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.

April 2, 1999 -- Vol. 3 Number 14

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If you are a scientist you believe that it is good to find out
how the world works, that it is good to find out what the
realities are, that it is good to turn over to mankind at large
the greatest possible power to control the world... It is not
possible to be a scientist unless you believe that the knowledge
of the world, and the power which this gives, is a thing which is
of intrinsic value to humanity, and that you are using it to help
in the spread of knowledge, and are willing to take the
consequences.
-- J. Robert Oppenheimer (1904-1967)

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Contents of This Issue:

1. M.I.T Acknowledges Bias Against Female Science Professors
2. On the Large-Scale Smoothness of the Universe
3. On Catalysis and Surface Science
4. Evidence Against a Hyperthermophilic Common Life Ancestor
5. Conversion of Neural Stem Cells into Blood Cells
6. Bacteriological Analysis of Infected Dog and Cat Bites

-- In Focus: On Differences Among Human Populations

-----------------------------------------------------------

1. M.I.T ACKNOWLEDGES BIAS AGAINST FEMALE SCIENCE PROFESSORS
One would suppose that in science, an enterprise that emphasizes
rationality, the general attitude would be to maximize the
utilization of scientific talent irrespective of gender. But as
in other areas of human endeavor, suppositions are not realities.
In what has been called an extraordinary admission, top officials
at the Massachusetts Institute of Technology, the most
prestigious science and engineering university in the US, have
issued a report acknowledging that female professors at the
institution suffer from pervasive discrimination. The report
concerns discrimination against women in the M.I.T. School of
Science, and documents a pattern of discrimination in areas
including employment, awards, promotions, inclusion in important
committees, and allocation of resources such as laboratory space
and research funds. At the present time, the M.I.T. School of
Science faculty consists of 8 percent women, and this percentage
has remained virtually unchanged for approximately 20 years. In
February 1999, the American Association of University Professors
issued a report indicating that although the percentage of
faculty women in general in the US grew to 34 percent from 23
percent since 1975, the salary gap for male and female professors
actually widened during this period. In the US, women now
comprise a substantial portion of undergraduate science students,
but only a minor portion of science faculties. Concerning gender
discrimination, Charles M. Vest, the president of M.I.T., is
quoted as saying, "I have always believed that contemporary
gender discrimination within universities is part reality and
part perception. True, but I now understand that reality is by
far the greater part of the balance."
-----------
Carey Goldberg: M.I.T. acknowledges bias against female
professors.
(The New York Times 23 Mar 98)
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 2Apr99
-------------------
Related Background:
WOMEN ON CHEMISTRY FACULTIES: EVIDENCE OF SLOW PROGRESS
Data compiled by the American Chemical Society for 1996, the most
recent year for which data are available, indicate that in the US
30.7 percent of PhDs in chemistry were awarded to women, up from
12.5 percent in 1976. But on chemistry faculties at the major US
research universities, women are barely represented. Here are
figures for some of the major US academic research installations:
-----
(Total tenure or tenure-track chemistry faculty/Women on tenure
or tenure-track chemistry faculty 1996-1997)
University of California Berkeley            53/5
California Institute of Technology           25/3
Harvard University                           20/1
Stanford University                          21/1
Massachusetts Institute of Technology        31/2
Cornell University                           30/2
Columbia University                          19/1
University of Illinois Urbana-Champaign      47/2
University of Wisconsin Madison              39/2
University of Chicago                        24/1
University of California Los Angeles         37/6
-----
QY: Mairin B. Brennan 
(Chem. & Eng. News 20 Jul 98) (Science-Week 7 Aug 98)
-------------------
Related Background:
US WOMEN IN SCIENCE LESS ACCEPTED THAN WOMEN IN BUSINESS
A meeting last month at the New York Academy of Sciences (US)
focused on the past 25 years of progress for women scientists and
engineers in the US. The apparent consensus at the conference was
that the climate for women in both industry and government has
improved much faster than in academia, with the changes in
industry mostly due to a drive by industry for diversity. The
Motorola Corporation (US) now has 43 women vice-presidents. In
1996, women were 51% of the US population, 46% of the labor
force, but only 22% of scientists and engineers. Nobel Laureate
Gertrude Elion advised women in science to follow Farragut's
order: "Damn the torpedoes -- full speed ahead."
(Chem. & Eng. News 6 Apr 98) (Science-Week 17 Apr 98)
-------------------
Related Background:
WOMEN NOW SUBSTANTIAL PORTION OF ALL NEW US CHEMISTS
The latest survey of the American Chemical Society, covering
chemists and chemical engineers who graduated between July 1996
and June 1997, shows the following statistics for new women
graduates (percentage of total graduates who are women):
Chemistry Bachelor's Degree: 48.2%
Chemistry Master's Degree: 46.2%
Chemistry PhD Degree: 31.6
Chemical Engineering Bachelor's Degree: 35.4%
Chemical Engineering Master's Degree: 29.3%
Chemical Engineering PhD Degree: 22.9%
-----------
QY: Michael Heylin 
(Chem. & Eng. News 9 Mar 98) (Science-Week 20 Mar 98)
-------------------
Related Background:
SWEDISH STUDY SHOWS SEX BIAS AFFECTS SCIENCE EMPLOYMENT
Two female Swedish scientists have published a study which
indicates that women must publish more often than men to compete
successfully for scientific jobs in Sweden. This is the first
scientific study of sex discrimination in the awarding of a
large number of research positions, and was financed by a
Swedish government grant. The researchers, Christine Wenneras
and Agnes Wold, are both from the University of Goteborg. The
journal Nature, which published the study, states that
the "results severely undermine the credibility of the
peer-review system, not just in Sweden but elsewhere in the
world.
(Nature 22 May 97) (Science-Week 22 May 97)


