19 November 2011 | NewScientist | 21

HOW kind you are could be affected by a change in a single gene. What’s more, others can tell if you have the gene even if you don’t speak a single word.

There are several variations of the gene that codes for the receptor for the hormone oxytocin. Aleksandr Kogan at the University of Toronto, Canada, and colleagues wanted to check whether these variations

influence behaviour, since high levels of oxytocin are believed to make people more sociable.

Kogan’s team asked 116 volunteers to watch 23 silent videos that were 20 seconds long. Each showed a person’s response to their partner telling them a story of personal suffering. The volunteers were asked to rate how kind and trustworthy the person in the video appeared to be.

Electron tweezers reveal their pluck

BEAMS of electrons can pick up and move tiny objects, just like optical tweezers that manipulate items using light.

Vladimir Oleshko at the US National Institute of Standards and Technology in Gaithersburg, Maryland, and a colleague found the effect while studying tiny droplets of aluminium and silicon using an electron microscope. When they moved the scope’s electron beam, nanoparticles of aluminium moved too.

Optical tweezers work thanks to the force generated when a particle refracts light, which pushes the object to the most intense part of a beam. Electron beams generate the same force, says Oleshko (Ultramicroscopy, DOI: 10.1016/ j.ultramic.2011.08.015). The new tweezers have a resolution and sensitivity 1000 times finer than optical techniques. Oleshko hopes to use them in the near future to manipulate single atoms.

Two’s company, three’s murder for cannibal shrimp

CANNIBALISTIC and willing to fight to the bitter end under the cover of darkness: Lysmata amboinensis shrimp have a brutally romantic side. They are so hell-bent on living in pairs that when placed in groups of three or four, they attack their peers until just one couple remains alive.

Each 6-centimetre-long cleaner shrimp is both male and female, but cannot self-fertilise, so needs a mate. Coupling up means they waste no energy on finding partners. Intense competition for food makes them aggressive to the point of killing off other shrimp that threaten their

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Nice genes, can we be friends? People with the so-called GG version of the oxytocin receptor gene were judged to be kinder than those with GA or AA versions. The difference? Those with GG variations used significantly more non-verbal empathetic gestures in their storytelling such as smiling and nodding.

Kogan expects that this is what influenced the observers’ judgements (Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1112658108).

livelihood, with the exception of their mating partners.Janine Wong at the University of Basel in Switzerland

placed sets of three or four shrimp together in tanks. During the day they barely interacted, but infrared cameras captured an entirely different scene at night. “They started to go crazy and chase one individual until they had killed it,” she says. This continued until just two shrimp remained. Come morning, the victors were eating their kill (Frontiers in Zoology, in press).

“Their behaviour is sort of hardwired,” says Wong. The shrimp fought to the death even when they had access to plenty of food, suggesting that it had nothing to do with resources and everything to do with living in pairs. This is surprising, says Wong, as hermaphroditic species normally have multiple partners.

RATS are four times the pest we thought they were.

Ken Aplin at the Smithsonian Institution in Washington DC looked at the genes of black rats (Rattus rattus) from 32 countries to work out their evolutionary history. He found that the rats fell into six distinct groups that diverged from one another about a million years ago, before modern humans evolved.

Four of these groups include rats that now live off humans, by eating our rubbish, for example. That means they became pests on at least four separate occasions, Aplin says (PLoS One, DOI: 10.1371/journal.pone.0026357).

Rats from different lineages may respond differently to rodenticides, says Aplin.

Rats hitch-hiked with us four times

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