Index:
BIOLOGY
Popping Polyps
ALTHOUGH LARGELY sedentary, corals are extravagant
builders. Over millions of years, the shells of these tiny
animals can accumulate into sprawling structures like
Australia's 80,000-square-mile Great Barrier Reef. Corals
grow and conquer new territory in two ways. Individual
polyps-mature coral animals-divide asexually, producing
clones; coral polyps also reproduce sexually, releasing
their eggs and sperm into the water. The resulting
generation of free-swimming larvae eventually anchor
themselves to the seafloor, mature into polyps, and begin a
new reef.
Biologists have believed that all corals reproduced in
these ways. But marine biologist Esti Kramarsky-Winter at
Tel Aviv University recently found corals that use a very
different propagation strategy. Shallow water corals in the
Red Sea and on the Mediterranean coast of Israel eject
fully formed polyps from their midst to pioneer colonies.
While diving in the Gulf of 'Aqaba in Israel,
Kramarsky-Winter came upon some vigorous colonies of the
coral Favia favus. She soon discovered that these colonies,
in addition to spawning sexually like most corals, grew
crops of fully formed polyps on short stems made of calcium
carbonate. Somehow the polyps pop off their stems, and the
ejected animals, carried by currents, start new colonies as
far as ten feet from the parent reef. When Kramarsky-Winter
harvested a few polyps and brought them back to the lab,
they cloned new colonies within two months. She has since
found another coral, Oculina patagonica, that has popping
polyps.
Kramarsky-Winter doesn't yet know how the popping mechanism
works, but its advantages are clear. The release of mature
polyps, she says, helps coral compensate for the hazards of
sexual reproduction. Heavy waves can foil a coral colony's
attempts to spawn, sweeping away immature larvae before
they have a chance to settle down and begin cloning a new
colony. "The polyp emerges fully formed, so it has many
fewer stages to go through than a larva," says
Kramarsky-Winter.
ARCHEOLOGY
Stone Age Surgery
TO RELIEVE PRESSURE from bleeding after a blow to the head,
surgeons often drill or cut into the skull to allow fluids
to drain. But people figured out the advantages of the
procedure long before the advent of modern surgery.
Trepanation, the removal of bone from the skull, is the
most ancient surgical technique known. Archeologists have
found trepanned skulls dating from the late Neolithic, some
5,000 years ago. Now a team of French and German
researchers has suggested that the procedure goes back even
further, to at least 7,000 years ago.
The evidence comes from the French village of Ensisheim. To
date, archeologists there have unearthed 45 graves
containing 47 individuals. One grave held the remains of a
50-year-old man who had two holes in his skull. Both holes
were remarkably free of surrounding cracks and were clearly
the result of surgery, not violence. One hole, in the
frontal lobe, is about 2.5 inches wide; the second, at the
top of the skull, is about an inch wider.
"Most questionable trepanations are rather small, and with
some you cannot tell the shape of the original hole that
was made within the skull, or whether it was a fracture,"
says archeologist Sandra Pichler of Freiburg University in
Germany, a member of the team. "But in our case you can
still see the very straight, slanting edges of the larger
trepanation, and this is artificial. There is no natural
explanation for a hole like that."
Both holes had time to heal before the man died-the smaller
hole is completely covered over with a thin layer of bone;
the larger is roughly two-thirds covered-and neither shows
signs of infection. "So they must have had a very good
surgeon, and there must have been some way or another of
avoiding infection," Pichler says. Pichler and her
colleagues estimate that it would take at least six months,
and perhaps as much as two years, for such extensive
healing. Since the two holes did not heal to the same
degree, it's likely they were made during two separate
operations.
The team doesn't know why the man was operated on. Nor can
they be sure exactly how the trepanations were performed,
although the cut marks indicate that the bone was removed
by a mixture of cutting and scraping. Stone Age tools were
certainly up to the task: flint knives are actually sharper
than modern scalpels.
"The trepanations were done so perfectly that this can't be
the oldest one," Pichler says. "They must have practiced
somehow, and the knowledge of how to do this kind of
operation must have been passed down," Pichler says. "The
fact that there are two trepanations is further
corroboration: if there had been just one, you could say
that they were lucky. But if you survived two such
operations, your surgeon must have known what he was
doing."
Image: Kurt W. Alt
Floating Frog
This little frog, floating weightlessly, was not
photographed aboard the space shuttle but right here on
Earth. Jan Kees Maan and Andre Geim, physicists at the
University of Nijmegen in the Netherlands, used a powerful
magnet to levitate the frog. Any living thing, when placed
in a magnetic field, itself becomes a magnet as the atoms
in its cells try to shift their electrons to oppose the
external magnetic field. This effect is usually very weak,
but in a field 100,000 times that of Earth's, the force
produced is strong enough to cancel gravity and levitate
the object, in this case a frog (which seems to have
suffered no ill effects). Apart from levity, Maan says the
experiment has a practical side. Scientists can now test
microgravity experiments before--or instead of--sending them
up in a space shuttle. "You come as close as you can
possibly get on Earth to spacelike conditions," says Maan.
