'Big Brain' Gene Led to Human Intelligence

It took millions of years of evolution for us to develop complex language and culture, and now scientists have discovered a "big brain" gene that may have been responsible for our unique human intelligence, according to a new study.

The gene in question reportedly led to a dramatic increase in the number of brain cells found in a key brain region, called the neocortex, which is involved in reasoning, language and sensory perception. It is found in modern-day humans, as well as Neanderthals and an extinct species of human called Denisovans, but not in chimpanzees.

Once modern humans and company arrived on the scene, the brain had expanded to roughly 85 cubic inches (1.4 liters) in volume, the majority of this growth occurring in the neocortex. Researchers suspect that our bigger brains may be due to a single gene, which gave the neocortex more room to store neurons.

"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 with the Max Planck Institute of Molecular Cell Biology and Genetics told Live Science.

Tests on mouse embryos confirmed that the gene, identified as ARHGAP11B, can have a profound impact on brain development. Embryos injected with the gene grew larger brain regions and some developed the folds like the human brain has, which allow for more surface area and therefore more neurons.

ARHGAP11B is a modified version of a far more common DNA strand that is found in organisms from simple yeast to mice. And because it likely showed up soon after humans split off from chimpanzees, it may have led to the rapid expansion of the human brain and paved the way for human intelligence.

"What is unique about humans is not going to come down to one gene only," Florio noted to The Guardian. "Cognition is a complex thing. We don't think a single gene makes us smarter than other animals. What we can say is that this is probably a key part of what makes us human."

The results were published in the journal Science.

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