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 16, 1999 -- Vol. 3 Number 16

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I can live with doubt and uncertainty and not knowing. I think
it's much more interesting to live not knowing than to have
answers which might be wrong. I have approximate answers and
possible beliefs and different degrees of certainty about
different things, but I'm not absolutely sure of anything and
there are many things I don't know anything about...
-- Richard Feynman (1918-1988)

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

Contents of This Issue:

1. Alarm Over Decline in Number of US Physician-Scientists
2. On Neutron Stars
3. On Chromosome Mechanics
4. Hypoglossal Canal Size and Hominid Speech
5. Chimpanzee Origin of HIV-1 Epidemic
6. Biology of Atherosclerosis

-- In Focus: On the Social Unit of the Higher Primates

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

1. ALARM OVER DECLINE IN NUMBER OF US PHYSICIAN-SCIENTISTS
In general, the term "physician-scientist" refers to MDs who
devote all or a majority of their professional effort to research
concerning health and disease. The designation thus includes
basic, disease-oriented, patient-oriented, population-oriented,
and prevention-oriented investigators. In the US, there is
apparently a current great concern about an evident "dangerous"
decline in the number of physician-scientists. ... ... Leon E.
Rosenberg (Princeton University, US) presents a short review of
the problem and a number of possible remedies, the author's
points including the following:
... ... 1) The decline is not a new problem, and was already
discussed 20 years ago. The problem has been repeatedly discussed
during the past 2 decades, particularly with respect to patient-
oriented research.
... ... 2) The author suggests the problem must be addressed now
for a number of reasons: a) The entire species of physician-
scientist is apparently at risk, not only those doing patient-
oriented research. b) Endangering physician-scientists endangers
everyone concerned with medical research. c) The actions taken to
date cannot solve the problem. d) The threat can be averted only
by bold, concerted action on the part of all the participants in
the US medical research enterprise.
... ... 3) The number of first-time MD applicants for National
Institutes of Health (NIH) research project grants decreased 31
percent from 1994 to 1997. If this progression continues
linearly, there will be zero applicants by 2003. (The drop in
first-time MD applicants was not compensated by an increase in
applications from MD/PhD applicants.)... The data indicate that
progressively fewer young MDs are interested in (or perhaps
prepared for) careers as independent NIH-supported investigators.
... ... 4) Since 1992, there has been a 51 percent decrease in
the total number of MD postdoctoral trainees supported by NIH
through individual fellowships and training grants. If this trend
continues, there will be no MDs in this pool by 2006.
... ... 5) Recent data from the Howard Hughes Medical Institute
(HHMI) indicate that in the past 2 years there has been a 57
percent decrease in the number of MDs applying for the
prestigious HHMI postdoctoral fellowships.
... ... 6) In 1989, 14 percent of graduating medical students
expressed a strong interest in research as a career; in 1996, the
number was 10 percent.
Concerning disincentives, the author points out that the debt
burden for US medical school graduates now averages US$80,000, a
debt difficult to manage via the modest stipends paid to
postdoctoral trainees. The author concludes: "We must act now to
create a national environment conducive to creating a new
generation of physician-scientists who have been trained
rigorously and are confident in their ability to compete and
succeed. Above all, these young investigators must be imbued with
the belief that their efforts are essential."
-----------
Leon E. Rosenberg: Physician-scientists -- endangered and
essential.
(Science 15 Jan 99 283:331)
QY: Leon E. Rosenberg [lrosenberg@molbio.princeton.edu]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 16Apr99
-------------------
Related Background:
ON THE OVERPRODUCTION OF US BIOMEDICAL RESEARCHERS
There are always practical problems concerning the training of
scientists, but two persistent questions are How many? and Where
do they work? Marincola and Solomon (2 installations, US), in a
recent editorial in the journal *Science*, review the current
problems in the training of biomedical research scientists (and
propose a solution), but the ideas are perhaps just as applicable
to physics and chemistry. The authors make the following points: 
1) Although the number of biomedical research trainees in the US
has expanded considerably over the past 20 years, the number of
tenured positions is declining. 2) The average time to obtain a
PhD rose from 4.4 years in the 1970s to 5.6 years in the 1990s.
3) Each principal investigator trains many times the single
scientist required to replace himself or herself. This intrinsic
instability could threaten the profession. 4) Many researchers
perceive that science is thriving at increasing and unacceptable
cost to those being trained. In strictly economic terms, it is in
the interest of senior investigators to maintain the number of
trainees, who work long hours in large numbers for little pay
over many years in return for the chance to develop a satisfying
career. 5) A solution may be to uncouple scientific productivity
from an investigator's ability to attract and employ trainees --
the creation of permanent research positions for scientists who
would neither compete for grants nor train others. They would be
supported through investigators who hold traditional academic
appointments. The authors give as an example the institution of
3-year positions for researchers at the Scripps Institute (US).
The essential idea, then, is the amplification of the number of
already existing non-tenure "research associate" positions, these
positions to be filled by PhDs on a continuing short-term
contract basis. The authors state: "This career track could be
recognized explicitly, legitimized, and nourished to become an
element of the research enterprise." The editorial does not
address the question of how this two-tier structure will satisfy
the career objectives of young scientists who are first-rate, but
because of lack of employment opportunities, are forced into the
second tier.
QY: Elizabeth Marincola 
(Science 31 Jul 98 281:64) (Science-Week 28 Aug 98)