2. ON THE LARGE-SCALE SMOOTHNESS OF THE UNIVERSE
In cosmology, what is called the "Cosmological Principle" is the
proposition that the Universe is homogeneous and isotropic, at
least on large scales. The principle is of theoretical
importance, since a consequence is the restriction of the set of
cosmological models compatible with general relativity theory.
A fractal is a distribution or shape that is in general not
homogeneous, but which possesses the property that each part is a
simulacrum of the whole, i.e., the distribution appears the same
on all scales. Fractals are ubiquitous in nature. A common
example is the coastline of a small peninsula: when drawn on
paper, the contour could equally well depict a large continent.
The apparent clustering of observable galaxies lends itself to a
fractal description, because the clumpiness prevails over a wide
range of scales. The important question for cosmology is whether
the distribution of matter in the Universe continues to be a
simple fractal beyond the scale of clusters of galaxies: if it
does, then the Cosmological Principle is invalid. ... ... K.K.S.
Wu et al (3 authors at 2 installations, UK IL) present a review
of current ideas concerning the distribution of matter in the
Universe, the authors making the following points: 1) Past
attempts to determine the distribution of matter have confronted
two important obstacles: a) Most of the mass in the Universe is
dark; we can detect it only by its gravitational effects on
observable objects, and it is still unclear how to relate the
distributions of light and of mass. b) Until recently, little was
known about the distributions of matter on scales intermediate
between those of local galaxy surveys and scales probed by the
*Cosmic Background Explorer (COBE) satellite. 2) Recent
observations of *radio galaxies and the *x-ray background can
effectively probe the intermediate scales, and current data
already strongly constrain any non-uniformities in the galaxy
distribution (as well as overall mass distribution). 3) The
Universe is apparently inhomogeneous -- and essentially fractal
-- on the scale of galaxies and clusters of galaxies, but most
cosmologists currently believe that on larger scales the Universe
becomes isotropic and homogeneous (the Cosmological Principle).
This principle was first adopted when observational cosmology was
in its infancy, and was then little more than a conjecture. The
data now available offer a quantitative picture of the apparent
gradual transition from the small-scale fractal behavior of
galaxies and clusters of galaxies to the large-scale homogeneity
of the Universe. The authors conclude: "There is a well-defined
sense in which our Universe is homogeneous on the largest
accessible scales; neither its mass distribution, nor that of the
galaxies, resembles a pure fractal. Cosmological parameters such
as *Omega therefore have a well-defined meaning -- indeed their
considerations tell us what volume we need to average in order to
determine them with any specified level of precision."
-----------
Editor's note: In addition to the background material below, see
the SW Focus Reports "Cosmology: Dark Matter", and "Cosmology:
Models and Extrapolations", both available at URL
[http://scienceweek.com/swfr.htm].
-----------
K.K.S. Wu et al: The large-scale smoothness of the Universe.
(Nature 21 Jan 99 397:225)
QY: Kelvin K.S. Wu, Institute of Astronomy, University of
Cambridge, Madingley Road, Cambridge CB3 0HA UK.
-----------
Text Notes:
... ... *Cosmic Background Explorer (COBE) satellite: A NASA
orbiting satellite launched in 1989 and dedicated to the study of
the *cosmic microwave background radiation. The most important
results were the discoveries of irregularities in the cosmic
background radiation on the level of one part in 10^(5), and the
confirmation that the spectrum of the cosmic background radiation
is that of a black body with a temperature of 2.73 degrees
kelvin.
... ... *cosmic microwave background radiation: The cosmic
microwave background is black-body radiation (the emission
radiation of a perfect absorber of radiation) at a present
temperature of 2.73 degrees Kelvin, and has an almost equal
intensity in all directions in space. The deviations from
isotropic intensity, however, are of extreme importance in
theoretical cosmology. The cosmic background radiation is
predicted by the Big Bang theory and is considered one of the
most important pieces of evidence for it.
... ... *radio galaxies: A galaxy which is an unusually powerful
emitter of radio waves, e.g., a million times greater emission
than our own galaxy. The source of the radio galaxy's energy is
believed to be a massive black hole in the galactic nucleus.
... ... *x-ray background: This refers to a diffuse x-ray
emission not associated with known individual sources, part of it
apparently arising from hot gas within our own galaxy. The origin
of the higher energy component is unknown.
... ... *Omega: Central to current cosmological considerations
are the distinctions between the geometries of a "flat"
(uncurved; infinite in both extent and lifetime), "closed"
(spherical; finite in both extent and lifetime), and "open"
(*hyperbolic; infinite and expanding forever) Universe. An
important quantity is the Omega parameter, defined as the ratio
of the density of matter (or energy) in the Universe to the
theoretical density required for flatness. An Omega with a value
of greater than 1 implies a closed Universe; a value less than 1
implies an open Universe; a value equal to 1 implies a flat
Universe. The problem for the past 60 years has thus been to
obtain an estimate of the mass density of the Universe from
observations. The current standard conception is that the
geometry of the Universe is flat.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 2Apr99
-------------------
Related Background:
AN EXCHANGE OF LETTERS CONCERNING FRACTALITY IN NATURE
A fractal is a geometrical shape whose structure is such that
magnification by a given factor reproduces the original object.
During the past several decades, the idea that fractal geometry
is an appropriate geometry to describe nature has been proposed
by many researchers. The mathematical constructs involved are
appealing because of their symmetries, and as in the development
of many appealing ideas, the use of the term "fractal" has
increased to the point where experimental observations in all the
sciences are being analyzed and interpreted as examples of
systems with apparently fractal properties. A recent article by
Avnir et al (cf., background item below) that reported a
literature review of experimental determinations of "fractal"
properties of various natural systems has provoked some
controversy and an exchange of letters on the subject, including
a letter from B. Mandelbrot, a chief proponent of the idea of the
universality of fractal geometries in nature. The Avnir group,
reviewing a large number of Physics Review journals papers,
reported that much of the quantitative data that have been
interpreted as identifying systems with fractal geometries do not
in fact satisfy the stringent mathematical requirements for
fractality, and there is thus no evidence that nature can be
described by a fractal geometry. In his response to the Avnir et
al report, Mandelbrot (Yale University, US) suggests the Avnir
group has dwelled on the statistics of implied and possible
failures, rather than on the variety and quality of the best
work, and that in the case of fractal geometry, the best work is
outstanding. Mandelbrot says many of the weak published evidences
of fractality are due to "enthusiasm, imperfectly controlled by
refereeing, for a new tool that was (incorrectly) perceived as
simple." P. Pfeifer (University of Missouri, US) says in a
contiguous letter that "the discovery of fractals requires a lot
more than fitting a power law through a set of points and asking
how many decades of length it spans." In the final letter, Avnir
et al (4 authors at Hebrew University, IL) respond that their
paper reported on "most comprehensive survey of experimental
measurements of fractals done thus far", and that Mandelbrot's
reaction to the outcome of the analysis is "uncalled for", and
that the central question of the "abundance of fractals"
determines either their central relevance to all fields of
natural sciences or their esotericity. Avnir et al say, "the data
we analyzed is not junk and cannot be dismissed: it comes from a
prestigious set of journals in the physics community, and they
represent beyond doubt the status of fractals in the natural
sciences."
QY: Benoit B. Mandelbrot, Yale University, Dept. Mathematics 203-
432-3791; Peter Pfeifer ;
David Avnir [biham@13.flounder.fiz.huji.ac.il] (Science 6 Feb 98)
-------------------
Related Background:
FRACTALS AND THE GEOMETRY OF NATURE
... To the mathematician... the definition of the property of
"fractality" involves a quantitative requirement of infinitely
many orders of magnitude of power-law scaling of the parameters
of the system -- certainly at least a spanning of many orders of
magnitude. Avnir et al (3 authors at 2 installations, IL), in a
review of the application of the mathematics of fractals to the
geometry of natural systems, point out that the application of
the term "fractal" by scientists to such systems is often
unjustified. The authors surveyed all experimental papers
reporting fractal analysis of data that appeared during a 7 year
period in Physical Review journals (Phys. Rev. A to E, and Phys.
Rev. Lett., 1990-1996), and found that in most cases the order of
magnitude spanning required for mathematical fractality was not
achieved, and that the use of the term "fractal" in these
contexts has at most a heuristic value. The authors suggest there
is at present no experimental evidence that the geometry of
nature is fractal.
QY: David Avnir [david@granite.fh.huji.ac.il]
(Science 2 Jan 98) (Science-Week 16 Jan 98)


