime exposure to UV radiation, such as farmers and sailors).
In contrast, melanoma occurs most commonly in areas of the body
exposed to the Sun intermittently, such as the back in men and
the lower legs in women, with relative sparing of more frequently
exposed sites such as the face, hands, and forearms. Melanoma is
most common in persons with predominantly indoor occupations
whose exposure to the Sun is limited to weekends and vacations.
Indeed the large increase in the incidence of melanoma in recent
decades has been attributed in part to the ability of large
numbers of people to travel long distances to obtain intense
exposure to the Sun in winter.
     7) The authors propose a hypothesis to explain the
epidemiology of melanoma as compared with non-melanoma skin
cancer, the authors suggesting that the data predict that a high-
dose first exposure to the Sun after a prolonged period of Sun
avoidance will cause substantial damage to DNA in *melanocytes
and *keratinocytes, both of which at that time have a relatively
low base-line capacity for DNA repair and a low melanin content.
The authors propose that the final effect of UV radiation is not
attributable simply to the cumulative dose -- the arithmetic sum
of all individual exposures over a lifetime -- but rather may be
strongly influenced by the dose per exposure and by the pattern
of exposures.
     8) The authors conclude: "Protection from the Sun is
critical to the prevention of both melanoma and non-melanoma skin
cancers, and protection is most effective when it is begun in
early childhood. It is especially important to protect against
intermittent Sun exposures, in order to reduce genomic damage at
a time of maximal cellular vulnerability and to reduce the risk
of melanoma."
----------
B.A. Gilchrest et al: The pathogenesis of melanoma induced by
ultraviolet radiation.
(New England J. Med. 29 Apr 99 340:1341)
QY: Barbara A. Gilchrest [bgilchre@bu.edu]
-----------
Text Notes:
... ... *basal-cell: A basal cell is a cell of the deepest layer
of stratified epithelium. In animals, including humans,
epithelial cells (epithelium) 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. The term "stratified
epithelium" is a general term for epithelium composed of several
layers of different cell types.
... ... *squamous-cell: The cells of the epithelium are for the
most part closely packed cells with little extracellular material
between adjacent cells, the cells arranged in continuous sheets
in either single or multiple layers. The cells may be flat,
cubelike, columnar, or a combination of shapes, and "squamous"
cells are flattened and scalelike.
... ... *carcinomas: In general, a carcinoma is any malignancy
derived from epithelial tissue.
... ... *melanoma: Melanomas are a group of skin cancers
involving *melanocytes, cells found throughout the lower layers
of the skin.
... ... *melanocytes: (melanodendrocytes) Pigment-producing cells
located in the deepest (basal) layer of the skin (epidermis) with
branching processes by means of which melanin-containing bodies
(melanosomes) are transferred to epidermal cells with a resultant
pigmentation of the epidermis.
... ... *keratinocytes: "Keratinocyte" is a generic term for any
mammalian epithelial cell that produces keratin, a group of
proteins present in cuticular structures (e.g., hair, nails).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 9Jul99
-------------------
Related Background:
BIOLOGY OF CANCER: ON SQUAMOUS CELL CARCINOMA
Epithelial tissue (also called epithelium) forms the outer layer
of the skin and the outer layers of some internal organs, the
inner lining of blood vessels, ducts, body cavities, and the
interiors of the respiratory, digestive, urinary, and
reproductive systems. The cells of the epithelium are for the
most part closely packed cells with little extracellular material
between adjacent cells, the cells arranged in continuous sheets
in either single or multiple layers. The cells may be flat,
cubelike, columnar, or a combination of shapes, and "squamous"
cells are flattened and scalelike. One of the most common forms
of skin cancer is squamous cell carcinoma. These cells usually
arise from preexisting lesions on sun-exposed skin, and they have
a variable tendency to metastasize. Approximately 90 percent of
the cells in the skin are keratinocytes, cells that produce the
protein keratin, which helps waterproof and protect the skin and
underlying tissues. ... ... N.M. Wikonkal and D.E. Brash present
a review of the cellular biology of squamous cell carcinoma, and
the authors make the following points: 1) Ultraviolet light
absorbed by DNA molecules in keratinocytes is the inciting cause
of squamous cell carcinoma of the skin. 2) Failure of DNA repair
enzymes to correct the UV-induced damage can lead to mutations
when cells divide. Particular mutations in the *tumor suppressor
gene  are characteristic of UV damage and are commonly found
in squamous cell carcinoma. 3) If mutations result in defective
p53 protein, the functions of this protein in *cell cycle control
and facilitation of *apoptosis will be absent, and this allows
*clonal expansion and eventual cancer. 4) A remarkable feature of
this type of cancer is that tumors closely resembling the human
clinical entity can be generated in the laboratory in mice,
allowing experiments that are not possible in humans. The
visibility and accessibility of squamous cell carcinoma of the
skin have made this tumor one of the best understood human
malignancies. 