2. ON NEUTRON STARS
During the terminal stages of the evolution of a star, part of
the mass of the star is blown off and lost. If the remnant mass
is between 1.4 and 2 to 3 solar-masses, the star will collapse
into a neutron star, a body with a radius of only 10 to 15
kilometers, but with a core so dense that its component protons
and electrons have merged into neutrons. The average density of a
neutron star is 10^(15) grams per cubic centimeter and the weight
of an object on the surface of a neutron star would be 10^(11)
times its weight on the surface of the Earth. Neutron stars
apparently have an outer shell of iron, but it is iron like no
Earth iron, an iron of 4 orders of magnitude greater density.
Theory predicts that a neutron star should rotate very rapidly,
be extremely hot, and have an intense magnetic field. *Pulsars,
sources of pulsed radio energy, are evidently spinning neutron
stars which emit beams of radiation from their magnetic poles. A
few pulsars have been found in *binary systems, and the empirical
estimated masses of the pulsars are consistent with the masses
predicted by neutron star models. ... ... L. Bildsten and T.
Strohmayer (2 installations, US) present a review of current
research concerning neutron stars, the authors making the
following points: 1) With a density comparable to that of an
atomic nucleus, a neutron star provides an extreme environment
for fast and violent phenomena. Matter orbiting a neutron star
can have a period as short as a millisecond. When such matter
crashes into the star (i.e., is "accreted" by the star), such
matter can be moving at one-third the speed of light. In general,
because their behavior can vary over readily observable
timescales, neutron stars can be rich sources of information
about nuclear physics, general relativity, and astrophysics. 2)
Though relatively elusive, neutron stars have been detected and
studied over a broad range of electromagnetic frequencies, from
radio frequencies to *gamma rays. To date, astronomers have
identified more than 1000 of the estimated 10^(8) neutron stars
in our galaxy. New orbiting astronomical satellites have produced
recent rapid growth in our knowledge of these objects, with much
of the progress occurring in our understanding of neutron stars
that undergo sudden large energy releases. 3) Although most
neutron stars have been discovered as radio pulsars, only a small
fraction of the radiated energy of a neutron star (typically
approximately 10^(-5)) is expected to be radio emission energy.
Most of the energy instead departs as photons with energies above
10^(8) *electronvolts. 4) The precise timing of radio pulsars has
yielded astonishing astronomical discoveries, such as multiple
Earth-mass planets orbiting a neutron star, and the direct
confirmation of the loss of orbital angular momentum due to
gravitational radiation in a double neutron star binary system
(for which Russell Hulse and Joseph Taylor received the 1993
Nobel Prize in Physics). 4) The brightest accreting neutron stars
reside in binary systems and accrete matter from their
companions. These accreting neutron stars typically have
luminosities more than a thousand times that of the Sun. 5) There
is every reason to believe that new classes of neutron stars will
be discovered by continued observations from the currently
orbiting satellites combined with the international fleet of new
x-ray and gamma-ray satellites planned for launch during the next
two years.
-----------
Editor's note: In addition to the background material below, see
the SW Focus Report "The Death of Stars" available at URL
[http://scienceweek.com/swfr002.htm]
-----------
L. Bildsten and T. Strohmayer: New views of neutron stars.
(Physics Today February 1999)
QY: Lars Bildsten, Univ. of Calif. Berkeley, 510-643-8520.
-----------
Text Notes:
... ... *Pulsars: Pulsars were originally discovered at
radio wavelengths, but there are optical, gamma-ray, and x-ray
pulsars, and some of the gamma-ray pulsars are extremely powerful
gamma-ray emitters.
... ... *binary systems: Binary stars are a pair of stars
revolving around a common center of mass under the influence of
their mutual gravitational attraction, and apparently the
majority of stars in the Universe are binaries and not singlets.
In some cases the binary system is resolvable into two
components, and in other cases the presence of a second star is
inferred by perturbations in the motion or emitted radiation of
the first star. If the binaries are close enough, they may share
stellar material, and this results in a particular kind of
stellar evolution.
... ... *gamma rays: Gamma rays are radiation of high energy,
from about 10^(5) *electronvolts to more than 10^(14)
electronvolts -- radiation with the shortest wavelengths and
highest frequencies, the gamma ray region of the electromagnetic
spectrum merging into the adjacent lower energy x-ray region.
... ... *electronvolts: An  electronvolt is defined as the energy
acquired by an electron falling freely through a potential
difference of one volt, and is equal to 1.6022 x 10^(-19) joule.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Apr99
-------------------
Related Background:
ON NEUTRON STARS AND THE FLUID PROPERTIES OF HOT ATOMIC NUCLEI
... ... Viola and Kwiatkowski (Indiana University Bloomington,
US), in a review of a current experimental approach to
understanding the dynamics of neutron star structure, make the
following points: 1) During the catastrophic collapse of stellar
material in the core of a star destined to become a neutron star,
gaseous nuclear matter is believed to condense to the liquid
phase. A giant nucleus, or neutron star, is formed in this
nuclear phase transition. 2) In order to understand the formation
of neutron stars and black holes, it is essential to know the
conditions under which nuclear matter changes from the gas phase
to the liquid phase. These conditions are expressed, both for
nuclear matter and for ordinary matter, in terms of an equation
of state  -- the thermodynamic equation that describes the phase
behavior of a substance as a function of temperature, pressure,
and composition. 3) In the case of the neutron star, the only
accessible approach is to study the reverse process, the
expansion and vaporization of heavy atomic nuclei, which approach
a neutron star's density and, in the intranuclear domain, share
many of its fluid properties. 4) The authors review their work
using ISiS (the Indiana Silicon Sphere detector), an apparatus
designed to study fragments ejected from an atomic nucleus after
the nucleus is "boiled" by the energy of a light-ion collision in
a particle accelerator. In the "soft explosions" analyzed by
ISiS, the nucleus vaporizes. By measuring the charges,
velocities, and flight paths of nuclear fragments, ISiS has
provided evidence that atomic nuclei indeed behave like droplets
of a liquid that expand as they are heated until they reach a
boiling point of approximately 10^(11) degrees Kelvin. 5) Various
tests distinguish between the extremes of boiling and shattering.
For example, a signature of phase transition (in this case,
boiling) is that fragments are emitted randomly in all
directions, rather than preferentially emitted in the direction
of the incident projectile. 6) Essentially, the result of these
experiments is that a class of collision events has been observed
that exhibits many characteristics expected for a phase
transition in nuclear matter. The major task is now to make a
quantitative connection between the data and nuclear
compressibility, in particular the nuclear compressibility of the
core of neutron stars and black holes.
QY: Vic Viola [vicv@iucf.indiana.edu]
(American Scientist October 1998) (Science-Week 4 Sep 98) 
-------------------
Related Background:
A MILLISECOND PULSAR IN AN X-RAY BINARY SYSTEM
A pulsar is a regularly pulsating source of radiation, the
pulsations believed to involve the magnetic field of a rotating
neutron star. Pulsars were originally discovered at radio
wavelengths, but they have also been detected at optical and
gamma-ray wavelengths. They can be powerful gamma-ray emitters
(gamma-ray pulsars), and there is also a class of x-ray pulsars.
The periods of pulsars range from approximately 1.5 milliseconds
to 4 seconds and can typically be measured to accuracies of one
part in 10^(10). Pulsars with periods shorter than approximately
0.01 seconds constitute the distinct class of millisecond
pulsars. Most pulsars are single stars, but binary pulsars are
known, about half of which are millisecond pulsars. The
millisecond-pulsar neutron star is believed to be rotating
hundreds of times per second, and a large number of millisecond
binary pulsars have been discovered in globular clusters. The
origin and evolution of pulsars has not been clear, but it has
been thought that millisecond radio pulsars, which are often
found in binary systems, start as ordinary pulsars, then lose
most of their magnetic field and "spin up" to millisecond periods
by the accretion of matter (and transfer of angular momentum)
from a companion star in an x-ray binary system. Until now, there
has been no direct proof of this idea in the form of predicted
coherent millisecond x-ray pulsations in the flux of an x-ray
binary. ... ... Wijnands and van der Klis (2 installations, NL
US) now report the discovery of such a pulsar, confirming
theoretical expectations. The authors suggest the source will
probably become a millisecond radio pulsar when the accretion
turns off completely. ... ... In a contiguous paper, Chakrabarty
and Morgan (Massachusetts Institute of Technology, US) report
that the orbital period of this binary system is 2 hours, and
that the system seems closely related to "black-widow"
millisecond radio pulsars, a class of pulsars that completely
consume their binary companions.
-----------
QY: Michiel van der Klis [michiel@astro.uva.nl]
QY: Deepto Chakrabarty [deepto@space.mit.edu]
(Nature 23 Jul 98 394:344,346) (Science-Week 14 Aug 98)


