“potentially, there are universal rules of arousal and
ways to communicate fear.” — daniEl BlumStEin
Chaos makes a scream seem real
By Rachel Ehrenberg
As horror-flick titles go, Night of the Living Chaos and Rosemary’s Nonlinearity
aren’t the catchiest. But filmmakers know
that chaos — the mathematical kind — is
scary. Now scientists know it too.
Filmmakers use chaotic, unpredictable
sounds to evoke particular emotions, a
team assessing screams and outbursts
from more than 100 movies reports
online May 25 in Biology Letters.
“Screams are basically chaos,” says
cognitive biologist W. Tecumseh Fitch
of the University of Vienna, who was
not involved in the study. “The classic
example would be a screaming baby on
an airplane, the kind you can’t ignore and
makes your life hell.”
Cries are harder to ignore when irregu-
lar and chaotic, research suggests. Scien-
tists believe that such noises, uttered or
roared when an animal is really worked
up, can play the crucial communication
role of frantically demanding attention.
Screeches that devolve into mathemat-
ical chaos evoke a visceral response.
horror films had a lot of harsh and atonal
screams. Dramas had fewer screams but
a lot of abrupt changes in acoustical frequency. Adventure films had a surprising
number of harsh male screams.
One bloodcurdling scream has
become a film favorite. More than 200
movies have used the Wilhelm scream,
named for a character who unleashed
it in the 1953 western The Charge at
Feather River.
Experts debate
hominid habitat
Discoverers dispute claim
that ardi roamed savannas
By Bruce Bower
An ancient hominid hung out on grassy
savannas, not in forests as first claimed,
a new study argues. Whether the species
trucked across savannas has major implications for understanding how and why
human ancestors began walking upright.
The discoverers of the species
Ardipithecus ramidus disagree with the new
study and say that other evidence keeps
these hominids in the woods.
When a 4.4-million-year-old partial
Ardipithecus skeleton was unveiled in
October 2009, its owner, dubbed Ardi,
was presented as a forest dweller that split
time between walking upright and crawling along tree branches (SN: 1/16/10, p. 22).
In this scenario, a two-legged gait had
evolved to support long-distance foraging by males seeking to impress potential
mates. But the new analysis, published
in the May 28 Science, supports a long-standing idea that shrinking African forests spawned the evolution of hominids
capable of walking across vast savannas.
In Ardi’s neck of the woods, at what is
now Aramis, Ethiopia, “there is abundant
evidence for open savanna habitats,” says
geologist Thure Cerling of the University
of Utah in Salt Lake City. Ardi could have
inhabited a grass- and shrub-covered
region in a thin wooded strip that bordered a river flowing through a savanna,
Cerling’s team suggests.
Cerling and colleagues analyzed data
from soil and plant fossils collected by
Ardi’s discoverers. Forms of carbon in fos-sil-bearing sediments indicate that tropical grasses covered much of Ardi’s home
area. Microscopic fossils of such grasses
found near Ardi’s remains also point to a
savanna, the researchers say.
Levels of carbon isotopes in teeth from
giraffes and other animals found among
Ardipithecus fossils resemble those of
browsing animals that range today from
woods bordering rivers to savannas, the
scientists say, noting that aridity and rainfall estimates for Ardi’s ancient homeland
are compatible with such a habitat.
In a response in the same issue of
Science, Ardi’s discoverers, including
anthropologist Tim White of the University of California, Berkeley, say that no
reliable way exists to estimate the extent
of savanna in Ardi’s corner of East Africa.
Fossil and geological evidence indicate
that Ardipithecus favored wooded areas
over savanna patches, in White’s opinion.
Groundwater and springs probably
deposited fossil wood, seeds and invertebrates near Ardi’s remains, White notes.
No evidence of an ancient river or lake
has been found at fossil sites in that area.
If Ardi’s kind frequented savannas,
as Cerling’s team proposes, a biological mystery emerges, White says. “What
were these large-bodied hominids doing
out on an open grassland, besides providing meals to resident predators?”
