Humans and chimpanzees are pretty similar, biologically. In fact, human and chimp DNA is nearly identical: We share around 95 percent of our DNA with our closest primate relatives.
So you may wonder: if human and chimp DNA is nearly the same, why are human brains so much larger than chimp brains?
Scientists at Duke University asked the same question, and did an experiment to see if they could find answers.
The researchers focused on short strands of DNA in both humans and chimps known as enhancers, which control gene activity. Specifically, they looked for enhancers involved in the early development of brain tissue.
They fixed on a particular enhancer located near a gene called Frizzled 8, which is known to play a role in early brain development.
The scientists then implanted the enhancers in mice embryos to see how they might affect the embryonic rodents' brain development. And sure enough, the human enhancer was more active earlier in the brains' development, resulting in the production of more brain cells.
Once the mouse embryos were almost fully developed, it became clear that those with the human enhancers had brains nearly 12 percent larger than embryos with the chimp enhancers.
What's remarkable is that human and chimp enhancers differed by only sixteen letters in their genetic code. Yet that was enough to make a large difference in brain area.
The scientists plan to keep studying the mice as they grow to learn more about how their brains continue to develop. Examining other human and chimp enhancers, they hope, will reveal even more about the evolution of the human brain.