3. ON CATALYSIS AND SURFACE SCIENCE
The term "catalysis" was invented in 1835 by the chemist J.J.
Berzelius (1779-1848) to describe chemical reactions in which the
progress of the reaction is affected by a substance that is not
consumed in the reaction and thus apparently not involved in the
reaction. But this definition, proposing no interaction by the
catalyst with reactants, is not useful, and it was later amended
by W. Ostwald (1853-1952), who proposed the more modern
definition: "A catalyst is a substance that accelerates the rate
of a chemical reaction without being part of its final products."
Essentially, as is now recognized, the catalyst acts by forming
intermediate compounds with the molecules involved in the
reaction, providing an alternate and more rapid path to the final
products. Catalysis is of vital importance: In biological
systems, enzymes are essential catalysts for various biosynthetic
pathways; in the chemical and petroleum industries, key processes
are based on catalysis; in environmental chemistry, catalysts are
essential to breaking down pollutants such as automobile and
industrial exhausts. ... ... G. Ertl and H-J. Freund (Friz Haber
Institute Max Planck Society Berlin, DE) present a review of the
basics of catalysis, the authors making the following points: 1)
If the catalyst and the reacting species are in the same phase
(e.g., in a liquid), then the process is known as "homogeneous
catalysis". More relevant in industrial processes is
"heterogeneous catalysis", where the catalyst is a solid and the
reacting molecules interact with the surface of the solid from
the gaseous or liquid phases. 2) The economic significance of
heterogeneous catalysis is reflected in the fact that the world
market for solid catalysts in the automotive, petroleum, and
other industries is of the order of US$100 billion per year and
growing rapidly. 3) In heterogeneous catalysis, the chemical
transformation typically occurs in a flow reactor through which
the reacting species pass. Atoms in the surface of the catalyst
may form chemical bonds with atoms in impinging molecules, a
phenomenon known as "chemisorption". If existing bonds in the
impinging molecule break, the process is known as "dissociative
chemisorption". The chemisorbed species are mobile on the surface
and may bond to other particles, thus leading to new molecules,
which eventually leave the surface (desorb) as the desired
reaction products. 4) Detailed identification and
characterization of these elementary processes of heterogeneous
catalysis are hampered by several fundamental problems: a) The
reacting systems exist merely as 2-dimensional phases for which
most of the usual methods of investigation are not well suited.
b) The surfaces of real catalysts are typically inhomogeneous as
a result of methods to increase catalytic efficiency. For
example, because in heterogeneous catalysis efficiency, in
general, increases with total surface area of the solid catalyst,
finely divided particles are usually applied to a support
material which is only relatively inert. Also, catalytic activity
is often further enhanced by the addition of compounds called
"promoters". At the present time, analysis of the fundamentals of
heterogenous catalysis is largely dependent on the use of surface
science models, real but simple systems such as single crystal
surfaces whose structure may be varied by choosing different
surface orientations.
-----------
G. Ertl and H-J. Freund: Catalysis and surface science.
(Physics Today January 1999)
QY: Gerhard Ertl, Fritz Haber Institute MPG, Berlin, DE.
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 2Apr99
-------------------
Related Background:
ON THE USE OF ANTIBODY CATALYSIS IN ORGANIC CHEMISTRY
An antibody is a protein molecule (immunoglobulin) produced by
vertebrates that binds with high specificity to a "foreign"
entity (*antigen) that has entered the system by one means or
another (for example, via bacteria, tissue grafts, or blood
transfusions). Antibodies are therefore key elements in all
vertebrate immune systems. That is the first point. The second
point is that we now know that enzymes work the way they do
mostly because they bind *transition state entities in chemical
reactions, this binding lowering the energy barrier to the
transition state, and thereby increasing the reaction rate
many-fold. Which provokes the notion that it might somehow be
possible to use the high specificity of antibodies in catalysis.
And the notion is correct. A catalytic antibody, sometimes called
an "abzyme", is an antibody capable of catalyzing specific
chemical reactions. The general strategy in producing catalytic
antibodies has been to 1) design and synthesize a molecule whose
charge and shape closely resemble those of the transition state
of the reaction to be catalyzed; 2) attach this molecule to a
larger molecule and provoke an immune response in a living system
to this complex; and 3) isolate the resultant antibodies for
catalytic activity of the type desired. These resultant
antibodies are highly specific for binding to the transition
state, and they will be potentially capable of catalyzing the
reaction. Antibody catalysis has become a multifaceted field of
research involving many bridges between the biological and
chemical sciences. ... ... Peter G. Schultz (University of
California Berkeley, US) presents a short review of past and
recent research in the field, the author making the following
points: 1) The use of catalytic antibodies in organic chemistry
began with the idea that chemists should be able to use the
complex machinery of the immune system, which is capable of
generating enormous chemical diversity through the processes of
*recombination and *somatic mutation, to create new molecular
functions, specifically highly selective catalysts. 2) The
earliest examples involved the use of transition state analogues
to select antibodies with maximal binding affinity toward the
rate-limiting transition state for a given reaction. Other
strategies then emerged, strategies in which many of the basic
concepts of biological catalysis (e.g., strain, proximity,
general acid/base catalysis) were used in the design of molecules
that could guide the generation of catalytic antibodies for a
wide variety of reactions. 3) More recently, efforts have focused
on detailed studies of catalytic antibodies to gain new insights
