8 | NewScientist | 3 November 2018NEWS & TECHNOLOGY
ORANGUTANS have staggeringly
low rates of infant mortality. They
are better at keeping their offspring
alive than people have been for most
of human history.
“We see this incredibly high survival
that’s higher than any [non-human]
mammal that we know of so far,”
says Maria van Noordwijk at the
University of Zurich in Switzerland.
Orangutan infants are raised solely
by their mothers. The high survival
rate is linked to orangutans’ lifestyle,
which is more solitary than other
apes. But the factors that help explain
the high rate – including a low birth
rate – may actually make orangutans
more vulnerable to a population crash.
Van Noordwijk and her colleagues
compiled data on births and infant
survival from two populations of
Sumatran orangutans and three
of Bornean orangutans. There is
also a third species, the Tapanuli
orangutan described in 2017,
but they haven’t been studied longOrangutan
mothers may
be best in world
Leah CraneEARTH may have a pair of “ghost
moons”, translucent clouds of
dust that orbit along with our
moon. New pictures seem to show
these clouds, which could be up
to 100,000 kilometres across,
in fresh detail, potentially ending
the debate over whether they
exist. But not everyone is
convinced.
The Earth-moon system has a
set of five gravitational balance
points, where the gravitational
forces from Earth and the moon
balance out. Objects can get
trapped in these regions, calledLagrange points, never being
pulled down to Earth or the moon.
In 1951, astronomer Józef
Witkowski predicted that cosmic
dust that floats through space
should collect at two particular
Lagrange points, each about
400,000 kilometres from Earth
and from the moon.
Then, in 1961, astronomer
Kazimierz Kordylewski took the
first pictures that seemed to show
bright spots near these areas and
used them as evidence that the
clouds existed. The collected dust
clouds are named Kordylewski
clouds after him.
But because these clouds areThe hunt for Earth’s
ghost moons
PEDRO NARRA/NATUREPL.COMenough to estimate survival rates.
Infants had a very good chance of
surviving. Overall, 91 per cent survived
until they were weaned – which in
orangutans sometimes doesn’t
happen until the infant is 8 years old.
What’s more, the researchers
discovered that 94 per cent of weaned
females made it to adulthood and
gave birth themselves. The teamOrangutans have better infant survival
rates than some human populations–so tenuous and dim, it has
been difficult to observe them
definitively, and astronomers
have debated whether they really
are there or just a theoretical idea.
A Japanese spacecraft that flew
through the two Lagrange points
in the early 1990s seemed to
settle the debate when it didn’t
find a clear increase in dust
levels, suggesting no dust clouds
are present.
But now there has been a twist
in the story. Gábor Horváth at
Eötvös Loránd University in
Hungary and his colleagues
claim to have pictured one of
the Kordylewski clouds in detail.
They took pictures of one of
these ghostly satellites using an
Earth-based telescope and filters
designed specifically to pick up
light that has been bounced
around by dust grains (Monthly
Notices of the Royal AstronomicalSociety, doi.org/cwf9).
They found lots of this
polarised light in the area
where we would expect one
of the Kordylewski clouds to
be. Their observations have
similar patterns to those seen
in earlier, lower-quality images.“We are sure that these clouds
are there,” says Horváth.
Nevertheless, other
astronomers aren’t convinced
that these observations show any
difference from the surrounding
areas. “Rather than a ‘smoking
gun’, this latest paper seems to be
more like the smell of gunsmoke,”
says Anthony Dobrovolskis at the
SETI Institute in California. ■couldn’t determine survival rates for
males after weaning, as they roam
and so are harder to track (Journal
of Human Evolution, doi.org/cwfg).
This is a better survival rate than
for any other great ape. It is also
better than in some humanpopulations. While children do have a
higher survival rate in many countries
today, not all achieve the orangutan’s
level of success.
Counter-intuitively, the key factor
to the high survival rate is that forests
in South-East Asia are unproductive,
and fruit availability is erratic, says
van Noordwijk. To ensure they get
enough food without travelling too
far, orangutans are solitary. This
reduces competition and aggression,
and protects them against disease.
They also spend more time in trees
than other great apes, protecting
them from predators. “Together the
protection against predation and
disease makes it possible to have this
high survival,” says van Noordwijk.
However, their slow lifestyle
puts them at risk. Humans are killing
orangutans and logging is carving up
their forest habitat. “It takes a very
long time to recover from a crash,”
says van Noordwijk. “It’s one infant
at a time.”
The crucial thing will be to protect
the largest possible habitats.
“Having large connected populations
is the best way of making sure they’ll
hang in there,” says van Noordwijk.
Michael Marshall ■“ It has been difficult to
observe them definitively,
and astronomers have
debated if they do exist”