When injected into a mouse embryo, the human version of a particular DNA sequence important for brain development caused the embryo to grow a considerably larger brain than other embryos treated with the chimpanzee version.

Humans and chimps split along the evolutionary ladder around four to six million years ago. Our brains then expanded dramatically as we picked up sophisticated abilities for things like abstract language, math, and reasoning. But it's not clear how that could happen without a larger DNA divergence.

The team at Duke went data mining through databases of human and chimp genomes. They identified 106 DNA enhancers – short bits of DNA that control gene activity – that are significantly different between the two species. Of these, six are believed to be involved in brain development. And one of those six, which the researchers dubbed HARE5, looked particularly promising because it is near a key gene in brain development and disease.