into the molecular mechanisms of biological catalysis and of the
immune response itself. For example, structural studies of
catalytic antibodies have resulted in important new perspectives
concerning the *combinatorial processes involved in the immune
response. 4) Another direction the field has taken involves
efforts to recapitulate the combinatorial processes of the immune
system in vitro. For example, strategies are now being developed
to directly select *bacteriophage mutants with enhanced catalytic
activities from large libraries of such mutants. Such strategies
are designed to provide a direct linkage between catalysis and
biological amplification in order to produce protein catalysts
for a broad range of chemical reactions. 5) A new strategy for
generating antibody catalysis involves "reactive immunization" --
a designed covalent interaction between immunogen and antibody,
and this technique has now been used to carry out the synthesis
of key intermediates that in turn simplify the synthesis of the
natural product epothilone, a powerful cytotoxic agent of
considerable biomedical interest [*Note #1].
-----------
Peter G. Schultz: Bringing biological solutions to chemical
problems.
(Proc. Natl. Acad. Sci. US 8 Dec 98 95:14590)
QY: Peter G. Schultz, Univ. of Calif. Berkeley 510-642-6000.
-----------
Text Notes:
... ... *antigen: In general, an antigen is any substance or
moiety that produces an immune response.
... ... *transition state: (activated state) In general, in any
chemical reaction, the "transition state" is the high energy
configuration through which the reactants must pass before
becoming products.
... ... *recombination: In general, integration of DNA fragments
into a particular site in a genome.
... ... *somatic mutation: In general, a mutation occurring in
non-germ cells, which means the mutation is not transmitted to
the next generation.
... ... *combinatorial processes: Certain aspects of the immune
response and its production of antibodies apparently mimic a
"combinatorial process" in the sense that many factors are
involved in various combinations, rather than one factor involved
as a predominant determinant. (Combinatorial analysis is a branch
of mathematics involving analysis by means of combinations,
permutations, etc.) Combinatorial chemistry is a recent
technology involving the automated rapid production and screening
of thousands of compounds for specific properties, the population
of compounds consisting of a large number of possible
permutations of chemical constituents. One method, for example,
produces thin-film "libraries" of up to 25,000 different
substances on a 3-inch diameter substrate. The methods are
increasingly used in molecular biology for the production and
screening of large libraries of antibodies, peptides, DNA
ligands, and so on. A random peptide library synthesis may
involve as many as 100 million different peptides, with
subsequent screening of the library for the purposes of drug
discovery.
... ... *bacteriophage: Bacteriophage is a virus that
infects bacteria, the virus essentially consisting of a naked
strand of DNA surrounded by a complex polyhedral shell ("capsid")
composed mainly of glycoproteins.
... ... *Note #1: The Schultz review is a commentary on a
research report appearing in the same issue of the journal: S.C.
Sinha et al: The antibody catalysis route to the total synthesis
of epothilones. ((Proc. Natl. Acad. Sci. US 8 Dec 98 95:14603)
Epothilones are powerful cytotoxic agents isolated from
*myxobacteria (Sorangium cellulosum), the substances exhibiting a
*taxol-like effect on cellular *microtubules.
... ... *myxobacteria: An order of bacteria bearing extracellular
slime.
... ... *taxol: An anti-tumor and anti-leukemic agent isolated
from the bark of the yew tree.
... ... *microtubules: Microtubules are part of the cytoskeleton
of biological cells, the quasi-rigid matrix that among other
things determines cell shape. The microtubules are 25 nanometers
in diameter, and composed of the protein tubulin. They occur in
regular arrays in cilia, flagella, the mitotic spindle, and in
the cytoplasm in general, and they contribute not only to cell
shape, but also to cell motility. 
-------------------
Summary & Notes by SCIENCE-WEEK  29Jan99
-------------------
Related Background:
ANALYSIS OF MONOLAYER FILM CATALYSIS
Substances that exhibit both hydrophilic (affinity for water) and
hydrophobic (affinity for nonaqueous liquids) properties in the
same molecule are called amphipathic, and when the molecular
architecture of amphipathic molecules is such that hydrophilic
and hydrophobic groups are at different ends of a more or less
linear molecule, the molecules of the substance will exhibit
certain special self-organizing properties when they are introd-
uced into an aqueous or nonaqueous liquid phase. In water, for
example, such molecules can form a monomolecular layer at the
surface, with the hydrophilic ends of the molecules interacting
with water, and the hydrophobic ends of the molecules in the
overlying air phase (essentially interacting with themselves).
Irving Langmuir (1881-1957) was the first to make a systematic
study of such interfacial monolayers, and he received the Nobel
Prize in Chemistry in 1932 for his work. Such monolayers can be
treated as two-dimensional phases exhibiting solid, liquid, and
gaseous states, and when compressed to a solid state by appropr-
iate use of mechanical boundaries, it is possible to transfer the
organized layers to a dipped solid surface, forming what are
known as Langmuir-Blodgett films. One can then use these films on
solid surfaces to examine the chemical properties of particular
substances organized in one or more organized molecular layers.
Tollner et al (4 authors at Weizmann Inst., Rehovoth IL) report
the use of catalytically active Langmuir-Blodgett films of a
rhodium complex to determine the effect of the molecular order of
metal complexes on catalytic activity. They found the complex
showed low catalytic activity in solution, but high catalytic
activity in the film, with the film activity highly dependent on
orientation of the complex. The authors suggest the observed rate
dependence on temperature strongly implicates the molecular order
of a metal complex as an important dimension in catalysis.
QY: David Milstein 
(Science 19 Dec 97) (Science-Week 9 Jan 98)


