Suppose you placed a baby in a room with a snake and a spider. Would they play with these creatures or leave them well alone?

This is not a hypothetical question. Researchers in the study of fear are actively looking into it.

It is already well-known that babies find live animals much more interesting than stuffed ones. Research has found that this interest persists even if those animals are snakes and spiders.

Studies like this are giving new insights into the nature of fear itself, and just how and when it is acquired.

A fear of snakes is one of the most common and intense fears in the world, according to fear researcher Judy DeLoache of the University of Virginia in Charlottesville, US, who was not involved in the new study.

The team set out to startle the babies to see how they would react

The simplest view, and one that many people would assume is true, is that we are innately scared of them. The idea is that, because some snakes are deadly, we have evolved to react to them all with fear.

Seemingly in line with that, 11-month-old infants were shown images of a snake paired with either a fearful or happy voice. The babies looked at snakes for longer when a fearful voice was presented than when a happy voice was heard.

Another study found similar results when using fearful versus happy faces, suggesting that young infants associate fear with snakes.

However those studies were not hard proof, and we can't ask babies if they are actually scared of snakes.

A new study re-assesses how babies react to snakes. Its authors are seeking to overturn the idea that babies – and therefore us - are innately scared of them.

The team measured babies' physiological responses as they watched videos of snakes and elephants, paired with both fearful and happy voices.

They then set out to startle the babies to see how they would react. They presented them with a "startle probe", which in this case was an unexpected bright flash of light as they watched a video.

A startle like this would be more intense if the babies were already scared: just like when we watch scary films, and jump more if we are already tense.

"What we found is that their startle responses were not bigger when watching a video of a snake, even when paired with a fearful voice," says co-author Vanessa LoBue at Rutgers University in New Jersey, US.

The findings have been published in the Journal of Experimental Child Psychology.

The babies' startle response was actually lower. Their heart response was also lower, which also indicates that babies were not scared.

In other words, though the babies paid more attention to the snakes, this did not invoke fear.

LoBue expected this result. Both human babies and monkeys are known to be more interested in snakes than other animals, suggesting that snakes are somehow special.

It is this heightened interest in snakes that can more easily be turned into fear in certain circumstances.

Children do not have an innate fear of snakes, agrees DeLoache. "Rather, they have a predisposition to detect and respond rapidly to snakes." For example, studies have shown that young children will quickly detect the presence of a snake in a photo among many other non-snake photos.

Far from this fear being hard-wired, for LoBue it is now clear that fear of snakes and spiders is culturally conditioned.

"While we find differential responses to snakes early on, meaning they are special, it doesn't seem to be related to fear early in development," she says. "It's possible that paying more attention to something might make fear learning easier later on. It facilitates fear learning."

LoBue says it is a good thing that we have not evolved an inborn fear of certain things. "It's not adaptive to have any hard-wired fear," she says, because it would limit a young infant's desire to explore new things.

Instead, we have evolved to quickly learn to be afraid of something if it turns out to be dangerous.