22 March 2014 | NewScientist | 17

YOU had me at “Hello”. It takes less than a second to form an impression of someone’s personality from their voice.

We know that our voices can transmit subtle signals about gender, age, even personality, but Philip McAleer at the University of Glasgow, UK, and his colleagues wondered whether we make an instant impression.

They recorded 64 people reading

a passage, then extracted the word “hello” and asked 320 people to rate the voices for 10 perceived personality traits. Each clip lasted just 390 milliseconds.

“We were surprised by just how similar people’s ratings were,” says McAleer. Using a scale in which 0 represents no agreement on a perceived trait and 1 reflects complete agreement, all 10 traits averaged 0.92 – meaning most

people agreed very closely on how far each voice represented a trait. (PLoS One, doi.org/rww).

The impression that our voices convey seems to be down to several factors. For example, pitch influenced how trustworthy a person seemed.

It makes evolutionary sense that decisions about personality should happen fast, says McAleer. “You want to quickly know if you can trust a person so you can approach them or run away.”

IN BRIEF

NA

DEE

M K

HAW

AR

/GET

TY

IMA

GES

Withering monsoon may have doomed past society

RAIN, rain, go away. The Indian summer monsoon abruptly

weakened 4200 years ago. The ensuing drought may

have led to the collapse of the Indus Valley Civilisation.

This lost society flourished around the Indus river, in

what is now Pakistan and north-west India. It was at its

height from 2600 BC to 1900 BC, but after that its cities

were mysteriously abandoned.

Yama Dixit and her colleagues at the University of

Cambridge dug up snail shells from Kotla Dahar, a lake

near one of the cities. The shells record changes in the

lake’s water level in their composition.

The team found that the lake was deep from 4500

to 3800 BC. Although it shallowed a little up to 2200 BC,

after this time there was a sharp drop in the water level,

suggesting the summer monsoon abruptly weakened for

200 years, meaning less rainfall (Geology, doi.org/rvt).

The Indus valley people relied on the monsoon for

crops, says Dixit. “It is inevitable that they were affected.”

The dates of the drought don’t match perfectly with the

collapse, but Dixit says both are uncertain.

The idea is credible because the results agree with

data elsewhere, says Supriyo Chakraborty of the Indian

Institute of Tropical Meteorology in Pune.

Shifts in the monsoon have also been linked to the fall

of China’s Tang dynasty, and of the Mayan civilisation in

South America, both around AD 900.

Voices reveal personality in an instant

Baby bugs dare ants to attack

TALK about reckless. The nymphs of one species of assassin bug are the only animals known that need their prey to attack them first.

Matthew Bulbert of Macquarie University in North Ryde, Australia, and his colleagues observed the nymphs (Ptilocnemus lemur) waving their hairy hind legs at larger predatory ants – often the venomous jack jumper ant (Myrmecia pilosula). But once the ant had grabbed its leg, the nymph turned the tables. It swivelled so it was on top, then pierced the back of the ant’s head.

It sounds a risky ploy, but the team never saw a nymph killed. Indeed, the nymphs nearly always killed the ants, securing a big meal. Nymphs only attacked if the ants did so first (Current Biology, DOI: 10.1016/j.cub.2014.02.006).

Bulbert says the trick may have begun as a way to ward off ants, but has since been transformed into predatory behaviour.

Steamy skies show planet smash-ups

WHEN young exoplanets crash into each other, heavy, salty skies could give them away.

According to theory, rocky planets like Earth grow when smaller bodies smash together and merge. But most traces of such events in our solar system have long since faded. Roxana Lupu at the SETI Institute in Mountain View, California, and her team think we could test the idea if we can find exoplanets that have just collided (Astrophysical Journal, doi.org/rw2).

If the planets resemble Earth, post-impact they should have thick, steamy atmospheres full of hydrogen chloride gas and vaporised minerals such as salt. Next-generation telescopes should be able to spot them.