4. EVIDENCE AGAINST A HYPERTHERMOPHILIC COMMON LIFE ANCESTOR
An apparent feature of genome sequences is the presence of traces
of extremely ancient evolutionary events, including perhaps the
very first steps of life on Earth. In the late 1970s, by
sequencing small-subunit *ribosomal RNA (rRNA) genes from various
*eukaryotic and prokaryotic species, Woese and colleagues
constructed for the first time a comprehensive picture of the
"universal tree of life". This work gave rise to conjectures
about the nature of the "most recent common ancestor" of extant
life forms. A hot *auxotrophic origin of life was hypothesized,
consistent with conjectures about the former temperature of
Earth. This scenario was later endorsed by numerous authors and
reached the status of a working hypothesis for the early
evolution of life on Earth. Some researchers, however, have
repeatedly criticized this view, arguing that present-day
*hyperthermophily may be a derived state. Resolution of the
question is considered to be dependent on molecular data, but the
molecular data are obscured by numerous nucleotide base
substitution events that have occurred during billions of years
of *diverging evolution. One approach is to construct realistic
models of molecular evolutionary processes in order to
discriminate between molecular evolutionary signals and noise.
... ... N. Galtier et al (3 authors at 3 installations, FR US)
present a modeling approach to the question of the "most recent
common ancestor". The authors consider the fact that the
nucleotide guanine + cytosine (G + C) content of ribosomal RNA
sequences is apparently strongly correlated with the optimal
growth temperature of prokaryotes. The authors propose that this
property allows inference of the environmental temperature of the
common ancestor to all life forms from knowledge of the G + C
content of the ribosomal RNA sequences of the supposed common
ancestor. The authors devised a model of sequence evolution,
assuming varying G + C content among lineages and unequal
substitution rates among genome sites, the purpose of the model
to estimate ancestral nucleotide base compositions. The authors
applied the model to ribosomal RNA sequences of various species
representing the major apparent lineages of life. The authors
report the inferred G + C content of the common ancestor to
extant life forms appears incompatible with survival at high
temperature, and they suggest this finding challenges the widely
accepted hyperthermophilic origin of life hypothesis. Concerning
extant hyperthermophilic species, the authors suggest these forms
evolved from mesophilic organisms via adaptation to high
temperatures. The authors state: "The hypothesis of a hot origin
of life cannot be ruled out (it may have preceded the "most
recent common ancestor"), but no support from rRNA sequences can
be claimed for it."
-----------
N. Galtier et al: A nonhyperthermophilic common ancestor to
extant life forms.
(Science 8 Jan 99 283:220)
QY: Nicolas Galtier, University C. Bernard, Lyon 1, FR.
-----------
Editor's note: In addition to the background material below, see
the SW Focus Reports "Origin of Life" and "Origin of Life (2)"
available at URL [http://scienceweek.com/swfr.htm].
-----------
Text Notes:
... ... *ribosomal RNA: A ribosome (not to be confused with
riboZYME) is a small particle, a complex of various ribonucleic
acid component subunits and proteins that functions as the site
of protein synthesis.
... ... *eukaryotic and prokaryotic species: Eukaryotes are cells
(and organisms consisting of such cells) that contain
intracellular membrane-bound compartments such as a nucleus
(membrane-bound "organelles"). Prokaryotes are cells (e.g.,
bacteria) without such compartments.
... ... *auxotrophic: An "auxotrophe" is a mutant species
variety, usually a microorganism, that will proliferate only when
its growth medium contains certain specific nutrients not
required by the wild-type (non-mutated) members of the species. 
... ... *hyperthermophily: In general, hyperthermophiles are 
microorganisms whose optimal growth temperature lies above 80
degrees centigrade.
... ... *diverging evolution: In this context, "divergence" is
the acquisition of dissimilar characteristics by related 
organisms in unlike environments.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 2Apr99
-------------------
Related Background:
ORIGIN OF LIFE: A MODEL FOR THE UNIVERSAL ANCESTOR
Biologists have long subscribed to the idea that all life on
Earth arose from a common ancestor. Until recently, nothing
concrete was said about this ancestor, but it was intuitively
assumed to be simple, often likened to a *prokaryote, and
generally held to have had little or no *intermediary metabolism.
Only when biology became defined on the level of molecular
sequences did it become possible to seriously consider the nature
of this ancestor. ... ... Carl Woese (University of Illinois
Urbana-Champaign, US) presents a "genetic annealing" model for
the universal ancestor of all extant life. Physical annealing
involves a first stage heating to a high temperature followed by
a slow cooling of the system to produce new structures,
particularly special crystalline forms. The term "annealing" is
also used in molecular biology to refer to the separation of DNA
strands by heating and the recombination of complimentary strands
by cooling. In Woese's model, the term "annealing" is used in
still a third sense. In the author's model, in the evolutionary
counterpart of physical annealing, the elements of the system are
primitive cells, mobile genetic elements, and so on, and physical
temperature becomes "evolutionary temperature", the evolutionary
"tempo". The evolutionary analog of "crystallization" is
emergence of new structures, new cellular subsystems that are
refractory to major evolutionary change. The author defines the
entities in which *translation had not yet developed to the point
that proteins of the modern type could arise as "progenotes", and
the era during which these were the most advanced forms as the
"progenote era". Concerning "evolutionary temperature", the
author points out that macroscopic evolutionists recognized long
ago a relationship between the "tempo" (rate) of evolution and
its "mode" (a measure of the outcomes). When microbial evolution
finally came into the picture, a similar phenomenon was
encountered on the molecular level, suggesting that this
tempo/mode relationship was a fundamental manifestation of the
evolutionary process. Because of high mutation rates and other
factors, the progenote era is proposed as one of very high
evolutionary tempo. In the author's model, progenotes were very
unlike modern cells, their component parts with different
ancestries, and the complexion of their components changing
drastically over time. Progenotes possessed the machinery for
gene expression and genome replication and at least some
rudimentary capacity for cell division, but the ordinary cellular
functions had no genealogical continuity, since they were too
subject to the confusion of *lateral gene transfer. According to
the author, the transition from progenotes to genotes turned upon
the evolution of translation, the conversion of messenger RNA
code into the specific amino acid sequences of specific proteins.
The author proposes the genetic annealing model as "an attempt to
develop a consistent general picture of the universal ancestor...
The ancestor cannot have been a particular organism, a single
organismal lineage. It was communal, a loosely knit, diverse
conglomeration of primitive cells that evolved as a unit... The
universal ancestor is not an entity, not a thing. It is a process
characteristic of a particular evolutionary stage." The author
concludes with a conjecture that genomes resulting from episodes
of rapid evolution will contain an abnormally high proportion of
foreign genes, and a suggestion that "genome sequences will soon
be available in sufficient number to properly test whether the
tempo/mode relationship (rapid evolution) invariably links
increased mutation rate and increased levels of lateral gene
transfer or vice versa."
QY: Carl Woese (carl@ninja.life.uiuc.edu)
(Proc. Natl. Acad. Sci. US 9 Jun 98 95:6854)
(Science-Week 3 Jul 98)
... ... *prokaryote: Prokaryotes are cells without a cell nucleus
and other membrane-bound organelles.
... ... *intermediate metabolism: The sum of all metabolic
reactions between the uptake of nutrients and the excretion of
waste products.
... ... *lateral gene transfer: This refers to the "horizontal"
transfer of genetic information between individuals of the same
generation, the mechanism involving the incorporation by the
genome of accessible new genetic elements. The process is common
among primitive life forms such as bacteria.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 3Jul98