-----------
N.M. Wikonkal and D.E. Brash (Yale University, US)
Squamous Cell Carcinoma
(Science & Medicine Sep/Oct 1998)
QY: Norbert M. Wikonkal, Yale University, 203-432-4771.
-----------
Text Notes:
... ... *tumor suppressor gene: Tumor suppressor genes code for
proteins that apparently either prevent cell division or provoke
cell death in defective cells.
... ... *cell cycle control: 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.
... ... *apoptosis:  In general, the term "apoptosis" refers to
programmed cell death, whether as a part of normal tissue
differentiation and development, or as a program activated in a
defective cell. In the molecular biology of cancer, apoptosis is
the name given to the programmed cell death provoked by the
proteins expressed by tumor suppressor genes. Thus, malignant
cells are defective cells with a deactivated apoptosis program,
and this allows malignant cells to survive and replicate. 
... ... *clonal expansion: This refers to the expansion of a
population of cells all derived from repeated replications of
progeny of a single cell.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 13Novl98
-------------------
Related Background:
SUNLIGHT EXPOSURE AND THE RISK OF EYE LENS OPACITIES
Despite advances in surgical procedures and targeted programs,
*cataract remains the leading cause of visual loss worldwide. In
the US, for example, cataract surgery is responsible for 12
percent of the Medicare budget (data for 1991). Exposure to *UV-B
radiation in sunlight has been shown to increase the risk of
cataract formation in high-risk occupational groups, but the risk
to the general population has not yet been quantified.
... ... West et al (7 authors at Johns Hopkins University, US)
report a study to determine the ocular exposure to UV-B radiation
in sunlight for a population of older persons, and to determine
the association between UV-B radiation and lens opacities. The
research group consisted of a total of 2520 community-dwelling 65
to 84 year old adults in Salisbury, Maryland (US) from 1993 to
1995. The study involves detailed quantitative assessment of all
apparently relevant factors, including the correlation variables.
The authors report that the odds of lens opacity increased with
increasing ocular exposure to UV-B (odds ratio = 1.10). Analysis
of the ocular dose by each age group after the age of 30 years
(based on questionnaires concerning past subject job history)
showed no vulnerable age group, suggesting damage is based on
cumulative exposure. The authors suggest their results add to the
growing body of knowledge that indicates even low levels of UV-B
radiation can harm the lens of the eye. The authors suggest
measures to avoid ocular exposure to UV-B radiation are simple:
the wearing of plastic glasses or sunglasses confers excellent
protection, and the mere wearing of a hat with a brim decreases
ocular exposure by 30 to 50 percent. The authors conclude: "These
measures should be part of any public health program to increase
awareness of sun damage and avoid unhealthy consequences."
QY: Sheila K. West 
(J. Amer. Med. Assoc. 26 Aug 98 280:714)
(Science-Week 11 Sep 98)
-------------------
Related Background:
... ... *cataract: In general, cataract is any developmental or
degenerative opacity of the lens of the eye. The cause of
degenerative cataract may be aging, exposure to x-rays, heat from
infrared exposure, systemic disease (e.g., diabetes mellitus),
various inflammations of the internal eye, and systemic
medication (e.g., corticosteroids).