3. ON CHROMOSOME MECHANICS
In biology, the full cycle from nondividing cell to dividing cell
to nondividing daughter cells is called the "cell cycle". In a
nondividing biological cell, DNA and its associated proteins are
loosely packed, forming a network called "chromatin". During cell
division, DNA and certain proteins condense and coil into rod-
shaped bodies called "chromosomes". Because of the coiling,
chromosomes contain a large amount of DNA relative to their size.
Each chromosome is apparently a single DNA molecule, highly
folded and coiled, combined with a variety of protein molecules.
This is the general DNA architecture for all living cells, but
cells with internal organelles such as a nucleus (eukaryotes) and
cells without such organelles (prokaryotes) differ in further
complexities. Through an electron microscope, chromatin in
eukaryote cells appears as "beads-on-a-string". Each bead is a
"nucleosome", consisting of double-stranded DNA wrapped twice
around a core of 8 proteins (*histones). The string between the
beads is called "linker DNA". The nucleosomes are folded into a
larger structure called a "chromatin fiber", and these fibers in
turn fold into large loops. In cells that are not dividing, this
is the extent of DNA packing. Before cell division, the DNA
duplicates and the chromatin strands subsequently shorten and
coil even further to form "chromatids". During the cell division
cycle, a pair of chromatids ("sisters") makes a new chromosome,
two identical sets of chromosomes are mechanically separated by a
specialized macromolecular apparatus (*spindle apparatus), the
entire cell cleaves into two daughter cells, and cell division is
thus completed. An apparently simple scheme in summary, but
surely one of the wonders of the natural world.
... ... Tatsuya Hirano (Cold Spring Harbor Laboratories, US)
presents a review of current research concerning chromosome
mechanics, the author making the following points: 1) The dynamic
behavior of chromosomes was described by cytologists long before
the central role of DNA as the genetic material was recognized,
and long before the biochemical basis of cell cycle progression
was elucidated. Nevertheless, the molecular mechanisms underlying
the structural changes of chromosomes during the cell cycle have
remained poorly understood. 2) A recent breakthrough in this
field was the discovery of a new family of chromosomal *ATPases,
called the "structural maintenance of chromosomes" family (SMC
family) that are apparently involved in chromosome condensation
and adhesion. These proteins are large polypeptides between 1000
and 1500 amino acids long that share in common several structural
motifs. 3) SMC proteins are apparently key components that
regulate a wide variety of chromosomal events from bacteria to
humans. Although recent studies have uncovered diverse cellular
functions and unique biochemical activities of these new
chromosomal ATPases, we still do not understand how they are
functionally related and mechanistically linked. 4) The author
suggests that ATP-modulated cross-linking of DNA represents the
key mechanism underlying all actions of SMC proteins, and that in
eukaryotes, combinatorial association of different SMC and non-
SMC subunits allows each SMC protein complex to acquire
specialized cellular functions.
-----------
Tatsuya Hirano: SMC-mediated chromosome mechanics: a conserved
scheme from bacteria to vertebrates?
(Genes & Development 1 Jan 99 13:11)
QY: Tatsuya Hirano [hirano@cshl.org]
-----------
Text Notes:
... ... *histones: The nucleosome is a tertiary structure of
chromosomal DNA found in eukaryotic cells. In chromosomes, about
every 200 nucleotides, the DNA double helix is coiled around a
complex of 8 histone proteins, the entire assembly having the
appearance of beads on a string. The beads of nucleosomes are in
turn supercoiled into a solenoid structure, and the entire
complex of the eukaryotic chromosome is called "chromatin". The
small histones proteins are basic (as opposed to acidic)
proteins, and they are essential in forming nucleosomes. The
nucleosomes are apparently one of the key elements in the
solution to the DNA packing problem. The packing problem can be
stated as follows: Were the DNA contained in a typical cell
nucleus extended, it would measure a meter or more in length.
Since the nucleus itself is usually no more than 5 to 10
micrometers in diameter, there is a topological problem in the
packing of the enormous length of DNA into a volume 6 orders of
magnitude less than the extent of the molecule. The topological
packing problem is solved by systematic and repeated foldings of
the DNA molecule in conjunction with nuclear protein molecules
that bind to DNA and fold it into chromatin fibers. Our
understanding of the details of these molecular arrangements
essentially began with the x-ray diffraction observations by
Wilkins in the late 1960s that purified chromatin fibers show a
repeating structure with a periodicity of 10 nanometers. A decade
later, new methods of preparation of chromatin for the electron
microscope provided the first visualization of the nucleosome
"beads-on-a-string" structure.
... ... *spindle apparatus: (mitotic spindle) A microtubule
apparatus appearing during cell division. 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. In
the case of cell division, the microtubules apparently generate a
sliding force that results in the pushing and pulling of cell
components and the eventual pulling apart of the two poles of the
cell.
... ... *ATPases: ATP (adenosine triphosphate) is the most
important chemical energy source in all living cells, intimately
involved in various cell functions and cell metabolism, and an