5. CONVERSION OF NEURAL STEM CELLS INTO BLOOD CELLS
In a multicellular living organism such as a human or a mouse,
what differentiates one cell type from another is apparently not
the genome, since the genome is the same in every cell, but which
parts of the genome are operational. In other words, each cell
type, skin cell, muscle cell, etc., has a particular gene profile
characteristic of that cell type. Cells of a particular cell type
are said to be "differentiated". Stem cells are undifferentiated
cells that in response to appropriate signals differentiate and
give rise to a variety of cell types. Stem cells are common in
embryos, but they have also been identified in adult tissues that
undergo extensive cell replacement due to physiological turnover
or injury, e.g., the *hematopoietic, intestinal, and *epidermal
systems. Stem cells have also been found in the central nervous
system, a tissue believed to be capable of only extremely limited
self-repair. Central nervous system stem cells can generate the 3
major cell types found in the adult brain: *astrocytes,
*oligodendrocytes, and neurons. This is consistent with the view
that the developmental potential of stem cells is restricted to
the differentiated elements of the tissue in which they reside.
But some developmental peculiarities suggest certain cells may be
able to differentiate into cell types that are not of the same
origin. ... ... C.R.R. Bjornson et al (5 authors at 4
installations, CA IT) now report an investigation to determine
whether stem cells are restricted to produce specific cell types,
namely, those from the tissue in which they reside. The authors
report that after transplantation into *irradiated host mice,
genetically labelled mouse neural stem cells were found to
produce a variety of blood cell types, including *myeloid and
*lymphoid cells, as well as early hematopoietic cells. The
authors suggest that neural stem cells appear to have a wider
differentiation potential than previously thought, and that if
they behave similarly to their mouse counterparts, human neuronal
stem cells may provide a renewable and characterized source of
cells that could be used in approaches aimed at hematopoietic
reconstitution in various blood diseases and disorders.
-----------
C.R.R. Bjornson et al: Turning brain into blood: A hematopoietic
fate adopted by adult neural stem cells in vivo.
(Science 22 Jan 99 283:534)
QY: Christopher R.R. Bjornson [adanac@u.washington.edu]
-----------
Text Notes:
... ... *hematopoietic: From hematopoiesis (hemopoiesis,
hematogenesis) Refers to the formation and development of the
various types of blood cells. 
... ... *epidermal: The term "epidermal" refers to the
superficial epithelial portion of the skin. 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.
... ... *astrocytes: (astroglia, macroglia) Glial cells are more
numerous than neurons in the brain, but their function has been
generally characterized as "metabolic" or "supportive", without
much discussion of details. Astrocytes are the largest glial
cells, with many extensions radiating outward like a starburst,
and at least one of their functions is apparently to maintain the
so-called "blood-brain barrier" effectively separating neural
tissue from blood.
... ... *oligodendrocytes: (oligodendroglia) Glial cells
characterized by sheet-like processes that are wrapped around
individual neuron axons to form the myelin sheath of nerve fibers
in the central nervous system. (The myelin sheath of a nerve
fiber is effectively a periodically interrupted insulation which
increases the propagation velocity of nerve impulses.)
... ... *irradiated host mice: In this investigation, host
animals were radiated before transplantation in order to reduce
the population of immune system blood cells, this reduction
apparently intensifying the signals resulting in donor stem cell
differentiation.
... ... *myeloid: Refers to bone marrow cells or cells derived
from bone marrow cells.
... ... *lymphoid cells: Refers to cells of the lymphatic system.
The lymphatic system is a complex network for the distribution of
lymph fluid (which is similar to blood plasma -- blood without
red cells).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 2Apr99
-------------------
Related Background:
RESEARCH USE OF STEM CELLS APPROVED BY NIH
It is probable that one of the major public debates in the coming
months will concern the use of human stem cells in research (see
related background report below). On 19 January 1999, the US
Department of Health and Human Services announced that a
Congressional ban on human embryo research does not apply to
human stem cells, and federally financed researchers will soon
be able to work on these cells. In its ruling, the Office of
the General Counsel of the US health department said that because
stem cells by themselves do not have the capacity to develop into
a human being, they cannot be considered embryos. Deriving the
cells from human embryos is legal, provided it is not done with
federal money. Harold E. Varmus, director of the US National
Institutes of Health, has stated it would still be illegal for
researchers to use federal money to derive their own stem cells
from human embryos, but they can now use federal money to work on
the cells obtained by others, in particular the stem cells
obtained by James Thompson (University of Wisconsin, US) from
human embryos created in surplus amounts in a fertility clinic.
The new US government ruling on the use of human stem cells is
opposed by the US National Conference of Catholic Bishops, and
the ruling is still subject to modification or elimination by the
new US Congress.
(New York Times 20 Jan 1999)
-------------------
Summary by SCIENCE-WEEK  29Jan99
-------------------
Related Background:
EMBRYONIC STEM CELLS DERIVED FROM HUMAN BLASTOCYSTS
*Embryonic stem cells are derived from *totipotent cells of the
early mammalian embryo and are capable of *unlimited and
undifferentiated proliferation in vitro. In *chimeras with intact
embryos, mouse embryonic stem cells contribute to a wide range of
adult tissues, including *germ cells, providing a powerful
approach for introducing specific genetic changes into the mouse
*germ line. ... ... J.A. Thompson et al now report the production
of human *blastocyst-derived *pluripotent cell lines that have
normal chromosome characteristics, express high levels of
*telomerase activity, and express *cell surface markers that
uniquely characterize primate embryonic stem cells. The authors
report that after undifferentiated proliferation in vitro for 4
to 5 months, these cells still maintained the developmental
potential to form *trophoblast, and to form derivatives of *all 3
embryonic germ layers, including gut *epithelium (mesoderm) and
neural epithelium, embryonic *ganglia, and *stratified squamous
epithelium (ectoderm). The authors suggest these cell lines
should be useful in human developmental biology, drug discovery,
and transplantation medicine. ... ... In a related commentary in
the same journal, J. Gearhart makes the following points: 1) A
renewable tissue-culture source of human cells capable of