... ... *UV-B radiation: In medical science, the ultraviolet part
of the spectrum is partitioned into 3 regions: UV-A is radiation
of wavelength 320-400 nanometers, causing skin tanning but only
weakly sunburn producing or carcinogenic; UV-B is radiation of
wavelength 290-320 nanometers, most effectively causing sunburn
and tanning, and carcinogenic for fair skin; UV-C is radiation of
wavelength 200-290 nanometers, and this radiation does not reach
the surface of the Earth from sunlight. UV-C radiation produced
by mercury arc lamps is germicidal, causes sunburn, and may cause
photokeratitis (light-induced inflammation of the cornea).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 11Sep98
-------------------
Related Background:
ALARM AT INCREASED INCIDENCE OF MELANOMA CANCERS
Melanocytes, cells which synthesize inclusions of the dark
pigment melanin, are found in the skin, choroid of the eye, and
hair. Melanocyte cancers are called melanomas, and if they are of
the rapidly proliferating type, and not caught early, they have a
high fatality rate. At the present time, the incidence of
melanoma in the U.S. is increasing faster than any other cancer,
and the statistics seem incredible: 0.0007 in 1935, 0.004 in
1977, 0.01 in 1997. According to projections, in the U.S. this
year, 40,300 new cases will be diagnosed, and 7,300 people will
die from the disease. The majority of oncologists and epidemi-
ologists believe this striking increase in incidence is real and
not a function of ambiguous diagnostic techniques. They point to
the simple fact that deaths from melanoma have increased along
with the incidence, even though early diagnosis and improved
treatment methods have increased the 5-year survival rate. The
projected U.S. incidence of melanoma in the year 2000 is 0.013,
which means at that time 1 in 75 people will expect to be
diagnosed with the disease.
(New York Times 6 Aug 97) (Science-Week 15 Aug 97)
-------------------
Related Background:
COMPANY OBTAINS PATENT FOR SKIN CANCER MELANOMA GENE
Under present U.S. and European patent law it is possible to
obtain a patent on a human gene in the same manner as one
obtains a patent on a chemical compound. Myriad Genetics, the
Salt Lake City company that has two patents pending for breast
cancer genes (BRC-1 and BRCA-2), has now received a patent for
the gene it claims causes melanoma (Multiple Tumor Suppressor 1
or MTS1), and for the method of testing for the presence of that
gene in humans. Lisa Cannon-Albright, a University of Utah
geneticist, Mark Skolnik, a Myriad geneticist, and Alexander
Kamb, a Myriad molecular biologist are listed as the inventors.
(New York Times 5 May 97) (Science-Week 8 May 97)


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

IN FOCUS: ON FUNCTION AND TELEOLOGY IN BIOLOGY
"Biology, and especially evolutionary biology, is rife with
claims concerning what various characteristics are "for". The
heart exists for the purpose of pumping blood. Bears have fur in
order to ward off the cold. Functional claims of this sort have
quite disappeared from physics. Whereas Aristotle thought that
planets, no less than living things, have goals, this
teleological conception of the physical world is now a relic of a
bygone age. Planets move as they do because of the laws of
motion; they do not act as they do for the good of anything.
Darwin is rightly famous for having introduced an important
materialist element into the science of life. But rather than
banishing functional notions from biology, he showed how they can
be domesticated within a materialist framework. Organisms are
goal-directed systems because they have evolved. Their behaviors
are suited to the tasks of survival and reproduction because
natural selection has allowed some traits, but not others, to be
passed from ancestors to descendants. Even if Darwinism
legitimates talk of goal and purpose within biology, the question
of what such talk means remains to be addressed. The heart does
many things. It pumps blood, but it also makes noise and takes up
space in our chests. Why are we inclined to say that pumping
blood is part of the heart's function, but making noise and
taking up space are not?"

-- Elliott Sober: _Conceptual Issues in Evolutionary Biology_
   (MIT Press, Cambridge 1995, p.x)


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