entity in numerous cyclic chemical pathways involved in the
synthesis of components. An ATPase is an enzyme that catalyzes
the hydrolysis of adenosine triphosphate to adenosine diphosphate
and orthophosphate.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Apr99
-------------------
Related Background:
MOLECULAR BIOLOGY: MEGAPLASMIDS VS. MINICHROMOSOMES
In general, the term "eukaryotes" refers to organisms with
internal membrane-bound compartments, and the term "prokaryotes"
refers to organisms without such compartments. Most biologists
now further dichotomize the prokaryotes into 2 major groups, the
bacteria and the archaebacteria. The bacteria have been studied
extensively, but many of the archaebacteria are difficult to
study in the laboratory (*Note #1). Most prokaryotic genes are
carried on a single circular chromosome containing approximately
4 million base pairs of DNA. But many prokaryotes contain
additional genes on smaller circular or linear molecules of DNA
called "plasmids", which contain from several thousand to 100,000
base pairs of DNA. These DNA entities (chromosomes and plasmids),
which contain genetic information necessary for their own
independent replication, are called "replicons". The classical
dogma concerning prokaryotes has been that they have only a
single circular chromosome, with essentially all smaller
replicons in these cells relegated to the status of plasmids
("extra-chromosomal elements"). In general, the idea has been
that the chromosome contains genes essential for cell viability,
while the plasmids are mainly auxiliary to the genome, containing
genes coding for proteins involved in special functions such as
chemical resistance, toxin-production, symbiosis, etc. But of the
many plasmids that have been characterized, several are
"megaplasmids" from a hundred kilobases to megabase size, and
during the past few years, some of these have been found to
contain genes that are normally thought to be essential for cell
viability. These findings have led to the suggestion that
prokaryotic genomes may be composed of multiple essential
replicons, and that some replicons originally classified as
megaplasmids may in fact be chromosomes. A problem is that at
present there is no apparent consensus concerning the criteria
for chromosomal status, and the criteria could involve essential
genes, size, replication control, evolutionary history, and so
on. ... ... W.V Ng et al (12 authors at 2 installations, US) now
report the complete nucleotide sequence of the plasmid (pNRC100)
of a *halobacterium strain and analysis of its elements and
coding capacity. The authors report this plasmid circle comprises
191,346 base pairs containing a total of 186 likely genes, a
number of which are considered to be genes critically essential
for viability, including a gene for a chromosome replication
initiator protein. The authors suggest the finding of such
essential genes on this plasmid raises the question of the
precise distinction between plasmids and chromosomes, and they
propose that certain replicons could be considered to occupy an
intermediate status between plasmids and chromosomes and may
represent evolutionary intermediates in the formation of new
chromosomes (or the breakdown of old ones).
-----------
W.V. Ng et al: Snapshot of a large dynamic replicon in a
halophilic archaeon: Megaplasmid or minichromosome?
(Genome Research November 1998 8:1131)
QY: Shiladitya DasSarma 
-----------
Text Notes:
... ... *Note #1: Some archaebacteria, for example, are killed by
contact with oxygen; others grow at temperatures exceeding that
of boiling water; the methanogens carry out an anaerobic
respiration that gives rise to methane; the halophiles demand
extremely high salt concentrations for growth; the thermo-
acidophiles require high temperature or acidity or both. It has
now been established that these archaebacteria prokaryotes share
biochemical traits that set the group entirely apart from all
other living organisms. (See below for background material on the
controversy concerning the classification of archaebacteria.)
... ... *halobacterium strain: The halobacterium strain (NRC-1)
involved in this study grows optimally at a nearly saturated (4.5
molar) sodium chloride concentration.
-------------------
Summary & Notes by SCIENCE-WEEK  1Jan99
-------------------
Related Background:
EVIDENCE FOR SELF-ORGANIZATION OF CELL MICROTUBULES
Biologists who study cells with the light microscope are always
presented with a panoply of striking visible events in time, the
cell movements, particularly those inside the cell, and especi-
ally those involved in cell division. Our understanding of what
is happening at the molecular level to produce these movements is
far from complete, but we do know much more than we did a decade
ago. Several cell "motor" protein molecules called kinesins have
been identified. The microtubules, along which the cell motors
appear to move, are thin hollow protein cylinders found in eukar-
yote cells and are assembled from globular monomers of the
protein "tubulin". Asters, classical structures, are spherical
arrays of microtubules that occur during cell division. Now F. J.
Nedelec et al (Princeton University, US; E.S. Physique et Chimie,
Paris FR) report that dynamic asters can be obtained from in
vitro solutions of tubulin and cell motors, with a variety of
self-organizing structures resulting from varying concentrations.
By studying this process in the constrained geometry of micro-
fabricated glass chambers, the same final structure can apparent-
ly be attained through different assembly pathways.
QY: S. Leibler [leibler@princeton.edu]
(Nature 18 Sep 97) (Science-Week 3 Oct 97)


