Ed Yong in Not Exactly Rocket Science:
Between 5 and 7 million years of evolution separate us humans from our closest relatives—chimpanzees. During that time, our bodies have diverged to an obvious degree, as have our mental skills. We have created spoken language, writing, mathematics, and advanced technology—including machines that can sequence our genomes. Those machines reveal that the genetic differences that separate us and chimps are subtler: we share between 96 and 99 percent of our DNA.
Some parts of our genome have evolved at particularly high speed, quickly accumulating mutations that distinguish them from their counterparts in chimps. You can find these regions by comparing different mammals and searching for stretches of DNA that are always the same, except in humans. Scientists started identifying these “human-accelerated regions” or HARs about a decade ago. Many turned out to be enhancers—sequences that are not part of genes but that control the activity of genes, telling them when and where to deploy. They’re more like coaches than players.
It’s tempting to think these fast-evolving enhancers, by deploying our genes in new formations, drove the evolution of our most distinguishing traits, like our opposable thumbs or our exceptionally large brains. There’s some evidence for this. One HAR controls the activity of genes in the part of the hand that gives rise to the thumb. Many others are found near genes involved in brain development, and at least two are active in the growing brain. So far, so compelling—but what are these sequences actually doing?
To find out, J. Lomax Boyd from Duke University searched a list of HARs for those that are probably enhancers. One jumped out—HARE5. It had been identified but never properly studied, and it seemed to control the activity of genes involved in brain development. The human version differs from the chimp version by just 16 DNA ‘letters’. But those 16 changes, it turned out, make a lot of difference.