That Time Scientists Electrocuted Twins to Learn About Arachnophobia

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Spiders are the most feared animals in the world, despite the fact that they are overwhelmingly helpful rather than harmful. Scientists decided to investigate why, by shocking a bunch of twins.

Twins the world over can make some decent extra money volunteering for experiments. Identical twins are the perfect subjects with which to tease out the role of genetics in human development. There are registries the world over that scientists can appeal to in order to recruit twins for studies. To add a little extra appeal, scientists offer money for participation.

In this study, both the fraternal and identical twins earned their money. The study authors had twins, both identical and fraternal, look at images on a screen. Some of the images were neutral geometric shapes like squares and circles. Others were images of animals people tend to fear, like spiders and snakes. Once the twins had become accustomed to the images, the scientists added a twist. They shocked the twins when certain images came up. It was a minor current, run through the index finger of the hand, but it still wasn't a ball for the people waiting to see if they were going to get a pang whenever the next image came up.


The twins were not being shocked for nothing. The study authors wished to see if people with certain genetics can be taught to be afraid more easily than others. Over the course of the study, the researchers found that, while the identical twins weren't more likely to be zapped into a state of fear than the fraternal twins, when one identical twin was prone to conditioned fear, the other identical twin was much more likely to be prone to it as well. One fraternal twin's conditioned fear, on the other hand, was much less likely to indicate that the other fraternal twin could be conditioned to fear a geometrical shape. There is a genetic component to learned fear.

There's also a genetic component to fear of spiders (and snakes). Identical twins could become afraid of circles and squares, but were much more likely to be zapped into fear of spiders and snakes than circles and squares. Although the study authors don't have enough data to conclude this absolutely, we're likely to be genetically predisposed to be afraid of certain things. We're primed to be afraid of spiders.


This still leaves us with questions. Considering spiders are so harmless, especially compared to animals like dogs - or, for that matter, snakes - why are we so afraid of them? Were spiders more fearsome in the past?

[Via A Twin Study of the Genetics of Fear Conditioning.]