The mutation, however, is not found in humans' closest living relatives, the chimpanzees.
As early humans evolved, they developed larger and more complex brains, capable of storing and processing a lot of information.
Scientists previously identified a human gene which they believe was behind the expansion of a key brain region known as the neocortex.
The gene likely arose about five or six million years ago, after the human line split off from chimpanzees.
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It may have led to the brain's expansion by dramatically boosting the number of brain cells found in this region, 'BBC News' reported.
"A point mutation in a human-specific gene gave it a function that allows expansion of the relevant stem cells that make a brain big," said Dr Wieland Huttner from Max Planck Institute.
"This one, as it is fixed in the human genome - so all living humans have the gene - apparently gave a tremendous selection advantage, and that is why we believe it spread in the human population," said Huttner.