Accidental intelligence: human brain size may be due to DNA 'typo'

Our brains are big and complex, able to take in and process a massive amount of information – and human brain size and complexity may be due in part to a ‘typo’ in our DNA, according to a new study.

The genetic mutation is likely to go back millions of years. Our closest cousins, the extinct Neanderthals and Denisovans, were brainiacs, too. It’s not present in our closest living relatives, chimpanzees, however. Their brains are about a third the size of our own.

That means the mutation probably cropped up no earlier than 5 or 6 million years ago, when the ancestors of humans and chimpanzees first started down separate evolutionary paths, the researchers said.

During that time period, between 2 and 6 million years ago, human ancestors began walking upright and using tools. At the same time, human brain size began expanding.

Eventually, early humans began traveling from Africa to other parts of the world. About 800,000 years ago, their brains began growing rapidly, around the same time early humans were learning how to adapt to new habitats and environments.

Last year, researchers found a gene that appeared to linked to growth of the neocortex, the part of the brain connected with vision, hearing, spatial reasoning, conscious thought, and language. In humans, about 76 percent of the brain is the neocortex.

Now, researchers have figured out why that gene works the way it does.

The tiny mutation to human DNA – called a point mutation – allows for certain stem cells to grow in a way that leads to a larger neocortex.

All living humans appear to have have this genetic mutation, the researchers said.

Scientists aren’t sure what caused the mutation, or if it was the only genetic change that played a role in developing modern humans’ intelligence.

Larger brains have been mostly beneficial to humanity. They’ve allowed for the myriad inventions and innovations that make modern life more comfortable.

However, human brain size has also made childbirth more dangerous for mothers and infants. Human infants have larger heads for their body size compared to other mammals, making childbirth painful for their mothers. Their skulls are also not yet fully developed – the “soft spots” allow room for their head and brain to grow extensively in the first years after birth, but also make them vulnerable.

The study was published in the journal Scientific Advances.

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By Olivia Harvey, Earth.com Staff Writer