differentiating into a wide variety of cell types would have
broad applications in basic research and transplantation
therapies. A major step in realizing this goal has now been taken
with the demonstration that human embryonic stem cells can be
grown in culture. 2) In the work of J.A. Thompson et al, four
cell lines tested produced *teratomas when grown in
*immunosuppressed mice. Histology of the tumors revealed
differentiated cells derived from all 3 embryonic germ layers
(ectoderm, mesoderm, and definitive endoderm) -- a result
consistent with pluripotency. 3) The derivation of human
embryonic stem cells now raises a whole new set of expectations.
On the basis of the already completed use and study of mouse
embryonic stem cells, the research and clinical potential for
human embryonic stem cells is enormous. They will be important
for in vitro studies of normal human embryogenesis, abnormal
development (through the generation of cell lines with targeted
gene alterations and engineered chromosomes), human gene
discovery, drug and *teratogen testing, and as a renewable source
of cells for tissue transplantation, cell replacement, and gene
therapies. These latter applications could eventually make
unnecessary the direct use of fetal tissue in transplantation
therapies [*Note #1].
-----------
J.A. Thompson et al (7 authors at 2 installations, US IL)
Embryonic stem cell lines derived from human blastocysts.
(Science 6 Nov 98 282:1145)
QY: James A. Thompson, University of Wisconsin 608-262-3961.
-----------
J. Gearhart (Johns Hopkins University, US)
New potential for human embryonic stem cells.
(Science 6 Nov 98 282:1061)
QY: John Gearhart 
-----------
Text Notes:
... ... *Embryonic stem cells: In general, the term "stem" cells
refers to undifferentiated cells that upon differentiation can
give rise to various specialized cell lines such as blood cells,
skin cells, nerve cells, etc. Adult bone marrow, for example,
contains stem cells that are the precursors of the various
specialized types of blood cells. "Embryonic" stem cells are
specifically stem cells derived from the embryo only.
... ... *totipotent cells: Cells that have the ability to
differentiate into any type of cell and thus form a new organism
or regenerate any part of an organism.
... ... *unlimited and undifferentiated proliferation in vitro:
In general, differentiated "normal" cells in tissue culture
produce a limited number of replications. In contrast, embryonic
stem cells and many types of cancer cells in tissue culture show
unlimited replications, and are thus called "immortal" cell
lines. In this context, "undifferentiated" proliferation is
simply proliferation without cell differentiation
(specialization).
... ... *chimeras: In this context, an animal that has received a
transplant of genetically and immunologically different tissue.
In this report, the transplant involves the injection of human
cultured stem cells into mice.
... ... *germ cells: In general, reproductive cells. All other
cells are "somatic" cells.
... ... *germ line: In general, this refers to the line of
differentiated germ cells.
... ... *blastocyst: A mammalian egg in the later stages of
*cleavage but before implantation in the uterus. The blastocyst
consists of a hollow fluid-filled ball of cells and an inner cell
mass (embryonic stem cells) from which the embryo develops.
... ... *cleavage: The early and rapid division stage that
divides the fertilized egg into smaller and smaller cells
(blastomeres) while retaining the same overall size of the
embryo.
... ... *pluripotent cell: A cell that has the potential,
depending on conditions, to give rise to many differentiated cell
lines but which lacks complete totipotency.
... ... *telomerase: Telomeres are defined ends of chromosomes
that contain specific repeated DNA sequences. They are 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.
... ... *cell surface markers: Cell surface proteins or protein
components that can be chemically identified.
... ... *trophoblast: In the early vertebrate embryo, the outer
ectodermal cell layer of the blastocyst. In mammals, it is the
trophoblast that attaches to the uterus and forms the placenta.
... ... *all 3 embryonic germ layers: In the embryos of higher
animals, there occurs the transformation of a single-layer
blastula into a 3-layered gastrula consisting of ectoderm,
mesoderm, and endoderm surrounding a cavity with one opening. The
3 layers are called the "germ layer", and these layers, via
further cell differentiation and proliferation, determine the
development of all the major body systems and organs.
... ... *epithelium: In animals, 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.
... ... *ganglia: (singular: ganglion) In the context of cells,
the original meaning of "ganglion" was any cluster of nerve cell
bodies in the central or peripheral nervous system. Currently,
the term "ganglion" refers to a aggregation of nerve cell bodies
located in the peripheral nervous system. Unfortunately, many
neuroanatomy texts still label certain neuron clusters in the
central nervous system in the old way (e.g., basal ganglia).
... ... *stratified squamous epithelium:  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. In this
context, "stratified squamous epithelium" refers to a structure
consisting of distinctly layered epithelial cells (layers varying
in size and shape of cells), the top layer of which are squamous
cells.
... ... *teratomas: A teratoma is a neoplasm (tumor) composed of
multiple tissues, including tissues not normally found in the
organ in which it arises. A teratoma in the adult human ovary,
for example, can contain hair, teeth, skin, heart muscle, nerve
cells, and so on -- all a result of "wild" cellular
differentiation of neoplastic cells, but with enough regulation
so that distinct tissues are formed. In the context of this
report, the teratomas occurred in mice after injection of
cultured human stem cells, thus demonstrating the ability of
those stem cells to differentiate into organized specific tissue-
producing cells.
... ... *immunosuppressed mice: In general, this refers to mice
whose immune system response has been suppressed by chemical,
biological, or physical means. In this report, the purpose of the
immunosuppression was to allow the development of a mouse
teratoma provoked by injection of human stem cells. Without
immunosuppression, the human stem cells would be immediately
attacked and possibly destroyed by the mouse immune system before
the stems cells could differentiate.
... ... *teratogen: Any drug or other agent that causes abnormal
fetal development.
... ... *Note #1: We repeat here a quotation that appeared at the
head of a recent issue of SW: "Between the fifth and tenth days
the lump of stem cells differentiates into the overall building
plan of the mouse embryo and its organs. It is a bit like a lump
of iron turning into the space shuttle. In fact it is the
profoundest wonder we can still imagine and accept, and at the
same time so usual that we have to force ourselves to wonder
about the wondrousness of this wonder." -- Miroslav Holub
-------------------
Summary & Notes by SCIENCE-WEEK  27Nov98