Photograph courtesy
Jan Kees Maan,
University of Nijmegen
Penguin Power
Boston's Charles River is the early-morning training ground
for at least three collegiate rowing teams and now for one
remote-controlled penguin boat. This unusual 12-foot vessel
is the first step in using simulated penguin propulsion to
bring down the cost, both monetary and environmental, of
worldwide shipping. Proteus, as the penguin boat is dubbed,
uses rigid flippers instead of propellers. The flippers
create less turbulence than propellers, so more of their
energy goes into pushing the boat forward. For a given
speed, Proteus uses 17 percent less power than a
propeller-driven craft of similar dimensions. Proteus's
handler, James Czarnowski, who developed the boat while at
MIT, says that conversion of even a small fraction of the
U.S. shipping fleet to such efficient propulsion would save
tens of millions of dollars and hundreds of millions of
gallons of fuel annually. Czarnowski must overcome just one
difficulty before he can develop a full-size 140-foot test
boat. He must develop a steering mechanism. He doesn't see
this as a difficult task. With a little tinkering, he says,
the flippers could also serve as rudders.
Photograph: Donna Coveney/MIT
ASTRONOMY
A Halo of Suns
MOST GALAXIES, including our own Milky Way, present only
part of themselves to our eyes. They hide much of their
mass in huge halos that envelop the more conspicuous
spirals. Astronomers know the halo matter is there because
it affects the motions of stars in galaxies. But they don't
know what it is. "It's hard to infer the properties of
stuff you don't see," says Rick Rudy, an astronomer with
the Aerospace Corporation in Los Angeles.
Rudy believes he may have partly solved the mystery. In
1994 astronomers found a faint gauzy glow around NGC 5907,
a galaxy about 36 million light-years away. The glow seemed
consistent with the size and shape of the matter needed to
make NGC 5907 spin the way it does, so astronomers hoped
that this might be the first sign that the dark halos were
made of ordinary stars and planets--albeit faint ones--rather
than exotic, yet-to-be discovered particles.
Rudy and Chick Woodward of the University of Wyoming
recently studied this glow to see what sort of stars caused
it. Based on the infrared signature of the faint light,
they found to their surprise that the glow seems to be
created by second- and third-generation stars-stars created
out of gas and dust that has been cooked in the hearts of
very large, short-lived stars. "The colors you expect from
a star depend on its composition," Rudy says. "Stars made
of primordial material have peculiar colors." But what Rudy
and Woodward saw around NGC 5907 resembled the light
emitted by stars the size of our sun and smaller.
Rudy and Woodward estimate that most of the glow comes from
a population of small, dim red stars with about a tenth of
the mass of the sun. The mysterious mass of the halo of at
least one galaxy thus comes from relatively dim bulbs that
were simply too faint for earlier generations of
instruments to detect.
Before astronomers can put the question of the halo mass to
rest, however, they must still explain our Milky Way: the
Hubble Space Telescope has not found large numbers of small
red stars swarming in our halo. If both of these studies
hold up, astronomers may have another mystery on their
hands--why two seemingly ordinary galaxies have halos made
of different kinds of stuff.
ANCIENT LIFE
The Trouble With Trilobites
DURING THEIR HEYDAY in the Cambrian Period, some 500
million years ago, trilobites were as common and as diverse
as their crustacean cousins are today. These shelled
arthropods crawled on seafloors the world over. Some were
fingernail size; others as long as a foot. Yet despite that
early success, by 250 million years ago they had vanished
from the world's oceans. What happened to them? Some
researchers speculate that predators--including primitive
jawed fish--wiped them out. "There is a precipitous decline
in trilobite diversity as the predator groups got more
abundant," says Danita Brandt, a paleontologist at Michigan
State University. But Brandt doubts that predation alone
can explain the trilobites' demise. Modern crustaceans, she
points out, have no trouble surviving in predator-filled
waters.
Brandt thinks another factor may have decided the
trilobites' fate: the way they molted. Like all arthropods,
trilobites were encased in a hard protective exoskeleton
that they had to shed periodically in order to grow. "Each
molt is a crisis," says Brandt. "During molting the animal
is very vulnerable to predators. They shed their hard
exoskeleton and then run around--actually, they hide--with
this soft new skeleton, which can take hours to harden. And
things can go wrong in the process of shedding: an
appendage can get stuck in the exoskeleton, and the animal
can get injured."
Presumably to minimize that danger, all modern crustaceans
have standardized the molting process. "They molt the same
way every time," Brandt says. "In shrimp, a suture opens up
between the front half of the exoskeleton and the back, and
the animal pops out; crabs also have a suture that opens up
every time." Even horseshoe crabs, ancient relatives of
crustaceans that have remained virtually unchanged for at
least the past 400 million years, always molt in exactly
the same way.
