The sight of eight long black legs scuttling over the floor makes some people scream and run – and women are four times more likely to take fright than men. Now a study suggests that females are genetically predisposed to develop fears for potentially dangerous animals.

, a developmental psychologist at Carnegie Mellon University in Pittsburgh, Pennsylvania, found that baby girls only 11 months old rapidly start to associate pictures of spiders with fear. Baby boys remain blithely indifferent to this connection.

In an initial training phase Rakison showed 10 baby girls and boys a picture of a spider together with a fearful face. In the following test phase he let them watch the image of a spider paired with a happy face, and the image of a flower paired with a fearful face.

Despite the spider’s happy companion, the girls looked significantly longer at it than at the flower. The researchers took this to mean that the girls expected spiders to be linked with fear. The boys looked for an equal time at both images.

Not born in me

With a different group of babies, Rakison first showed a spider with a happy face, and a flower with a fearful face. Now the girls too looked at both images for the same length of time – implying that they did not have an inborn fear of spiders.

The results suggest that girls are more inclined than boys to learn to fear dangerous animals. By contrast, says Rakison, modern phobias such as fear of flying or injections show no sex difference.

He attributes the difference to behavioural differences between men and women among our hunter-gatherer ancestors. An aversion to spiders may help women avoid dangerous animals, but in men evolution seems to have favoured more risk-taking behaviour for successful hunting.

It makes evolutionary sense to acquire spider fear at a certain age, rather than to be born with it, he adds. “There is little reason for an infant to fear an object unless it can respond to it, for example by crawling away,” he says.

But if being scared of spiders is genetically predisposed, is there any point in seeing a shrink? “Even if a person is heavily predisposed to develop spider phobia, exposure therapy would still be effective,” says , a clinical psychologist from Washington University in St Louis. “But it may be more difficult to ‘unlearn’ the association between spiders and a fearful response,” she says.

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Most influenza infections affect the respiratory system, but there have long been suspicions that they are also linked to neurological disorders. The H1N1 flu pandemic in 1918 was followed by an outbreak of encephalitis and later by an unusually high number of cases of Parkinson’s disease.

Hard evidence of such a link has been hard to find, however. So of the St Jude Children’s Research Hospital in Memphis, Tennessee, sprayed a solution containing a highly pathogenic subtype of H5N1 avian flu into the noses of 225 mice. The team found that the virus infected nerves in the gut, then entered the brain stem and finally reached the brain. In the brain, it led to chronic activation of the immune system, even long after the viral infection had been cleared.

This immune system activity later led to protein aggregation and neuron loss in the brain, and to symptoms like tremor and loss of coordination – the hallmarks of Parkinson’s and Alzheimer’s.

Brain strains

“Infection with influenza virus might leave the brain vulnerable to damage from future infections with new influenza strains,” says Smeyne, adding that this is more likely to happen in young children or during an flu pandemic.

Smeyne suspects that all flu viruses, including the current H1N1 swine flu pandemic, could cause symptoms of encephalitis, or inflammation of the brain. But he says that there is currently no proof that flu viruses other than the H5N1 he worked with can enter the central nervous system.

Reports of extra encephalitis during outbreaks of seasonal flu in Japan and the US, and most recently of , hint at a related mechanism, however.

“The link between flu infection and neurological disorders has been the elephant in the room [ever since 1918],” says virologist , a virologist at Barts and The London School of Medicine and Dentistry, Queen Mary, University of London.

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