4. HYPOGLOSSAL CANAL SIZE AND HOMINID SPEECH
The mammalian *hypoglossal canal transmits the *nerve that
supplies the *motor innervation to the tongue. Hypoglossal canal
size has been used to date the origin of human-like speech
capabilities to at least 400,000 years ago, and to assign modern
human vocal abilities to *Neandertals. These conclusions are
based on the hypothesis that the size of the hypoglossal canal is
indicative of speech capabilities. ... ... D. DeGusta et al (3
authors at 2 installations, US) now present the results of a
study to test the hypothesis that hypoglossal canal size is
indicative of speech. The authors report they measured the
following: a) the hypoglossal canals of 75 nonhuman primates and
104 modern humans; b) the hypoglossal canal in specimens of the
early *hominid *taxa *Australopithecus afarensis and
*Australopithecus boisei; c) both the nerve and canal diameter
and estimated nerve axon number in a sample of human cadavers.
The authors report the following results: a) Many nonhuman
primate specimens have hypoglossal canals that are absolutely and
relatively within the size range of modern humans. b) The
hypoglossal canals of Australopithecus afarensis,
Australopithecus boisei, and *Australopithecus africanus are also
within the modern human size range. c) The size of the
hypoglossal nerve and the number of axons it contains do not
appear to be significantly correlated with the size of the
hypoglossal canal. The authors conclude: "The size of the
hypoglossal canal is not a reliable indicator of speech.
Therefore the timing of the origin of human language and the
speech capabilities of Neandertals remain open questions." [*Note
#1].
-----------
Editor's note: The authors present this report essentially as a
refutation of a paper by R.F. Kay et al, a summary of which
appears in the background material below. Also, for more
generally related material, see the SW Focus Report
"Anthropology: Human Evolution" at URL
[http://scienceweek.com/swfr017.htm].
-----------
D. DeGusta et al: Hypoglossal canal size and hominid speech.
(Proc. Natl. Acad. Sci. US 16 Feb 99 96:1800)
QY: David DeGusta [degusta@uclink.berkeley.edu]
-----------
Text Notes:
... ... *hypoglossal canal: This canal, at the level of the
brainstem, is a passageway through bone for the XII cranial
nerve, the nerve bundle that innervates the tongue.
... ... *nerve: In general, the term "nerve" refers to a bundle
of nerve axons (nerve fibers; neuron axons), the nerve usually
visible to the naked eye. Nerves can contain large number of
individual axons: the optic nerve in humans, for example,
contains approximately 1 million nerve fibers. The hypoglossal
nerve, the cranial nerve of relevance in this report, contains
mostly nerve axons whose cell bodies are in the hypoglossal
nucleus in the brainstem (efferent fibers carrying information to
activate the muscles of the tongue), and perhaps some axons
carrying information from sensory receptors in the tongue to the
central nervous system (afferent fibers).
... ... *motor innervation: This refers to the anatomical
connections of nerve fibers to muscle cells, the electrical
activity of the nerve axons resulting in the activation of the
muscle cells.
... ... *Neandertals: (Neanderthals) About 10 kilometers east of
Dusseldorf in Germany, in the valley of the Dussel, there is a
little town called Neander. One hundred and forty-one years ago,
in the summer of 1856, some workmen broke into a cave to get at
the limestone inside and discovered a set of ancient bones. Most
of the bones were smashed to bits by the workmen, but some of the
bones, including part of the skull, survived, and the skeleton
was soon recognized by anthropologists as belonging to an ancient
race of men who came to be known as the Neanderthals. A
Neanderthal fossil had actually been discovered some years
earlier in Gibraltar, but not recognized as such. Neanderthal-
like fossils have also been found in France, Spain, Italy,
Yugoslavia, Iraq, China, Java, and Israel. For more than a
century, one of the central questions in paleoanthropology has
been whether modern man evolved from this race.
... ... *hominid: The term "hominid" refers to any primate in the
human family (Hominidae) of which Homo sapiens (modern man) is
the only living specimen.
... ... *taxa: In general, a grouping defined in terms of shared
similar characters.
... ... *Australopithecus afarensis: The first record of human
footprints, of hominids walking upright, was discovered at
Laetoli in East Africa, and has been dated at 3.6 million years
ago. This ancestor, Australopithecus afarensis, probably weighed
25 to 50 kilograms (60 to 120 lbs.) as an adult.
... ... *Australopithecus boisei: Discovered by Mary Leakey in
the Olduvai Gorge in Tanzania, this fossil has been dated at 1.75
million years ago.
... ... *Australopithecus africanus: Apparently derived from
Australopithecus afarensis were several species, including
Australopithecus africanus, a species which is believed to have
appeared approximately 3 million years ago.
... ... *Note #1: Although the focus in this report is on the
role of the neural innervation of the tongue in human speech, it
must be emphasized that the organization of information and motor
output necessary for speech apparently occurs concomitantly in
several localized region of the cerebral cortex, and the
evolution of these regions of the brain most likely played a
significant role in the appearance of speech in humans.
Essentially, the hypoglossal nerve merely transmits information
originating in the brain, and both the origin and transmission of
this information must be considered in any analysis of the
evolution of human speech. Unfortunately, the brain is soft
tissue and is not preserved in fossils; what we have is bone, and
the data provided by bone and relevant archeological entities.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Apr99
-------------------
Related Background:
ORIGIN OF HUMAN VOCAL BEHAVIOR: AN ANATOMICAL CONSIDERATION
It can be argued that language is the most important behavioral
attribute that distinguishes humans from other animals, and one
of the important problems in anthropology and human evolution is
to demarcate as narrowly as possible the time frame during which
language in humans first appeared. Such demarcations have been
based on either apparent anatomical correlates (e.g., bone and
soft tissue analysis) or apparent archeological correlates (e.g.,
analysis of apparent symbolic behavior), with no firm specific
consensus among specialists. One of the important anatomical
features related to language is the nerve supply controlling the
muscles of the tongue. The mammalian hypoglossal canal is a bony
canal that contains the trunk of nerve fibers that constitute
this nerve supply. This canal is absolutely and relatively larger
in modern humans than it is in the African apes. ... ... Kay et
al (3 authors at Duke University, US) report a study of the
cross-sectional areas of hypoglossal canals in adult skulls of
contemporary humans, African apes, and several key fossil
hominids. They propose that hypoglossal canal size in fossil
hominids may provide an indication of the motor coordination of
the tongue and reflect the evolution of speech and language. What
they report is that the hypoglossal canals of gracile
Australopithecus, and possibly Homo habilis, fall within the
range of extant African apes, and are significantly smaller than
those of modern Homo. The canals of Neanderthals and an early
"modern" Homo sapiens (Skhul 5), as well as of African and
European middle Pleistocene Homo (Kabwe and Swanscombe), fall
within the range of contemporary Homo and are significantly
larger than those of Pan troglodytes (a chimpanzee species). In
summary, the authors suggest these anatomical findings indicate
the vocal capabilities of Neanderthals were the same as those of
humans today. The authors further suggest that the vocal
abilities of Australopithecus were not advanced significantly
over those of chimpanzees, whereas those of Homo may have been
essentially modern by at least 400,000 years ago, which is
consistent with the evidence for accelerated encephalization
rates in middle Pleistocene Homo. The authors conclude: "Thus,
human vocal abilities may have appeared much earlier in time than
the first archeological evidence for symbolic behavior."
QY: Richard F. Kay (Rich.Kay@baa.mc.duke.edu)
(Proc. Natl. Acad. Sci. US 28 Apr 98 95:5417)
(Science-Week 19 Jun 98)
 

