A new study may explain why babies don't seem too worried about heights and steep edges for most of their first year. Researchers have linked the emergence of such fears with another crucial development: crawling.

In a paper published in the journal Psychological Science, a team of scientists from the University of California, Berkley and Doshisha University of Kyoto studied how babies' sense of their surroundings develops as they begin to physically navigate it on their own. To examine this development, they enrolled babies who had not yet begun to crawl in an experiment where some of them were trained to use a motorized "baby go-cart" to move around a designated area. They later found that infants trained to use the tiny vehicle were more likely to get upset when exposed to "threats" such as moderate heights, steep edges, and erratic movement.

From this, the team concluded that after infants gain locomotor experience, they begin to interpret visual information as data that influences movement through space. Steep edges and heights suddenly assume a new, hazardous dimension, as they now entail a downward, uncontrollable movement.

For someone navigating a world like our own, this refined interpretation is crucial.

So why don't babies develop this sense of movement and space earlier? An infant who has not yet begun to crawl seems more vulnerable than one who has. For this reason, wouldn't the defense mechanism benefit all babies, regardless of age?

"One major benefit of such a delay is that infants are more prone to explore their environment and the movement possibilities afforded by that environment when they are less concerned about the consequences of their actions," the researchers explain. "Paradoxically, a tendency to explore risky situations may be one of the driving forces behind skill development."

Rather than being born with a pre-programmed set of threats, babies are able to establish their own "rules" as they begin to navigate physically the world around them. The researchers believe that this method of assessment allows babies to develop more diverse movement strategies, which can be used to navigate a variety of different surfaces.

In addition, a person's sense of space and danger, uniquely developed through trial and error, would explain why some people bungee-jump from radio towers while others get nauseated from standing on a step stool.

Source: Audun Dahl, Joseph J. Campos, David I. Anderson, Ichiro Uchiyama, David C. Witherington, Mika Ueno, Laure Poutrain-Lejeune, and Marianne Barbu-Roth. "The Epigenesis of Wariness of Heights." Psychological Science. 2013.