Scientists have examined closely the strand of DNA exclusive to humans that set them apart from all other living beings.

According to the Guardian, authors of a study published in the journal Science believe both the Neanderthals and the Denisovans carried the gene. The latter is much less known, as evidence of their existence comes from bone fragments in Siberia.

Led by Wieland Huttner, director of the Max Planck Institute of Molecular Cell Biology and Genetics, the researchers said the brain's neocortex gets a neuron boost to fuel functions such as reasoning, language and sensory perception. These traits are what make the human brain the most complex in the animal kingdom.

"Our ultimate goal has always been to identify the changes in the genome that were responsible for us humans having larger brains than other primates," Huttner told the Guardian. "What we now have is a gene that is characteristic of a 1.3 liter to 1.4 liter brain, and that makes it very exciting."

For their study, the researchers injected the gene into mouse embryos, which in turn caused their brains to grow larger and develop wrinkles known to fit more tissue in the skull.

"Will they learn better, or have better memories? That's hard to say. But we should know that later this year," Huttner said. "We saw cortical folding in half of the mice. So the gene is sufficient to do that, but it won't necessarily do it every time."

But Huttner and his team will have to wait for the mice to grow older so their brains can develop. Afterward, the researchers will see if the gene also increases the mice's cognitive abilities.

"It is so cool that one tiny gene alone may suffice to affect the phenotype of the stem cells, which contributed the most to the expansion of the neocortex," study lead author Marta Florio, a doctoral candidate in molecular and cellular biology and a Max Planck colleague of Huttner's, told Live Science. "The neocortex is so interesting because that's the seat of cognitive abilities, which, in a way, make us human - like language and logical thinking."