5. CHIMPANZEE ORIGIN OF HIV-1 EPIDEMIC
In general, the term "zoonosis" refers to a disease of humans
acquired from an animal source. HIV-1 is the subtype of HIV
(human immune-deficiency virus) that causes most cases of AIDS in
the Western Hemisphere, Europe, and Central, South, and East
Africa. HIV-2 is a subtype of HIV, apparently prevalent only in
West Africa, and much less virulent than HIV-1. In general, the
HIV virus is a spherical entity 80 to 100 nanometers in diameter.
Only approximately 40 percent of the genome sequences of HIV-1
and HIV-2 are identical. HIV is a retrovirus (subclass
lentivirus), and retroviruses are single-stranded RNA viruses
that have an enzyme called reverse transcriptase. With this
enzyme the viral RNA is used as a template to produce viral DNA
from cellular material. This DNA is then incorporated into the
host cell's genome, where it codes for the synthesis of viral
components. The viral components assemble into new viral
entities, and new viruses leave the host cell in great numbers by
budding from the host cell membrane. Although the primate
reservoir (i.e., origin) of HIV-2 has been identified as the
sooty mangabey monkey (Cercocebus atys), the origin of HIV-1
remains uncertain. Viruses related to HIV-1 have been isolated
from the common chimpanzee (Pan troglodytes), but only 3 such
chimpanzee-simian-immune deficiency virus (SIVcpz) infections
have been documented. A signal fact is that HIV-1 will replicate
in experimentally inoculated chimpanzees but not in any species
of monkey. Both mangabey monkeys and chimpanzees are commonly
hunted for food in Africa. ... ... F. Gao et al (12 authors at 7
installations, US UK FR) now present the results of a search for
the HIV-1 reservoir. The authors report they have sequenced the
genome of a new SIVcpz strain (denoted as SIVcpzUS), and have
determined by *mitochondrial DNA analysis the subspecies identity
of all known SIVcpz-infected chimpanzees. The authors report that
2 chimpanzee subspecies in Africa, the central African Pan
troglodytes troglodytes (P.t. troglodytes) and the eastern
African Pan troglodytes schweinfurthii (P.t. schweinfurthii),
harbor SIVcpz in 2 viral lineages. The authors report that all
HIV-1 strains known to infect humans are closely related to just
one of these lineages, that found in P.t. troglodytes. The
authors suggest that these results, together with the observation
that the natural range of P.t. troglodytes coincides uniquely
with areas where HIV-1 is *endemic, indicate that P.t.
troglodytes is the primary reservoir for HIV-1 and has been the
source of at least 3 independent introductions of SIVcpz into the
human population.
-----------
Editor's note: In addition to the background material below, see
the SW Focus Reports "Viruses", and "HIV and Aids" available at
URL [http://scienceweek.com/swfr.htm].
-----------
F. Gao et al: Origin of HIV-1 in the chimpanzee Pan troglodytes
troglodytes.
(Nature 4 Feb 99 397:436)
QY: Beatrice H. Hahn [bhahn@uab.edu]
-----------
Text Notes:
... ... *mitochondrial DNA: Mitochondrial DNA has found important
uses in evolutionary studies. The mitochondria are cell
organelles that may have originated as separate organisms that
became resident in eukaryotic cells (cells with internal
membrane-bound organelles such as a nucleus). Mitochondrial DNA
is independent of nuclear DNA. It consists of a circular
molecule, 16,569 base pairs long in humans, with a known
nucleotide sequence. Mitochondrial DNA is inherited primarily
through the maternal lineage, and accumulates mutations at a rate
an order of magnitude greater than nuclear DNA, which facilitates
comparisons between groups. In general, modern DNA sequencing
techniques have made possible the tracing of mitochondrial DNA
differences among individuals to reveal evolutionary
relationships. (In this report, mitochondrial DNA analysis was
used to determine the subspecies identity of various varieties of
chimpanzees.)
... ... *endemic: (enzootic) In general, this term refers to a
disease prevailing continually in a region, as opposed to
"epidemic", which generally refers to a transient prevalence
(e.g., an "outbreak")
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Apr99
IDENTIFICATION OF HIV-1 SEQUENCE IN 1959 HUMAN VIRAL SAMPLE
HIV-1 is the subtype of HIV (human immune-deficiency virus) that
causes most cases of AIDS in the Western Hemisphere, Europe, and
Central, South, and East Africa. ... ... Zhu et al (6 authors at
4 installations, US UK) report the laboratory amplification and
characterization of viral sequences from a 1959 African plasma
sample previously found to be HIV-1 seropositive. Multiple
phylogenetic analyses authenticate this case as the oldest known
HIV-1 infection, and place its viral sequence near the ancestral
node of subtypes B and D in the major group. The authors suggest
their results indicate these HIV-1 subtypes, and perhaps all
major-group associated viruses, may have evolved from a single
introduction into the African population not long before 1959,
and that the diversification of HIV-1 in the past 40 to 50 years
portends even greater viral heterogeneity in the coming decades,
and underscores the need for continued surveillance.
QY: David D. Ho  (Nature 5 Feb 98)
-------------------
Related Background:
ESTIMATED 20 MILLION INFECTED WITH AIDS IN SUB-SAHARAN AFRICA
There is perhaps too much of a tendency in many quarters to think
of a plague only as a state of affairs in which people drop dead
in expensive restaurants and get hauled away in trucks containing
piles of bodies. Our current plague, although not as dramatic as
some plagues of the past, is no less an international calamity. 
The United Nations AIDS Program recently released a report
containing the following: 
-- In 1997, 5.8 million people worldwide were newly infected with
HIV.
-- The number of new HIV infections this year rose 9% over 1996.
-- The total number of infected adults is now a little under 30
million, about 1% of the world's adult population.
-- This year, the total number of people infected with HIV
increased by 13%
-- More than 20 million people in sub-Saharan Africa are infected
with HIV, which is 7% of that adult population.
-- This year, 2.3 million people worldwide will have died of
AIDS, the consequent stage of HIV infection.
-- In South and Southeast Asia, 6 million people are infected
with HIV.
-- In Latin America, 1.3 million people are infected with HIV.
-- In North America, 860,000 people are infected with HIV.
-- In Western Europe, 150,000 people are infected with HIV.
(Nature 27 Nov 97) (Science-Week 19 Dec 97)


