Know Your Brain: The Neocortex — The Light Upstairs

In The Beginning

Lucy, the small primate who once roamed the valleys of Tanzania some 3 million years ago, was our remote ancestor — but chances are she spent much of her life in trees, with limbs adept for leaping across branches. It was only as we began to leave the trees that our brains grew larger; increasingly becoming more equipped to solve problems, to build tools, and to think the deep thoughts we’ve become accustomed to today — cognitive attributes we owe to our brain’s neocortex.

As monumental as conquering the grasslands for the first time probably was, it may have largely been a typo in our own genetic code that made it possible. According to research just unveiled this year at the Max Planck Institute of Molecular Cell Biology and Genetics, in Germany, a point mutation occurred in our brains, paving the way for the existence of the neocortex, one of the most recent evolutionary developments in mammal brains.

This same mutation has been found in prehistoric humans that our own ancestors roamed the Earth with — that is, the Neanderthals and Denisovans, whom you might think of as our evolutionary cousins. Yet, the chimpanzees, our closest surviving relatives, whose genome is 96 percent similar to our own, don’t share this mutation with us — one that would allow stem cells to expand into neurons, thus growing our brains larger, into the ones we know today.

The simple reason for this decisive variation could be one of the minimal differences in our DNA, occurring as our genes mutated. Researchers replaced a single nucleotide — or genetic building block in the gene — changing the C (base cytosine) to G (guanine), and were able to stop the stem cells from developing. And as we began to develop reasoning and language, evolution would set us even further apart from the chimps — as these advancements allowed us to interact with each other and expand our brains even further, as our brains needed to grow in order to support the size of the neocortex region. Today, our ratio for neocortical gray matter to brain size is 60–1, compared to 30–1 for chimps.

While Lucy had not abandoned tree life entirely, newly uncovered evidence suggests that her species used tools and hunted — two advanced skills for primates. She and her family lived in perilous times, when cooperation among the tribe would be rewarded with gathering enough food for survival, and competition, as well as constant attacks from predators, rewarded abilities like swift thinking and spatial reasoning — a process of natural selection that encouraged the neocortex to continue growing.

Expanding Our Minds

The neocortex is made up of the brain’s gray matter connected by unmyelinated fibers — one of the major components of our central nervous system, consisting of sensory and motor neurons, and located in the cerebrum of the brain. It represents the largest portion of the cerebral cortex, covering both of the brain’s hemispheres. In fact, about 76 percent of our brain is included in the neocortex. The structure is then broken up into the brain’s frontal, parietal, occipital, and temporal lobes, divided by cranial sutures.

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