Why is the human brain so much larger than that of chimpanzees? Newly-published research suggests it’s the result of orders from DNA.

Researchers at Duke University believe the answer lies in a section of DNA known as human-accelerated regulatory enhancer, or HARE5. It’s part of what was once labelled junk DNA in the (apparently misguided) belief that it didn’t do anything useful.

The researchers found that HARE5 determined how many neural stem cells an embryo produces, and in turn the number of brain cells and thus the size of the brain.

In a study, published in Current Biology, the researchers experimented by placing HARE5 in mouse embryos, then doing the same with the equivalent stretch of DNA from chimpanzees. Measured just before birth, the brains of the mice with the human DNA inserted were 12 percent bigger than those with the chimp DNA.

It’s still a relatively primitive finding as it doesn’t prove what difference is made by the larger brains. The idea is that a larger number of brain cells also allows for a larger number of neuron connections and in turn more sophisticated processing. That could be the difference that allows humans to display the specific abilities that we usually label as human intelligence.

The next step is likely to be further study of what practical difference HARE5 makes to the behavior and abilities of mice as they grow into adults. It’s also possible that a future study might involve completely replacing the mice equivalent of HARE5 rather than merely adding the material from chimps and humans.