6. BIOLOGY OF ATHEROSCLEROSIS
"Arteriosclerosis" is a generic term for several diseases in
which the arterial wall becomes thickened and loses elasticity,
and "atherosclerosis" is a form of arteriosclerosis characterized
by patchy thickening (atheroma) in the subintimal layer (i.e.,
immediately below the innermost layer) of medium and large
arteries, the thickening capable of reducing or obstructing blood
flow. In this context, the term "plaque" refers to any patch or
small differentiated area in or on arterial endothelium. In
general, the term "endothelium" refers to a layer of flat cells
lining blood vessels, lymphatic vessels, the heart, etc.
Atherosclerotic plaque consists of accumulated intracellular and
extracellular lipids, smooth muscle cells, connective tissue, and
*glycosaminoglycans. Two main hypothesis have been proposed to
explain the pathogenesis of atherosclerosis: a) the lipid
hypothesis postulates that an elevation in plasma low-density-
lipoprotein (LDL) cholesterol levels results in penetration of
LDL into the arterial wall with a consequent series of cellular
events leading to the formation of plaque; b) the chronic
endothelial injury hypothesis postulates that endothelial injury
by various mechanisms produces loss of endothelium and a
consequent series of events (inflammatory response) involving
blood cellular entities, the events leading to the formation of
plaque. The current consensus is that these two hypotheses are
probably interrelated. ... ... Russell Ross (University of
Washington Seattle, US) presents a review of atherosclerosis with
a focus on atherosclerosis as an *inflammatory disease, the
author making the following points: 1) Atherosclerosis is an
inflammatory disease. Because high plasma concentrations of
cholesterol, in particular those of low-density lipoprotein (LDL)
cholesterol, are one of the principle risk factors for
atherosclerosis, the process of atherogenesis has been considered
by many to consist largely of the accumulation of lipids within
the artery wall. However, the disease is much more than that.
Despite changes in lifestyle and the use of new pharmacologic
approaches to lower plasma cholesterol concentrations,
cardiovascular disease continues to be the principal cause of
death in the US, Europe, and much of Asia. In fact, the lesions
of atherosclerosis represent a series of highly specific cellular
and molecular responses that can best be described, in aggregate,
as an inflammatory disease. 2) The lesions of atherosclerosis
occur principally in large and medium-sized elastic and muscular
arteries and can lead to *ischemia of the heart, brain, or
extremities, resulting in *infarction. They may be present
throughout a person's lifetime. In fact, the earliest type of
lesion, the so-called "*fatty streak", which is common in infants
and young children, is a pure inflammatory lesion, consisting
only of *monocyte-derived *macrophages and *T-lymphocytes. In
persons with *hypercholesterolemia, the influx of these cells is
preceded by the extracellular deposition of amorphous and
membranous lipids. The author suggests that by asking questions
about arterial inflammation, we may be able to gain insight into
the process of atherogenesis. 3) The author proposes the
following as possible causes of endothelial dysfunction (and a
concomitant inflammatory response) leading to atherosclerosis: a)
elevated and modified LDL; b) free radicals caused by cigarette
smoking, *hypertension, and *diabetes mellitus; c) generic
alterations; d) elevated plasma *homocysteine concentrations; e)
infectious microorganisms such as *herpesviruses or *Chlamydia
pneumoniae; e) combinations of these or other factors. The author
suggests that regardless of the cause of endothelial dysfunction,
atherosclerosis is a highly characteristic response of particular
arteries. 4) The author concludes: "Atherosclerosis is clearly an
inflammatory disease and does not result simply from the
accumulation of lipids."
-----------
Russell Ross: Atherosclerosis -- an inflammatory disease.
(New England J. Med. 14 Jan 99 340:115)
QY: Russell Ross [rross@u.washington.edu]
-----------
Text Notes:
... ... *glycosaminoglycans: In general, any polysaccharide
containing a substantial proportion of aminomonosaccharide
residues.
... ... *inflammatory disease: In general, inflammation is a
fundamental pathologic process consisting of a dynamic complex of
cellular and chemical reactions occurring in affected blood
vessels and adjacent tissues in response to an injury or abnormal
stimulation caused by physical, chemical, or biological agents.
... ... *ischemia: In general, a sudden loss of blood supply to a
tissue caused by blockage of a blood vessel.
... ... *infarction: (infarct) An area of necrosis caused by a
sudden insufficiency of blood supply.
... ... *fatty streak: Consists of lipid-laden *monocytes and
*macrophages (together, in a fatty streak, called "foam cells"),
plus *T-lymphocytes. Later, these cell types are joined by
various numbers of smooth muscle cells, the entire mass partially
obstructing the lumen of the artery.
... ... *monocyte: The monocytes are the largest of the
leukocytes (white blood cells). macrophages are amoeba-like
leukocytes that are able
to surround and digest foreign entities such as bacteria and
protozoa.
... ... *macrophages: Amoeba-like leukocytes that are able
to surround and digest foreign entities such as bacteria and
protozoa.
... ... *T-lymphocytes: (T-cells) Lymphocytes (lymph cells,
lympho-leukocytes) are a type of leukocyte (white blood cell)
involved in the immune response. There are two classes of such
lymphocytes: 1) the B-cells, which after a cascade of immune
system events involving a specific antigen change into
proliferating specific antibody producing plasma cells; 2) the
T-cells, one subclass of which (cytotoxic T-cells) interacts
directly with foreign invaders such as bacteria and viruses,
while the other subclass of T-cells (helper T-cells) is involved
in the proliferation of antibody-specific B-cells.  
... ... *hypercholesterolemia: The presence of an abnormally
large amount of cholesterol in the cells and plasma of
circulating blood.
... ... *hypertension: In general, high blood pressure.
... ... *diabetes mellitus: Diabetes mellitus is a metabolic
disease in which carbohydrate utilization is reduced and that of
lipid and protein enhanced. The disease is caused by an absolute
or relative deficiency of insulin, and there are many forms of
the disease recognized. The term "diabetes" can refer to either
diabetes mellitus or diabetes insipidus, both diseases
characterized by chronic excretion of large amounts of urine
(polyuria). But when the term "diabetes" is used alone, what is