6. BACTERIOLOGICAL ANALYSIS OF INFECTED DOG AND CAT BITES
Each year, several million people in the US are bitten by
animals, resulting in approximately 300,000 visits to emergency
departments, 10,000 hospitalizations, and 20 deaths, mostly among
young children. Ninety percent of these animal bites are from
dogs and cats, and 3 to 18 percent of dog bites and 28 to 80
percent of cat bites become infected, with occasional sequels of
*meningitis, *endocarditis, *septic arthritis, and *septic shock.
Microbiological studies of dog and cat bites have previously been
limited to case series of small numbers of selected patients at
single centers that used inexact infection criteria and variable
techniques of specimen collection and pathogen isolation.
... ... D.A. Talan et al (24 authors at 17 installations, US) now
report a study to delineate the bacteriology of common dog and
cat bites infections and to improve the accuracy of empirical
therapy. The authors conducted a multicenter study of dog bites
and cat bites that met specific criteria for infection and that
included culturing of specimens for both *aerobic and anaerobic
bacteria at a research laboratory. The authors report that
*pasteurella species were the most frequent isolates from both
dog bites (50 percent) and cat bites (75 percent). Other common
aerobes included *streptococci, *staphylococci, *moraxella, and
*neisseria. Common anaerobes included *fusobacterium,
*bacteroides, *porphyromonas, and *prevotella. In total, over 100
different microbial species were isolated, with a number of
isolates from the wounds not been previously identified as human
pathogens. The authors suggest that infected dog and cat bites
have a complex microbiological mix that usually includes
pasteurella species, but which may also include many other
organisms not routinely identified by clinical microbiology
laboratories and not previously recognized as bite-wound
pathogens.
-----------
D.A. Talan et al: Bacteriologic analysis of infected dog and cat
bites.
(New England J. Med. 14 Jan 99 340:85)
QY: David A. Talan, Univ. of Calif. Los Angeles 310-825-4321.
-----------
Text Notes:
... ... *aerobic and anaerobic bacteria: An "aerobe" is an
organism that can live and grow in the presence of oxygen. An
"anaerobe" refers to a life form or process sustained in
the absence of free (gaseous or dissolved) oxygen.
... ... *meningitis: In general, this term refers to any
inflammation of the connective tissue membranes (meninges) of the
brain or spinal cord.
... ... *endocarditis: In general, any inflammation of the
endocardium, the innermost layer (tunic) of the heart.
... ... *septic arthritis: In general, any form of arthritis
caused by infectious pathogens.
... ... *septic shock: In this context, shock is a sudden
physical or mental disturbance, and "septic shock" is such a
disturbance caused by a pathogenic invasion.
... ... *pasteurella: A genus of bacteria, parasites of humans
and other animals, and with species common to domestic dogs and
cats.
... ... *streptococci: A genus of bacteria parasitic in humans
and other animals, common in the mouth and intestines.
... ... *staphylococci: A genus of bacteria parasitic in humans
and other animals. Found on the skin, in skin glands, on nasal
and other mucous membranes of warm-blooded animals, and in
various food products.
... ... *moraxella: A genus of bacteria parasitic on the mucous
membranes of man and other animals.
... ... *neisseria: A genus of bacteria parasitic in animals.
... ... *fusobacterium: A genus of bacteria found in body
cavities of man and other animals.
... ... *bacteroides: A genus of bacteria found in the oral,
respiratory, intestinal, and urogenital cavities of humans and
other animals.
... ... *porphyromonas: A genus of bacteria common in man and
other animals.
... ... *prevotella: A genus of bacteria found in man and other
animals.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 2Apr99


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
IN FOCUS: ON DIFFERENCES AMONG HUMAN POPULATIONS

"To what extent are the differences among human populations based
on either adaptation to specific environments or on the history
of the population, race, or nation? Unless differences are
adaptive, they cannot have evolved by natural selection. However,
differential adaptiveness is not necessarily the result of
biological evolution alone. If a learned trait can be transmitted
faithfully by cultural means from one generation to the next, it
is also subject to selection and can spread because of its
adaptive value. Furthermore, a culturally transmitted trait can
spread and alter the way of life of a population much more
rapidly than one based on genes. The spread of genes is greatly
retarded by the length of human generations. If subject to
selection pressures similar to those in insect populations, a
human gene would require hundreds of years to become fully
established in a population of moderate size. By contrast,
cultural traits have spread through large populations in less
than a decade. Faced with new and drastic environmental
challenges, human populations can become adjusted far more
rapidly by cultural means than by biological evolution.
Sociobiological theory has paid too little attention to this
basic fact."

-- G. Ledyard Stebbins: _Darwin to DNA, Molecules to Humanity_
   (W.H. Freeman, New York 1982, p.390)


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