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Distinguishing between identical twins can be a difficult task since twins do have the exact same genes after all. However, as identical as two people could get, parents often report characteristic differences that help them tell their children apart from one another. In a new study, researchers attempted to find a way to differentiate between identical twins. The researchers from the German Center for Neurodevelopmental Disease in Dresden found that at least for identical twin mice, a key distinguishing factor was curiosity.

The research team, composed of Gerd Kempermann a neuroscientist from the center and his colleagues, recruited 40 female mice. No male mice were used in the study due to territorial behaviors. All of the mice were genetically modified to resemble human identical twins. The mice were placed in a three-story maze that provided a lot of room and toys for exploration. The researchers observed the behaviors of the mice and then their brain development when they reached adulthood.

The researchers noticed that the majority of the mice acted naturally, which meant that they were more timid and tended to stick to routines. There were a select few mice that were bolder and thus, they were more adventurous in terms of exploring outside of the familiar territory. The researchers found that these mice had more cells in their hippocampus region in the brain by the time they grew into adults.

"It's probably just small coincidences that make them [behave] differently to start with," Jonas Frisen commented. Frisen is a molecular biology professor from Sweden's Karlinska Institutet and was not a part of the study. "What they show is that [the mice] are very similar at the onset of the study but become increasingly different over time."

The researchers believe that since the mice that explored more engaged more frequently with toys that could be challenging, these mice might have developed more brain cells. This study's findings provide more evidence for the nature versus nurture debate. The results suggest that even though two people might be genetically identical, their experiences could greatly affect how they develop biologically as people.

"The most surprising and most important finding is that it shows [not only] that our brains are altered by the environment we live in, but that the life we life affects the structure of the brain," Frisen added.

The research was published in Science.