Not so for the hapless trilobites. When Brandt studied
thousands of fossilized molted exoskeletons from the genus
Flexicalymene, she found that most of the time a suture
would open up across the head, and the animal would neatly
fall out. But sometimes, it seems, that clean suture failed
to open; instead a crack split the segments on the
trilobite thorax, and the trilobite then wriggled out as
best it could, sometimes getting entangled in the process.
Molting in at least a dozen other trilobites has been
studied by other researchers; none show a consistent
pattern.
"I won't go so far as to say that this inefficient molting
habit is the reason the trilobites are extinct," Brandt
says. "If it had been a problem from the beginning, we
wouldn't have seen this huge diversity. What I am
suggesting is that an inefficient molt habit plus an
increase in predators may have been a one-two punch they
couldn't recover from."
Occupational Hazards of Monkdom
Around 500 A.D., the Byzantine monastery of St. Stephen,
just outside Jerusalem, was a bustling refuge for up to
10,000 monks. Custom dictated that when a monk died, his
body was put in a crypt beneath the monastery. When the
body had decomposed, the bones went into a repository.
Susan Sheridan, an anthropologist at Notre Dame, has
studied some 6,000 of these bones and found that the monks
were a fairly robust group. "They were the healthiest
population I've ever studied," says Sheridan, except in one
respect--almost all the monks seem to have had arthritic
knees. Many of their kneecaps' edges were
worn smooth and shiny as a result of rubbing directly
against their thighbones. Sheridan saw the characteristic
roughening of arthritis at the points where muscles used in
kneeling attach to the bone. Historical records show that
the monks spent an impressive amount of time kneeling;
praying at midnight, sunrise, twice during the day, at
sunset, and again at night. One monk wrote about his
nightly practice of descending 18 steps into a holy cave
and making 100 genuflections on each step. "If you think
about what that's doing to your legs as you come up and
down that hard pavement," says Sheridan, "you can do some
damage."
ARCHEOLOGY
Ancient Abuse
WHEN ARCHEOLOGIST Brenda Baker unearthed a 4,000-year-old
female skeleton from a cemetery at Abydos--an ancient
Egyptian provincial town about 100 miles north of Luxor--her
examination of the bones suggested that the woman had been
fatally stabbed in the back when she was about 35, perhaps
with a dagger like one of those shown here. Her left rear
fifth and sixth ribs were sliced, and no new bone had been
laid down--a sign that the wound never had time to heal.
But according to Baker, who works at the New York State
Museum in Albany, the woman's troubles probably began long
before her violent death. Her body bore the signs of a
lifetime of abuse. Three ribs and a bone in her left hand
had been fractured and had subsequently healed. A break in
her right wrist showed signs of infection-channels in the
bone that probably formed to drain away pus.
The pattern of injuries--some healed, some not--suggests that
the wounds were not the result of one accident. Her
injuries resemble those of battered women, who frequently
suffer broken ribs when punched or kicked in the chest. The
fractured wrist probably resulted from an attempt to break
a fall.
Although healed fractures can be seen in two male skeletons
from the site--one had a dent in the skull, the other a
broken arm--the woman's injuries were by far the most
extensive. She was probably a farmer or a householder, says
Baker, since she was buried in a simple wooden coffin in
the sand in an area reserved for common people, many of
whose bones showed signs of malnutrition and
osteoarthritis-afflictions often found in manual laborers.
So she may have been an abused servant in an elite
household. Alternatively, her assailant could have been her
husband or father.
The woman's skeleton--and those of others around her--reveals
a great deal about the lives of Egyptian working women in
the second millennium B.C. "Seeing these skeletons helps us
learn something about the kinds of conditions that they
survived," says Baker. Or, in this woman's case, did not.
Photograph courtesy Brenda Baker;
daggers on display at the Royal Ontario Museum, Toronto
Bat Spit
The sugary, acidic diet of a fruit bat would corrode the
teeth of just about any other mammal. But fruit bats
don't have problems with
tooth decay. Anatomist Elizabeth Dumont of Northeastern
Ohio Universities College of Medicine thought that the
saliva of fruit bats might buffer the acids in their food,
thus protecting their teeth. To find out, she measured the
acidity of saliva from a number of species of fruit bat. In
some bats the pH dropped close to 5.5, the acidity at which
human teeth begin to decay. To Dumont's surprise, the
saliva of some old-world fruit bats was just as acidic
after their food had cleared the mouth and digestive
system, 20 minutes later, and remained so for six hours.
She isn't sure why the bats' teeth don't rot, but she
thinks the acidity of their saliva may help bats extract
all the nutrients they can from their food. "Fruit is a
low-quality food," Dumont says, "so the bats draw a little
more food out in the short 20 minutes they have to get it."