usually meant is diabetes mellitus.
... ... *homocysteine: An intermediate in the biosynthesis of
cysteine, recently considered to be of significance in
cardiovascular disease.
... ... *herpesviruses: The herpesviruses are a class of viruses
producing the complex of herpes diseases. The outstanding
property of herpesviruses is their ability to establish lifelong
persistent infections in their hosts and to undergo periodic
reactivation. They are large viruses, 150 to 200 nanometers in
diameter, with a core of double-stranded DNA.
... ... *Chlamydia pneumoniae: A common species of pathogenic
gram-negative bacteria. Worldwide, 30 to 50 percent of people
have antibodies to this pathogen.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 16Apr99
-------------------
Related Background:
A RECEPTOR IDENTIFIED AS A KEY IN CHOLESTEROL TRANSPORT
Cholesterol is a sterol lipid found in all animals, the molecule
an important component of cell membranes as well as a precursor
for the steroid hormones. Since cholesterol is insoluble in
plasma, it is transported via lipoprotein carriers. Dysfunctions
in cholesterol metabolism or cholesterol transport can have
severe consequences. In particular, deposition of cholesterol in
arterial walls can cause a type of arteriosclerosis called
atherosclerosis. The deposited plaques thicken and harden the
arterial walls and the lumen of the vessels narrow, and the end
result can be a severe reduction of blood supply to the heart and
brain. High density lipoprotein (HDL) is a type of protein in
blood plasma involved in the transport of cholesterol and other
lipids from the blood to the tissues. Another type is low density
lipoprotein (LDL), and one important difference between the two
types of lipoprotein is the much greater cholesterol content of
LDL carriers. Defects in either HDL or LDL metabolism can be
involved in cholesterol pathologies. Krieger et al (Massachusetts
Inst. of Technology, US; Univ. Texas Southwestern Medical School,
US) now report the identification of the gene that expresses the
HDL receptor (SR-B1) in the mouse. Further studies will show
whether defects in this receptor contribute to the development of
human atherosclerosis. The authors suggest that even if this
receptor is not directly involved in causing human athero-
sclerosis, the receptor might still be a target for drugs to
prevent the condition. Michael Brown, who shared the Nobel Prize
in 1985 for work relating LDL to atherosclerosis, calls this new
report a "crucial step in obtaining a complete  understanding of
cholesterol transport."
QY: Monty Krieger, U. Texas Southwestern Med. Sch. 214-648-2670
(Science 14 Nov 97) (Science-Week 5 Dec 97)
-------------------
Related Background:
EVALUATION OF CARDIOVASCULAR EFFECTS OF ANTIOXIDANTS
The term "oxidation" originally meant a chemical reaction in
which oxygen was introduced into another substance, but the usage
of the term has long been broadened to include any reaction in
which electrons are transferred. Oxidation and reduction always
occur simultaneously, and the substance which gains electrons is
termed the oxidizing agent. Autoxidation is the term describing
reactions of molecular oxygen at ambient temperatures. These
reactions are normally slow, but their rates can be markedly
affected by the presence of free radicals, molecules that for a
short time (for example, 1 nanosecond) have unpaired electrons.
Free radicals have also been implicated in mutative chemical
alterations of DNA. Oxidation is a corruption mechanism in many
organic chemical systems, particularly in biological systems, and
deleterious oxidations have been suggested to be implicated in a
number of pathologies. It is known, for example, that free
radicals catalyze lipid peroxidation, a continual biologic
process that damages cellular and intracellular structures.
Increased free radical production has been implicated in aging in
general and in Alzheimer's disease in particular. Antioxidants
are substances that inhibit oxidation. They are widely used in
industry as preservatives of foods and various industrial
polymers, and they are well known in biology in the form of
vitamin E and vitamin C. A number of epidemiological studies have
suggested an association between increased intake of vitamin E
and vitamin C and reduced incidence and mortality from coronary
heart disease. The idea is that the genesis of atherosclerotic
heart disease is initiated by the oxidation of the lipids in low-
density lipoproteins (called lipid peroxidation), and that
antioxidants inhibit this oxidation. This week Marco N. Diaz et
al (various installations in US) report an evaluation of the
current literature involving antioxidants and vascular disease,
and they conclude there is definitely an inverse relation between
coronary artery disease and antioxidant intake, particularly the
supplementary intake of vitamin E. They suggest there is also
evidence that plaque stability, vasomotor function, and the
tendency to thrombosis are modifiable by specific antioxidants.
QY: J. F. Keaney Jr., Boston University 617-353-2300.
(New England J. Med. 7 Aug 97) (Science-Week 8 Aug 97)


=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
 
IN FOCUS: ON THE SOCIAL UNIT OF THE HIGHER PRIMATES
"The availability of food, and probably to a lesser extent, the
degree of danger from predators, are two basic influences in the
relations between individuals within a species; and here the
rules that operate for primates also operate for all other
species. The higher primates are special because, by their
nature, they have a propensity to be social rather than solitary.
Differences in environmental conditions therefore tend to
determine the _way_ in which they are social, rather than
_whether_ they are social. The reason the higher primates tend to
be social animals is that group living offers the opportunity for
prolonged learning during childhood; and learning is a pastime in
which primates engage far more than any other animal. Learning is
a pastime with a purpose, however -- namely to equip individuals
in a group with a more effective knowledge of the environment in
which they must survive. Greater knowledge implies a greater
chance of survival -- which is what evolution is all about. A
period of childhood education implies dependency on an adult, and
this turns out to mean that, without exception, the basis of all
primate social groups is the bond between mother and infant. That
bond constitutes the social unit out of which all higher orders
of society are constructed."

-- R.E. Leakey and R. Lewin: _Origins_
   (E.P. Dutton, New York 1977, p.61)


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